Mason, S., Dubey, J.P., Smith, J.E. & Boag, B. 2015, 'Toxoplasma gondii coinfection with diseases and parasites in wild rabbits in Scotland.', Parasitology, vol. 142, no. 11, pp. 1415-1421.
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In wild rabbits (Oryctolagus cuniculus) on an estate in Perthshire, central Scotland, the seroprevalence of Toxoplasma gondii was 18/548 (33%). The wild rabbit could be a T. gondii reservoir and it has potential value as a sentinel of T. gondii in environmental substrates. Toxoplasma gondii was associated with female sex (P < 0001) and with relatively heavy infections by Eimeria stiedae (P = 0036). It was not associated with the intensity of coccidial oocysts, the severity of myxomatosis caused by the virus Myxomatosis cuniculi, the intensity of roundworm eggs, the year or season, rabbit age or distance from farm buildings. Coinfections could have been affected by gestational down regulation of type 1 T helper cells. A sudden influx or release of T. gondii oocysts might have occurred. This is the first report of T. gondii in any wild herbivore in Scotland and also the first report of lapine T. gondii as a coinfection with E. stiedae, M. cuniculi and helminths.
Darlay, R., Stear, M.J., Mason, S., Smith, J. & Shaw, M.A. 2014, 'The heritability of abortion in pedigree Charollais flocks.', Animal reproduction science, vol. 149, no. 3-4, pp. 297-304.
Foetal death, or abortion at term, in sheep is of major significance to the livestock industry, accounting for more than £24million lost per annum. We have investigated whether there is a genetic component to abortion within two flocks of pedigree Charollais sheep, one followed from 1989 to 2006, the other from 1992 to 2006. Abortion occurred at a rate of 5.74-8.78% per annum against a total mortality rate of 14-24%. By model covariate analysis we have shown that 15.5% aborting ewes went on to have one or more abortions and that this risk increased with parity (p=0.006). Heritability estimates were approximately 0.08 as calculated by SOLAR, pedigreemm and ASReml3, with sire and dam components of 0.046 and 0.048, respectively. Where the lamb was aborted, heritability estimates were highly variable according to the method employed, 0.046-0.378, with sex of the lamb being a significant covariate. This variability indicated one or more underlying, significant factors that were not measured in these analyses, potentially including infectious agents that may be involved. Nevertheless, the ASReml3 estimate (0.179) resolved to 0.074 variance attributable to the sire and 0.092 attributable to the dam, which, while not significant, was suggestive that genetic variants passed by the dam to the lamb may be of more weight than that from the sire in determining whether a lamb will abort.
Frost, C.L., Pollock, S.W., Smith, J.E. & Hughes, W.O. 2014, 'Wolbachia in the flesh: symbiont intensities in germ-line and somatic tissues challenge the conventional view of Wolbachia transmission routes.', PloS one, vol. 9, no. 7, p. e95122.
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Symbionts can substantially affect the evolution and ecology of their hosts. The investigation of the tissue-specific distribution of symbionts (tissue tropism) can provide important insight into host-symbiont interactions. Among other things, it can help to discern the importance of specific transmission routes and potential phenotypic effects. The intracellular bacterial symbiont Wolbachia has been described as the greatest ever panzootic, due to the wide array of arthropods that it infects. Being primarily vertically transmitted, it is expected that the transmission of Wolbachia would be enhanced by focusing infection in the reproductive tissues. In social insect hosts, this tropism would logically extend to reproductive rather than sterile castes, since the latter constitute a dead-end for vertically transmission. Here, we show that Wolbachia are not focused on reproductive tissues of eusocial insects, and that non-reproductive tissues of queens and workers of the ant Acromyrmex echinatior, harbour substantial infections. In particular, the comparatively high intensities of Wolbachia in the haemolymph, fat body, and faeces, suggest potential for horizontal transmission via parasitoids and the faecal-oral route, or a role for Wolbachia modulating the immune response of this host. It may be that somatic tissues and castes are not the evolutionary dead-end for Wolbachia that is commonly thought.
Dubuffet, A., Smith, J.E., Solter, L., Perotti, M.A., Braig, H.R. & Dunn, A.M. 2013, 'Specific detection and localization of microsporidian parasites in invertebrate hosts by using in situ hybridization.', Applied and environmental microbiology, vol. 79, no. 1, pp. 385-388.
We designed fluorescence in situ hybridization probes for two distinct microsporidian clades and demonstrated their application in detecting, respectively, Nosema/Vairimorpha and Dictyoceola species. We used them to study the vertical transmission of two microsporidia infecting the amphipod Gammarus duebeni.
Jahnke, M., Smith, J.E., Dubuffet, A. & Dunn, A.M. 2013, 'Effects of feminizing microsporidia on the masculinizing function of the androgenic gland in Gammarus duebeni.', Journal of invertebrate pathology, vol. 112, no. 2, pp. 146-151.
Feminizing parasites enhance their vertical transmission to the host offspring by converting genetic male hosts into phenotypic females. Crustacea are the only invertebrates where sexual differentiation is controlled by a specialised endocrine organ, the androgenic gland, rather than by the gonads. We showed that a feminizing microsporidian Microsporidium sp. inhibits androgenic gland differentiation. We investigated the effect of Microsporidium sp. and a second feminizing microsporidium, Nosema granulosis, on the masculinizing function of the androgenic gland in Gammarus duebeni. Androgenic gland implants had a masculinizing effect on the sexual characteristics and sexual behaviour of recipient female hosts, reflecting the masculinizing function of the androgenic gland. Individuals that had received androgenic glands showed changed morphology in comparison with controls; they were bigger overall, they lost their oostegite marginal setae, developed calceoli and acquired a male-like behaviour. This effect was observed in uninfected females, as well as in females infected with the Microsporidium sp. The masculinizing effect of androgenic gland implants was smaller in N. granulosis infected individuals. N. granulosis and Microsporidium sp. fall into distinct clades of the Microspora. It appears that these divergent parasites both act by inhibiting the development of the androgenic gland. However, they differ in their ability to inhibit the host's response to the hormone that controls male sexual differentiation.
Evison, S.E.F., Roberts, K.E., Laurenson, L., Pietravalle, S., Hui, J., Biesmeijer, J.C., Smith, J.E., Budge, G. & Hughes, W.O.H. 2012, 'Pervasiveness of parasites in pollinators', PLoS ONE, vol. 7, no. 1.
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Many pollinator populations are declining, with large economic and ecological implications. Parasites are known to be an important factor in the some of the population declines of honey bees and bumblebees, but little is known about the parasites afflicting most other pollinators, or the extent of interspecific transmission or vectoring of parasites. Here we carry out a preliminary screening of pollinators (honey bees, five species of bumblebee, three species of wasp, four species of hoverfly and three genera of other bees) in the UK for parasites. We used molecular methods to screen for six honey bee viruses, Ascosphaera fungi, Microsporidia, and Wolbachia intracellular bacteria. We aimed simply to detect the presence of the parasites, encompassing vectoring as well as actual infections. Many pollinators of all types were positive for Ascosphaera fungi, while Microsporidia were rarer, being most frequently found in bumblebees. We also detected that most pollinators were positive for Wolbachia, most probably indicating infection with this intracellular symbiont, and raising the possibility that it may be an important factor in influencing host sex ratios or fitness in a diversity of pollinators. Importantly, we found that about a third of bumblebees (Bombus pascuorum and Bombus terrestris) and a third of wasps (Vespula vulgaris), as well as all honey bees, were positive for deformed wing virus, but that this virus was not present in other pollinators. Deformed wing virus therefore does not appear to be a general parasite of pollinators, but does interact significantly with at least three species of bumblebee and wasp. Further work is needed to establish the identity of some of the parasites, their spatiotemporal variation, and whether they are infecting the various pollinator species or being vectored. However, these results provide a first insight into the diversity, and potential exchange, of parasites in pollinator communities. © 2012 Evison et al.
Ironside, J.E., Smith, J.E., Hatcher, M.J. & Dunn, A.M. 2011, 'Should sex-ratio distorting parasites abandon horizontal transmission?', BMC evolutionary biology, vol. 11, p. 370.
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BACKGROUND: Sex-ratio distorting parasites are of interest due to their effects upon host population dynamics and their potential to influence the evolution of host sex determination systems. In theory, the ability to distort host sex-ratios allows a parasite with efficient vertical (hereditary) transmission to dispense completely with horizontal (infectious) transmission. However, recent empirical studies indicate that some sex-ratio distorting parasites have retained the capability for horizontal transmission. RESULTS: Numerical simulations using biologically realistic parameters suggest that a feminising parasite is only likely to lose the capability for horizontal transmission if its host occurs at low density and/or has a male-biased primary sex ratio. It is also demonstrated that even a small amount of horizontal transmission can allow multiple feminising parasites to coexist within a single host population. Finally it is shown that, by boosting its host's rate of population growth, a feminising parasite can increase its own horizontal transmission and allow the invasion of other, more virulent parasites. CONCLUSIONS: The prediction that sex-ratio distorting parasites are likely to retain a degree of horizontal transmission has important implications for the epidemiology and host-parasite interactions of these organisms. It may also explain the frequent co-occurrence of several sex-ratio distorting parasite species in nature.
Darlay, R.J., McCarthy, A.J., Illot, N.E., Smith, J.E. & Shaw, M.A. 2011, 'Novel polymorphisms in ovine immune response genes and their association with abortion.', Animal genetics, vol. 42, no. 5, pp. 535-543.
The sheep has worldwide agricultural importance, yet the genetic control of the immune responses underlying susceptibility or resistance to ovine disease is little understood. Here, we identify six novel polymorphisms in the ovine immune response genes interferon- (IFNG), tumour necrosis factor- (TNF), interleukin-1 (IL1B) and interleukin-4 (IL4) in pedigree Charollais flocks. We confirm the presence of previously reported polymorphisms in IFNG and IL1B in Charollais. Restriction fragment length polymorphism (RFLP) genotyping assays have been developed for four polymorphisms, IFNGg.168C>T, IFNGg.285A>G, IL1Bg.689C>T and TNFg.3UTRA>G, and a Taqman genotyping assay has been developed for IL4g.485C>T. The previously described IL2g.647C>T polymorphism is adapted for RFLP analysis. Allele frequencies are described in Charollais, Lleyn and Suffolk cross sheep. Polymorphisms are typed in both Charollais ewes and lambs and analysed against abortion phenotypes. A subset of animals have also been analysed for the presence of Toxoplasma gondii, an abortion-causing protozoan. The IFNGg.168T allele is shown to be associated with increased risk of a ewe having an abortion, while the IFNGg.285G allele is associated with increased risk of a lamb being aborted. These assays provide tools for the investigation of the genetic basis of other phenotypes in sheep, including infectious disease susceptibility.
Frost, C.L., Fernández-Marín, H., Smith, J.E. & Hughes, W.O. 2010, 'Multiple gains and losses of Wolbachia symbionts across a tribe of fungus-growing ants.', Molecular ecology, vol. 19, no. 18, pp. 4077-4085.
Although the intracellular bacterium Wolbachia is ubiquitous in insects, it has a unique relationship with New World ants on which particular bacterial strains have specialized. However, data are from distantly related hosts and detailed phylogenetic information which could reveal transmission dynamics are lacking. Here, we investigate host-Wolbachia relationships in the monophyletic fungus-growing ant tribe Attini, screening 23 species and using multilocus sequence typing to reliably identify Wolbachia strains. This technique reduces the significant problem of recombination seen using traditional single gene techniques. The relationship between Wolbachia and the fungus-growing ants appears complex and dynamic. There is evidence of co-cladogenesis, supporting vertical transmission; however, this is incomplete, demonstrating that horizontal transmission has also occurred. Importantly, the infection prevalence is frequently different between closely related taxa, with the Acromyrmex leaf-cutting ants appearing particularly prone to infection and there being no consistent relationship with any of the major life history transitions. We suggest that infection loss and horizontal transmission have driven epidemics or selective sweeps of Wolbachia, resulting in multiple gains and losses of infection across the fungus-growing ants.
Galbreath, J.G.M.S., Smith, J.E., Becnel, J.J., Butlin, R.K. & Dunn, A.M. 2010, 'Reduction in post-invasion genetic diversity in Crangonyx pseudogracilis (Amphipoda: Crustacea): A genetic bottleneck or the work of hitchhiking vertically transmitted microparasites?', Biological Invasions, vol. 12, no. 1, pp. 191-209.
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Parasites can strongly influence the success of biological invasions. However, as invading hosts and parasites may be derived from a small subset of genotypes in the native range, it is important to examine the distribution and invasion of parasites in the context of host population genetics. We demonstrate that invasive European populations of the North American Crangonyx pseudogracilis have experienced a reduction in post-invasion genetic diversity. We predict that vertically transmitted parasites may evade the stochastic processes and selective pressures leading to enemy release. As microsporidia may be vertically or horizontally transmitted, we compared the diversity of these microparasites in the native and invasive ranges of the host. In contrast to the reduction in host genetic diversity, we find no evidence for enemy release from microsporidian parasites in the invasive populations. Indeed, a single, vertically transmitted, microsporidian sex ratio distorter dominates the microsporidian parasite assemblage in the invasive range and appears to have invaded with the host. We propose that overproduction of female offspring as a result of parasitic sex ratio distortion may facilitate host invasion success. We also propose that a selective sweep resulting from the increase in infected individuals during the establishment may have contributed to the reduction in genetic diversity in invasive Crangonyx pseudogracilis populations. © Springer Science+Business Media B.V. 2009.
Mason, S., Quinnell, R.J. & Smith, J.E. 2010, 'Detection of Toxoplasma gondii in lambs via PCR screening and serological follow-up.', Veterinary parasitology, vol. 169, no. 3-4, pp. 258-263.
Toxoplasma gondii in sheep is important as a cause of lambing losses and as a food hazard. We aimed to assess the prevalence of infection in lambs via development of a standardised PCR technique applied to neonates together with follow-up serology at age 4 months. We measured the sensitivity of PCR targeting the T. gondii sequences B1, SAG1, 5'SAG2, 3'SAG2 and SAG3 in the presence of abundant sheep DNA. B1-PCR was the most sensitive protocol, achieving 50% positivity when 0.02 parasite genome copies were present in an assay testing 10 ng of template. Standardised B1-PCR, and serological follow-up using the modified agglutination test (MAT), were used to estimate infection prevalence in lambs from two flocks in Northern England. Neonatal prevalence detected by PCR on umbilical cord did not differ significantly between viable Charollais (16/243 (6.6%)) and viable Swaledale (30/264 (11.4%)). In contrast, at age 4 months seroprevalence was higher (P<0.001, OR=4.42) in Charollais (50/411 (12.2%)) than in Swaledale (10/335 (3.0%)). There was no evidence of a relationship between the results of PCR and those of serology. In addition, prenatal exposure was not associated with mortality: among non-viable lambs, 3/54 Charollais but 0/16 Swaledale were PCR positive, and 1/26 Charollais and 1/14 Swaledale were seropositive. These results indicate that both standardised B1-PCR, and serology, can be used to detect T. gondii in lambs. Frequent prenatal exposure was detected without mortality and sometimes without an IgG response. Some lambs, without PCR evidence of prenatal exposure, seroconverted early.
Hide, G., Morley, E.K., Hughes, J.M., Gerwash, O., Elmahaishi, M.S., Elmahaishi, K.H., Thomasson, D., Wright, E.A., Williams, R.H., Murphy, R.G. & Smith, J.E. 2009, 'Evidence for high levels of vertical transmission in Toxoplasma gondii.', Parasitology, vol. 136, no. 14, pp. 1877-1885.
Toxoplasma gondii is a highly ubiquitous and prevalent parasite. Despite the cat being the only definitive host, it is found in almost all geographical areas and warm blooded animals. Three routes of transmission are recognised: ingestion of oocysts shed by the cat, carnivory and congenital transmission. In natural populations, it is difficult to establish the relative importance of these routes. This paper reviews recent work in our laboratory which suggests that congenital transmission may be much more important than previously thought. Using PCR detection of the parasite, studies in sheep show that congenital transmission may occur in as many as 66% of pregnancies. Furthermore, in families of sheep on the same farm, exposed to the same sources of oocysts, significant divergent prevalences of Toxoplasma infection and abortion are found between different families. The data suggest that breeding from infected ewes increases the risk of subsequent abortion and infection in lambs. Congenital transmission rates in a natural population of mice were found to be 75%. Interestingly, congenital transmission rates in humans were measured at 19.8%. The results presented in these studies differ from those of other published studies and suggest that vertical transmission may be much more important than previously thought.
Smith, J.E. 2009, 'The ecology and evolution of microsporidian parasites.', Parasitology, vol. 136, no. 14, pp. 1901-1914.
The phylum Microspora is ancient and diverse and affects a wide range of hosts. There is unusually high use of vertical transmission and this has significant consequences for transmission and pathogenicity. Vertical transmission is associated with low pathogenesis but nevertheless can have significant impact through associated traits such as sex ratio distortion. The majority of microsporidia have mixed transmission cycles and it is not clear whether they are able to modify their phenotype according to environmental circumstances. There is a great need to understand the mechanisms controlling transmission and one of the first challenges for the genomics era is to find genes associated with life cycle stages. Similarly we cannot currently predict the ease with which these parasites might switch between host groups. Phylogenetic analysis suggests that there are strong relationships between Microsporidia and their hosts. However closer typing of parasite isolates, in relation to host range and disease phenotype, is required to assess future environmental risk from these pathogens.
Hommola, K., Smith, J.E., Qiu, Y. & Gilks, W.R. 2009, 'A permutation test of host-parasite cospeciation.', Molecular biology and evolution, vol. 26, no. 7, pp. 1457-1468.
We introduce a statistical method that explores host-parasite coevolution by testing the null hypothesis that hosts and their associated parasites evolved independently. This test is simple and intuitive and involves only suitable randomization of the observed data. It is not even necessary to construct host and parasite phylogenetic trees, as the test can be performed directly on distance matrices. Statistical power of the test was evaluated using simulated data consistent with the alternative hypothesis of cospeciation. Results were compared with the method of Mantel (1967) and the ParaFit method of Legendre et al. (2002). We observed that our method has greater power overall and thus a higher ability to detect cospeciation in closely related host-parasite systems. Our test was also successful when applied to the pocket gopher and chewing lice system.
Bontell, I.L., Hall, N., Ashelford, K.E., Dubey, J.P., Boyle, J.P., Lindh, J. & Smith, J.E. 2009, 'Whole genome sequencing of a natural recombinant Toxoplasma gondii strain reveals chromosome sorting and local allelic variants.', Genome biology, vol. 10, no. 5, p. R53.
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BACKGROUND: Toxoplasma gondii is a zoonotic parasite of global importance. In common with many protozoan parasites it has the capacity for sexual recombination, but current evidence suggests this is rarely employed. The global population structure is dominated by a small number of clonal genotypes, which exhibit biallelic variation and limited intralineage divergence. Little is known of the genotypes present in Africa despite the importance of AIDS-associated toxoplasmosis. RESULTS: We here present extensive sequence analysis of eight isolates from Uganda, including the whole genome sequencing of a type II/III recombinant isolate, TgCkUg2. 454 sequencing gave 84% coverage across the approximate 61 Mb genome and over 70,000 single nucleotide polymorphisms (SNPs) were mapped against reference strains. TgCkUg2 was shown to contain entire chromosomes of either type II or type III origin, demonstrating chromosome sorting rather than intrachromosomal recombination. We mapped 1,252 novel polymorphisms and clusters of new SNPs within coding sequence implied selective pressure on a number of genes, including surface antigens and rhoptry proteins. Further sequencing of the remaining isolates, six type II and one type III strain, confirmed the presence of novel SNPs, suggesting these are local allelic variants within Ugandan type II strains. In mice, the type III isolate had parasite burdens at least 30-fold higher than type II isolates, while the recombinant strain had an intermediate burden. CONCLUSIONS: Our data demonstrate that recombination between clonal lineages does occur in nature but there is nevertheless close homology between African and North American isolates. The quantity of high confidence SNP data generated in this study and the availability of the putative parental strains to this natural recombinant provide an excellent basis for future studies of the genetic divergence and of genotype-phenotype relationships.
Allan, F., Rollinson, D., Smith, J.E. & Dunn, A.M. 2009, 'Host choice and penetration by Schistosoma haematobium miracidia.', Journal of helminthology, vol. 83, no. 1, pp. 33-38.
Schistosome parasites commonly show specificity to their intermediate mollusc hosts and the degree of specificity can vary between parasite strains and geographical location. Here the role of miracidial behaviour in host specificity of Schistosoma haematobium on the islands of Zanzibar is investigated. In choice-chamber experiments, S. haematobium miracidia moved towards Bulinus globosus snail hosts in preference to empty chambers. In addition, miracidia preferred uninfected over patent B. globosus. This preference should benefit the parasite as patent snails are likely to have mounted an immune response to S. haematobium as well as providing poorer resources than uninfected snails. Miracidia also discriminated between the host B. globosus and the sympatric, non-host species Cleopatra ferruginea. In contrast, S. haematobium did not discriminate against the allopatric Bulinus nasutus. Penetration of the host by miracidia was investigated by screening snails 24 h after exposure using polymerase chain reaction (PCR) with S. haematobium specific DraI repeat primers. There was no difference in the frequency of penetration of B. globosus versus B. nasutus. These responses to different snail species may reflect selection pressure to avoid sympatric non-hosts which represent a transmission dead end. The distribution of B. nasutus on Unguja is outside the endemic zone and so there is less chance of exposure to S. haematobium, hence there will be little selection pressure to avoid this non-host snail.
Gaskell, E.A., Smith, J.E., Pinney, J.W., Westhead, D.R. & McConkey, G.A. 2009, 'A unique dual activity amino acid hydroxylase in Toxoplasma gondii.', PloS one, vol. 4, no. 3, p. e4801.
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The genome of the protozoan parasite Toxoplasma gondii was found to contain two genes encoding tyrosine hydroxylase; that produces L-DOPA. The encoded enzymes metabolize phenylalanine as well as tyrosine with substrate preference for tyrosine. Thus the enzymes catabolize phenylalanine to tyrosine and tyrosine to L-DOPA. The catalytic domain descriptive of this class of enzymes is conserved with the parasite enzyme and exhibits similar kinetic properties to metazoan tyrosine hydroxylases, but contains a unique N-terminal extension with a signal sequence motif. One of the genes, TgAaaH1, is constitutively expressed while the other gene, TgAaaH2, is induced during formation of the bradyzoites of the cyst stages of the life cycle. This is the first description of an aromatic amino acid hydroxylase in an apicomplexan parasite. Extensive searching of apicomplexan genome sequences revealed an ortholog in Neospora caninum but not in Eimeria, Cryptosporidium, Theileria, or Plasmodium. Possible role(s) of these bi-functional enzymes during host infection are discussed.
Morley, E.K., Williams, R.H., Hughes, J.M., Thomasson, D., Terry, R.S., Duncanson, P., Smith, J.E. & Hide, G. 2008, 'Evidence that primary infection of Charollais sheep with Toxoplasma gondii may not prevent foetal infection and abortion in subsequent lambings.', Parasitology, vol. 135, no. 2, pp. 169-173.
A study carried out on a sheep farm examined whether Toxoplasma gondii foetal infection and associated abortion occur in successive lambings. We identified 29 ewes that gave birth to lambs on at least 2 successive years over our study period, 2000-2003. Tissue samples from the progeny of these ewes were analysed by PCR to determine infection status with T. gondii. T. gondii-infected lambs were born in 31% of successive pregnancies. T. gondii-positive lambs were aborted in successive pregnancies in 21% of lambings during study period, 2000-2003. The frequency of successive abortions within this flock over the period 1992-2003 was 18%. If a lamb was congenitally infected there was a high risk (69%) that the successive lamb from that ewe would also be congenitally infected. Similarly, if a lamb was aborted there was a high risk (55%) of abortion in the next lamb produced. These data suggest that life-long immunity to T. gondii infections may not always be acquired following an initial infection and raises the question as to whether the mechanisms of T. gondii transmission prior to and during ovine pregnancies are fully understood.
Lindström, I., Sundar, N., Lindh, J., Kironde, F., Kabasa, J.D., Kwok, O.C., Dubey, J.P. & Smith, J.E. 2008, 'Isolation and genotyping of Toxoplasma gondii from Ugandan chickens reveals frequent multiple infections.', Parasitology, vol. 135, no. Pt 1, pp. 39-45.
The genetic make-up of an infecting Toxoplasma gondii strain may be important for the outcome of infection and the risk of reactivation of chronic disease. In order to survey the distribution of different genotypes within an area, free-range chickens act as a good model species. In this study 85 chickens were used to investigate the prevalence, genotype and mouse virulence of T. gondii in Kampala, Uganda. Antibodies were detected in 40 chickens, of which 20 had MAT-titres of 1:20 or higher and were also positive by PCR. Genotyping of 5 loci (SAG1, SAG2, SAG3, BTUB and GRA6) showed that 6 strains belonged to genotype I, 8 to Type II and 1 to Type III. Five chickens had multiple infections; 3 individuals with Type I plus Type II and a further 2 harbouring Types I, II and III. Isolates were obtained from 9 chickens via bioassay in mice, 6 were Type II strains and 3 were from animals with mixed infection. This is the first set of African T. gondii strains to be genotyped at multiple loci and in addition to the 3 predominant lineages we found a small number of new polymorphisms and a high frequency of multiple infections.
Hide, G., Gerwash, O., Morley, E.K., Williams, R.H., Hughes, J.M., Thomasson, D., Elmahaishi, M.S., Elmahaishi, K.H., Terry, R.S. & Smith, J.E. 2007, 'Does vertical transmission contribute to the prevalence of toxoplasmosis?', Parassitologia, vol. 49, no. 4, pp. 223-226.
Toxoplasma gondii is a ubiquitous parasite with a widespread distribution both in terms of geographical and host range. Although the definitive host is the cat, it is also a major health hazard to domestic animals and humans. Three routes of transmission are recognised (infection from the cat, carnivory and congenital transmission). We aimed to assess the relative importance of congenital transmission, using sheep as a model system, due to the lack of carnivory. We report, using PCR as a diagnostic tool, that congenital transmission occurs with high frequency (69%). If transmission from oocysts was important in sheep, we would expect sheep reared under the same environmental conditions (i.e. a single farm) to have a random distribution of Toxoplasma infection. Using breeding records in conjunction with PCR, some families were found to have high Toxoplasma prevalence and abortion while others were free of Toxoplasma infection and abortion (P < 0.01). This supports the notion that Toxoplasma may be transmitted vertically. In humans, we conducted a similar study and showed that Toxoplasma was transmitted from mother to baby in 19.8% of cases. Vertical transmission in Toxoplasma may be more important than previously thought and this knowledge should be considered in any eradication strategies.
Dalton, J.E., Cruickshank, S.M., Egan, C.E., Mears, R., Newton, D.J., Andrew, E.M., Lawrence, B., Howell, G., Else, K.J., Gubbels, M.J., Striepen, B., Smith, J.E., White, S.J. & Carding, S.R. 2006, 'Intraepithelial gammadelta+ lymphocytes maintain the integrity of intestinal epithelial tight junctions in response to infection.', Gastroenterology, vol. 131, no. 3, pp. 818-829.
BACKGROUND & AIMS: Intestinal epithelial integrity and permeability is dependent on intercellular tight junction (TJ) complexes. How TJ integrity is regulated remains unclear, although phosphorylation and dephosphorylation of the integral membrane protein occludin is an important determinant of TJ formation and epithelial permeability. We have investigated the role intestinal intraepithelial lymphocytes (iIELs) play in regulating epithelial permeability in response to infection. METHODS: Recombinant strains of Toxoplasma gondii were used to assess intestinal epithelial barrier function and TJ integrity in mice with intact or depleted populations of iIELs. Alterations in epithelial permeability were correlated with TJ structure and the state of phosphorylation of occludin. iIEL in vivo reconstitution experiments were used to identify the iIELs required to maintain epithelial permeability and TJ integrity. RESULTS: In the absence of gammadelta+ iIELs, intestinal epithelial barrier function and the ability to restrict epithelial transmigration of Toxoplasma and the unrelated intracellular bacterial pathogen Salmonella typhimurium was severely compromised. Leaky epithelium in gammadelta+ iIEL-deficient mice was associated with the absence of phosphorylation of serine residues of occludin and lack of claudin 3 and zona occludens-1 proteins in TJ complexes. These deficiencies were attributable to the absence of a single subset of gammadelta T-cell receptor (TCR-Vgamma7+) iIELs that, after reconstituting gammadelta iIEL-deficient mice, restored epithelial barrier function and TJ complexes, resulting in increased resistance to infection. CONCLUSIONS: These findings identify a novel role for gammadelta+ iIELs in maintaining TJ integrity and epithelial barrier function that have implications for understanding the pathogenesis of intestinal inflammatory diseases associated with disruption of TJ complexes.
Hughes, J.M., Williams, R.H., Morley, E.K., Cook, D.A., Terry, R.S., Murphy, R.G., Smith, J.E. & Hide, G. 2006, 'The prevalence of Neospora caninum and co-infection with Toxoplasma gondii by PCR analysis in naturally occurring mammal populations.', Parasitology, vol. 132, no. Pt 1, pp. 29-36.
Neospora caninum and Toxoplasma gondii are closely related intracellular protozoan parasites associated with bovine and ovine abortion respectively. Little is known about the extent of Neospora/Toxoplasma co-infection in naturally infected populations of animals. Using nested PCR techniques, based on primers from the Nc5 region of N. caninum and SAG1 for T. gondii, the prevalence of N. caninum and its co-infection with T. gondii were investigated in populations of Mus domesticus, Rattus norvegicus and aborted lambs (Ovis aries). A low frequency of infection with N. caninum was detected in the Mus domesticus (3%) and Rattus norvegicus (4.4%) populations. A relatively high frequency of infection with N. caninum was detected in the brains of aborted lambs (18.9%). There was no significant relationship between N. caninum and T. gondii co-infection. Investigation of the tissue distribution of Neospora, in aborted lambs, showed that Neospora could not be detected in tissues other than brain and this was in contrast to Toxoplasma where the parasite could be frequently detected in a range of tissues.
Weedall, R.T., Robinson, M., Smith, J.E. & Dunn, A.M. 2006, 'Targeting of host cell lineages by vertically transmitted, feminising microsporidia.', International journal for parasitology, vol. 36, no. 7, pp. 749-756.
Feminising microsporidian parasites are transmitted vertically from generation to generation of their crustacean hosts. Little is known about the mechanisms underpinning vertical transmission, in particular, parasite transmission to the host gonad during host development. Here, we investigate the burden and distribution of two species of vertically transmitted, feminising microsporidia (Dictyocoela duebenum and Nosema granulosis) during early embryogenesis (zygote to eight-cells) of the Gammarus duebeni host. Parasite burden differs between the two parasites with N. granulosis being higher by a factor of 10. Whilst D. duebenum replicates during the first few host cell divisions, there is no increase in N. granulosis burden. Only merogonic parasite stages were observed in the host embryo. Distribution of both parasites was non-random from the two-cell embryo stage, indicating biased parasite segregation at host cell division. Dictyocoela duebenum burden was low in the germline and somatic gonad progenitor cells but was highest in the ectoderm precursors, leading us to propose that the parasite targets these cells and then secondarily infects the gonad later in host development. Targeting by N. granulosis was less specific although there was a persistent bias in parasite distribution throughout host cell divisions. Parasite burden was highest in the ectoderm precursors as well as the germline progenitors leading us to suggest that, in addition to using the ectodermal route, N. granulosis may also target germline directly. Biased segregation will be adaptive for these parasites as it is likely to lead to efficient transmission and feminisation whilst minimising virulence in the host.
Weedall, R.T., Robinson, M. & Smith, J. 2006, 'Distribution of two vertically transmitted, feminising microsporidia during host embryogenesis', International Journal for Parasitology, vol. 36, pp. 749-756.
Morley, E.K., Williams, R.H., Hughes, J.M., Terry, R.S., Duncanson, P., Smith, J.E. & Hide, G. 2005, 'Significant familial differences in the frequency of abortion and Toxoplasma gondii infection within a flock of Charollais sheep.', Parasitology, vol. 131, no. Pt 2, pp. 181-185.
A study was carried out to investigate the frequencies of abortion and congenital Toxoplasma gondii infection within 27 families (765 individuals) of a pedigree Charollais sheep flock maintained on a working farm in Worcestershire, UK, since 1992. Pedigree lambing records were analysed to establish the frequency of abortion for each family. The frequency of congenital infection was determined for each family by PCR analysis of tissue samples taken from newborn lambs. A total of 155 lambs were tested for congenital T. gondii infection, which were all born during the study period 2000-2003. Significant differences in the frequency of abortion between sheep families within this flock were observed with frequencies ranging between 0% and 48% (P < 0.01). Significantly different infection frequencies with T. gondii were also observed for different families and ranged between 0% and 100% (P<0.01). Although the actual cause of each abortion was not verified, a highly significant positive correlation was found to exist between the frequency of abortion and the frequency of T. gondii infection in the same families (P<0.01). The data presented here raise further questions regarding the significance of congenital transmission of T. gondii within sheep populations, the possible successive vertical transmission of T. gondii within families of sheep, and the potential role of inherited genetic susceptibility to abortion with respect to T. gondii infection. This work invites further study into the epidemiology of ovine toxoplasmosis and may have implications for sheep husbandry methods in the future.
Williams, R.H., Morley, E.K., Hughes, J.M., Duncanson, P., Terry, R.S., Smith, J.E. & Hide, G. 2005, 'High levels of congenital transmission of Toxoplasma gondii in longitudinal and cross-sectional studies on sheep farms provides evidence of vertical transmission in ovine hosts', Parasitology, vol. 130, no. 3, pp. 301-307.
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Recent research suggests that vertical transmission may play an important role in sustaining Toxoplasma gondii infection in some species. We report here that congenital transmission occurs at consistently high levels in pedigree Charollais and outbred sheep flocks sampled over a 3-year period. Overall rates of transmission per pregnancy determined by PCR based diagnosis, were consistent over time in a commercial sheep flock (69%) and in sympatric (60%) and allopatric (41%) populations of Charollais sheep. The result of this was that 53.7% of lambs were acquiring an infection prior to birth: 46.4% of live lambs and 90.0% of dead lambs (in agreement with the association made between T. gondii and abortion). No significant differences were observed between lamb sexes. Although we cannot distinguish between congenital transmission occurring due to primary infection at pregnancy or reactivation of chronic infection during pregnancy, our observations of consistently high levels of congenital transmission over successive lambings favour the latter. © 2004 Cambridge University Press.
Elizabeth McClymont, H., Dunn, A.M., Terry, R.S., Rollinson, D., Littlewood, D.T. & Smith, J.E. 2005, 'Molecular data suggest that microsporidian parasites in freshwater snails are diverse.', International journal for parasitology, vol. 35, no. 10, pp. 1071-1078.
Microsporidian parasites infect almost all invertebrate and vertebrate hosts and have significant effects on individual and population fitness. Phylogenetic analysis demonstrates that the phylum is highly divergent and that some lineages show strong associations with host taxa. We here examine the diversity and distribution of parasites in gastropod molluscs to test for host-parasite co-association. 16 populations representing 10 species of freshwater snails were screened using microsporidian specific small subunit rDNA primers. Four novel microsporidian parasite sequences were detected within populations of three host species from the genera Bulinus, Biomphalaria and Planorbis. Prevalence ranged from 5 to 84%. Phylogenetic analysis of these novel sequences reveals that they group together as a paraphyletic assemblage in the microsporidian tree basal to the two lineages containing the genera Encephalitozoon and Nosema. Preliminary observation of one microsporidian infection, show parasites distributed in all tissue systems of Bulinus globosus. However, infection is most prevalent in the digestive gland while also in the egg sacs, suggesting that the microsporidium is using a mixed strategy of horizontal and vertical transmission in this population.
Ford, A.T., Rodgers-Gray, T.P., Davies, I.M., Dunn, A.M., Read, P.A., Robinson, C.D., Smith, J.E. & Fernandes, T.F. 2005, 'Erratum: Abnormal gonadal morphology in intersex, Echinogammarus marinus (Amphipoda): A possible cause of reduced fecundity? (Marine Biology (2005) DOI: s00227-005-1601-1)', Marine Biology, vol. 147, no. 4, p. 1053.
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Dunn, A.M. & Smith, J.E. 2005, 'Parasitic sex ratio distortion', Biologist, vol. 52, no. 3, pp. 144-148.
Parasites that are vertically transmitted (passed from mother to offspring via the gametes) have an unusual relationship with their hosts. Vertically transmitted parasites depend on successful host reproduction for transmission to the next generation of hosts. As a result, these parasites tend to have little effect on host growth, survival or reproduction. However, many vertically transmitted parasites including some viruses, bacteria and microsporidia, manipulate host reproduction and cause sex ratio distortion in the host population either through killing male hosts or by converting males into females. This review asks why parasites distort host sex ratios and considers the implications of sex ratio distorting parasites for host ecology and evolution.
Morris, D.J., Terry, R.S., Ferguson, K.B., Smith, J.E. & Adams, A. 2005, 'Ultrastructural and molecular characterization of Bacillidium vesiculoformis n. sp. (Microspora: Mrazekiidae) in the freshwater oligochaete Nais simplex (Oligochaeta: Naididae).', Parasitology, vol. 130, no. Pt 1, pp. 31-40.
The development of a new species, Bacillidium vesiculoformis n. sp. (Microspora, Mrazekiidae), is described from the freshwater oligochaete Nais simplex (Oligochaeta, Naididae). Initial stages of parasite development consist of a monokaryotic merogony within a haemocyte of the intestinal blood sinus. The resulting hypertrophied haemocyte is attached to the chloragocytes of the sinus by fine cytoplasmic extensions with the sinus around the cell becoming greatly enlarged. The meronts within the haemocyte form diplokaryotic sporonts that undergo sporogenesis directly within the cytoplasm of the host cell. The infected cell becomes packed with spores and developmental stages, causing it dramatically to increase in size, eventually rupturing the oligochaete and cell. Sporogony appears to be disporoblastic. Released spores were observed to have an adhesive quality. Transmission studies conducted with mature spores failed to transmit the parasite horizontally although vertical transmission was observed. Phylogenetic analysis of the parasite demonstrated that B. vesiculoformis clustered with microsporidian parasites of bryozoa and two other microsporidians, Janacekia debaiseuxi and an unidentified Bacillidium sp.
Egan, C.E., Dalton, J.E., Andrew, E.M., Smith, J.E., Gubbels, M.J., Striepen, B. & Carding, S.R. 2005, 'A requirement for the Vgamma1+ subset of peripheral gammadelta T cells in the control of the systemic growth of Toxoplasma gondii and infection-induced pathology.', Journal of immunology (Baltimore, Md. : 1950), vol. 175, no. 12, pp. 8191-8199.
gammadelta T cells are a diverse population of T cells that are widely distributed and are a common feature of pathogen-induced immune responses. It is not clear, however, whether different populations of gammadelta T cells have specific functions, and what factors determine the functional properties of individual populations. A murine model of peroral Toxoplasma gondii infection was used to determine the contribution Vgamma1+ intestinal intraepithelial lymphocytes (IELs) vs systemic Vgamma1+ T cells make to the acute and chronic stages of the host immune response, and whether the macrophage cytocidal activity of Vgamma1+ T cells described in bacterial infections is seen in other, unrelated infectious disease models. In response to oral infection with virulent type 1 or avirulent type II strains of T. gondii, TCR-delta-/- mice rapidly developed severe ileitis. In contrast, in mice deficient in Vgamma1+ T cells and IELs and wild-type mice, inflammation was delayed in onset and less severe. The protective effect of (Vgamma1-) IELs to Toxoplasma infection was unrelated to their cytolytic and cytokine (Th1)-producing capabilities. Systemic Vgamma1+ T cells were shown to play an essential role in limiting parasite growth and inflammation in peripheral tissues and, in particular, in the CNS, that was associated with their ability to efficiently kill parasite-elicited and infected macrophages. These findings suggest that macrophage cytocidal activity of Vgamma1+ T cells may be a universal feature of pathogen-induced immune responses and that microenvironmental factors influence the involvement and function of gammadelta T cells in the host response to infection.
Ford, A.T., Rodgers-Gray, T.P., Davies, I.M., Dunn, A.M., Read, P.A., Robinson, C.D., Smith, J.E. & Fernandes, T.F. 2005, 'Abnormal gonadal morphology in intersex, Echinogammarus marinus (Amphipoda): A possible cause of reduced fecundity?', Marine Biology, vol. 147, no. 4, pp. 913-918.
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Recent reports have demonstrated a cost associated with intersexuality in Amphipoda, including reduced fecundity and fertility. In this study, the gross morphology of the gonads in normal and intersex Echinogammarus marinus (Amphipoda) were compared to determine whether resource allocation to gonadal tissue accounted for this reduced fitness. Evidence for the presence of the male sex-determining hormone, androgenic gland hormone (AGH), was compared between sexual phenotypes using MALDI mass spectrometry. Two distinct intersex phenotypes ('male' intersex and 'female' intersex) were found, with variation in gonadal structure corresponding with external phenotype. Examination of male intersexes revealed normal testicular development (testes, seminal vesicles and vas deferens), but also revealed the formation of an oviduct. Ovaries of intersex females showed normal ovarian development, but were reduced in length by approximately 20% due to the presence of vas deferens. The number of vas deferens in intersex females was equal to the number (one or two) of genital papillae. We hypothesise that the reduced ovarian length observed in intersex females is a likely cause of the reduced brood size previously reported in intersex females of this species. Variation in the sexual phenotype corresponded both to development of the androgenic gland and to expression of a peptide fragment corresponding to the A chain of androgenic gland hormone (AGH). Androgenic glands and a putative AGH peptide were present in males. However, in both normal and intersex females, the androgenic glands were only present in a rudiment form and the peptide was not detected. Intersex males were found to possess abnormal glands that appeared hypertrophied. However, AGH peptides were not detected, supporting the suggestion that the intersex phenotype is manifested via perturbations of AGH. © Springer-Verlag 2005.
Williams, R.H., Morley, E.K., Hughes, J.M., Duncanson, P., Terry, R.S., Smith, J.E. & Hide, G. 2005, 'High levels of congenital transmission of Toxoplasma gondii in longitudinal and cross-sectional studies on sheep farms provides evidence of vertical transmission in ovine hosts.', Parasitology, vol. 130, no. Pt 3, pp. 301-307.
Recent research suggests that vertical transmission may play an important role in sustaining Toxoplasma gondii infection in some species. We report here that congenital transmission occurs at consistently high levels in pedigree Charollais and outbred sheep flocks sampled over a 3-year period. Overall rates of transmission per pregnancy determined by PCR based diagnosis, were consistent over time in a commercial sheep flock (69%) and in sympatric (60%) and allopatric (41%) populations of Charollais sheep. The result of this was that 53.7 % of lambs were acquiring an infection prior to birth: 46.4% of live lambs and 90.0% of dead lambs (in agreement with the association made between T. gondii and abortion). No significant differences were observed between lamb sexes. Although we cannot distinguish between congenital transmission occurring due to primary infection at pregnancy or reactivation of chronic infection during pregnancy, our observations of consistently high levels of congenital transmission over successive lambings favour the latter.
Rodgers-Gray, T.P., Smith, J.E., Ashcroft, A.E., Isaac, R.E. & Dunn, A.M. 2004, 'Mechanisms of parasite-induced sex reversal in Gammarus duebeni.', International journal for parasitology, vol. 34, no. 6, pp. 747-753.
The amphipod Gammarus duebeni is host to the feminising microsporidian parasite Nosema granulosis that converts males into functional females. To test the hypothesis that the parasite acts through endocrine disruption we compared the morphology of the gonad and activity of the androgenic gland, which coordinates male sexual differentiation, in infected and uninfected animals. Male gonad consisted of testis, seminal vesicle and vas deferens that was anchored to the genital papilla on segment 7. The androgenic gland was associated with the distal end of the vas deferens. In female and intersex animals the bi-lobed ovary opened into the oviduct at segment 5, vestigial vas deferens and vestigial androgenic gland were retained. The majority of parasitised individuals (38/39) were either phenotypic females or intersexes with fully developed ovaries and an undifferentiated androgenic gland. Our data suggest that the parasite prevents differentiation of the androgenic gland. In further support of this hypothesis, mass spectrometry of a single androgenic gland from males revealed a dominant molecular ion with a mass/charge ratio of 4818.4+H, corresponding to a peptide of androgenic gland hormone from Armadillidium vulgare. In contrast the vestigial androgenic gland from parasitised and unparasitised females showed only low intensity peaks. Our observations demonstrate that the parasite manipulates host sex by preventing androgenic gland differentiation, androgenic gland hormone production and consequently male differentiation. This is in agreement with observations of A. vulgare with inherited Wolbachia infection, suggesting that phylogenetically distant feminisers manipulate hosts through a common mechanism. The high frequency of infection in intersexes (89.3%) suggests that this phenotype results from incomplete feminisation by the parasite.
Terry, R.S., Smith, J.E., Sharpe, R.G., Rigaud, T., Littlewood, D.T., Ironside, J.E., Rollinson, D., Bouchon, D., MacNeil, C., Dick, J.T. & Dunn, A.M. 2004, 'Widespread vertical transmission and associated host sex-ratio distortion within the eukaryotic phylum Microspora.', Proceedings. Biological sciences / The Royal Society, vol. 271, no. 1550, pp. 1783-1789.
Vertical transmission (VT) and associated manipulation of host reproduction are widely reported among prokaryotic endosymbionts. Here, we present evidence for widespread use of VT and associated sex-ratio distortion in a eukaryotic phylum. The Microspora are an unusual and diverse group of eukaryotic parasites that infect all animal phyla. Following our initial description of a microsporidian that feminizes its crustacean host, we survey the diversity and distribution of VT within the Microspora. We find that vertically transmitted microsporidia are ubiquitous in the amphipod hosts sampled and that they are also diverse, with 11 species of microsporidia detected within 16 host species. We found that infections were more common in females than males, suggesting that host sex-ratio distortion occurs in five out of eight parasite species tested. Phylogenetic reconstruction demonstrates that VT occurs in all major lineages of the phylum Microspora and that sex-ratio distorters are found on multiple branches of the phylogenetic tree. We propose that VT is either an ancestral trait or evolves with peculiar frequency in this phylum. If the association observed here between VT and host sex-ratio distortion holds true across other host taxa, these eukaryotic parasites may join the bacterial endosymbionts in their importance as sex-ratio distorters.
Slothouber Galbreath, J.G., Smith, J.E., Terry, R.S., Becnel, J.J. & Dunn, A.M. 2004, 'Invasion success of Fibrillanosema crangonycis, n.sp., n.g.: a novel vertically transmitted microsporidian parasite from the invasive amphipod host Crangonyx pseudogracilis.', International journal for parasitology, vol. 34, no. 2, pp. 235-244.
Parasitism is known to be an important factor in determining the success of biological invasions. Here we examine Crangonyx pseudogracilis, a North American amphipod invasive in the United Kingdom and describe a novel microsporidium, Fibrillanosema crangonycis n.sp., n.g. The primary site of infection is the female gonad and the parasite is transovarially transmitted to the eggs. PCR screening reveals a female bias in the distribution of parasites (96.6% of females, N=29; 22.2% of males, N=27), which is indicative of host sex ratio distortion. The morphological and molecular characterisations of this new microsporidium place it outside all currently established genera. On the basis of these differences, we erect the new genus Fibrillanosema n.g. While F. crangonycis is morphologically identical to uncharacterised microsporidia from populations of North American amphipods, it is distinct from microsporidia found in European populations of amphipods. These data support the hypothesis that vertically transmitted parasites may be selectively retained during invasion events. Furthermore where vertical transmission is combined with host sex ratio distortion these parasites may directly enhance host invasion success through increased rates of population growth.
Robinson, S.A., Smith, J.E. & Millner, P.A. 2004, 'Toxoplasma gondii major surface antigen (SAG1): in vitro analysis of host cell binding.', Parasitology, vol. 128, no. Pt 4, pp. 391-396.
Previous studies have indicated that SAG1, the major surface molecule of the protozoan parasite Toxoplasma gondii, is an important attachment ligand for the host cell. However, the research data that supports this claim comes largely from studies investigating tachyzoite binding, and not SAG1 binding per se. In this study we successfully developed an in vitro attachment assay to directly evaluate the mechanism of SAG1-host cell binding. Competition experiments were then performed using SAG1 that had been pre-treated with the neoglycoprotein BSA-glucosamide or with antibody. Soluble BSA-glucosamide blocked SAG1 attachment to MDBK cells in a dose-dependent manner, implying that SAGI binding is mediated, in part, via attachment to host cell surface glucosamine. Interestingly, pre-incubation of SAG1 in polyclonal sera from chronically infected mice failed to block binding. This challenges the assumption that anti-SAG1 antibodies block parasite attachment through the masking of SAG1 host cell binding domains. Taken together, this evidence presents new strategies for understanding SAG1-mediated attachment.
Marshall, P.A., Hughes, J.M., Williams, R.H., Smith, J.E., Murphy, R.G. & Hide, G. 2004, 'Detection of high levels of congenital transmission of Toxoplasma gondii in natural urban populations of Mus domesticus.', Parasitology, vol. 128, no. Pt 1, pp. 39-42.
The relative importance of different transmission routes of Toxoplasma gondii has been a matter for debate. This ubiquitous parasite is generally thought to be transmitted by infective oocysts excreted by the definitive host, the cat. Ingestion of undercooked meat has also been considered an important route of transmission in many mammals while congenital transmission has generally been considered relatively rare. Experimental studies demonstrate the ability of T. gondii to be transmitted congenitally, but few studies have investigated the frequency of this transmission route in natural populations. We use PCR amplification of the SAG1 gene to investigate the frequency of congenital transmission in a wild population of mice (Mus domesticus) and show that congenital transmission is occurring in 75% of pregnancies in this population. Furthermore, for infected pregnant mice, transmission occurs to at least one foetus in 100% of cases while variable penetrance of congenital infection is observed. These high levels of congenital transmission in this wild population of mice, taken together with other recent data on congenital transmission in sheep, suggests that this phenomenon might be more widespread than previously thought.
Liu, J.P., Cao, Y., Smith, J. & Xu, X.U. 2004, 'Studies of the application of PCR molecular diagnosis to silkworms with simulated pebrine disease', Scientia Agricultura Sinica, vol. 37, pp. 1925-1931.
Liu, J.P., Cao, Y., Smith, J. & Xu, X.U. 2004, 'Preliminary studies on the application of PCR diagnosis on the silkworm eggs and moths with simulated Pebrine disease infection', ACTA Sericologica Sinica, vol. 30, pp. 1925-1931.
MacNeil, C., Dick, J.T., Hatcher, M.J., Terry, R.S., Smith, J.E. & Dunn, A.M. 2003, 'Parasite-mediated predation between native and invasive amphipods.', Proceedings. Biological sciences / The Royal Society, vol. 270, no. 1521, pp. 1309-1314.
Parasites can structure biological communities directly through population regulation and indirectly by processes such as apparent competition. However, the role of parasites in the process of biological invasion is less well understood and mechanisms of parasite mediation of predation among hosts are unclear. Mutual predation between native and invading species is an important factor in determining the outcome of invasions in freshwater amphipod communities. Here, we show that parasites mediate mutual intraguild predation among native and invading species and may thereby facilitate the invasion process. We find that the native amphipod Gammarus duebeni celticus is host to a microsporidian parasite, Pleistophora sp. (new species), with a frequency of infection of 0-90%. However, the parasite does not infect three invading species, G. tigrinus, G. pulex and Crangonyx pseudogracilis. In field and laboratory manipulations, we show that the parasite exhibits cryptic virulence: the parasite does not affect host fitness in single-species populations, but virulence becomes apparent when the native and invading species interact. That is, infection has no direct effect on G. d. celticus survivorship, size or fecundity; however, in mixed-species experiments, parasitized natives show a reduced capacity to prey on the smaller invading species and are more likely to be preyed upon by the largest invading species. Thus, by altering dominance relationships and hierarchies of mutual predation, parasitism strongly influences, and has the potential to change, the outcome of biological invasions.
Sokolova, Y.Y., Dolgikh, V.V., Morzhina, E.V., Nassonova, E.S., Issi, I.V., Terry, R.S., Ironside, J.E., Smith, J.E. & Vossbrinck, C.R. 2003, 'Establishment of the new genus Paranosema based on the ultrastructure and molecular phylogeny of the type species Paranosema grylli Gen. Nov., Comb. Nov. (Sokolova, Selezniov, Dolgikh, Issi 1994), from the cricket Gryllus bimaculatus Deg.', Journal of invertebrate pathology, vol. 84, no. 3, pp. 159-172.
The ultrastructure of the microsporidian parasite Nosema grylli, which parasitizes primarily fat body cells and haemocytes of the cricket Gryllus bimaculatus (Orthoptera, Gryllidae) is described. All observed stages (meront, meront/sporont transitional stage ("second meront"), sporont, sporoblast, and spore) are found in direct contact with the host cell cytoplasm. Nuclei are diplokaryotic during almost all stages of the life cycle, but a brief stage with one nucleus containing an abundance of electron-dense material is observed during a "second merogony." Sporogony is disporous. Mature spores are ovocylindrical in shape and measure 4.5+/-0.16micromx2.2+/-0.07 microm (n=10) on fresh smears and 3.3+/-0.06 micromx1.4+/-0.07 microm (n=10) on ultrathin sections. Spores contain 15-18 coils of an isofilar polar filament arranged in one or two layers. Comparative phylogenetic analysis using rDNA shows N. grylli to be closely related to another orthopteran microsporidian, Nosema locustae, and to Nosema whitei from the confused flour beetle, Tribolium confusum. Antonospora scoticae, a parasite of the communal bee Andrena scotica, is a sister taxon to these three Nosema species. The sequence divergence and morphological traits clearly separate this group of "Nosema" parasites from the "true" Nosema clade containing Nosema bombycis. We therefore propose to change the generic name of N. grylli and its close relative N. locustae to Paranosema n. comb. We leave N. whitei in former status until more data on fine morphology of the species are obtained.
Ironside, J.E., Smith, J.E., Hatcher, M.J., Sharpe, R.G., Rollinson, D. & Dunn, A.M. 2003, 'Two species of feminizing microsporidian parasite coexist in populations of Gammarus duebeni.', Journal of evolutionary biology, vol. 16, no. 3, pp. 467-473.
The amphipod crustacean Gammarus duebeni hosts two species of vertically transmitted microsporidian parasites, Nosema granulosis and Microsporidium sp. A. Here it is demonstrated that these co-occurring parasite species both cause infected females to produce female-biased broods. A survey of European G. duebeni populations demonstrates that these two parasites co-occur in six of 10 populations. These findings contrast with the theoretical prediction that two vertically transmitted feminizing parasites should not coexist in a panmictic population of susceptible hosts at equilibrium. Possible explanations for the co-occurrence of the two feminizing microsporidia in G. duebeni include the recent invasion of a new parasite, horizontal transmission of one or both parasites and the spread of alleles for resistance to the dominant parasite in host populations.
Terry, R.S., MacNeil, C., Dick, J.T., Smith, J.E. & Dunn, A.M. 2003, 'Resolution of a taxonomic conundrum: an ultrastructural and molecular description of the life cycle of Pleistophora mulleri (Pfeiffer 1895; Georgevitch 1929).', The Journal of eukaryotic microbiology, vol. 50, no. 4, pp. 266-273.
The classification of a microsporidian parasite observed in the abdominal muscles of amphipod hosts has been repeatedly revised but still remains inconclusive. This parasite has variable spore numbers within a sporophorous vesicle and has been assigned to the genera Glugea, Pleistophora, Stempellia, and Thelohania. We used electron microscopy and molecular evidence to resolve the previous taxonomic confusion and confirm its identification as Pleistophora mulleri. The life cycle of P. mulleri is described from the freshwater amphipod host Gammarus duebeni celticus. Infection appeared as white tubular masses within the abdominal muscle of the host. Light and transmission electron microscope examination revealed the presence of an active microsporidian infection that was diffuse within the muscle block with no evidence of xenoma formation. Paucinucleate merogonial plasmodia were surrounded by an amorphous coat immediately external to the plasmalemma. The amorphous coat developed into a merontogenetic sporophorous vesicle that was present throughout sporulation. Sporogony was polysporous resulting in uninucleate spores, with a bipartite polaroplast, an anisofilar polar filament and a large posterior vacuole. SSU rDNA analysis supported the ultrastructural evidence clearly placing this parasite within the genus Pleistophora. This paper indicates that Pleistophora species are not restricted to vertebrate hosts.
Ironside, J.E., Dunn, A.M., Rollinson, D. & Smith, J.E. 2003, 'Association with host mitochondrial haplotypes suggests that feminizing microsporidia lack horizontal transmission.', Journal of evolutionary biology, vol. 16, no. 6, pp. 1077-1083.
The amphipod crustacean Gammarus duebeni hosts two feminizing microsporidian parasites, Nosema granulosis and Microsporidium sp. Samples of G. duebeni were collected from three sites on the Scottish island of Great Cumbrae and screened for microsporidia using polymerase chain reaction. Associations between the prevalence of the two feminizing parasites and haplotypes of the host mitochondrial gene cytochrome oxidase I (COI) were investigated. The prevalence of both parasites varied significantly among the host's COI haplotypes, suggesting that horizontal transmission is rare or absent in the life cycles of the feminizing microsporidia and that all transmission must therefore be vertical. Life cycles in which all transmission is vertical are common among bacterial parasites but have never before been demonstrated in Eukaryotic parasites.
Hogg, J.C., Ironside, J.E., Sharpe, R.G., Hatcher, M.J., Smith, J.E. & Dunn, A.M. 2002, 'Infection of Gammarus duebeni populations by two vertically transmitted microsporidia; parasite detection and discrimination by PCR-RFLP.', Parasitology, vol. 125, no. Pt 1, pp. 59-63.
We screened a population of the brackish water crustacean Gammarus duebeni from the Isle of Cumbrae for the presence of vertically transmitted microsporidia. We compared 2 screening techniques; light microscopy and PCR-based detection using generic 16S rDNA microsporidian primers. Fifty percent of females from this population tested positive for vertically transmitted microsporidia. The PCR screen was 100% efficient in comparison with existing LM based screening. In addition, the PCR screen produced bands of 2 sizes suggesting that more than 1 species of microsporidian was present. Sequencing revealed 2 distinct species of vertically transmitted microsporidia; 33% of females were infected with the feminizer Nosema granulosis and 17% were infected with a new species which we provisionally designate Microsporidium sp. On the basis of sequence information, we developed a discriminatory PCR-RFLP test based on MspI and HaeIII digests. This screen allows rapid detection and discrimination of vertically transmitted microsporidia in natural field populations. We applied the PCR-RFLP screen to a second G. duebeni population from the Isle of Man. This population also hosted these 2 parasite species. In total 45% of females harboured N. granulosis and 10% harboured Microsporidium sp. No dual-infected individuals were found in either population. The occurrence of 2 vertically transmitted parasites within a population has implications for our understanding of parasite-host relationships in the field and we discuss factors affecting the dynamics of parasite-parasite competition and coexistence.
Duncanson, P., Terry, R.S., Smith, J.E. & Hide, G. 2001, 'High levels of congenital transmission of Toxoplasma gondii in a commercial sheep flock.', International journal for parasitology, vol. 31, no. 14, pp. 1699-1703.
Our current understanding of congenital transmission of Toxoplasma gondii from ewe to lamb dictates that infection frequently results in abortion and the death of the developing foetus, that the birth of live infected lambs occurs rarely and that the cat is the predominant source of infection in ewes. Using direct polymerase chain reaction detection of T. gondii, we report high levels of congenital transmission occurring in a commercially managed sheep flock. We sampled foetal-derived placental tissue and tissues from aborted lambs and showed that congenital transmission was detected in these tissues from 61% of all pregnancies. Where pregnancies resulted in the death of one or more lambs, T. gondii was detected in the lamb tissue for all but one of 18 (94%) pregnancies. Of the successful pregnancies resulting in the birth of live lambs we were able to detect T. gondii in foetal-derived placental tissue from 37 of 70 (42%) pregnancies. These results show that congenital transmission is occurring in a high percentage of lambings including normal healthy lambings, at this farm, suggesting that this route of transmission from generation to generation may be much more significant than that reported previously. These results may have implications for sheep husbandry and future epidemiological studies of T. gondii.
Terry, R.S., Smith, J.E., Duncanson, P. & Hide, G. 2001, 'MGE-PCR: a novel approach to the analysis of Toxoplasma gondii strain differentiation using mobile genetic elements.', International journal for parasitology, vol. 31, no. 2, pp. 155-161.
The position of mobile genetic elements (MGE) within eukaryotic genomes is often highly variable and we have exploited this phenomenon to develop a novel approach to strain differentiation in Toxoplasma gondii. Two PCR based strategies were designed in which specific primers were used to amplify T. gondii MGE's revealing information on element size and positional variation. The first PCR strategy involved the use of a standard two primer PCR while the second strategy used a single specific primer in a step-up PCR protocol. This approach was applied to T. gondii reference strains which were either acute virulent or avirulent to mice. The use of a standard two primer PCR reaction revealed the presence of a virulence related marker in which all avirulent strains possessed an additional 688 bp band. The single primer PCR strategy demonstrated that all virulent strains had identical banding patterns suggesting invariance within this group of strains. However, all avirulent strains had different banding patterns indicating the presence of a number of individual lineages within this group. The applicability and sensitivity of MGE-PCR in epidemiological studies was demonstrated by direct amplification of T. gondii from sheep tissue samples. All sheep isolates, tested in this way, gave identical banding patterns suggesting the presence of an endemic Toxoplasma strain on this farm.
Dunn, A.M. & Smith, J.E. 2001, 'Microsporidian life cycles and diversity: the relationship between virulence and transmission.', Microbes and infection / Institut Pasteur, vol. 3, no. 5, pp. 381-388.
The microsporidia are obligate intracellular parasites which have diverse life cycles involving both horizontal and vertical transmission and parasitise a wide range of vertebrate and invertebrate hosts. In this paper we consider the life cycles and diversity of the microsporidia. We focus in particular on the relationship between parasite transmission and virulence and its implications for host-parasite coevolution. The use of horizontal and vertical routes of transmission varies between species and there is a strong link between transmission and virulence. Horizontal transmission is characterised by a high parasite burden and associated pathogenicity. In contrast, vertical transmission is characterised by low virulence, which has led to under-reporting of this important transmission route. Vertically transmitted microsporidia may also cause male killing or feminisation of their host, with implications for host population sex ratio and stability. Phylogenetic analysis shows that vertical transmission occurs in diverse branches of the Microspora. We find that there is evidence for vertical transmission in both vertebrate and invertebrate hosts and conclude that it is a common or possibly even ubiquitous transmission route within this phylum.
Appleford, P.J. & Smith, J.E. 2000, 'Strain and stage specific variation in Toxoplasma gondii antigens.', International journal for parasitology, vol. 30, no. 11, pp. 1187-1191.
The antigenic profile of virulent (RH, ENT, Martin) and avirulent (RRA, DEG, ME49) Toxoplasma strains was compared directly by western blotting using a panel of immune mouse sera. Dominant antigens of approximate MR 30-33, 21 and 25 x 10(3) were common to tachyzoites of all strains, however, there were significant quantitative and qualitative differences in the antigen profiles, indicating a moderate degree of strain specific polymorphism in tachyzoite antigens. We found no specific association between antigenic variation and strain virulence. Comparison of tachyzoite and bradyzoite antigens from homologous strains (RRA, DEG, ME49) confirmed the existence of stage specific antigens and demonstrated a conserved antigen profile among bradyzoites.
Terry, R.S., Smith, J.E., Bouchon, D., Rigaud, T., Duncanson, P., Sharpe, R.G. & Dunn, A.M. 1999, 'Ultrastructural characterisation and molecular taxonomic identification of Nosema granulosis n. sp., a transovarially transmitted feminising (TTF) microsporidium.', The Journal of eukaryotic microbiology, vol. 46, no. 5, pp. 492-499.
A novel microsporidian parasite is described, which infects the crustacean host Gammarus duebeni. The parasite was transovarially transmitted and feminised host offspring. The life cycle was monomorphic with three stages. Meronts were found in host embryos, juveniles, and in the gonadal tissue of adults. Sporoblasts and spores were restricted to the gonad. Sporogony was disporoblastic giving rise to paired sporoblasts, which then differentiated to form spores. Spores were not found in regular groupings and there was no interfacial envelope. Spores were approximately 3.78 x 1.22 microns and had a thin exospore wall, a short polar filament, and an unusual granular polaroplast. All life cycle stages were diplokaryotic. A region from the parasite small subunit ribosomal RNA gene was amplified and sequenced. Phylogenetic analysis based on these data places the parasite within the genus Nosema. We have named the species Nosema granulosis based on the structure of the polaroplast.
Terry, R.S., Dunn, A.M. & Smith, J.E. 1999, 'Segregation of a microsporidian parasite during host cell mitosis.', Parasitology, vol. 118 ( Pt 1), pp. 43-48.
We investigated the segregation of an intracellular microsporidian parasite during host cell division. A time-course experiment was carried out to examine the distribution of parasites relative to host chromosomal DNA via light and electron microscopy. Fluorescent light microscopy and EM studies showed that the parasite lay in the perinuclear zone of the host cell during interphase and segregated to daughter cells at mitosis. At metaphase, the parasite was frequently closely associated with host microtubules and mitochondria. Electron-dense bridges were observed between the parasites and the host microtubules and also between host mitochondria and microtubules. The study suggests that both the parasite and the host cell organelles segregate in association with spindle microtubules.
Sasono, P.M. & Smith, J.E. 1998, 'Toxoplasma gondii: an ultrastructural study of host-cell invasion by the bradyzoite stage.', Parasitology research, vol. 84, no. 8, pp. 640-645.
The invasion of Toxoplasma gondii tachyzoites and bradyzoites was followed in bovine kidney cells via electron microscopy. The process of invasion differed between bradyzoites and tachyzoites. In the early stages of entry there was evidence of localised formation of membrane projections in the host cell adjacent to the parasite. Parasite reorientation and rhoptry release appeared to be necessary for invasion; however, the tight junction could not be clearly discerned and there was no evidence of constriction or of any membrane shedding from the parasite. The resulting parasitophorous vacuole was smaller than the tachyzoite vacuole and parasites were frequently found to lie immediately under the host cell membrane. The vacuole was rapidly adapted by the release and formation of an intra-phagosomal membrane network, while the parasitophorous vacuole formed a relationship with host-cell endoplasmic reticulum.
Terry, R.S., Smith, J.E. & Dunn, A.M. 1998, 'Impact of a novel, feminising microsporidium on its crustacean host', Journal of Eukaryotic Microbiology, vol. 45, no. 5, pp. 497-501.
We describe the transmission and pathogenic effects of a novel, feminising microsporidium, probably a Nosema species, on its crustacean host Gammarus duebeni. The parasite prevalence in the field was high (46% of females were infected) and the parasite was transovarially transmitted to 91% of embryos of infected females. The impact of the parasite on the host was assessed by means of a host breeding experiment. The parasite feminised 66% of infected host young and was transovarially transmitted by these individuals to the next host generation. The parasite differed from other feminising microsporidia in G. duebeni in that early embryos had a high parasite burden (288 parasites per embryo) and the infection was pathogenic, causing a reduction in both the growth rate of young hosts and in adult size. This study suggests that feminising microsporidia are a diverse group in which a variety of host/pathogen relationships have evolved.
Smith, J. 1998, ''Textbook of Immunology' ed Bona, CA & Bonilla, FA', Journal of Biological Education, vol. 32, pp. 75-75.
Terry, R.S., Dunn, A.M. & Smith, J.E. 1997, 'Cellular distribution of a feminizing microsporidian parasite: a strategy for transovarial transmission.', Parasitology, vol. 115 ( Pt 2), pp. 157-163.
The cellular distribution of a vertically transmitted, feminizing microsporidian was followed in its host Gammarus duebeni. In adult females the parasite was restricted to gonadal tissue, in particular primary and secondary follicle cells. Spores were diplokaryotic with a thin spore wall and a short polar filament, characteristics typical of 'early' spores involved in autoinfection. The diplokaryotic life-cycle, absence of spore groupings and of a pansporoblast membrane typify the genus Nosema. However, the unusual globular polaroplast of the spore and restriction of this stage to host ovarian tissue have not previously been described in Nosema. Sporogony occurred only in follicle cells adjacent to developing oocytes and was in synchrony with the process of vitellogenesis. Oocytes were infected after formation of intracellular connections with follicle cells but harboured only vegetative stages of the parasite. Parasites were associated with the perinuclear cytoplasm and, in developing embryos, segregated to daughter cells along the axis of the spindle. In juvenile animals there was no evidence of pathology linked with feminization and the parasite was found at low density in cells under the cuticle. The parasite is highly adapted to transovarial transmission with an efficient mechanism of oocyte infection and no evidence of pathology.
Appleford, P.J. & Smith, J.E. 1997, 'Toxoplasma gondii: the growth characteristics of three virulent strains.', Acta tropica, vol. 65, no. 2, pp. 97-104.
We have studied the phenotype of three mouse virulent strains of Toxoplasma gondii (RH, Martin and ENT), monitoring cellular factors which may relate to virulence. There was variation between these three strains in three separate criteria: invasion, growth and tachyzoite-bradyzoite interconversion. The ENT strain exhibited consistently higher invasion rates, a shorter doubling time and a lower frequency of bradyzoite production than Martin or RH strains. In addition to variation in growth rate, there were also differences in the morphology of the parasites, with the ENT strain exhibiting highly synchronous division giving rise to characteristic rosettes. The Martin strain produced bradyzoites at a higher frequency and, in culture, parasites were often seen in tight clusters, which were reminiscent of early tissue cysts. These phenotypic variations amongst mouse-virulent strains of the parasite may imply underlying genetic differences within the group.
Smith, J., Boothroyd, J.C., Hunter, C.J. & Peterson, E. 1997, 'Progress in toxoplasmosis research', Parasitology Today, vol. 13, pp. 245-246.
Lane, A., Soete, M., Dubremetz, J.F. & Smith, J.E. 1996, 'Toxoplasma gondii: appearance of specific markers during the development of tissue cysts in vitro.', Parasitology research, vol. 82, no. 4, pp. 340-346.
Cultures were initiated in Madin-Darby bovine kidney (MDBK) cells from ME49 strain bradyzoites. Specific antibody staining showed that two populations of parasites exist, one being a predominant population of tachyzoites that were positive for the tachyzoite-specific marker SAG1 and negative for the bradyzoite-specific marker P36. All of these parasites expressed the dense granule molecule GRA5, which in larger clusters was seen faintly in the membrane of the parasitophorous vacuole. No rosette formation or monolayer destruction was observed. Also seen was a sub-population of bradyzoites that were positive for P36 and negative for SAG1. Approximately 90% of these parasites expressed the matrix molecule P29. These parasites were also positive for the dense granule molecule GRA5, which was highly concentrated in the wall of the cyst. These bradyzoite clusters contained fewer parasites and were smaller in diameter than those expressing tachyzoite markers.
Grimwood, J. & Smith, J.E. 1996, 'Toxoplasma gondii: the role of parasite surface and secreted proteins in host cell invasion.', International journal for parasitology, vol. 26, no. 2, pp. 169-173.
The potential role of the 5 surface proteins of Toxoplasma gondii tachyzoites in host cell invasion was investigated using an in vitro neutralization assay. Supporting earlier findings, TG05.54, a monoclonal antibody recognizing the major surface protein SAG 1, was shown to cause a consistent and significant blockade of invasion into bovine kidney cells, indicating a functional role for this protein in host cell invasion. The neutralizing effect was only seen with certain anti-SAG 1 monoclonal antibodies, suggesting the presence of a functional ligand within the molecule. A second surface protein, SAG 2 was also shown to be involved in the invasion process. Anti-SAG 2 antibodies prevented parasite reorientation, leaving zoites immobilized on the host cell membrane and resulting in increased internalization of tachyzoites. Antibodies recognizing other surface, rhoptry, dense granule and microneme molecules had no effect on invasion.
Jackson, H.C., Biggadike, K., McKilligin, E., Kinsman, O.S., Queener, S.F., Lane, A. & Smith, J.E. 1996, '6,7-disubstituted 2,4-diaminopteridines: novel inhibitors of Pneumocystis carinii and Toxoplasma gondii dihydrofolate reductase.', Antimicrobial agents and chemotherapy, vol. 40, no. 6, pp. 1371-1375.
Four novel, disubstituted diaminopteridines have been identified which antagonize the uptake of a folate precursor (para-aminobenzoic acid) by rat-derived Pneumocystis carinii maintained in short-term axenic culture at concentrations ranging from 4.5 to 26 microM. The compounds were at least 10 to 100 times more active than trimethoprim in this assay. None of these entities exhibited toxicity to mammalian cell lines at < 100 microM. The same structures also caused significant inhibition of Toxoplasma gondii tachyzoite replication within Madin-Darby bovine kidney cells at concentrations ranging from 0.1 to 10 microM. Three of the structures (GR92754, AH10639, and AH2504) were at least an order of magnitude more potent than the standard anti-T. gondii agent, pyrimethamine. All three entities were also significantly more potent and selective than pyrimethamine as inhibitors of T. gondii dihydrofolate reductase (DHFR), with 50% inhibitory concentrations within the range of 0.018 to 0.033 microM. One of these compounds, 6,7-dibutyl-2,4-diaminopteridine (GR92754), was also a potent and selective inhibitor of P. carinii DHFR (50% inhibitory concentration, 0.082 microM). GR92754 is the first DHFR inhibitor described that exhibits greater potency, selectivity, and intracellular activity against both organisms than any of the DHFR agents used clinically, namely, trimethoprim, pyrimethamine, and trimetrexate. This information could provide the starting point for examination of the pharmacokinetic and therapeutic potential of GR92754 and related chemical entities with animal models.
Zhang, Y.W. & Smith, J.E. 1995, 'Toxoplasma gondii: reactivity of murine sera against tachyzoite and cyst antigens via FAST-ELISA.', International journal for parasitology, vol. 25, no. 5, pp. 637-640.
The murine serological response to Toxoplasma gondii tachyzoite and cyst antigens was determined using FAST-ELISA. The serum IgG response to tachyzoite antigen was much stronger than that to cyst antigen. Adsorption of immune sera with tachyzoite antigen sharply reduced the reactivity in ELISA with tachyzoite antigen, but had no effect on the titre against cyst antigen, implying that there is virtually no antigenic overlap between the 2 stages. In sequential sera from infected mice the IgG antibody response against tachyzoites was always higher than the response to cyst antigen, whereas the IgM response to cysts was always higher than that to tachyzoites and remained detectable for at least 11 months.
Zhang, Y.W., Fraser, A., Balfour, A.H., Wreghitt, T.G., Gray, J.J. & Smith, J.E. 1995, 'Serological reactivity against cyst and tachyzoite antigens of Toxoplasma gondii determined by FAST-ELISA.', Journal of clinical pathology, vol. 48, no. 10, pp. 908-911.
AIMS: To obtain quantitative data on the human serological response to Toxoplasma gondii tachyzoite and bradyzoite antigens. METHODS: Serum samples from 30 patients who had positive antibody titres against T gondii and from 14 who were seronegative, together with sequential serum samples from four infected individuals, were screened by FAST-ELISA. RESULTS: Serum samples from the 30 seropositive patients showed high IgG and IgM titres against the T gondii tachyzoite antigen but very low responses to cyst antigen. This result was borne out in sequential serum samples from patients with toxoplasmosis. CONCLUSION: Antibody recognition of the cystic stage of T gondii is low, implying that either this stage is poorly immunogenic or that the antigen load is low.
Smith, J.E. 1995, 'A ubiquitous intracellular parasite: the cellular biology of Toxoplasma gondii.', International journal for parasitology, vol. 25, no. 11, pp. 1301-1309.
Toxoplasma gondii shares many features with other apicomplexan parasites but is unusual in its extremely broad host and tissue specificity. The parasite exhibits typical 'zoite' morphology, its highly polar structure being dictated by the complex cytoskeleton. Molecules on the surface of the zoite are prime candidates for interaction with the host cell and in vitro assays have implicated 2 of the 5 tachyzoite surface molecules in invasion: SAG1 as a ligand mediating host cell invasion, and SAG2 in enabling reorientation prior to invasion. The functional roles of other molecules, secreted from internal organelles during invasion and intracellular development, are also becoming clear through immuno-EM and biochemical studies, and from sequence data. Molecules from the rhoptries including the penetration enhancing factor ROP1 are secreted at the point of invasion and are integral to the newly formed parasitophorous vacuole membrane. Release of the dense granule molecules GRA 1-6, appears to be calcium regulated and occurs within 10 min of invasion leading to formation of the tubular membranous network and stabilization of the vacuole. The interaction between Toxoplasma and the host cell is stage specific. The tachyzoite divides rapidly and synchronously forming rosettes and causing host cell lysis, while the bradyzoite exhibits slow asynchronous division secreting a granular matrix and becoming enclosed within a cyst wall. This altered phenotype is a reflection of changes in gene expression. Bradyzoite specific molecules are found internally, on the parasite surface, and in the cyst matrix while important tachyzoite proteins such as SAG1 and SAG2 are downregulated. Differentiation between the 2 stages is reversible and is influenced by immunomodulatory agents. However a strong genetic element is involved and it is notable that virulent strains show a very low frequency of cyst production.
Grimwood, J. & Smith, J.E. 1995, 'Toxoplasma gondii: redistribution of tachyzoite surface protein during host cell invasion and intracellular development.', Parasitology research, vol. 81, no. 8, pp. 657-661.
Immunoperoxidase localisation of antigen at the electron microscope level confirms that parasite surface proteins, in association with membrane, are shed from the surface of the zoite on invasion, while varying amounts are also internalised. SAG 1 is stable on intracellular zoites for up to 48 h, although new protein is also synthesised. SAG1 is present on the surface of daughter zoites and is found throughout the infected cell in distinct vacuoles; these vacuoles represent either direct extensions of the parasitophorous vacuole or true export of parasite surface material. Conflicting reports exist concerning the presence of SAG1 on the developing intraphagosomal membrane (IPM) network immediately post-invasion (Sibley et al. 1986; Dubremetz et al. 1993). It is not known whether the molecule continues to be expressed during intracellular development. The current study follows the fate of SAG1 during invasion and over the first 48 h of parasite multiplication within the host cell, using pre- and postinvasion labeling techniques at the electron microscope level.
Zhang, Y.W. & Smith, J.E. 1995, 'Toxoplasma gondii: identification and characterization of a cyst molecule.', Experimental parasitology, vol. 80, no. 2, pp. 228-233.
Monoclonal antibodies were raised against the RRA strain of Toxoplasma gondii, and those with specific reactivity against tissue cysts were selected by differential FAST-ELISA screen. One clone, E7B2, reacted with a novel cyst-specific molecule of approximate molecular weight 29,000. The molecule is predominantly found in soluble fractions from intact cysts and bradyzoites, and immunofluorescence studies suggest that it accumulates in the matrix of the cyst. Western blotting experiments show the molecule to be a minor antigen recognized by polyclonal antisera from infected mice.
Smith, J.E. 1994, 'Intersexuality in the crustacean gammarus duebeni', Invertebrate Reproduction and Development, vol. 25, no. 2, pp. 139-142.
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We describe the external and internal morphology of intersex Gammarus duebeni from Budle Bay, Northumberland and present the first scanning electron micrograph of the external morphology of an intersex. The pattern of intersex expression in this population differs from that previously described in a German population: intersexes are more frequent in the UK population; and all conform to the intermediate form of the intersex types described in the German population. Such a contrast between populations has not previously been described and may provide a tool to understand the phenomenon. The distribution of a feminizing microsporidian is examined. However, parasitism is not the main agent of intersexuality. © 1994 Taylor & Francis Group, LLC.
Smith, J.E. 1994, 'Functional molecules on the surface of parasitic protozoa.', Parasitology, vol. 108 Suppl, pp. S1-S2.
Fraser, A. & Smith, J. 1994, 'Toxoplasma gondii: a comparison of productivity of antigen sources, and efficacy in diagnostic assay', Serodiagnosis and Immunotherapy in Infectious Disease, vol. 6, no. 2, pp. 98-102.
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Antigens derived from freeze-thawed tachyzoites of Toxoplasma gondii are commonly used in commercial enzyme-linked immunosorbent assay (ELISA) systems for detection of toxoplasmosis. Antigen production from three sources (mice, cotton rats and tissue culture) was analysed quantitatively and quanlitatively, using Coomassie-stained sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) gels and Western blotting. The antigen extracts were tested with a murine FAST-ELISA system to ascertain their effectiveness in detecting antibodies against Toxoplasma. Cotton rats were found to provide the highest yield of parasites, with low host cell contamination. Antigen extracts prepared from cotton rat exudates were also found to give optimum results when tested in the FAST-ELISA system. © 1994.
Fraser, A., Balfour, A. & Smith, J. 1994, 'The use of cotton rat-derived tachyzoite antigens in the development of a sensitive ELISA for the diagnosis of toxoplasmosis', Serodiagnosis and Immunotherapy in Infectious Disease, vol. 6, no. 3, pp. 159-163.
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Cotton rats have previously been found to be a reliable source of high quality Toxoplasma gondii tachyzoite antigen. A human IgG enzyme-linked immunosorbent assay (ELISA) was developed using this antigen, and was evaluated with a panel of 414 human sera to analyse assay performance. Pools of positive and negative sera were included as controls and used to convert readings into enzyme immunoassay units (EIU). Measured against the dye test, sensitivity was calculated as 96.5%, specificity as 98.1% with a positive predictive value of 99.3% and a negative predictive value of 91.0%. This indicates that cotton rat-derived antigens gave excellent results in this indirect ELISA, and may have uses in other diagnostic tests for T. gondii. © 1994.
Zhang, Y.W., Lee, D.L. & Smith, J.E. 1993, 'Biochemical characterisation of Trichinella spiralis and T. pseudospiralis stichocyte antigens.', Applied parasitology, vol. 34, no. 4, pp. 291-294.
One and two dimensional Western blots of Trichinella spiralis and Trichinella pseudospiralis extracts were probed with a monoclonal antibody (7C2C5) which recognizes molecules found in the stichocytes. Three major antigens were revealed in excreted:secreted (E/S) preparations at approx Mr 45, 53 & 60 X 10(3). The Mr 45 X 10(3) molecule was the most abundant secreted antigen, on two dimensional analysis it resolved into many isoforms with a pI range 4.5-6.4 in T. spiralis and into four isoforms pI range 5.1-5.7 in T. pseudospiralis.
Dunn, A.M., Adams, J. & Smith, J.E. 1993, 'Transovarial Transmission and Sex Ratio Distortion by a Microsporidian Parasite in a Shrimp', Journal of Invertebrate Pathology, vol. 61, no. 3, pp. 248-252.
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Transovarial transmission was found to be the major transmission route of a microsporidian infecting Gammarus duebeni. The parasite was found in 31% of females in a field population but was never found in males. The infection was localized in the ovary and, in laboratory investigations, had no discernible effect on the growth rate, survival, or reproductive output of infected hosts. More than 90% of the offspring of an infected mother became female. Parasite-induced feminization of the host is a major factor in the maintenance of the microsporidian in the host population. © 1993 Academic Press. All rights reserved.
Dunn, A.M., Adams, J. & Smith, J.E. 1993, 'Is intersexuality a cost of environmental sex determination in Gammarus duebeni?', Journal of Zoology, vol. 231, no. 3, pp. 383-389.
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Three possible causes of intersexuality in Gammarus duebeni, a crustacean with environmental sex determination, were investigated. Intersexuality appears to be a cost of the flexible sexdetermining mechanism of this species: the occurrence of intersexes is influenced by photoperiod, which also cues sex determination. Intersexuality is heritable: intersex mothers produce more intersex offspring than do true females. Parasitism by a feminizing microsporidian is ruled out as a significant cause of intersexuality. Copyright © 1993, Wiley Blackwell. All rights reserved
Woodison, G., Balfour, A.H. & Smith, J.E. 1993, 'Sequential reactivity of serum against cyst antigens in Toxoplasma infection.', Journal of clinical pathology, vol. 46, no. 6, pp. 548-550.
AIMS: To compare the recognition of Toxoplasma gondii tachyzoites and cysts by sera, from 10 patients. METHODS: Recognition of antigens from purified tachyzoites (RH strain) and bradyzoites (18691 strain) was compared using western immunoblotting. Sequential serum samples from 10 patients and one laboratory acquired RH infection were used. RESULTS: Recognition of cyst antigens was relatively low and occurred late in infection. The two stages were antigenically distinct with only a few shared bands. CONCLUSION: Immunological recognition of the cystic stage of T gondii is low. This implies that either cysts are poorly immunogenic or that cyst antigen is not available for processing and presentation.
Mineo, J.R., McLeod, R., Mack, D., Smith, J., Khan, I.A., Ely, K.H. & Kasper, L.H. 1993, 'Antibodies to Toxoplasma gondii major surface protein (SAG-1, P30) inhibit infection of host cells and are produced in murine intestine after peroral infection.', Journal of immunology (Baltimore, Md. : 1950), vol. 150, no. 9, pp. 3951-3964.
Monoclonal and polyclonal, monospecific antibodies to the major surface antigen of Toxoplasma gondii (SAG-1, P30) inhibit infection of human fibroblasts and murine enterocytes. Fab prepared from polyclonal, monospecific antibody to P30 also have this inhibitory effect on invasion, which indicates that this antibody directly blocks parasite infection of host cells rather agglutinating the parasite. Antibodies to another surface protein (P22) did not alter in vitro infection. If the inhibitory effect of antibody to P30 was due to steric hindrance or complexing of surface epitopes contiguous to P30, antibodies to other surface epitopes would also be inhibitory and they are not. Urea treatment of antibody (which permits discrimination of high and low avidity antibody) did not alter the effect of anti-P30 antibody. This observation indicates that the effect of the antibody to P30 was not an artifact of differences in the avidity of the antibody to P22 and P30. Heat inactivated antisera from mice infected with either RH or PTg strain T. gondii (P30+) inhibit infection of fibroblasts when challenged with autologous wild-type parasites by 87 and 40%, respectively. In contrast, these antisera have little inhibitory effect (13 and 19%, respectively) against infection of human fibroblasts by a P30-deficient mutant (PTgB). Antisera raised to the P30-deficient mutant had no significant effect on infection of cells by wild-type strains that have surface P30. The neoglycoprotein, BSA-glucosamide, competitively blocks infection of human fibroblasts by P30+ tachyzoites with surface P30 in higher level than those without surface P30. This observation indicates that there is likely to be a glycosylated host cell receptor to which T. gondii's major surface Ag SAG-1 (P30) binds. Mice infected perorally develop intestinal IgA antibody to the major 30-kDa epitope of T. gondii. Thus, the major surface epitope of T. gondii, SAG-1 (P30), has an important, functional role in infection of h...
Grimwood, J. & Smith, J.E. 1992, 'Toxoplasma gondii: the role of a 30-kDa surface protein in host cell invasion.', Experimental parasitology, vol. 74, no. 1, pp. 106-111.
C1E3, a monoclonal antibody recognizing protein P30, a major surface antigen of Toxoplasma gondii tachyzoites, was shown to have a consistent effect on invasion in adult bovine kidney cells. In 10 replicate assays, the overall invasion was reduced to 37% of control values (P less than 0.0001). These results support the role of a functional role for P30 in mediating invasion.
Grimwood, J. & Smith, J.E. 1991, 'Kinetics of the growth and variation in infectivity of Toxoplasma gondii in mice.', Annals of tropical medicine and parasitology, vol. 85, no. 6, pp. 659-661.
Smith, J.E. & Dunn, A.M. 1991, 'Transovarial transmission', Parasitology Today, vol. 7, no. 6, pp. 146-148.
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The success of a parasite depends upon its ability to transmit itself to new hosts. Many parasites are passed on from mother to daughter in a process known as vertical, or linear, transmission. Vertical transmission includes parasites transmitted across the placenta or via milk but in this review Judy Smith and Alison Dunn concentrate specifically on intracellular parasites. Transovarial transmission is widely used by a range of organisms but its importance, particularly in transmission of parasites, has rarely been studied. © 1991.
Woodison, G. & Smith, J.E. 1990, 'Identification of the dominant cyst antigens of Toxoplasma gondii.', Parasitology, vol. 100 Pt 3, pp. 389-392.
Brain cysts from three strains of Toxoplasma gondii were purified and analysed by SDS-PAGE and immunoblotting. Western blot analysis revealed the presence of major cyst/bradyzoite antigens at Mr 25,000, 36,000 and 67,000 common to all strains and recognized by many individual sera. There was also evidence of strain variation in cyst antigens with, for example, antigens at Mr 88,000, 28,000 and 26,000 unique to the 17025 strain. There was some overlap in the molecular weight of cyst and tachyzoite antigens, but the major tachyzoite surface antigen (P30) could not be detected in brain cysts.
Dunn, A.M., Adams, J. & Smith, J. 1990, 'Intersexes in a shrimp: a possible disadvantage to environmental sex determination', Evolution, vol. 44, pp. 1875-1878.
Carter, C. & Smith, J. 1989, 'Parasite antigens and vaccination', Parasitology Today, vol. 4, pp. 288-289.
Winger, L.A., Tirawanchai, N., Nicholas, J., Carter, H.E., Smith, J.E. & Sinden, R.E. 1988, 'Ookinete antigens of Plasmodium berghei. Appearance on the zygote surface of an Mr 21 kD determinant identified by transmission-blocking monoclonal antibodies.', Parasite immunology, vol. 10, no. 2, pp. 193-207.
Zygotes and ookinetes of the rodent malaria Plasmodium berghei can be enriched 50-fold, from whole blood cultures by ammonium chloride lysis. Three monoclonal antibodies (MoAbs) raised against such enriched preparations specifically bind to a determinant of Mr 21 kD as assessed by 125I-labelled goat anti-mouse IgG probed immunoblots of Western transfers of SDS-PAGE gels. Indirect immunofluorescence indicates that the 21 kD determinant bound by specific MoAbs, whilst not detectable on gametocytes or gametes, appears on the parasite surface within 2 h of exflagellation/fertilization and increases thereafter. The three MoAbs specifically binding the 21 kD determinant block oocyst development in mosquitoes by at least 90%, as assessed either by in-vitro membrane feeds or by live feeds on passively immunized mice. These MoAbs reduce ookinete formation in vitro by between 52 and 100%. Possible mechanisms of action of these MoAbs are discussed.
Smith, J.E. & Alexander, J. 1986, 'Evasion of macrophage microbicidal mechanisms by mature sporozoites of Plasmodium yoelii yoelii.', Parasitology, vol. 93 ( Pt 1), pp. 33-38.
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Sporozoites of Plasmodium yoelii yoelii were incubated for 40 min with BALB/c peritoneal macrophages in the presence of nitro-blue tetrazolium (NBT). While immature oocyst sporozoites triggered the macrophage respiratory burst, as visualized microscopically by the localized reduction of NBT to insoluble formazan, 97.6% of mature salivary gland sporozoites did not induce such a response. The macrophage oxidative response was also induced by 82.7% of heat-inactivated and 95.7% of trypsin-treated salivary gland sporozoites. The relationship of these results to the infectivity and immunogenicity of malarial sporozoites is discussed.
Meis, J.F., Rijntjes, P.J., Verhave, J.P., Ponnudurai, T., Hollingdale, M.R., Smith, J.E., Sinden, R.E., Jap, P.H., Meuwissen, J.H. & Yap, S.H. 1986, 'Fine structure of the malaria parasite Plasmodium falciparum in human hepatocytes in vitro.', Cell and tissue research, vol. 244, no. 2, pp. 345-350.
Recent advances in the ability to culture the hepatic forms of mammalian malaria parasites, particularly of the important human pathogen Plasmodium falciparum have provided novel opportunities to study the ultrastructural organisation of the parasite in its natural host cell the human hepatocyte. In this electron-microscopic and immunofluorescence study we have found the morphology of both parasite and host cell to be well preserved. The exoerythrocytic forms, which may be found at densities of up to 100/cm2, grow at rates comparable to that in vivo in the chimpanzee. In the multiplying 5- and 7-day schizogonic forms of the ultrastructural organisation of the parasite bears striking resemblances to other mammalian parasites, e.g., the secretory activity and distribution of the peripheral vacuole system, but also homology with avian parasites, e.g., in nuclear and nucleolar structure and mitochondrial form. The latter homologies support earlier suggestions of the close phylogenetic relationship of P. falciparum with the avian parasites. Evidence is also presented showing the persistence of the cytoskeleton of the invasive sporozoite within the cytoplasm of the ensuing rapidly growing vegetative parasites.
Smith, J.E., Minski, M.J. & Rao, L.S. 1986, 'Assay of antimonial compounds by activation analysis: its use in monitoring the clearance of free and liposomally-entrapped sodium stibogluconate by isolated perfused rat liver.', Annals of tropical medicine and parasitology, vol. 80, no. 1, pp. 143-145.
Smith, J.E., Meis, J.F., Ponnudurai, T., Verhave, J.P. & Moshage, H.J. 1984, 'In-vitro culture of exoerythrocytic form of Plasmodium falciparum in adult human hepatocytes.', Lancet (London, England), vol. 2, no. 8405, pp. 757-758.
Smith, J. & Lunn, P.G. 1984, 'Albumin synthesizing capacity of hepatocytes isolated from rats fed diets differing in protein and energy content', Annals of Nutrition and Metabolism, vol. 28, pp. 281-287.
Smith, J. & Alexander, J. 1984, 'The interaction of rodent malaria sporozoites with peritoneal macrophages in vitro', Parasitology, vol. 89.
Smith, J., Minski, M.J. & Rao, L.S. 1984, 'The uptake of free and liposome entrapped Pentostam by isolated perfused rat liver, as measured by activation analysis', Parasitology, vol. 89.
Smith, J.E., Pirson, P. & Sinden, R.E. 1983, 'Studies on the kinetics of uptake and distribution of free and liposome-entrapped primaquine, and of sporozoites by isolated perfused rat liver.', Annals of tropical medicine and parasitology, vol. 77, no. 4, pp. 379-386.
The kinetics of uptake and the distribution of free primaquine differed markedly from that of liposome-entrapped primaquine. The uptake of the liposome-entrapped drug (LPQ) was gradual, reaching a plateau of 60% of the initial load after 20 minutes of perfusion. However, clearance of the free drug was almost immediate, reaching its maximum uptake of 44% within five minutes. Some interactions also seen between liposomes and malarial sporozoites. In mixed perfusions the removal of LPQ was enhanced whilst the uptake of sporozoites remained normal. Liposome uptake was significantly lower in livers obtained from silica-treated animals, in which Küpffer cell numbers are depleted. Further, analysis of the radioactive content of hepatocyte and Küpffer cell fractions following perfusion with 3H and 14C labelled liposomes suggested that the vesicles were concentrated in the latter cell type.
Smith, J.E. & Barker, R.J. 1982, 'Culture of microsporidia from invertebrates in vertebrate cells', Parasitology, vol. 85, no. 3, pp. 427-435.
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Nosema algerae and N. eurytremae were successfully cultured in embryonic rat brain, Xenopus XTC-6 and Chang liver cells, and in embryonic rat brain and XTC-6 cells respectively. No parasites grew in cultures incubated at 38 °C but development took place in cells incubated at 34 °C and 27 °C. Increased levels of infections of the cultured cells were achieved by centrifugation of the spores on to the cells. The level of infection was also related to the type of medium used for hatching the spores, modified NMRI giving better results than Leibowitz L15, and to the interval between adding the spores to the cell cultures and centrifugation. © 1982, Cambridge University Press. All rights reserved.
Smith, J.E. & Sinden, R.E. 1982, 'Studies on the role of host serum in the retention of malarial sporozoites by isolated perfused rat liver.', Transactions of the Royal Society of Tropical Medicine and Hygiene, vol. 76, no. 1, pp. 45-47.
The binding of host serum components to malarial sporozoites has been proposed as a mechanism for the specific phagocytic uptake of these parasites, and hence the specificity of host infection (SCHULMAN et al., 1981). We therefore observed the kinetics of uptake of sporozoites of Plasmodium yoelii nigeriensis and P. gallinaceum by isolated perfused rat livers in the presence of homologous or heterologous sera. In the homologous system (P. y. nigeriensis sporozoites in rat serum) sporozoite uptake followed zero order kinetics, total uptake being achieved within 20 min. Substitution of rat serum with either chick or foetal calf serum did not change the pattern of uptake. The uptake of P. gallinaceum sporozoites in rat serum was similar to that of P. y. nigeriensis. Further, the uptake of P. y. nigeriensis sporozoites was the same in the absence of serum as in its presence. These observations suggest that the specific attachment of serum components to homologous malaria sporozoites is unlikely to be responsible for the specificity of host infection.
Sihden, R.E. & Smith, J.E. 1982, 'The role of the Kupffer cell in the infection of rodents by sporozoites of Plasmodium: uptake of sporozoites by perfused liver and the establishment of infection in vivo.', Acta tropica, vol. 39, no. 1, pp. 11-27.
The uptake of Plasmodium yoelii nigeriensis sporozoites by isolated perfused rat liver was very rapid and efficient. 67% of the initial load was removed from the perfusion media in the first passage through the liver, and 95% after 15 min of perfusion. Much of the uptake was explained by mechanical trapping in the liver. Up to 75% of the sporozoite load was retained after 15 min both by heat killed liver and liver cooled to 4 degrees C, therefore at least 20% of the sporozoite uptake in perfused normal livers was due to a biologically active process. In perfused normal livers, non-infective (heat-killed or trypsin-treated) sporozoites were taken up with an efficiency equal to infective sporozoite controls. However, a reduction in Kupffer cell number and activity, induced by silica treatment, resulted in a very significant decline in uptake of infective sporozoites by the perfused liver--and a parallel fall in the successful infection of the host by inoculated sporozoites in vivo. Since silica treatment produced no significant detectable pathological changes in hepatocytes, and infected blood passage results in a normal parasitaemia in silica treated animals it was concluded that the Kupffer cell was a component of the natural route of infection of the mammalian host by the majority of the infecting population of sporozoites of Plasmodium yoelii nigeriensis.
Smith, J. & Sinden, R.E. 1981, 'Studies on the uptake of sporozoites of P. yeolii nigeriensis by perfused rat liver', Transactions of the Royal Society of Tropical Medicine and Hygiene, vol. 75, no. 1, pp. 188-189.
Smith, J., Sinden, R.E., Beadle, J. & Hartley, R. 1981, 'The effect of silica treatment on the uptake and infectivity of Plasmodium yoelii sporozoites in vivo and in vitro', Transactions of the Royal Society of Tropical Medicine and Hygiene, vol. 75, pp. 605-606.
Sinden, R.E. & Smith, J. 1980, 'Culture of the liver stages (exoerythrocytic schizonts) of rodent malaria parasites from sporozoites in vitro.', Transactions of the Royal Society of Tropical Medicine and Hygiene, vol. 74, no. 1, pp. 134-136.
Smith, J. & Sinden, R.E. 1980, 'A technique for the culture of Nosema algerae in primary cultures of rat brain', Journal of Protozoology, vol. 27, no. 176.
Smith, J. & Sinden, R.E. 1979, 'In vitro culture of the exoerythrocytic stages of Plasmodium berghei', Journal of Protozoology Research, vol. 26, no. 749.