Guo, ZG & Johnson, AM 1996, DNA polymorphisms associated with murine virulence of Toxoplasma gondii identified by RAPD-PCR.
Johnson, MS, Broady, KW, Angelici, M & Johnson, AM 2003, 'The relationship between nucleoside triphosphate hydrolase (NTPase) isoform and Toxoplasma strain virulence in rat and human toxoplasmosis', Microbes and Infection, vol. 5, pp. 797-806.View/Download from: Publisher's site
Lew, AE, Dluzewski, AR, Johnson, AM & Pinder, JC 2002, 'Myosins of Babesia bovis: Molecular characterisation, erythrocyte invasion, and phylogeny', Cell Motility and the Cytoskeleton, vol. 52, no. 4, pp. 202-220.View/Download from: Publisher's site
Using degenerate primers, three putative myosin sequences were amplified from Australian isolates of Babesa bovis and confirmed as myosins (termed Bbmyo-A, Bbmyo-B, and Bbmyo-C) from in vitro cultures of the W strain of B. bovis. Comprehensive analysis of 15 apicomplexan myosins suggests that members of Class XIV be defined as those with greater than 35% myosin head sequence identity and that these be further subclassed into groups bearing above 50-60% identity. Bbmyo-A protein bears a strong similarity with other apicomplexan myosin-A type proteins (subclass XIVa), the Bbmyo-B myosin head protein sequence exhibits low identity (35-39%) with all members of Class XIV, and 5′-sequence of Bbmyo-C shows strong identity (60%) with P. falciparum myosin-C protein. Domain analysis revealed five divergent IQ domains within the neck of Pfmyo-C, and a myosin-N terminal domain as well as a classical IQ sequence unusually located within the head converter domain of Bbmyo-B. A cross-reacting antibody directed against P. falciparum myosin-A (Pfmyo-A) revealed a zone of approximately 85 kDa in immunoblots prepared with B. bovis total protein, and immunofluorescence inferred stage-specific myosin-A expression since only 25% of infected erythrocytes with mostly paired B. bovis were immuno-positive. Multiplication of B. bovis in in vitro culture was inhibited by myosin- and actin-binding drugs at concentrations lower than those that inhibit P. falciparum. This study identifies and classifies three myosin genes and an actin gene in B. bovis, and provides the first evidence for the participation of an actomyosin-based motor in erythrocyte invasion in this species of apicomplexan parasite. © 2002 Wiley-Liss, Inc.
Dobbin, CA, Smith, NC & Johnson, AM 2002, 'Heat shock protein 70 is a potential virulence factor in murine Toxoplasma infection via immunomodulation of host NF-kappa B and nitric oxide', JOURNAL OF IMMUNOLOGY, vol. 169, no. 2, pp. 958-965.View/Download from: Publisher's site
Dobbin, CA, Smith, NC & Johnson, AM 2002, 'Heat shock protein 70 is a virulence factor in murine Toxoplasma infection via immunomodulation of host nuclear factor kappa B and nitic oxide', Journal of Immunology, vol. 169, no. N/A, pp. 958-965.
Mugridge, N, Morrison, DJ, Jakel, T, Heckroth, A, Tenter, AM & Johnson, AM 2000, 'Effects of Sequence Alignment and Structural Domains of Ribosomal DNA on Phylogeny Reconstruction for the Protozoan Family Sarcocystide', Molecular Biology and Evolution, vol. 17, no. 12, pp. 1842-1853.View/Download from: Publisher's site
Miller, CM, Soilemezis, C, Johnson, AM & Smith, NC 2000, 'The Production of a 70 kDa Heat Shock Protein by Toxoplasma gondii RH Strain in Immunocompromised Mice', International Journal for Parasitology, vol. 30, no. 0, pp. 1467-1473.
Gleeson, MT & Johnson, AM 1999, 'Physical characterisation of the plastid DNA in Neospora caninum', INTERNATIONAL JOURNAL FOR PARASITOLOGY, vol. 29, no. 10, pp. 1563-1573.View/Download from: Publisher's site
Mugridge, NB, Morrison, DA, Heckeroth, AR, Johnson, AM & Tenter, AM 1999, 'Phylogenetic analysis based on full-length large subunit ribosomal RNA gene sequence comparison reveals that Neospora caninum is more closely related to Hammondia heydorni than to Toxoplasma gondii', International Journal for Parasitology, vol. 29, no. 10, pp. 1545-1556.View/Download from: Publisher's site
Since its first description in the late 1980s, Neospora caninum has been recognised as a prominent tissue cyst-forming parasite due to its ability to induce congenital disease and abortion in animals, especially cattle. It is found worldwide and is a cause of significant economic losses for the livestock industry. However, its place within the family Sarcocystidae, like that of several other taxa, remains unresolved. Neospora caninum shares several morphological and life cycle characters with Hammondia heydorni, although it is most commonly thought of as being a close relative of Toxoplasma gondii. This study presents information regarding the phylogenetic relationship of N. caninum to species currently classified into the genus Hammondia, as well as to two strains (RH and ME49) of T. gondii based on the full-length large subunit ribosomal RNA gene. Phylogenetic analyses using two alignment strategies and three different tree-building methods showed that the two species in the genus Hammondia are paraphyletic. Neospora caninum was shown to form a monophyletic clade with H. heydorni instead of T. gondii, which in turn was shown to be most closely related to H. hammondi. The finding that N. caninum and H. heydorni are closely related phylogenetically may aid the elucidation of currently unknown aspects of their biology and epidemiology, and suggests that H. heydorni should be considered in the differential diagnosis of N. caninum from other apicomplexan parasites.
Munro, SC & Johnson, AM 1999, 'Isolation of the plastid DNA of toxoplasma gondii', Journal of Protozoology Research, vol. 9, no. 4, pp. 122-134.
The plastid DNA from different strains of Toxoplasma gondii has been isolated using a variety of techniques. The relative effectiveness of these isolation techniques is compared. Initially, clones were isolated from genomic DNA libraries, but 100% positive identification of these clones proved difficult, due to variations in the plastid sequences and the lack of comparable sequences. Purification techniques using commercial columns gave eluates highly enriched in plastid DNA, but other contaminating DNA was also shown to be present. Finally, the novel long polymerase chain reaction technique (long-PCR) was trialed and was found to be the most efficient isolation and purification method. Copyright® 1999, The Research Center for Protozoan Molecular Immunology.
Miller, CM, Smith, NC & Johnson, AM 1999, 'Cytokines, Nitric Oxide, Heat Shock Proteins And Virulence In Toxoplasma', Parasitology Today, vol. 15, no. 10, pp. 418-422.View/Download from: Publisher's site
Elucidating the factors that play important roles in the expression of virulence by parasites is crucial to understanding disease pathogenesis and to developing control strategies rationally. Here, Kate Miller, Nick Smith and Alan Johnson, using Toxoplas
Johnson, MS, Broady, KW & Johnson, AM 1999, 'Differential recognition of Toxoplasma gondii recombinant nucleoside triphosphate hydrolase isoforms by naturally infected human sera', International Journal for Parasitology, vol. 29, no. 12, pp. 1893-1905.View/Download from: Publisher's site
Toxoplasma gondii possesses a highly active nucleoside triphosphate hydrolase, which has been shown to be an immunodominant antigen in mice and humans. Two isoforms (I and II) which exhibit different activities with respect to hydrolysis of ATP exist. Past studies suggest that all strains of T. gondii contain the less active nucleoside triphosphate hydrolase II, whilst only virulent strains contain the nucleoside triphosphate hydrolase I isoform. In order to further investigate the correlation between nucleoside triphosphate hydrolase isoform and biological significance, we cloned and expressed as glutathione S-transferase fusion proteins the full-length nucleoside triphosphate hydrolase I and II isoforms and two truncations of the nucleoside triphosphate hydrolase I isoform in Escherichia coli. We then used ELISAs with the full-length recombinant nucleoside triphosphate hydrolases as antigens to examine 188 naturally infected T. gondii-positive sera and 83 T. gondii-negative sera for antibody reactivity. All positive sera reacted to T. gondii whole tachyzoite lysate antigen, 31 sera reacted to both nucleoside triphosphate hydrolase isoforms, three sera reacted specifically to nucleoside triphosphate hydrolase I and two sera reacted to only nucleoside triphosphate hydrolase II. Immunoblot analysis of the five sera reacting to either nucleoside triphosphate hydrolase I or II revealed both quantitative and qualitative differences in reactivity to the two isoforms. Comparative immunoblot analysis using the truncations of the nucleoside triphosphate hydrolase I isoform, and one of these positive sera identified a presumptive differential epitope between the nucleoside triphosphate hydrolase I and II isoforms within an 81-aa region (aa 445-526) at the C-terminus of the nucleoside triphosphate hydrolase I isoform. This differential reactivity was further localised to the 12-residue region of greatest variability between the two isoforms (residues 488-499) using synthet...
The nucleoside triphosphate hydrolase (NTPase) of Toxoplasma gondii demonstrates an unusually high level of ATP hydrolysis, which, among the apicomplexan parasites, has only been observed in T. gondii and the closely related Neospora caninum. In T. gondii, NTPase has been shown to be highly expressed (constituting up to 8% of the tachyzoite protein) and is an immunodominant antigen in mice and humans. Two isoforms exist - NTPasel and NTPasell. NTPasel demonstrates a 4.5 fold greater activity than NTPasell with respect to ATP hydrolysis. Past studies suggest that only virulent strains possess the highly active NTPasel isoform. We have recently identified a B cell epitope (aa 484-502) on the NTPase isoforms which, despite some cross reactivity, is differentially recognised by a naturally infected human serum sample. In this study we used competitive antigen ELISAs and have identified that this serum sample reacts specifically to the NTPasel epitope, whilst the corresponding region on NTPasell isoform is the less specific cross reactive epitope. These results are consistent with the hypothesis that this patient has been infected with a virulent strain of T. gondii. Copyright© 1999, The Research Center for Protozoan Molecular Immunology.
Biñas, M & Johnson, AM 1998, 'A polymorphism in a DNA polymerase alpha gene intron differentiates between murine virulent and avirulent strains of Toxoplasma gondii.', International journal for parasitology, vol. 28, no. 7, pp. 1033-1040.View/Download from: Publisher's site
The IC intron, found within the DNA polymerase alpha gene of Toxoplasma gondii, was used to evaluate the genetic relationship among 10 strains of T. gondii. Sequence comparison detected polymorphisms within this 652 bp intron which correlated with murine virulence. The results reported here suggest that T. gondii contains two lineages, corresponding with their virulence, evolving independently following their separation. The extensive homology of the IC sequences within the virulent and avirulent groups affirms the close relationship of the strains within the group, as reflected by the identical nucleotide substitutions and dinucleotide insertions/deletions observed. In addition, the presence of the Nde I restriction enzyme site within the IC intron of avirulent strains allows definition of a T. gondii strain as murine virulent or avirulent without needing to test it in vivo.
Biñas, M & Johnson, AM 1998, 'Characterization of the gene encoding the catalytic subunit of the DNA polymerase alpha from Toxoplasma gondii', Biochemical and Biophysical Research Communications, vol. 253, no. 3, pp. 628-638.View/Download from: Publisher's site
The gene encoding the catalytic subunit of the Toxoplasma gondii DNA polymerase α enzyme has been isolated. The coding region is 6487 bp in length, containing three introns, and specifies a protein of 1690 aa. The seven conserved regions which characterize the polα polypeptide, as well as four of the five polα-specific aa domains, were found in the T. gondii gene. The absence of one of these domains, as well as the presence of a unique cysteine cluster between domains IV and B in the T. gondii polα, may result in a slight difference in the secondary or even tertiary structure compared with the human homologue and thus may be suitable for designing anti-Toxoplasma drugs. A number of amino acid differences within the seven conserved regions between the human and T. gondii polα, as well as variations in the spacings of these regions, were also observed.
Carreno, RA, Schnitzler, BE, Jeffries, AC, Tenter, AM, Johnson, AM & Barta, JR 1998, 'Phylogenetic analysis of coccidia based on 18S rDNA sequence comparison indicates that Isospora is most closely related to Toxoplasma and Neospora', Journal of Eukaryotic Microbiology, vol. 45, no. 2, pp. 184-188.View/Download from: Publisher's site
The phylogenetic relationships and taxonomic affinities of coccidia with isosporan-type oocysts have been unclear as overlapping characters, recently discovered life cycle features, and even recently discovered taxa, continue to be incorporated into biological classifications of the group. We determined the full or partial 18S ribosomal RNA gene sequences of three mammalian Isospora spp., Isospora felix, Isospora ohioensis and Isospora suis, and a Sarcocystis sp. of a rattlesnake, and used these sequences for a phylogenetic analysis of the genus Isospora and the cyst-forming coccidia. Various alveolate 18S rDNA sequences were aligned and analyzed using maximum parsimony to obtain a phylogenetic hypothesis for the group. The three Isospora spp. were found to be most closely related to Toxoplasma gondii and Neospora caninum. This clade in turn formed the sister group to the Sarcocystis spp. included in the analysis. The results confirm that the genus Isospora does not belong to the family Eimeriidae, but should be classified together with the cyst-forming coccidia in the family Sarcocystidae. Furthermore, there appear to be two lineages within the Sarcocystidae. One lineage comprises Isospora and the Toxoplasma/Neospora clade which share the characters of having a proliferative phase of development preceding gamogony in the definitive host and an exogenous phase of sporogony. The other lineage comprises the Sarcocystis spp. which have no proliferative phase in the definitive host and an endogenous phase of sporogony.
Johnson, AM 1998, 'Is there more than one species in the genus Toxoplasma??', The Tokai journal of experimental and clinical medicine, vol. 23, no. 6, pp. 383-389.
A complete life cycle for the ubiquitous protozoan parasite Toxoplasma was proposed over 25 years ago. Since that time, despite attempts to make the genus polyspecific, there has been only one species, Toxoplasma gondii, consistently recognised in the genus. Recent studies on taxa in genera closely related to Toxoplasma such as Neospora, Hammondia, Frenkelia, Isospora and Sarcocystis, have convincingly showed the need for a reclassification of many of the species in these genera. However, in addition to these genus level studies, over the last 10 years several laboratories have used molecular techniques including isoenzyme electrophoresis, restriction fragment length polymorphism analyses, random amplified polymorphic DNA - polymerase chain reaction, and comparisons of the small subunit ribosomal RNA gene, DNA polymerase alpha intron, and 70 kDa heat shock protein gene nucleotide sequences to investigate the genetic diversity among strains in the species T. gondii. Overall, the results of these analyses confirm that the strains in the genus Toxoplasma comprise a limited number of clonal lineages, directly correlated with their virulence in mice. The aim of this presentation is to review the molecular research in this area in order to raise the hypothesis that there may be more than one species in the genus Toxoplasma, which may contain taxa with distinct and different life cycles.
Guo, ZG, Gross, U & Johnson, AM 1997, 'Toxoplasma gondii virulence markers identified by random amplified polymorphic DNA polymerase chain reaction', Parasitology Research, vol. 83, no. 5, pp. 458-463.View/Download from: Publisher's site
Genomic DNAs from 35 Toxoplasma gondii strains were amplified by random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) using 18 arbitrary 10-mer primers. At least four primers were found to generate DNA fragments that discriminate the 35 T. gondii strains into a genotype of virulent strains and a genotype of avirulent strains. Primer B12 was found to generate a virulence-specific fragment and primers B5, C8, and C20 were found to generate avirulence-specific fragments, which in all cases clearly identified either the virulence phenotype or the avirulence phenotype, respectively. In addition, the DNA polymorphic bands detected were analyzed by parsimony and distance analysis. A similar genetic relationship among the T. gondii strains was determined by the two phylogenetic methods, which use completely different assumptions. Consistent with the division of the 35 strains into a genotype of virulent strains and a genotype of avirulent strains, both analyses revealed 2 clonal lineages directly correlated with murine virulence. These results strongly support the hypothesis that the genus Toxoplasma may actually contain two clonal lineages correlated with virulence, which have evolved independently following their initial separation.
Jeffries, AC, Schnitzler, B, Otto Heydorn, A, Johnson, AM & Tenter, AM 1997, 'Identification of synapomorphic characters in the genus Sarcocystis based on 18S rDNA sequence comparison', Journal of Eukaryotic Microbiology, vol. 44, no. 5, pp. 388-392.View/Download from: Publisher's site
In order to further investigate synapomorphic characters in the genus Sarcocystis, the small subunit ribosomal RNA gene sequences of Sarcocystis capracanis and Sarcocystis moulei were determined and used to infer the phylogenetic position of these two organisms within the cyst-forming coccidia. Phylogenies derived using distance, maximum parsimony and maximum likelihood methods demonstrated that S. capracanis groups with Sarcocystis tenella and Sarcocystis arieticanis as a clade that shares the characteristic of using canids as their definitive host. S. moulei was shown to group with Sarcocystis gigantea and Sarcocystis fusiformis as a clade that shares the characteristic of using felids as their definitive host.
Johnson, AM 1997, 'Speculation on possible life cycles for the clonal lineages in the genus toxoplasma.', Parasitology today (Personal ed.), vol. 13, no. 10, pp. 393-397.View/Download from: Publisher's site
Recent evidence suggests that the strains currently classified in the genus Toxoplasma, ie. within the species Toxoplasma gondii, may actually comprise at least two clonal lineages correlated with their virulence in mice. Here, Alan Johnson reviews these data in the context of evolution and speciation within the genus, and raises hypotheses on how the virulent lineage may undergo an asexual life cycle in nature, similar to that found for the very closely related coccidian, Neospora camnum. The putative vertical transmission life cycle of this mouse virulent lineage of T. gondii could involve passage to the foetus late in pregnancy, or transmission in milk to the neonate after birth.
Luton, K & Johnson, AM 1997, 'Cloning and sequence analysis of the DNA polymerase or gene of Leishmania donovani: Comparison with the human homologue', Biochemical and Biophysical Research Communications, vol. 234, no. 1, pp. 95-100.View/Download from: Publisher's site
The gene encoding the DNA polymerase α catalytic subunit of the kinetoplastid parasite L. donovani has been isolated, sequenced and compared with other eukaryotic homologues. The coding region is 4020 bp in length and specifies an inferred protein sequence of 1339 amino acids (aa). There is a high level of variability between the human and L. donovani gene sequences, but functional substrate-binding residues identified in humans and yeast appear to also be conserved in this parasite. The discovery of a cysteine-rich region located in the midst of the active sites of the enzyme, which appears to be unique to the Kinetoplastids, and aa differences found between some of the conserved regions implicated in catalytic function, may aid in drug design. The putative DNA binding Zn finger at the C-terminus of the protein appears highly species specific and may have potential as a drug target for blocking enzyme catalysis in the parasite.
Jeffries, AC & Johnson, AM 1996, 'The growing importance of the plastid-like DNA of the Apicomplexa', International Journal for Parasitology, vol. 26, no. 11, pp. 1139-1150.View/Download from: Publisher's site
Organisms in the phylum Apicomplexa possess, in addition to their mitochondrial genome, an extrachromosomal DNA that possesses significant similarities with the extrachromosomal genomes of plastids. To date, the majority of data on these plastid-like DNAs have been obtained from the human malarial organism, Plasmodium falciparum. In common with plastid DNAs, the plastid-like DNA of P. falciparum possesses genes for DNA-dependent RNA polymerase subunits β and β' and for organellar-like large- and small-subunit ribosomal RNAs. Both the polymerase subunit and ribosomal RNA gene sequences share a number of features with those from plastid DNAs. In addition, the ribosomal RNA genes are organised in an inverted repeat arrangement, reminiscent of plastid DNAs. Additional molecular features shared between the 2 genomes are discussed. Plastid-like DNAs have also been identified in other Plasmodium species as well as Toxoplasma gondii, Eimeria tenella, Babesia bovis and a number of Sarcocystis species. A cryptic organelle often observed in apicomplexans has been proposed as the organelle that harbours the plastid-like DNAs, but conclusive evidence for this has not yet been obtained. Although approximately 1/4 of the plastid-like DNA of P. falciparum has been sequenced to date, no function has yet been ascribed to this DNA or its putative organelle. Phylogenetic inferences based on sequence data from this DNA have indicated an evolutionary origin from photosynthetic organisms, but the true provenance of the plastid-like DNAs remains to be determined. Because of the specific nature of the plastid-like DNAs, they may prove useful as effective targets for chemotherapeutics.
Jeffries, AC, Amaro, N, Tenter, AM & Johnson, AM 1996, 'Genetic diversity in Sarcocystis gigantea assessed by RFLP analysis of the ITS1 region.', Applied parasitology, vol. 37, no. 4, pp. 275-283.
The genetic diversity among Sarcocystis gigantea isolates derived from individual cysts within a given infected animal at two abattoirs in Australia and one abattoir in Germany was studied using Restriction Fragment Length Polymorphism (RFLP) analysis of the intergenic transcribed spacer region 1 (ITS 1) of the ribosomal RNA gene operon. S. gigantea isolates were obtained from infected sheep from Blayney (New South Wales), Katanning (Western Australia), and Detmold (North-Rhine Westfalia, Germany) in order to assess the level of diversity among isolates from different geographic locations. Polymerase chain reaction amplification and RFLP analysis of the ITSI region with the restriction enzymes HaeIII, NlaIII, and Sau3AI found no genetic variation among the isolates within one animal or among animals in the same or different locations. To our knowledge, such a field study has not yet been performed on a species in the genus Sarcocystis.
Mertens, C, Tenter, AM, Vietmeyer, C, Ellis, JT & Johnson, AM 1996, 'Production Of A Recombinant Fusion Protein Of Sarcocystis Tenella And Evaluation Of Its Diagnostic Potential In An Elisa', Veterinary Parasitology, vol. 65, no. 3-4, pp. 185-197.View/Download from: Publisher's site
We have isolated a cDNA clone encoding an antigenic polypeptide of Sarcocystis tenella by screening a cystozoite-derived cDNA library in lambda gt11 with antibodies from sheep infected experimentally with S. tenella. This clone, termed STC29, was subclon
Ellis, JT, Luton, K, Hanlon, PL, Whitworth, G, Tenter, AM & Johnson, AM 1995, 'Phylogenetic-relationships Between Toxoplasma And Sarcocystis Deduced From A Comparison Of 18s RDNA Sequences', Parasitology, vol. 110, pp. 521-528.View/Download from: Publisher's site
The current taxonomy of parasites in the genus Sarcocystis is largely based on morphological characteristics as well as on host specificity and life-cycle structure. Recently, phylogenetic analyses of partial ribosomal RNA (rRNA) sequences provided suppo
Mackenstedt, U & Johnson, AM 1995, 'Genetic differentiation of pathogenic and nonpathogenic strains of Entamoeba histolytica by random amplified polymorphic DNA polymerase chain reaction', Parasitology Research, vol. 81, no. 3, pp. 217-221.View/Download from: Publisher's site
The random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) method was used to compare pathogenic and nonpathogenic strains of Entamoeba histolytica. DNA polymorphisms were detected among the different strains and dendrograms were constructed by PHYLIP and PAUP analyses to study the relationship of the strains. Both analyses resulted in identical results, which indicated that pathogenic strains of E. histolytica are closely related and clearly separated from the nonpathogenic strains. The results of this study agree with classification of the strains based on isoenzyme analyses. This suggests that RAPD-PCR is a valuable method in differentiating between strains of this parasite, and the results are consistent with the concept that pathogenic and nonpathogenic Entamoeba represent two different species. © 1995 Springer-Verlag.
Ellis, JT, Luton, K, Whitworth, G & Johnson, AM 1995, 'Phylogenetic relationships between Toxoplasma and sarcocystis deduced from a comparison of 18S rDNA sequences', Parasitology, vol. 110, no. 5, pp. 521-528.View/Download from: Publisher's site
The current taxonomy of parasites in the genus Sarcocystis is largely based on morphological characteristics as well as on host specificity and life-cycle structure. Recently, phylogenetic analyses of partial ribosomal RNA (rRNA) sequences provided support for paraphyly of Sarcocystis. We have tested the validity of this hypothesis by sequencing the complete 18S rRNA genes of Sarcocystis arieticanis, Sarcocystis gigantea and Sarcocystis tenella and comparing them with gene sequences derived from other taxa of the phylum Apicomplexa. The results obtained from this study do not reject the hypothesis of monophyly of Sarcocystis species, although the bootstrap data were inconclusive for some species. © 1995, Cambridge University Press. All rights reserved.
Biñas, M & Johnson, AM 1994, 'Scientific hypothesis: a new strategy for the design of anti-protozoal drugs--DNA polymerase as a drug target.', Applied parasitology, vol. 35, no. 3, pp. 157-168.
Chemotherapy against protozoan diseases has been practised since ancient times. Although still widely used, antiparasitic drugs are seldom completely effective. Complete elimination of an extensive protozoan infection usually requires a combination of drugs which target parasitic mechanisms very similar to the human host, as manifested by a multitude of side effects of varying severity. Furthermore, there is an escalating problem of widespread resistance to commonly used chemotherapeutic agents. Here we present an alternative strategy for the design of antiprotozoal agents using the principal enzyme involved in DNA replication as a possible drug target--DNA polymerase.
ELLIS, J, LUTON, K, BAVERSTOCK, PR, BRINDLEY, PJ, NIMMO, KA & JOHNSON, AM 1994, 'THE PHYLOGENY OF NEOSPORA-CANINUM (VOL 64, PG 303, 1994)', MOLECULAR AND BIOCHEMICAL PARASITOLOGY, vol. 67, no. 2, pp. 341-342.View/Download from: Publisher's site
Mackenstedt, U, Luton, K, Baverstock, PR & Johnson, AM 1994, 'Phylogenetic relationships of Babesia divergens as determined from comparison of small subunit ribosomal RNA gene sequences', Molecular and Biochemical Parasitology, vol. 68, no. 1, pp. 161-165.View/Download from: Publisher's site
Rohde, K, Luton, K, Baverstock, PR & Johnson, AM 1994, 'The phylogenetic relationships of Kronborgia (Platyhelminthes, Fecampiida) based on comparison of 18S ribosomal DNA sequences', International Journal for Parasitology, vol. 24, no. 5, pp. 657-669.View/Download from: Publisher's site
Approximately 580 bp at the 5' end of the small subunit RNA gene were amplified by PCR for 19 platyhelminth taxa, and Homo and Anemia were used as outgroups. These were analysed to test the hypothesis that fecampiids and Neodermata are sister groups. No evidence was found that the fecampiid Kronborgia isopodicola is closely related to the Neodermata or to the Rhabdocoela (in which the fecampiids are usually included). Morphological, including ultrastructural, characters and DNA data do not support a close relationship of fecampiids with any other platyhelminth taxon, although the DNA sequence analysis provides some evidence that the Acoela and Tricladida are closest. Fecampiids are sufficiently different from any other platyhelminth group to warrant establishment of a class, Fecampiida, for them. A diagnosis of the new class is given. © 1994.
ELLIS, J, LUTON, K, BAVERSTOCK, PR, BRINDLEY, PJ, NIMMO, KA & JOHNSON, AM 1994, 'THE PHYLOGENY OF NEOSPORA-CANINUM', MOLECULAR AND BIOCHEMICAL PARASITOLOGY, vol. 64, no. 2, pp. 303-311.View/Download from: Publisher's site
Ellis, JT, Morrison, DJ, Avery, D & Johnson, AM 1994, 'Codon Usage And Bias Among Individual Genes Of The Coccidia And Piroplasms', Parasitology, vol. 109, pp. 265-272.View/Download from: Publisher's site
Codon usage has been analysed in individual gene sequences, derived from a variety of parasitic protozoa in the class Sporozoa of the phylum Apicomplexa using metric multidimensional scaling. The two groups of codon usage patterns detected reflect the tw
Makioka, A, Stavros, B, Ellis, JT & Johnson, AM 1993, 'Detection And Characterization Of DNA-polymerase-activity In Toxoplasma-gondii', Parasitology, vol. 107, pp. 135-139.View/Download from: Publisher's site
A DNA polymerase activity has been detected and characterized in crude extracts from tachyzoites of Toxoplasma gondii. The enzyme has a sedimentation coefficient of 6.4 S, corresponding to an approximate molecular weight of 150000 assuming a globular sha
Ryan, P, Hurley, SF, Johnson, AM, Salzberg, M, Lee, MW, North, JB, Mcneil, JJ & Mcmichael, AJ 1993, 'Tumours of the brain and presence of antibodies to Toxoplasma gondii', International Journal of Epidemiology, vol. 22, no. 3, pp. 412-419.View/Download from: Publisher's site
The possible association between prior infection with the protozoan Toxoplasma gondii and development of brain tumours was investigated as part of two Australian population-based case-control studies of adult brain tumours. One study, based in Adelaide, South Australia, collected blood from 73 subjects with glioma, 53 subjects with meningioma and 348 controls. The other study, based in Melbourne, Victoria, collected blood from 44 subjects with glioma and 67 controls. All tumours had been verified histologically. IgG antibodies to T. gondii ware measured using Enzyme Unked Immunosorbent Assay (ELISA) techniques. In both the centre-specific and combined analyses, there was no difference between subjects with glioma and controls in the prevalence of antibody test-positivity (35% test-positive in glioma versus 33% in controls, age-, sex- and centre-adjusted odds ratio (OR)=1.00, 95% confidence interval (Cl): 0.64-1.56). In the Adelaide study, there was a statistically significant increased risk of meningioma associated with antibody test-positivity (47% test-positive in meningloma versus 31% in controls, P=0.02, adjusted OR=2.09, 95% Cl: 1.14-3.83). Our results do not support the hypothesis that antibody positivity to T. gondii is a risk factor for glioma, but suggest that it might be associated with meningioma. © 1992 International Epidemiological Association.
ELLIS, J, GRIFFIN, H, MORRISON, D & JOHNSON, AM 1993, 'ANALYSIS OF DINUCLEOTIDE FREQUENCY AND CODON USAGE IN THE PHYLUM APICOMPLEXA', GENE, vol. 126, no. 2, pp. 163-170.View/Download from: Publisher's site
Makioka, A, Stavros, B, Ellis, JT & Johnson, AM 1993, 'Detection and characterization of DNA polymerase activity in Toxoplasma gondii', Parasitology, vol. 107, no. 2, pp. 135-139.View/Download from: Publisher's site
A DNA polymerase activity has been detected and characterized in crude extracts from tachyzoites of Toxoplasma gondii. The enzyme has a sedimentation coefficient of 6.4 S, corresponding to an approximate molecular weight of 150000 assuming a globular shape. Like mammalian DNA polymerase a, the DNA polymerase of T. gondii was sensitive to N-ethylmaleimide and inhibited by high ionic strength. However, the enzyme activity was not inhibited by aphidicolin which is an inhibitor of mammalian DNA polymerases α, δ and ∊ and also cytosine-β-D-arabinofuranoside-5'-triphosphate which is an inhibitor of a polymerase. The activity was inhibited by 2,3-dideoxythymidine-5'-triphosphate which is an inhibitor of mammalian DNA polymerase β and γ. Magnesium ions (Mg2+) were absolutely required for activity and its optimal concentration was 6 mM, The optimum potassium (K+) concentration was 50 mM and a higher concentration of K+ markedly inhibited the activity. Activity was optimal at pH 8. Monoclonal antibodies against human DNA polymerase a did not bind to DNA polymerase of T. gondii. Thus the T. gondii enzyme differs from the human enzymes and may be a useful target for the design of toxoplasmacidal drugs. © 1993, Cambridge University Press. All rights reserved.
Rohde, K, Hefford, C, Ellis, JT, Hanlon, PL, Johnson, AM, Watson, NF & Dittmann, S 1993, 'Contributions To The Phylogeny Of Platyhelminthes Based On Partial Sequencing Of 18s Ribosomal DNA', International Journal For Parasitology, vol. 23, no. 6, pp. 705-724.View/Download from: Publisher's site
Partial sequencing of the 18S ribosomal DNA gene of one nemertean and 13 free-living and parasitic Platyhelminthes (556 nucleotides), and of one nemertean and 20 Platyhelminthes (556 nucleotides) was used to test several hypotheses concerning the phyloge
Tenter, AM, Vietmeyer, C & Johnson, AM 1992, 'Development of ELISAs based on recombinant antigens for the detection of Toxoplasma gondii-specific antibodies in sheep and cats', Veterinary Parasitology, vol. 43, no. 3-4, pp. 189-201.View/Download from: Publisher's site
ELISAs using recombinant parasite polypeptides as antigens were developed to measure Toxoplasma gondii-specific antibodies in the sera of sheep and cats. Compared with an ELISA based on traditional parasite antigen, the ELISA for sheep sera had a sensitivity of 79% and a negative predictive value of 80%, and the ELISA for cat sera had a sensitivity of 100% and a negative predictive value of 100%. Both ELISAs had specificities of 100% and positive predictive values of 100%. These ELISAs appear to be a useful cost-effective alternative to ELISAs based on traditional parasite antigen for the measurement of T. gondii-specific antibodies in the sera of sheep and cats. © 1992.
ELLIS, J, HEFFORD, C, BAVERSTOCK, PR, DALRYMPLE, BP & JOHNSON, AM 1992, 'RIBOSOMAL DNA-SEQUENCE COMPARISON OF BABESIA AND THEILERIA', MOLECULAR AND BIOCHEMICAL PARASITOLOGY, vol. 54, no. 1, pp. 87-95.View/Download from: Publisher's site
Johnson, A & Dubey, JP 2018, 'Diagnosis of Toxoplasmosis' in Foodborne Disease Handbook: Volume II: Viruses, Parasites, Pathogens, and HACCP, CRC Press, Boca Raton, pp. 389-405.View/Download from: Publisher's site
The diagnosis of toxoplasmosis usually is based on one or more of the following: clinical signs, parasite isolation, antibody detection, cell-mediated responses, and antigen detection. However, the detection of Toxoplasma gondii DNA by polymerase chain reaction for diagnosis has become widespread. The clinical diagnosis of toxoplasmosis in humans is complicated due to the vast range and variation in degree of severity of symptoms. The most characteristic feature of acquired toxoplasmosis in the immunoincompetent host is central nervous system involvement. Along with the loss and reduction in quality of human life, toxoplasmosis causes great financial loss in the agricultural industry. Many serological tests have been used for the detection of immunoglobulin G T. gondii antibodies: Sabin-Feldman dye test, indirect hemagglutination, complement fixation, modified agglutination test, latex agglutination, indirect fluorescent antibody, and enzyme-linked immunosorbent assay. The diagnosis of toxoplasmosis has been confirmed by direct immunohistological detection of the parasite in tissue.