Development of genomic probes to Sarcocystis cruzi (Apicomplexa)

Use of genomic DNA probes for the diagnosis of acute sarcocystosis in experimentally infected cattle

Two clones of 1.4 and 4.33 kilobase pairs (kbp) DNA inserts, were selected from a Sarcocystis cruzi sporozoite genomic library constructed in bacteriophage lambda gt10. These clones strongly hybridized with sporozoite and merozoite DNA and were evaluated as probes for detection of merozoite DNA in clinical samples. Of five calves in the experiment, four were each orally dosed with approximately 200,000 S. cruzi sporocysts; one calf served as non-infected control. Subsequently, blood was collected from the calves twice weekly for 3.5 months and fractionated into buffy coats, polymorphonuclear cells, and plasma. Total cellular DNA extracted from these fractions was dot blotted on nylon membranes and hybridized with the probes radiolabeled with [alpha-32P]dATP. The probes detected merozoites on Day 22 post infection in the buffy coats and intermittently from Day 25-39 in the granulocyte fraction. Parasitemia (i.e. merozoites in blood) was also detected by indirect fluorescent antibody technique (IFAT) and direct microscopy, Diagnosis of sarcocystosis in cattle using genomic DNA probes by dot blot hybridization provides an alternative method of detecting parasitemia that is more rigorous than the other two tests (IFAT, direct microscopy) which rely on morphology of the merozoite and visualization by the examiner. As probes detected merozoite DNA in the granulocyte fraction, polymorphonuclear cells may be involved in the pathogenesis of S.cruzi; however this hypothesis requires further study.

Rapid and sensitive identification of Neospora caninum by in vitro amplification of the internal transcribed spacer 1

Neospora caninum and N. caninum-like organisms are cyst-forming coccidian parasites known to cause neuromuscular disorders in dogs and abortion in cattle. In this article we report on the use of the polymerase chain reaction (PCR) for the detection of DNA from N. caninum. After determining the sequence of the internal transcribed spacer 1 (ITS1) of N. caninum and Toxoplasma gondii, and part of the sequences for 4 species of Sarcocystis, we designed a primer set for the amplification of a 279-base-pair fragment of ITS1 from N. caninum. The PCR system made possible the specific detection of 5 N. caninum organisms and no amplification was observed from any of the other cyst-forming coccidia tested, including the closely related T. gondii. Furthermore, we were also able to demonstrate the presence of N. caninum in brain and lung tissue samples from experimentally infected mice. Our data also link the 5.8S rRNA gene for T. gondii and N. caninum to the 16S-like rRNA gene, within the rDNA unit.

Current research on Sarcocystis species of domestic animals

The genus Sarcocystis is composed of about 130 species of heteroxenous cyst-forming coccidia with differences in life cycle and pathogenicity. Pathogenic Sarcocystis spp. can cause disease in their intermediate hosts, in particular in ruminants. Research on Sarcocystis infections has been impeded by several facets of the parasites. Intermediate as well as definitive hosts can be parasitized by several different species with similarities in biology and morphology. Antigen preparations derived from pathogenic Sarcocystis spp. are highly cross-reactive with antibodies directed against non-pathogenic species. As a consequence, none of the currently available immunological tests is species-specific and can differentiate between pathogenic and non-pathogenic Sarcocystis spp. Over the last decade, new techniques in immunology, protein chemistry and molecular biology have facilitated more advanced studies on the molecular composition and molecular biology of Sarcocystis spp. in various laboratories. The development of species-specific monoclonal antibodies and analyses of the molecular composition of some life-cycle stages of Sarcocystis spp. of cattle and sheep showed that species-specific proteins and antigens exist in these species, although they are not highly abundant. In addition, comparisons of rRNA genes of different Sarcocystis spp. identified unique sequences in the rRNA of pathogenic Sarcocystis spp. that are suitable targets for species-specific identification. Thus, tools have become available that facilitate the development of methods for species-specific identification and differentiation of Sarcocystis spp. as well as the identification and study of molecules that are associated with pathogenicity of some of these parasites.

Specific amplification of Sarcocystis cruzi DNA using a randomly primed polymerase chain reaction assay

The polymerase chain reaction (PCR) method to randomly amplify polymorphic DNA (RAPD) was used to differentiate between Sarcocystis cruzi DNA and bovine DNA. This assay was also exploited to identify a S. cruzi DNA fragment which may be useful as a probe. Five primers ranging in length from 16 to 20 nucleotides were analyzed for their ability to direct the amplification of either bovine or parasite DNA fragments. Two primers, TGA and TGD, preferentially amplified bovine DNA in a mixture of S. cruzi and bovine DNA. The primers TGB and TGF each directed the amplification of S. cruzi DNA instead of bovine DNA. Assays using TGF and S. cruzi DNA resulted in the production of a unique 0.8 kilobase (kb) DNA fragment. This fragment was not amplified from two other closely related coccidian species, Toxoplasma gondii and Sarcocystis campestris. When the 0.8 kb DNA fragment was purified and used as a DNA probe, it only hybridized with DNA from S. cruzi. The results of this study indicate that this DNA fragment may be developed into a useful DNA probe for S. cruzi, and that the RAPD-PCR method may be successfully exploited for the rapid development of DNA probes for parasites and other organisms.

Protozoal causes of reproductive failure in domestic ruminants

Protozoan parasites are a significant cause of abortion and infertility in domestic ruminants. Toxoplasma gondii, a widespread cause of abortion in sheep and goats, and Sarcocystis spp., which cause a common, frequently asymptomatic infection of domestic ruminants, both have a two-host life cycle. Carnivorous definitive hosts spread the infection through their feces and domestic ruminants are intermediate hosts. A similar, recently recognized protozoa, Neospora sp., has emerged as an important cause of reproductive disease, especially as an abortifacient in dairy cattle. Neospora is presumed to also have a two-host life cycle, although the definitive host(s) has not been identified. The venereally transmitted Tritrichomonas foetus is an important cause of pregnancy loss in naturally bred cattle throughout the world. In the absence of effective methods for vaccination or treatment, control of these parasites is based on management procedures to reduce infection and transmission.

Differentiation of seven Eimeria species by random amplified polymorphic DNA

Eimeria species were differentiated by the polymerase chain reaction using random amplified polymorphic DNA. Seven arbitrary primers ranging in length from ten to 20 nucleotides were used with DNA of seven species of eimerian oocysts to generate unique DNA fingerprints. DNA fragments ranging from 200 to 2200 base pairs (bp) were synthesized in the different reactions. Species-specific DNA fragment mobility patterns were observed in most cases. In several assays, multiple DNA fragments were synthesized and, in the majority of assays conducted, the Eimeria species could be easily differentiated. Only six of the 49 assays performed failed to generate DNA fragments.