Genetic comparison of Neospora caninum with Toxoplasma and Sarcocystis by random amplified polymorphic DNA-polymerase chain reaction.

To determine the relationship of Neospora caninum to protozoa classified in the family Sarcocystidae of the phylum Apicomplexa, the genomes of N. caninum, three Toxoplasma gondii strains (RHa, CEP, TPR) and three Sarcocystis species (S. tenella, S. muris, S. gigantea) that were thought to be closely related coccidia were compared by the random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) technique. The genomic DNAs were amplified by the use of seven 10-mer arbitrary sequence primers to generate polymorphic DNA. Significant DNA polymorphisms were observed among Neospora, Toxoplasma and Sarcocystis. It appears that one primer tested may have value in a diagnostic RAPD-PCR to differentiate T. gondii from other closely related protozoa. The high level of genetic divergence of N. caninum from T. gondii strains and several Sarcocystis species observed in this study is consistent with the hypothesis that N. caninum is indeed an independent species of protozoan parasite. As compared with the Sarcocystis species tested, a closer genetic relationship of N. caninum to T. gondii was not observed. By contrast, a closer genetic relationship of S. muris to T. gondii was revealed in this study.