[Cyst-forming Coccidia: Toxoplasma, Neospora, Sarcocystis].

The most important cyst-forming coccidian parasites in human and veterinary medicine belong the genera of Toxoplasma, Neospora and Sarcocystis. Toxoplasma gondii shows its clinical relevance in congenital infections and opportunistic infections in immunodeficient patients. In veterinary medicine the parasite is predominantly the cause of important economic loss in livestock production. Neospora causes diseases resembling toxoplasmosis; neosporosis is one of the most important causes of bovine abortion in the US. Neospora caninum leads to myositis and paralysis in dogs. The potential implication of Neospora in toxoplasmosis-like diseases in humans is not yet known. Sarcocystis is usually a relatively harmless intestinal parasite in humans. Recent data from tropical areas suggest that man can also become an intermediate host for certain Sarcocystis species, which potentially represents a source of opportunistic infection and disease in areas with increasing HIV prevalence. In veterinary medicine, Sarcocystis causes muscle diseases and also abortion or myeloencephalitis with lethal outcome in certain animal species. Molecular-epidemiological investigations have resulted in a new understanding of biological and population-genetic mechanisms relevant to the disease. Recently developed molecular techniques, such as transfection in protozoan parasites, are presently used not only to elucidate molecular-pathogenetic events in the course of disease, but also to prepare potential new immuno-therapeutic tools for future vaccination against infection or disease.