Australian-German collaborative studies on the immunology of Sarcocystis infections.

This paper reviews a decade of collaborative studies performed between two laboratories in Germany and Australia on the life cycle, pathogenicity and immunology of infections by the cyst-forming sporozoan parasites Sarcocystis spp. in domestic animals. Experimental transmission studies demonstrated that certain parasite species could cause an acute clinical disease in sheep and pigs severely affecting their health, productivity and reproductivity. Despite the high prevalence of infections found in farm animals, few outbreaks of naturally-occurring clinical disease have ever been recorded. Host animals exposed to low levels of infection were found to develop a strong protective immunity against subsequent lethal challenge and clinical disease even though parasites were not completely eliminated nor prevented from further establishment (premunitive immunity rather than sterile immunity). Modern molecular biological techniques are currently being used to examine the parasite antigens and host immune responses involved in the acquisition of the protective immunity.