Coccidiosis is caused by a protozoal parasite called Eimeria.
• E. ovinoidalis and E. crandallis can cause severe disease in sheep. They are host specific, only infecting sheep. Eimeria ovinoidalis is more pathogenic than E. crandallis.
• There are many other species of Eimeria but few cause disease in sheep. There is no cross-protective immunity amongst different species. • Each gram of feces may contain millions of oocysts, and 1 oocyst ingested can destroy 50 million intestinal cells, resulting in excretion of 10,000 new oocysts.