Coccidiosis. Light micrograph (LM) of a section through an hepatic bile duct infected with coccidian protozoa (purple). Coccidiosis is a parasitic disease of the intestinal tract of animals, (including dogs, chickens, cattle and goats) caused by coccidian protozoa. The disease spreads from one animal to another by contact with infected faeces or ingestion of infected tissue. Diarrhoea, which may become bloody in severe cases, is the primary symptom. Most animals infected with coccidia are asymptomatic, but young or immunocompromised animals may suffer severe symptoms and death. Magnification: x100 when printed at 10 centimetres wide.