Blackhead disease (also known simply as blackhead) is a commercially important avian disease that affects chickens, turkeys and other poultry. It is a form of histomoniasis caused by the protozoan parasite Histomonas meleagridis. Blackhead disease affects turkeys more than chickens.
The most common symptom of Blackhead disease is yellow watery bird droppings. To reduce the spreading of Blackhead disease, the sick birds must be removed and their litter changed.
This protozoan is commonly associated with Heterakis infections of fowl.