Histomoniasis is a commercially important illness of poultry, most notably of chickens and turkeys, caused by parasite infection with a protozoan. The nematode parasite transmits the protozoan to the bird. Poultry and wild birds typically host a variety of parasitic worms that cause only minor health concerns. Turkeys are far more prone to blackheads than chickens. As a result, hens can be diseased carriers for a long time since their owners do not remove or medication them, and they do not die or stop defecating. Histomoniasis is caused by a protozoan that affects gallinaceous birds such as chickens, turkeys, ducks, geese, grouse, guineafowl, partridges, pheasants, and quails. The eggs are extremely resistant to external conditions, and the protozoan remains viable inside the eggs for years. Birds become infected when they consume the nematode's eggs in soil, or when earthworms consume the egg-contaminated soil. Cyanosis of the head and sulfur-yellow diarrhoea are visible symptoms of this disease. The pathogen causes cecal and liver lesions. Ulcerations and expansion of the ceca occur, and caseous masses form within them. The parasite migrates to the mucosa and submucosa, where it causes extensive and severe tissue necrosis. Necrosis is caused by inflammation and progressive ulceration, which causes the cecal wall to thicken.