Histomonas meleagridis is a species of parasitic protozoan that infects a wide range of birds including chickens, turkeys, peafowl, quail and pheasants, causing infectious enterohepatitis, or histomoniasis (blackhead diseases).

Histomonas meleagridis is a microscopic, pleomorphic protozoan, and can exist in two forms, amoeboid and flagellated.

Within the tissue, it is present as an amoeboid protozoan, while in the lumen or free in the contents of cecum, it lives as an elongated flagellated form.

Histomonads, either released from the heterakid nematode larvae in the ceca or after direct infection via the cloaca, replicate rapidly in the cecal tissues.

It induces extensive and severe necrosis of the tissues of the mucosa and submucosa of cecum and parenchyma of the liver.

[7] The symptoms appear within seven to 12 days after infection, and include depression, reduced appetite, poor growth, increased thirst, sulphur-yellow diarrhoea, listlessness, drooping wings, and unkempt feathers.

However, outbreaks in chickens may result in high morbidity, moderate mortality, and extensive culling, leading to overall poor flock performance.

[6] Concurrence of Salmonella typhmurium and E. coli was found to cause high mortality in broiler chickens.

However good management of the farm and sanitation are the essential effective strategies to control the spread of infection.

Billic, Ivana; Jaskulska, Barbara; Souillard, Rozenn; Liebhart, Dieter; Hess, Michael (21 March 2014).