Histomonas

Histomonas meleagridis
Scientific classification
Domain:	Eukaryota
(unranked):	Excavata
Phylum:	Metamonada
Class:	Parabasalia
Order:	Trichomonadida
Family:	Monocercomonadidae
Genus:	Histomonas
Species:	H. meleagridis
Binomial name
*Histomonas meleagridis* (Smith, 1895)

Histomonas meleagridis is species of parasitic protozoan that infects a wide range of birds including chickens, turkeys, peafowl, quail and pheasants, causing blackhead disease, infectious enterohepatitis, or histomoniasis. H. meleagridis can infect many birds, but it is most deadly in turkeys. It inhabits the lumen of cecum and parenchyma of liver, where it causes extensive necrosis. It is transmitted by another cecal parasite, the nematode Heterakis gallinarum.

H. 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. The amoeboid form is typically 8-15 μm in diameter, whereas the flagellated form can reach up to 30 μm in diameter.