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). 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.
Description
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. The amoeboid form is typically 8–15 μm in diameter, whereas the flagellated form can reach up to 30 μm in diameter.
Histomonads do not possess mitochondria, but instead produce energy inside hydrogenosomes.
The flagellum shows the common 9x2+2 type. They migrate to the submucosa and muscularis mucosae and cause severe necrosis. The parasites then move to the liver through the vascular system. There, they cause typical crater-like necrotic lesions. Mortality in turkey flocks can be very high (80-100%).
Pathogenicity
Histomonas meleagridis is the causal organism of histomoniasis of gallinaceous birds. It induces extensive and severe necrosis of the tissues of the mucosa and submucosa of cecum and parenchyma of the liver. The lesions are sometimes exacerbated by other pathogens such as Escherichia coli and coccidia. 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.
References
External links
- PoultryHub
- Organicvet
- ThePoultrySite