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histomoniasis
Histomoniasis (or histomonosis) is a disease of birds, particularly of chickens and turkeys, due to parasitic infection of a protozoan, ''Histomonas meleagridis''. It is a form of blackhead disease in poultry. The parasite specifically infects the cecum and liver. Symptoms of the infection include depression, reduced appetite, poor growth, increased thirst, sulphur-yellow diarrhoea, listlessness, and dry, ruffled feathers. The head may become cyanotic (bluish in colour), hence the common name of the disease, blackhead; thus the name 'blackhead' is in all possibility a misnomer for discoloration.〔Davidson DR, Doster GL . (Blackhead Disease does not Really Cause Black Heads. ) NWTF Wilflife Bulletin No. 25, pp. 25(1-4).〕 It is particularly highly fatal in poultry, and less in other birds. Currently, no prescription drug is available to treat this disease.
== Etiology ==
A protozoan ''H. meleagridis'' is responsible for histomoniasis of gallinaceous birds ranging from chickens, turkeys, ducks, geese, grouse, guineafowl, partridges, pheasants, and quails. The protozoan parasite is transmitted through the eggs of a nematode, ''Heterakis gallinarum''. The eggs are highly resistant to environmental conditions, and ''H. meleagridis'' is, in turn, highly viable inside the eggs, even for years. Birds are infected once they ingest the eggs of the nematode in soil, or sometimes through earthworms which had ingested the egg-contaminated soil. Outbreak can occur rapidly from the heavily infected bird in a flock readily through normal contact between uninfected and infected birds and their droppings in the total absence of cecal worms. For this reason, infection can spread very quickly. Once inside the digestive system of the host, the protozoan is moved to the cecum along with the eggs of ''H. gallinarum''.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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