Blackhead disease (also known simply as blackhead) is a commercially important avian disease that affects chickens, turkeys and other poultry birds. The disease carries a high mortality rate and primarily affects the liver and cecum. It is a form of histomoniasis which is transmitted by the protozoan parasite Histomonas meleagridis. The protozoan is in turn transmitted by the nematode parasite Heterakis gallinarum.[1][2] H. meleagridis resides within the eggs of H. gallinarum so that birds ingest the parasites along contaminated soil or food.[3] Earthworms can act as a paratenic host [1]. Symptom of the infection is characterized by the development of cyanotic (bluish) discoloration on the head and hence the common name, but apparently a misnomer, of the disease, "blackhead".[4]
Poultry (especially free-ranging) and wild birds, commonly harbor a number of parasitic worms with only mild health problems for them. Turkeys are much more susceptible to getting blackhead than are chicken. Thus chicken can be infected carriers for a long time because they aren't removed or medicated by their owner, and they don't die or stop eating/defecating. H. gallinarum eggs can remain infective in soil for four years [2] thus there is a high risk of transmitting blackhead to turkeys if they graze areas with chicken feces [3] in this time frame. Thermophilic composting is known to sanitize soil from ascarid (another nematode) eggs.
The most common symptom of blackhead disease is yellow watery bird droppings. To reduce the spreading of Blackhead disease, the sick birds must be removed and their litter changed.
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