Blackhead disease

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Large, pale areas in the liver of a bird infected with Histomonas sp.

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 birds ingest the parasites along with contaminated soil or food.[3] Earthworms can also act as a paratenic host. A characteristic symptom of the infection is the development of cyanotic (bluish) discoloration on the head, giving rise to the common name of the disease, "blackhead".[4]

Poultry (especially free-ranging) and wild birds commonly harbor a number of parasitic worms with only mild health problems from them. Turkeys are much more susceptible to getting blackhead than are chickens. Thus, chickens can be infected carriers for a long time because they are not removed or medicated by their owners, and they do not die or stop eating/defecating. H. gallinarum eggs can remain infective in soil for four years, a high risk of transmitting blackhead to turkeys remains if they graze areas with chicken feces[5] in this time frame.

The most common symptom of blackhead disease is yellow, watery bird droppings. To reduce the spreading of the disease, sick birds must be removed and their litter changed.


  1. ^ Lund EE, Chute AM, Wilkins GC (1975). "The wild turkey as a host for Heterakis gallinarum and Histomonas meleagridis". J Wildl Dis. 11 (3): 376–381. doi:10.7589/0090-3558-11.3.376. PMID 1171270. 
  2. ^ Brener B, Tortelly R, Menezes RC, Muniz-Pereira LC, Pinto RM (2006). "Prevalence and pathology of the nematode Heterakis gallinarum, the trematode Paratanaisia bragai, and the protozoan Histomonas meleagridis in the turkey, Meleagris gallopavo" (PDF). Mem Inst Oswaldo Cruz 101 (6): 677–681. doi:10.1590/s0074-02762006000600017. PMID 17072483. 
  3. ^ McDougald LR (1998). "Intestinal protozoa important to poultry". Poultry Science 77 (8): 1156–1158. doi:10.1093/ps/77.8.1156. PMID 9706082. 
  4. ^ Davidson DR, Doster GL . Blackhead Disease does not Really Cause Black Heads. NWTF Wildlife Bulletin No. 25, pp. 25(1-4).
  5. ^

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