Blackhead

BlackheadBlackhead (Histomoniasis) in Peacocks, Quail, Turkeys and Chickens

Blackhead (Histomoniasis) is caused by an amoeba-like parasite, Histomonas meleagridis, that lives in the caeca of chicken, turkeys, quail, pheasants and other gallinaceous (chicken-like) birds. The caeca are blind portions of the intestine, the equivalent to the human appendix, which are paired and large in gallinaceous birds.

Life Cycle. This is complicated! Histomonas is typically carried by Heterakis roundworms that also live in the caeca. Histomonas parasites are passed in Heterakis worm eggs in the droppings; the thick shell of the worm egg protects the fragile Histomonas organisms. If the eggs are ingested by another gallinaceous bird, the eggs hatch out in the caeca producing both more round worms as well as allowing the Histomonas organism to escape andmultiply and possibly cause disease.

Peacock, turkeys and quail (both native button quail (Turnix spp) as well as domestic quail (Coturnix spp)  are typically more susceptible to Blackhead than chickens. A common scenario is that if these species are kept where they can come into contact with chicken droppings containing Histomonas contaminated  Heterakis worm egg, the chickens themselves, because of their greater natural immunity, may remain well and show no signs of disease while the other species may become very ill and die.

Great care must be taken to ensure appropriate worming if chickens are kept on the same soil as turkeys, peacocks of quail. Preferably these species should be housed separately from chickens.

Disease Histomonas  is especially dangerous as when it is ingested it does not remain solely in the gastrointestinal system but can migrate first to the liver and then to other organs such as spleen, kidneys and lungs. While migrating the parasites can cause haemorrhages and severe tissue damage resulting in high mortalities. If birds survive, extensive scarring occurs which can result in secondary complications.

Diagnosis Blackhead can be suspected in birds passing typical Heterakis worm eggs (identified by microscopic examination of droppings and/or a faecal flotation test) that are showing signs of illness. It needs to be differentiated from other diseases such as coccidiosis, bacterial  or viral infections. A blood panel will typically show elevated liver enzymes.

Treatment consists of dosing with drugs such as metronidazole, dimetronidazole or ronidazole. Instructions will vary depending on which drugs is selected and manufacturer’s recommendations. Veterinary advice should be sought as some drugs (e.g.dimetronidazole, Emtryl) can be toxic if over dosed (e.g. if birds drink excessive medicated drinking water on hot days) and care needs to be taken with administration.