Blackhead (Histomoniasis meleagridis) protozoan parasite in domestic poultry

Blackhead (Histomoniasis meleagridis) can infect most domestic poultry and game birds, including turkeys, chickens, partridges, peacocks, pheasants and quail. It is a parasitic protozoan transmitted by the caecal worm Heterakis gallinarum that causes lesions in the caeca (and liver of turkeys).

Transmission bird to bird is thought to occur only in turkeys, one of the reasons they are so susceptible to disease. In contrast chickens and other birds are only infected directly by caecal worm larvae or their eggs that are carrying the disease that they ingest via earthworms, beetles and insects. General disturbance of the ground is also linked to histomonas outbreaks as this may recirculate buried caecal worm eggs.

turkeys are more prone to blackhead than other birds


It is a very serious disease and turkeys are notoriously susceptible. A characteristic sign is yellow sulphur-coloured droppings caused from severe damage to the liver and bile pigments excreted through the kidneys. The caecal discharge (droppings) may also contain blood. Other non-specific signs include drowsiness, dropped wings, stilted gait, closed eyes, loss of appetite, head down close to the body or tucked under a wing. Sick birds are often also seen huddling together.


Birds are infected with blackhead via a caecal worm carrying the blackhead protozoa. While there are no tests to detect the protozoa, caecal worm eggs o show up on a worm egg count which is the primary route of detection.


The priority is to reduce the presence of caecal worms and other potential vectors in the environment, so ensure hen house is well drained to reduce bacteria and likelihood of earthworms.

Regularly clean, disinfect and change litter and have a good insect and rodent control programme to minimise the presence of E. coli. which is thought to exacerbate likelihood of infection. Spreading a lime-based product can help destroy worm eggs and use pre and probiotics, apple cider vinegar in water to strengthen the birds.


There is no direct treatment for blackhead so prevention is key. Birds diagnosed with Blackhead (Histomoniasis meleagridis) should be kept warm and quiet and supported with pre or probiotics. Try apple cider vinegar in water to strengthen birds.