Histomoniasis/Blackhead Disease

Histomoniasis, also known as Blackhead Disease (or appendicitis of the liver), is an infectious disease caused by the unicellular intestinal parasite Histomonas meleagridis. Blackhead disease is mainly transmitted by certain gastrointestinal roundworms, the awl tails. These very small roundworms colonize the appendix of the chickens and cause nodular growths there, each of which contains a worm. Any of these worms can be carriers of the histomonas parasite and lead to blackhead disease.

However, other secondary diseases that might have already weakened the chicken’s immune system usually play a role.


Blackhead disease can be transmitted in several ways. On the one hand, the eggs or larvae of the roundworm are taken in by the chickens. On the other hand, through earthworms, which serve as hosts for the parasite.


The intestinal parasite introduced into the appendix attacks the cells of the mucosa (mucous membrane) and submucosa (tissue layer between the mucous membrane) and causes massive tissue damage there. This tissue damage leads to inflammation, lumen-side diphteroid coatings and the appendix fills with a purulent, hardened substance.

Unspecific symptoms:

  • Aphatic behavior
  • Shut eyes
  • Stilted gait
  • Respiratory problems

Specific symptoms:

  • Slimy diarrhoea (rarely sulphur yellow diarrhoea)
  • Rarely a black coloured comb
  • Black tinted scalp, which, however, does not always occur

Symptoms that can only be detected postmortem:

  • Severe damage to the appendix (caecum) and liver (especially in turkeys)
  • Severe inflammation of the appendix
  • Thickening of the mucosa
Histomoniasis is associated with an enormously high mortality rate. Infected animals usually die suddenly and after a few days.


A cure is also not possible for this disease, as most of the products for the treatment of laying hens are no longer approved for example in Germany.


Today, the best prophylactic measure so far is regular worm removal, as well as sufficient stable hygiene.

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