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Blackhead disease (also known simply as blackhead) is a commercially important avian disease that affects chickens, Turkeys and other poultry. It is a form of histomoniasis caused by the protozoan parasite Histomonas meleagridis. Blackhead disease affects turkeys more than chickens.

Life History of the Disease

Histomonas meleagridis is most often transmitted to turkeys in the eggs of a second parasite, the cecal worm, commonly found in both chickens and turkeys. The eggs of the cecal worm may remain infective in the soil for three years of longer and could transmit the blackhead-causing protozoan during this period. H. meleagridis may also be transmitted by earthworms that accidentally eat the cecal worm eggs. The cecal worm larva released from the egg and the blackhead parasite within that larva may remain in the earthworm for a year of more. When chickens or turkeys eat infected earthworms, the cecal worm larvae containing the blackhead parasites are released and a blackhead infection may result. Turkeys may acquire the blackhead organism directly from the droppings of infected birds. However, meleagridis found free in the droppings and not protected by a namatode egg die quickly, particularly during warm dry weather.


  • Darkened face
  • Signs of illness (weight loss, ruffled feathers, loss of appetite, etc...)
  • Blood in the droppings


  • Remove infected birds and cull, no treatment available
  • Clean pen thoroughly and sanitize to keep from spreading
  • Oregano oil extract has been used successfully in prevention when mixed with the feed.
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