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Blackhead

Histomonosis, Histomoniasis, Infectious Typhlohepatitis, Infectious Enterohepatitis

Histomoniasis, also known as Blackhead, is a destructive protozoan disease of predominately turkeys, and sometimes chickens. Infected birds often appear droopy, stop eating, and develop yellowish-brown, watery feces that appears foamy. The disease is caused by Histomonas meleagridis, a protozoan parasite that is commonly found within the cecal worm (Heterakis gallinarum), which is often harbored in earthworms. The nickname "blackhead" came from the dark colored (almost black) head and wattles of infected birds. The disease is often acute in nature, with affected individuals dying quickly, especially in younger chickens less than 6-weeks of age.

Once H. meleagridis gains access to the digestive tract, it can multiple within the ceca and destroy the outer lining of the chicken's cecal, piling it up to form a cheese-like, foul smelling yellow substance that is composed of the dead cecal cells and blood. H. meleagridis will eventually move on to other organs.

Transmission
H. meleagridis may spread directly through contact with contaminated feces or indirectly by ingestion of the infected egg of the cecal worm Heterakis gallinae or ingestion of an earthworm containing cecal worm eggs.

Chickens are somewhat resistant to blackhead, and can often become carriers. Carrier chickens will regularly shed cecal worm eggs in their feces, where they can remain in the soil. H. meleagridis can survive for up to 3 years in the soil. Due to this risk, turkeys and chickens should never be raised together in the same area, and turkeys should never be raised in areas that were previously used to raise chickens.

Symptoms

Watery or sulfur-yellow droppings
Droopiness
Increased thirst
Dry, rumpled feathers
Loss in appetite
Lethargy
Pale, shrunken comb and wattles

Diagnosis

  • History
  • Clinical signs
  • Necropsy
  • ELISA

Treatment

MethodDetails
Hot pepper powderHas shown varying success as an alternative natural treatment
ManagementRelocate flock to fresh ground and isolate sick birds.

Prevention

  • Do not raise chickens and turkeys together in the same area
  • Turkeys should never be raised in areas that were previously used to raise chickens if less than two years
  • Separate poultry flock species by species and age
  • Biosecurity
  • Good sanitation
  • Histostat (Nitarsone) feed additive
  • Natustate feed additive

Prognosis

It is associated with a high mortality rate in turkeys, ranging from 80 to 100%.

Scientific References

Risk Factors

  • Poor sanitary practices
  • Ingestion of earthworms
  • Raised on property previous inhabited by turkeys