The threat of histomoniasis: turkeys and chickens cannot be housed together!

Emily Martin

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2021;25(3):21.

Histomonas meleagridis, the causative agent of Blackhead disease (histomoniasis), is a protozoan parasite with a complex life cycle.  Avian species that are susceptible to natural infection include, in order of susceptibility: turkeys, pea fowl, guinea fowl, chicken, chukar, pheasant, and bobwhite quail.  Histomonas is a fragile organism and can only last minutes to hours in the environment, therefore, an intermediate host is needed for it to survive.  Direct transmission is thought to be possible only in turkeys, by direct contact or ‘cloacal drinking’.  Ducks can also be asymptomatic carriers of Histomonas.

Intermediate hosts for Histomonas include the cecal roundworm, Heterakis gallinarum, as well as earthworms.  Heterakis eggs are resistant to commonly-used disinfectants and can live in the soil for months to years, harbouring Histomonas.  Mechanical transmission of Heterakis eggs is also possible. The bird hosts for Heterakis gallinarum that are most likely to contaminate soil are pheasants, guinea fowl and chickens. 

Lesions of histomoniasis are located primarily in the ceca.  Liver lesions are common in turkeys but not in other birds.  Protozoa may also migrate through the bloodstream to other organs such as spleen, kidney, and pancreas.

Prevention of histomoniasis is based on three principles:

  1. controlling Heterakis gallinarum;
  2. separation of susceptible avian species from birds that are reservoirs of Histomonas meleagridis and/or Heterakis gallinarum;
  3. stringent biosecurity measures.

Please refer to ‘AHL LabNote 54 – Blackhead (histomoniasis) in small turkey flocks’ for more information and a list of preventative measures to take for this disease:  AHL


Abdul-Aziz T, McDougald LR, Barnes HJ. Histomoniasis slide study set #33, AAAP Conference; 2012 Aug 4-7; San Diego, California.