Histomonas

Histomonas meleagridis

Blackhead lesions in turkey liver - Milton Friend

Heterakis gallinarum - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

• Infects chickens and turkeys

• Causes Blackhead in turkeys
  • Infectious entero-hepatitis or histomonosis
  • Head and wattle become cyanotic

• Worldwide distribution

Recognition

• 10-25μm long

• Round or oval

• 1 flagellum in the intestinal form
  • The tissue form has no flagellum

• Pseudopial movement

Life Cycle

• Histomonas carried by larval stage inside the egg of the caecal nematode worm Heterakis gallinarum (vector)

• Histomonas released from larva when egg hatches in intestine

• Penetrates caecal wall

• Carried by hepatic portal system to the liver parenchyma

• Intestinal Histomonas infects Heterakis gallinarum and passes to worm ovary

• Worm passes Histomonas-infected eggs in droppings

• Infected eggs swallowed by birds or earthworms
  • Earthworms act as transport hosts carrying larvae in their tissues

Pathogenicity

• Necrotic circular caecal lesions and liver lesions
  • Lesions begin small but soon enlarge and become necrotic
  • The plug detaches with the caecal contents forming a caseous plug
  • Lesions can be up to 1cm in diameter
  • Lesions found both on the surface and in the substance of the liver

• Mortality may reach 100%

• Recovered birds may have a permanently scarred caecum and liver

• Generally affects turkey poults under 14 weeks old

• A few days after infection the bird will become dull with ruffled feathers

• The faeces will become sulphur yellow in colour

• In older turkeys, recovery and immunity is likely

Diagnosis

• Clincal signs
  • Cyanotic head and wattles
  • Yellow droppings

• Post-mortem
  • Necrotic mucosa in caecum
  • Circular lesions in liver 1cm in diameter which stain poorly

Control

• Do not rear turkeys on ground used by chickens
  • Chickens are asymptomatic carriers

• Chemical control now withdrawn due to fears of human toxicity