Occurrence: Worldwide. Species affected: Mostly turkeys, occasionally in chicken, quail, pheasants, grouse, chukar partridges, guinea fowl. Age affected: Young.

Causes: Amoeboid protozoan Histomonas meleagridis.

Effects: Enterohepatitis has a 7-12 day incubation period. In chickens, morbidity (to 100%) occurs, a cyanotic head and bloody caecal diarrhoea. In turkeys, signs include drowsiness, drooping of wings, stilted gait, closed eyes, head down and anorexia. Mortality occurs up to 100%.

It is called blackhead because birds may have a dark discoloured head. Young turkeys, chickens, quail, pheasants, grouse, chukar partridges and guinea fowl are susceptible to this acute to chronic disease. Enterohepatitis is caused by Histomonas meleagridis, a highly pleomorphic amoeboid protozoa with a stout flagellum and pseudopodia.

Chicken caecal worm (Heterakis gallinae) engulfs and packages Histomonas oocysts in its egg. Earthworms also consume Histomonas oocysts. Birds become infected by eating caecal or earthworms or caeca worm egg, which contains oocysts. Oocysts can also develop (sporulate) in worms and histomonads enter the tissues of the worm.

It is quite destructive in turkeys.

Enterophepatitis has a 7-12 day incubation period. Signs include drowsiness, drooping of wings, stilted gait, closed eyes, head down and anorexia in turkeys. Mortality and morbidity are high (to 100%) in turkeys, a cyanotic head, and bloody caecal diarrhoea occur in chickens.

The caeca have an ulcerated (cheesy core) or haemorrhagic exudates. Crater-like liver lesions (bulls eye) and an enlarged green coloured liver can also be seen.

Coccidiosis should first be eliminated, as enterohepatitis simulates caecal coccidiosis. Clinical signs, gross lesions (intestine and liver lesions) and hestopathologic observations of (diarrhoea) life cycle stages near the lesions are diagnostic.

Enterohepatitis is controlled by controlling the spread of the helminths, which spread disease. This is done by changing the litter or using antihelmintic drugs in the feed or water. Chickens and turkeys should always be kept separate to prevent introduction of caecal worms.

Dimetridazol (0.015%), Carbasone (0.025%), Ipronidazole (0.00625%), Nitarsone (0.01875%) or Furazolidone (0.011%), are effective drugs, though not licensed in Western Europe.

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