Histomonas meleagridis

Location and host

• Found in caecum and liver of turkey and sometimes in fowls also
• Occurs in young between 2-12 weeks of age
• Also occurs in chicken, pea fowl, guinea fowl, pheasant, partridge and quail

Morphology

• Pleomorphic organism, with morphology depending on the organ location and stage of disease
• In caecum, organism is round or oval shaped, amoeboid, with clear cytoplasm and granular endoplasm
• Size: 6-20 µm in diameter
• Bears single flagellum but appears to be lost when in mucosal tissue or liver
• Nucleus is vesicular and flagellum arises from small blepharoplast near nucleus
• There are four forms of parasite i.e. invasive form, vegetative form, resistant form and flagellated form

Invasive form

• Found in early caecal and liver lesions and at periphery of older lesions
• Amoeboid, extracellular and 8-17 µm long
• Feeds by phagocytosis

Vegetative form

• Found near the center of the lesions and in slightly older lesion
• Larger in size i.e. 12-15 µm
• Less active than invasive form and are packed tightly together and cause disruption of the tissue

Resistant form

• They do not form cyst and more resistant than the others
• Measures 4-11 µm in diameter and are compact and enclosed in dense membrane
• These forms occur singly or packed together and are extracellular
• These may be taken up by phagocytes or giant cells

Flagellated form

• Occur in lumen of caeca
• Same form is found in cultures
• Body is amoeboid and 5-30 µm in diameter
• Basal granule or blepharoplast is present near the nucleus from which the flagella arise
• Commonly, there is a typical single short flagellum but there may be as many as four
• No axostyle and undulating membrane

Life cycle

• Birds gets infection either through ingestion of embryonated eggs of caecal worm ‘Heterakis gallinarium’ containing Hostomonas meleagridis.
• Eggs hatches in intestine and histomonads are released from larva
• They enter caecal mucosa and multiply causing ulceration and necrosis
• Reach liver in portal stream and colonize liver parenchyma, producing circular necrotic foci which increase in size as parasite multiply in the periphery of the lesion.
• Next phase of life cycle is not clear, but it is assumed that Heteratis worms become infected with caecal histomonads possibly by ingestion and these protozoan reaches ovary of worm
• Released out in faeces of host incorporated in eggs of caecal worm

Transmission

• Ingestion of embryonated eggs of heterakis gallinarum containing histomonas
• Ingestion of earthworms carrying both heteratis eggs and larvae
• Ingestion of contaminated food and water
• Transmission can also occur through arthropods

Pathogenesis

• Organisms ‘Histomonas meleagridis’ are released from H. gallinarum eggs or larva.
• Organism invade caecal wall and multiply causing characteristic ulceration and necrosis
• They migrate to liver through blood stream and colonize liver parenchyma, producing circular necrotic foci which increase in size as parasite multiplies
• Incubation period is 15-21 days
• Disease caused by this parasite is called ‘black head’ or ‘infectious enterohepatitis’ or ‘histomoniasis’.

Clinical signs

• Droopiness is first sign of disease
• Birds appear weak, drowsy and stand with lowered head, ruffled feathers and dropping wings
• Yellow-colored diarrhea
• Head may or may not become dark, due to cardiac insufficiency

Lesions

• One or both caeca may be involved and earliest lesion consist of small, raised pin-point ulcers, in which large number of organisms are present
• Caecal mucosa becomes thickened and necrotic and covered with characteristic, foul-smelling, yellowish exudate, forming dry hard, cheesy plug that fills caecum
• Pathognomonic lesion in liver is focal necrosis to produce circular, depressed, yellowish to yellow-green areas. These lesions may heal in older birds following fibrinous and lymphoid tissue reaction.

Diagnosis

• Characteristic Sulphur yellow droppings in sick birds are suggestive of enterohepatitis.
• On PM, lesion of liver is pathognomonic
• Demonstration of trophozoites in faeces is also useful

Treatment

• 2 anino-5-nitrothiazole (Enheptin -T) or Entramin is given orally in feed or drinking water @ 0.05 % as preventive or 0.1 % as curative
• Nithiazide is more effective and less toxic. It is given @0.02% and 0.025 % in feed and drinking water respectively.
• Furazolidone @ 0.015% in feed for preventive and @0.04 % for treatment
• Nitrofurazone is given in food @0.1-0.4%.

Control

• Good management and hygiene
• Turkey and chickens should be raised separately
• Young birds should be kept separately
• Use of anthelmintics for control of heterakis worms can be effective control measure in limiting infection and spread.