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Endoparasites - Habronema (Not in New Zealand)

Habronema muscae, H. microstoma, Habronema (Draschia) megastoma: Equine stomach worms. (H. megastoma has been reported to occur in New Zealand).

 

General Description: .

Life Cycle: Habronema microstoma and D. megastoma deposit larvae, but H. muscae lays eggs containing larvae. The larvae are ingested by housefly (Musca) or stablefly (Stomoxys ) maggots which develop in manure. The larval worms develop inside the maggot, becoming infective third - stage larvae at about the time that the adult fly emerges from its pupa. Larvae are deposited on the lips, nostrils, and wounds of horses as the flies feed. If licked and swallowed by the host, the larvae mature in the stomach. If larvae are deposited in wounds they do not complete their development and remain circumscribed to the area of the wound causing cutaneous habronemiasis. Another method of infection is by ingestion of infected flies with the water or feed.

Location: Habronema muscae and H. microstoma occur on the horse stomach mucosa under a layer of mucus. D. megastoma is found in tumours of the stomach wall.

Geographical Distribution:

Significance: Habronema (Not in New Zealand) are of little concern, but ocular and cutaneous larvae cause annoyance and disfigurement. Also tumours which develop in gastric mucosa may subsequently rupture.

Effect on Host: Draschia megastoma (not significant in New Zealand) provokes the formation of tumour-like growths on the stomach wall which may rupture or occasionally block the passage of food from the stomach. Ocular or cutaneous habronemiasis (summer sores) are of much greater significance. Larvae deposited in wounds migrate and feed, extending the wound and preventing healing. These infections tend to heal spontaneously in the following winter but often recur in subsequent warm seasons when flies are prevalent. Larvae deposited in the eye cause wart-like lesions of the conjunctiva accompanied by watering eyes and sometimes photophobia (sensitivity to sunlight). Mild digestive disorders may result from gastric habronemiasis.

Diagnostic Information:

Control:

Posterior Habronema    
Posterior end of Habronema spp showing bursa and spicule   Cutaneous habronemiasis   D.megastoma– stomach lesion

       

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