Habronema muscae, H. microstoma, Habronema (Draschia) megastoma: Equine stomach worms.

General Description: Adult worms are whitish and 10 to 25 mm. long.

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: Common in many countries.

Significance: Adult Habronema 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 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: Adult worms may be found during postmortem examinations. Ova or larvae in faeces are diagnostic. Larvae in lesion scrapings are indicative of ocular and cutaneous habronemiasis.

Control: Fly prevention, by stacking manure and using insecticides, is important for control. Skin breaks should be avoided during the fly season, and existing wounds may be treated with fly repellents. Cutaneous lesions may be treated or removed surgically in the winter. EQUIMEC kills the larvae responsible for summer sores.

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