Habronemiasis: Biology, Signs, and Diagnosis, and Treatment and Prevention of the Nematodes and Vector Flies

Habronemiasis is a parasitic disease of horses and other equids which is caused by the invasion of Draschia megastoma, Habronema majus, and H. muscae nematodes and is transmitted by house flies, face flies, and stable flies. The adult nematodes live in the horse's stomach, laying eggs, which pass out in the horse's feces. The carrier flies lay eggs in the horse's manure, which becomes infested with larvae while the flies feed in the manure. The nematode larvae molt while in the fly larvae and develop into infective L3 larvae by the time the adult flies emerge from their pupal stage. The infective larvae are then transmitted to the horse when flies feed on secretions or discharges from hosts' eyes, nostrils, mouths, wounds, and other openings. The L3 larvae are ingested by the horse and are then able to complete their lifecycle. The most common aberrant forms (conjunctival and cutaneous habronemiasis) are associated with the nematode larvae being deposited in these areas, not completing its life cycle, with resultant signs probably associated with local hypersensitivity. This article details the biology of nematode parasites, diagnosis and treatment of this condition, and methods of prevention and control of the transmitting flies.