Habronemiasis, summer sores, granular dermatitis, jack sores are all similar conditions that horses can be exposed to through fly contact. House flies, face flies, and stable flies are all intermediate hosts for the stomach worm, Habronema spp, that cause the sores. The stomach worms can cause inflammation of the lining of the horse’s stomach, however they usually do the most damage on fresh wounds or moist areas on the horse’s body. The lower abdomen, lips, prepuce, and fetlock area are all common areas that flies feed therefore lesions are most commonly seen in those locations.

Flies pick up the stomach worm larvae in horse manure, rotten feed, old bedding, and other decaying material in the horse’s environment. The flies then deposit the larvae while feeding on fresh wounds, or areas of moisture. The irritation caused by the larvae cause the horse to chew at the lesion delaying the healing process and often causing proud flesh. If not treated the lesion can get worse over time, and last for long periods of time.

Treatment of the lesions start with deworming the horse with Ivermectin to kill the parasite. A topical ointment is also often prescribed to reduce inflammation and itching. Fly control is the number one way to help prevent the summer sores. Keeping manure picked up, feeding insect growth regulators, and using fly masks, fly sprays, and fly traps are all ways to decrease the number of flies your horse is exposed to.