August 2012 Summer Sore Alert

Recent outbreaks of ‘summer sores’ on horses have prompted us to issue this alert to let horse owners know how to recognize this alarming condition.

Summer sores, also known as Habronemiasis, are seen in the summer during fly season, and are the results of infected flies depositing the larvae of the equine stomach worm Habronema on wounds and moist areas of a horse’s body.Commonly affected areas are the eyelids, the sheath, the corners of the mouth and skin wounds.Infected tissues become inflamed and swell suddenly, with affected skin wounds producing excessive granulation tissue which protrudes above the surrounding skin.Severe itching is often seen.Infected wounds often have characteristic yellow granules which can be seen in the reddish wound surface that are about the size of a grain of rice.These are the dead larvae surrounded by inflammatory debris.

During fly season if your horse has a minor skin wound that suddenly looks much worse, or suddenly develops swelling of the eyelid, lips or sheath it may be Habronemiasis.Have your veterinarian examine your horse.

The treatment of Habronemiasis involves administering an avermectin dewormer (ivermectin or moxidectin), as well as topical treatment of the area.Systemic medications may also be given to control the severe inflammation which can result.

If caught early, summer sores are easily treated.In all cases treatment needs to be aggressive.In severe cases treatment may need to continue until fly season ends in the fall.

Life Cycle

The life cycle of the stomach worm is dependent on house and stable flies.Adult stomach worms live in the lining of the stomach and lay eggs which are shed in the feces.House and stable flies then lay their eggs in the same feces and the developing fly maggots ingest the Habronema larvae which develop within the growing fly maggots.The maggots then pupate into adult flies which then deposit the Habronema larvae on the lips of horses.The horses swallow the Habronema larvae which develop into adults in the stomach, and the life cycle is complete.