Summer Sores in Horses

Habronemiasis Treatment

summer sores in horses may originally start as a small superficial scratch.
Summer sore on a horse’s leg.

Hot, humid climates create the perfect environment for flies to thrive, and therefore, contribute to many irritating issues for horses. Summer sores, medically known as habronemiasis, are one of the most serious problems caused by flies. They may originally be spotted as a small, superficial scratch. However, they can fester into a serious condition and persist for weeks to months if not properly diagnosed and treated.

What are Summer Sores in Horses?

Summer sores are lesions on the skin caused by the larvae of certain stomach worms, called Habronema. These worms in the horse’s stomach produce eggs that pass through the digestive tract and are shed in the horse’s feces. Barn flies then gather on and around the manure, consequently collecting the parasite’s larvae on their extremities.  Summer sores will ensue when flies carrying the larvae lay their eggs onto an open wound or the mucous membranes of a horse (usually areas such as the prepuce, lower abdomen, corners of the eyes, and margins of the lips). The larvae cause an inflammatory reaction, typically with discharge and the production of granulation tissue infected with larvae.

Signs of summer sores in horses:

  • Non-healing skin lesions
  • Intense itching
  • Formation of exuberant granulation tissue (proud flesh)
  • Calcified necrosis (dead tissue) 

Identifying Summer Sores in Horses

“Firstly, it is incredibly important that the owner does not assume a lesion is a summer sore because of its appearance or their experience with summer sores,” said Dr. Meredith Mitchell, a Palm Beach Equine Clinic veterinarian who often treats patients with this condition. “Granulation tissue can look like a summer sore but actually be the result of a different infection or skin issue. So, it is crucial to contact a veterinarian at the first sign of a potential summer sore before any treatment is administered.”

summer sore on the hind leg of a horse
Summer sore on a horse’s back leg.

Summer sores commonly appear as proud flesh with small, yellow-colored beads which are the larvae within the horse’s skin, and a mucopurulent (mucus or pus) discharge associated with the wound.

Treating Summer Sores in Horses

For treatment of the visible summer sore, corticosteroids are administered to reduce the inflammatory hypersensitivity reaction and antimicrobials to treat any secondary infection that may develop because of the open wound. If not treated quickly and appropriately by a veterinarian, summer sores can persist for months and possibly require a surgical procedure to remove the granulated tissue and larvae.

“The standard summer sore treatment is debridement of the wound and an injection of Ivermectin (Noromectin),” Dr. Mitchell said. “However, more medicine is not more effective with summer sores. The larvae and flies can develop a resistance to the treatment, so it is always best to consult with your veterinarian for dosage information. Also, this specific treatment does not include preservatives, so it is imperative than an unopened bottle is always used to prevent contamination that could lead to an abscess in the injection site.”

Additionally, there are local injections that can be administered directly around or into the lesion itself to promote healing. Dr. Mitchell also relies on oral treatments, such as Prednisolone and Dexamethasone tablets, depending on the patient’s case.

Summer Sore Prevention

Prevention strategies are key to controlling summer sore outbreaks and protecting horses. The most effective summer sore prevention methods include:

  • Fly control with automatic fly repellent spray systems, fly masks, sheets, boots, and a sheath protector.
  • Proper and timely manure removal from the stalls, stable, paddocks, and property. Removal of trash, wet straw, and other materials that could be breeding sites for flies and maggots is very important.
  • Appropriate wound care using topicals such as a silver nitrate stick (when not bleeding) and bandages to protect wounds from flies.
  • Implementing an effective de-worming program with your veterinarian. The de-wormer will disrupt the parasite’s life cycle internally, killing both adult worms in the stomach and the larvae formed in the skin tissue.
summer sore on a horse's ankle
Summer sores can be difficult to treat and must be diagnosed by a veterinarian.

Many owners also chose to actively prevent summer sores by supplementing their horse’s diet with immune boosting natural supplements. “Sometimes with patients that have stagnant, non-healing summer sores, they can really benefit from being prescribed herbal medicines. I’ve seen many horses do well on the Chinese Herb Wei Qi Booster in particular,” Dr. Mitchell mentioned.

If you suspect your horse may have a summer sore, contact your veterinarian at Palm Beach Equine Clinic by calling 561-793-1599 to discuss treatment and an effective de-wormer program for your horse.

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