Summer Sores
Each of these wounds is a "summer sore" located in different areas of the body (eye, leg, sheath/penis, and commissures of the mouth).
Habronemiasis, or "summer sores" as it is more commonly referred to, is a condition that affects many horses in our area and throughout the United States. It is usually manifested as a dermatologic condition, and is the result of infestation of the affected region with the larvae of certain types of parasites called nematodes. The common house fly and stable fly are intermediate hosts for these parasites, meaning that they ingest and harbor the immature larval stages, and then deposit them on horses’ skin while biting. Often times,
the larvae are deposited around the muzzle, which then results in ingestion by the horse. Adult stages of the nematode then live in the stomach, producing larvae, which are subsequently passed in manure. When ingested by maggots (immature flies), the cycle is repeated.
Cutaneous habronemiasis presents as ulcerative skin nodules typically in the spring and summer, with regression in winter months, when the flies die. There is no breed or sex predilection, meaning that any
horse can be affected, and some seem to be more prone to the condition, developing lesions year after year. Common areas to be affected include the legs, penis and sheath, eyes, and any open skin wounds. The condition is the result of the horse’s own immune system mounting a hypersensitivity reaction (a type of allergic reaction) to the larvae. The lesions are often itchy, and resemble granulation tissue with tiny yellow granules often times visible. Patients whose eyes are affected often times have excessive tearing and squinting. Geldings and stallions that have infestation of the penis or sheath may exhibit difficulty urinating.
Diagnosis is generally based on the clinical appearance of the lesions. Biopsy is required to make a definitive diagnosis. Treatment is aimed at decreasing the horse’s immune response to the parasite by use of topical and/or systemic steroids. Deworming with an Ivermectin based product is also important in controlling the disease. One factor that is of paramount importance in the treatment and prevention of cutaneous habronemiasis is that of FLY CONTROL, as flies deposit the inflammatory larvae into the wounds. This is best accomplished using a combination of fly repellents and fly masks/sheets, particularly those that cover the underside of the horse. The use of fans on stall doors will also help to decrease the number of flies in the environment, as will fly strips. If your horse does have an open wound that cannot be covered, topicals such as SWAT can be applied around the lesion to prevent flies from landing and depositing Habronema larvae. It is also crucial to maintain a clean environment, disposing of soiled bedding/shavings that may attract insects. Maintaining a clean environment includes manure pile management to decrease the breeding grounds of the flies. Effective composting of manure and/or removal of manure can significantly decrease the fly population. Fly predators can also help substantially. If you suspect that your horse may have summer sores, contact your veterinarian to determine the appropriate treatment protocol for your animal.
If you see lesions like the ones above on your horse, please call your Veterinarian for evaluation and treatment.
