SUMMER SORE is a common term for a skin wound (dermatitis) caused by the Habronema worm larvae. The adult Habronema live and lay eggs in the stomach of infected horses. Once the eggs hatch, the larvae are then passed into the manure of the horse, where they are ingested by fly maggots. Once the maggots mature into adult flies, they transfer the infected larvae back into the horse by landing around the horse’s mouth, eyes or open skin wounds.
Cutaneous habronemiasis (infected skin wounds) can occur in all horses and donkeys. When larvae are deposited in aberrant locations (eyes, skin wounds, etc.), they cannot mature, which leads to localized inflammation. The area becomes red, itchy, may have a “greasy” appearance, and proud flesh may form. The wounds can appear similar to sarcoids and squamous cell carcinoma, so it is important to have your veterinarian evaluate the wound to determine the appropriate treatment.
Diagnosis of habronemiasis is usually made based on the patient’s response to treatment as the larvae are not easily identified. Summer sores are treated with a combination of medical therapies and treatments that may include antibiotics, anti-inflammatories, dewormers such as Ivermectin, bandaging, and corticosteroids. Antibiotics are indicated if there are secondary infections due to selftrauma; corticosteroids are effective for controlling the immune reaction and severe itchiness, and bandaging is often needed in severe cases to control the area and keep medication in contact with the wound.
Summer sores are most often seen during the spring and summer months, coinciding with increased fly activity. Prevention of summer sores involves fly control, manure management, and appropriate treatment of wounds and infections before they become infested with larvae. As summer sores can be misdiagnosed as sarcoids or other diseases that require very different treatments, it’s important to contact your veterinarian for advice before beginning any treatment regime.
column by DR. KATIE HENNESSY
BIO: Dr. Katie Hennessy graduated from the University of Illinois College of Veterinary Medicine in 2008 with a degree in large animal health and equine medicine. She completed an advanced internship at The Equine Medical Center of Ocala and is currently the owner and practicing veterinarian at Polk Equine. Her expertise ranges from small and exotic creatures to large animals, specializing in equine medicine.