Summer Equine Dermatitis
By Agricultural Communications, Texas A&M University System • May 08, 2011 • Article #27318
As a modern term, "sweet" denotes pleasure and enjoyment. But for a horse, sweet itch is anything but sweet.
"Sweet itch, also known as summer eczema or equine dermatitis, is one of several seasonal allergies that your horse may encounter," notes Glennon Mays, DVM, clinical associate professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences.
"Equine dermatitis can have varying causes," explains Mays. "Allergens may irritate your horse's skin, but viruses and bacteria might also manifest themselves as dermatitis. These foreign agents can cause inflammatory conditions in the skin and may affect your horse's hair coat. Equine sweet itch is a seasonal allergic skin condition that can be caused by fly bites or midge bites. Horses that suffer from sweet itch have developed an allergy to these bites."
Insects flourish in the summer, and horses can have sensitivities to insect bites, notes Mays. In particular, black flies (also known as buffalo gnats) are known to seek out horses as hosts. These flies feed on mammals' blood and are attracted to hosts by smell, heat, and sight. They prefer to feed on the host's head, hair, and ears but will also bite any exposed skin.
"The female black flies are blood feeders," explains Mays. "The fly bites by cutting into the skin and feeding on the pooled blood. Anticoagulants injected (by the fly) into the feeding site cause an allergic reaction, and antigens in their saliva can cause allergic reactions as well."
Mays notes, "Additionally, the black fly bite can become painful and itchy as blisters form. Therefore, protecting the face and ears from flies eliminates a major source of irritation for your horse."
Equine dermatitis will usually result in horses scratching or biting the affected area, crusts, hair coat damage or loss, flaky dandruff, and thickened skin, explains Mays. The itchy skin can be further irritated when the horse rubs the area (on fences or stalls, for example) to the point of hair loss and scabbed skin. This is when secondary bacteria can enter the skin and cause infection.
"Repeated exposure to the allergen, in this case fly bite, is required for the allergy to develop," Mays adds.
To help reduce the incidence of sweet itch, begin preventive measures before fly season is in full force, suggests Mays. .
Black flies feed during the day, so Mays suggests stabling animals during the day when fly populations are likely be more abundant. Also, use a fan in your horse's stall. The constant airflow deters flies from lighting and biting, as most biting flies are not good flyers.
If possible, place fine-mesh screens over barn openings to prevent flies from entering stalls. Install automated insecticide mist systems to help control fly populations.
Finally, fly repellents focused on the chest, belly, and ears can be effective if applied to the horse daily, added Mays. Consult your local veterinarian for the best insecticide to use in your stable and on your horse. Equine fly apparel (i.e., fly masks and fly sheets) can be used for additional protection.
If your horse has an annual encounter with summer sweet itch, help him to manage the itch by taking preventive measures to lessen the severity of an annoying allergy.