Summer seasonal recurrent dermatitis, also known as summer eczema and sweet itch is a skin disease caused by allergic reaction to insect bites. Summer Seasonal Recurrent Dermatitis (SSRD), commonly referred to as sweet itch, or summer eczema is considered to be caused by an allergic reaction to the saliva of Culicoides flies (also called midges and "no-see-ums"), grass protein, and filariad worm larvae. Sweet itch occurs only in the late spring and summer when insects are present; during the winter months the skin heals and the hair grows back. The majority of horses do not have an allergic reaction to midge bites, but in an unfortunate 5% the immune system over-reacts producing irritable skin conditions. Horses which are not introduced to the antigens of the biting insects early in life, are most predisposed to develop hypersensitivity to midges saliva.
The fly bites form blisters. Areas of hair loss, crusting, and scaling can be found on the head, neck, shoulders, mane and tail. The allergic reaction to the fly bites starts as a very small, itchy nodule, and the horse will rub and bite at itself. Initially the hair is lost and crusts are seen on the ears and the base of the tail. Eventually the whole back of the horse can become reddened, with crusts and scaly materila over the surface for prolonged periods. Untreated cases develop skin sores and ulcers that are impossible to heal.
Diagnosis is made based on the history, signs, location of the lesions and response to treatment. Diagnosis is difficult since other allergies and other skin parasites cause similar types of wounds. The allergy becomes a chronic condition and requires costant treatment with oral or topical steroids to stop the cycle and anti-inflammatory drugs to control swelling and ease discomfort. Other lotions and remedies have been used, but they will only alleviate the problem temporarily. Moving the horse at least 1/2 mile from the breeding areas od the midges is the key to successful treatment.
Prevention of Summer Eczema
The only effective way to prevent the lesions in hypersensitive horses is to protect them from the bites of Culicoides midges each year.
Various management changes can significantly reduce the number of flies and the type of flies
- The house fly and stable fly breed in piles of horse manure. Their breeding and numbers can be reduced greatly by effective removal and desinfection of horse manure.
- Spraying the walls and partitions of the stables with insecticides (every few days to weeks) will kill flies.
- Spraying the horse with an insecticide.
- Keeping horses away from water where flies breed will prevent attack on hot days.
- Use screens and insecticide strips.
- Use neck straps and head-collar strips or tags with insecticide.
- Keep horses indoors when the insects feed: from two hours before dusk to two hours after dawn.
- Keep horses covered with sheets and fly masks.
A new vaccine designed to alleviate the distress of sweet itch is available for horse owners to try. The vaccine, which works at removing the excessive reaction to the bites of Culicoides midges, has had promising effects in preliminary trials. Sweet Itch vaccine trial