Definition: Technically known as insect bite hypersensitivity, sweet itch is an allergic reaction to the saliva of biting insects, most often the Culicoides species of midges and gnats.
Signs: intense itchiness, wheals, and swelling, primarily on the neck (under the mane), face, shoulders, withers, belly, and rump (over the tail). The skin might be rubbed until it is crusty, weepy, raw, and hairless. Location of the lesions might depend on the specific species of gnat; most prefer to bite on the neck and along the topline, but some target the chest, belly, tail, and groin.
Diagnosis: Skin scrapings and cultures might be needed to distinguish sweet itch from other causes of itchy dermatitis, such as mites, lice, and fungal infections.
Treatment: Antihistamines or corticosteroids might help ease the itch and inflammation, providing relief to the itchy horse; antibiotics or antimicrobial shampoos can help prevent secondary infections. Pentoxifylline can be used to decrease skin reactivity, and in some cases allergy serum is worth trying.
5 Ways to Prevent Sweet Itch in Horses
Sweet itch can make a horse miserable. The intense itchiness can cause him to rub away patches of hair, leaving the skin underneath raw and weepy. If a case is severe enough, the horse might become restless and thin, as he spends more time scratching than eating.
Technically known as insect bite hypersensitivity, sweet itch is a severe allergic reaction to the saliva of biting insects, primarily Culicoides spp. midges and gnats but also possibly blackflies or deer flies. Sweet itch reactions can occur anywhere on a horse’s body but are usually seen on the areas where the insects tend to bite: on the underside of the belly, under the mane, or the dock of the tail.
The condition is usually worse at the times of year when insects are most active. It might subside during the winter. Fewer than 10% of horses in the United States develop sweet itch. Most won’t begin to show signs until they are at least 2 to 4 years old. The condition is more common among Shires, Welsh Ponies, and horses imported from Iceland, but it can occur in any breed.
Research is underway to develop a reliable immunotherapy treatment for sweet itch. In the meantime, veterinarians might prescribe antihistamines and corticosteroids to help relieve the signs of the condition. Steroids carry a low but real risk of serious side effects, including laminitis. So if your horse is susceptible to sweet itch, you’ll want to reduce his exposure to the insects that cause it. Here are steps you can take:
- Stable your horse during peak biting hours. Culicoides spp. are most active at dusk and dawn, so bring your horse into a stall during those hours. For additional protection, install ultrafine screens in stall windows. Set up fans to provide a continuous breeze over stabled horses. Gnats are weak flyers, and even a slight breeze will keep them away. You might also consider applying a spray repellent designed for use on stall walls and other surfaces inside the barn.
- Keep him covered. One way to reduce bites is to keep a fly sheet on your horse during insect season. Made of fine mesh and equipped with closures to keep out bugs, clothing designed specifically for horses with sweet itch has extensions to cover the neck, belly, and tail, the areas where Culicoides spp. are most likely to bite. A fine-mesh mask might also be needed to protect the horse’s face and ears.
- Use fly-control products. The most potent products combine repellents with pesticides. Look for ones labeled for use against gnats and midges. You’ll need to be diligent about applying the sprays and wipes as often as the manufacturers’ instructions allow.
- Restrict your herd’s access to marshy areas. Gnats breed in marshy, shady ground with rotting vegetation. If possible, move your horse to a pasture in a drier, more exposed location away from boggy terrain. Around your barn, clear up standing water in ditches and gutters and keep them free of leaves and other debris. Place manure and compost piles as far away from the horses as possible.
- Try over-the-counter products. You’ll find a number of products for horses with sweet itch. These range from feed supplements formulated to reduce inflammation to topical preparations meant to soothe itchy, inflamed skin. Thick, oily, or sticky ointments are messy but might keep gnats from landing on the horse’s skin. They might also help keep bugs from getting to the skin to bite. Anecdotal evidence suggests these products offer relief, at least in some horses. When trying a new topical product, start by applying it to a small area to make sure it will not further irritate sensitive skin. Be careful with tea tree oil, lavender, and other herbals. They are soothing to some horses but can irritate the skin in others.
Take-Home Message
Sweet itch is an uncomfortable condition that can be very difficult to manage. Fortunately, strategies such as fly control, stable ventilation, and protective coverings can go a long way toward preventing signs of sweet itch from popping up in the first place.
Related Reading:
- How To Choose (and Use) the Right Fly Spray for Horses
- Navigating 4 Common Horse Skin Issues
- Tips for Minimizing Flies on Your Horses and Property
This article originally ran on EQUUS.
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