What is Sweet Itch in Horses?

The midges that cause sweet itch tend to avoid the legs, so you might not see fly boots on a horse with sweet itch.

Sweet Itch is an Insect Bite Hypersensitivity (IBH)

Insect bite hypersensitivity (IBH) creates severe itching in horses, to the point of scratching the skin aggressively, creating sores and secondary infections.

The saliva of some biting bugs, usually a type of gnat called Culicoides midges, triggers an allergic reaction. Sometimes, black flies from the genus Simulium are to blame. The intense itching results from an overreaction of the horse’s immune system, often creating hives as well.

Equine sweet itch is also known by these names:

• Summer equine dermatitis
• Recurrent seasonal pruritis
• Equine summer eczema
• Insect bite hypersensitivity (IBH)
• Queensland itch
• It’s known as Queensland itch because 60% of horses in this part of Australia suffer from sweet itch. Other parts of the world hover at about 5-20%.

This horse’s mane is almost gone due to rubbing. She’s about a few days away from having open sores.

The Cause of IBH in Horses – The Severity Varies

• Sweet itch is a skin condition stemming from the allergic reaction to the bite of the midge, genus Culicoides. The salivary proteins present in the bites of culicoides midges trigger this allergic response.

• These bugs are also called gnats, no-see-ums, sand flies, or midges.

• This tiny bug (about 4 mm long for a big one) lives on blood for part of its life cycle and will feed on your horse. Typically, the midges bite around your horse’s mane, tail, and dorsal midline (topline).

• The subsequent allergic reaction to the bite, an immune response in your horse, triggers a series of events that can be hard to stop.

• The intense itching leads to scratching, often creating broken hairs, hair loss, open sores, scaly skin, and oozing skin lesions.

• As the areas keep getting bitten, there’s more itching and thus more skin damage from the allergic reaction and the self-trauma.

• Secondary infections and prolonged healing times go hand-in-hand with sweet itch in horses.

Diagnosis of equine insect bite hypersensitivity

• It’s helpful for your vet to confirm a diagnosis of insect bite hypersensitivity. Many other allergens, bacteria, fungi, and parasites can create a similar reaction in horses. These conditions all have different treatments, and it’s a waste of time and money to treat for the wrong condition.

• Your vet will consider clinical signs, like lesions and their location, time of year, genetic factors, and sometimes allergy testing to diagnose a culicoides hypersensitivity.

Sores and bald patches on this horse’s face from sweet itch.

Treatment Options for Lesions

• Finding the best treatments for sweet itch involves boosting overall skin health, managing environmental factors, and working to fight the specific species of midge in your area. For such a severe allergic reaction, topical and oral medications may help, too.

Feeding for skin health

• You can add flax to your horse’s diet. A recent study suggested that the extra omega-3 fatty acids in flax help their immune response and healing. Omega-3 fatty acids are anti-inflammatory agents that work throughout your horse’s body. In addition to helping your horse shine, Omega-3s are delicious, affordable, and safe.

Medications

• Antihistamines and steroids are two medications often used to treat a hypersensitivity reaction like sweet itch, as well as general allergies, like hives.

• Oral steroids are contraindicated for some horses with metabolic disorders or with a history of laminitis. Potential side effects of steroids include triggering a laminitic response.

Topical medications

• Medicated shampoo and topical cream can help your horse tremendously. Be warned that some prescriptions, even for topical medications, will test positive at shows.

• Some essential oil sprays show promising relief for horses and, in some cases, also work as a fly spray. Remember that insect species hunt their prey differently and are attracted to different sights, movements, and smells. Essential oils may repel some bugs but attract others.

More mane hair loss, showing bare skin. This horse’s skin could break open after a few more days of rubbing. Then the scab, rub, open sore cycle starts.

Immunotherapy for allergens

• In the world of new and exciting research, there’s work underway to understand equine interleukin-5 (IL-5). IL-5 is a protein involved in the immune response.

• IL-5 recognizes the saliva of the midges as something to react to and sends eosinophils, a type of white blood cell, to facilitate the allergic reaction. Current research is working on a vaccine that quiets this response, thus providing relief to horses and horse owners everywhere.

Read more about new technologies here.

Help Prevent Sweet Itch in Horses (and Other Allergies, too)

• The first is prevention. Fly spray needs to become your friend; look for permethrin and benzyl benzoate as ingredients. You may also want to add a fatty acid-based fly spray to cover all bases.

• Notice your horse’s favorite rubbing areas, and work to make them less likely to damage the skin.

• Keep your affected horses tucked away in the barn during peak midge activity hours, early morning and dusk.

• Use superfine screens around their stalls and stable doors to keep the buggers out. Don’t forget to cover the top of the stall. You can also use a fan in the stall at dusk and dawn to ward off the flies.

• Midges like to hang out near water, so have a barn-wide hunt for water sources that can be drained. Fix leaky sprinklers that puddle, dump standing water, and work on drainage. Move affected horses away from standing or stagnant water sources.

• Also, make friends with a specialty fly sheet. Several companies make a fly sheet specific for midges, covering your whole horse except the head and legs. Your horse’s tailhead, belly, neck, and face are all covered with awesomely designed panels with velcro and elastic. Your horse will appear in a bio-hazard suit, but that’s precisely what they need.

Is sweet itch contagious?

Insect bite hypersensitivity in horses is not contagious. The unique reaction of a horse’s immune system creates the problem. However, some genetic components make sweet itch in horses hereditary. This is why certain breeds, like Icelandic horses, are more susceptible.

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