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The Itchy Horse: Insect Bite Hypersensitivity

By Zoe Davidson, DVM, MRCVS

Insect Bite Hypersensitivity (IBH)

While we are all still reveling in the glorious months of summer, this time of year can bring a number of health issues to our equine friends.

One of the most common conditions is Insect Bite Hypersensitivity. Insect Bite Hypersensitivity (IBH, Queensland itch, sweet itch, equine summer eczema) is the most common pruritic ( itchy) disease of horses. Definitely a common topic of discussion within the equine world, but yet not fully understood and frequently mismanaged. The goal of this article is to provide a quick simple run down of the cause, classic symptoms, and what we can do as vets and owners to keep our horses happy and healthy!


Allergic sensitivity to the saliva of Culicoides spp., biting midges; and a variety of insect species. There is a genetic component that does predispose some breeds to a more severe reaction than others. Your horse can develop hypersensitivity and associated symptoms even if you do not see your horse being actively bitten. There is much more than meets the eye going on below the skin surface. Simply put, the severity of the clinical signs is not always correlated with the number and frequency of insect bites, but rather the severity of their individual immune mediated reaction. Certain horses develop a much stronger reaction to the saliva than others, and once their system is primed, worse the clinical signs are.

Horse with hives

Classic Itchy Horse Symptoms

IBH can look different in each horse. Most commonly the symptoms include urticaria “hives”, generalized pruritis (“itchiness”) leading to lesions associated with self trauma (e.g skin thickening, lesions, scaling, crusting, hives, and hair loss, which can result in extreme discomfort.) In severe cases the secondary lesions induced by self -mutilation cause open sores and become infected. Lesions in horses are usually found on the trunk, face, mane, tail, and ears, with locations varying depending on the biting characteristics of the particular insect(s). The external signs can be accompanied by a dull, depressed, lethargic temperament.

Insect Bite Hypersensitivity (IBH) symptoms
Horse Fly Spray

Luckily, it is one of the most well understood of the allergic skin diseases of the horse which means we have developed very effective management practices to help keep our horses happy and healthy this season!


Horse Fly Sheet

1. Catch Early - prevention is always the best cure! Monitor your horse twice daily for the signs mentioned above!

2. Fly Control - prevent the flies from biting!

  • Effective fly spray applied 2X/day

  • Routine sheath cleanings

  • Comprehensive fly mask and fly sheet

  • Clean out stalls 2X/day; place manure piles far from barn

  • Place a fan on your horse's stall door!

Horse Stall Fan

Fun Fact: Flies are actually pretty weak fliers!

3. Supplements: Platinum Performance Skin and Allergy as well as Kinetic Vet Equishield (Skin and Allergy) have been proven to be effective! Omega-3 fatty acids can aid in reducing skin inflammation.

When to call a Vet?

Hives accompanied by agitation, elevated respiratory rate, effort and/ or depressed lethargic demeanor, Lesions on the head, neck, mane, tail and or belly (ventral midline) that are being rubbed raw, swollen, runny eyes cough. Sometimes your horse may be reacting to a variety of different stimuli, and in this case a thorough examination and further testing is indicated in order to diagnose and effectively treat.

Medical Treatments

At this time, there are only a few effective treatments once your horse has developed more extensive IBHS. Our options include antihistamines and corticosteroids, both of which are variably effective and do not come without their own potential side effects. In more severe cases, your vet may discuss drawing your horse's blood for an allergy panel. Subsequently, the exact cause of the allergy can be identified, and a specific immunomodulator developed to help reduce their symptoms. A pricey, length and often not always effective option!

With this in view, prevention and management are by far the best methods of keeping your horse

comfortable, happy and healthy! If you are concerned about your horse, and eager to discuss any of the

above information further, please do not hesitate to reach out. We would love to hear from you!


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Insect Bite Hypersensitivity (IBH)_) Managing the Itchy Horse
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