Diagnosis, and Treatment of insect-bite hypersensitivity in horses:

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INSECT BITE HYPERSENSITIVITY (IBH) is an allergic reaction to the saliva of biting insects such as Culicoides, mosquitoes, black flies, and horn flies.

The bites elicit an allergic response from sensitive horses, resulting in hives (urticaria) and/or crusty patches of bumps.

Some other names for the condition:

Culicoides sensitivity ❙ Sweet itch ❙ Queensland itch ❙ Kasen ❙ Summer

The bites and sores are usually on a horse’s:

Ears ❙ Back ❙ Mane ❙ Tail ❙ Anus ❙ Belly


 The most significant insects casuse insect-bites hypersensitivity:

InsectBreeding AreaFeeding Times
Stable flies
Manure and rotting vegetation
Horn flies
Cattle manure
Horse and deer flies
Vegetation and water
Culicoides spp
Standing water and
Twilight to dawn

Simulium (black) flies
Running water
Morning and evening
Table off insects

Diagnosis of insect-bite hypersensitivity in horse:

A diagnosis of insect hypersensitivity is based on lesion distribution or owner observation of an insect biting the horse, resulting in a lesion at the site of the bite. For instance, horn fly skin lesions are localized to the umbilical area. In classic Culicoides spp hypersensitivity reactions, skin lesions develop around the mane and tail or on the entire ventrum. Deerfly and horsefly hypersensitivity reactions result in ulcerated dermal nodular lesions on the chest, flanks, and/or proximal legs. Blackfly hypersensitivity may result in development of skin lesions limited to the ears and face

Some diagnostic tests can also be useful.

Skin cytologies and/or cultures are useful in determining whether a bacterial and/or fungal infection is present.

In addition, skin scrapings are helpful in ruling out ectoparasite problems such as ChorioptesSarcoptesPsoroptes, and Demodex spp infections.

Control and Treatment of insect-bite hypersensitivity in horse:

  • Topical ointments containing antihistamines and/or corticosteroids might also offer your horse relief.
  • However, there’s no IBH cure, and multimodal management is usually the best option .
  • Feed omega-3s Research shows that omega-3 fatty acids, which are abundant in flaxseeds, might help reduce the inflammatory response associated with IBH.
  • Limit insect habitat
  •  Many biting insects reproduce in water or wet areas. Eliminate these habitats by dumping standing water from buckets.
  • Use a fly sheet and other barriers
  • Fine-mesh fly sheets and masks that cover your horse’s body, chest, and belly can protect him from biting insects.
  • Some fly sheets even come pre-impregnated with insecticides.
  • Certain insecticides can offer some protection to your horse from biting insects.
  • Bring your horse inside
  •  Biting insects are busiest during dusk hours, so bring your horse inside—away from the bugs—when they’re active.
  • Talk to your veterinarian about allergy testing and treatments
  • Veterinarians use serum or skin testing and immunotherapy on horses with varying degrees of success. Talk to your veterinarian to find out what solutions are best for your horse


Several types of insects can cause allergies in horses. These insects have different feeding preferences and environmental requirements for reproduction. To manage horses allergic to insects, it is important to know which type of insect is causing the problem. This information can be determined by lesion distribution, the owner observing the horse being bitten by the insect and developing the lesion or allergy testing. Using an insecticidal agent with or without flysheets and fly masks is an essential part of treatment.

Eliminating or limiting exposure of the horse to the ideal insect-breeding environment (e.g., removing feces, placing a fan in the stall for Culicoides spp) is also important.

Hyposensitization therapy has been used, and the success rate varies. If various insect allergy extract preparations are developed and become commercially available, they may be more consistently effective in hyposensitization therapy.

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