The most common allergic skin disease in horses is Insect Bite Hypersensitivity (IBH). It is
the leading cause of pruritus in the horse. Most commonly, IBH is caused by the bite of the
Culicoides species. Less commonly it can be attributed to the bite of other insects. These
include Blackflies, Stable flies, Horn flies, Mosquitoes, Deerflies, and Horseflies. The type
of insect varies on their feeding location and the time of feeding. For example, Culicoides
usually feed dorsally at mane and tail and on the abdomen. In contrast, Blackflies feed on
the ears, face, and ventral abdomen in morning and evening. The exact cause of the allergy
is a hypersensitivity to the salivary antigens of the insects. The disorder represents a type I
and type IV hypersensitivity.
Clinically, IBH is the number one cause of the allergic and pruritic horse. Its distribution is
worldwide and can be seen in any breed, all ages and any sex. Genetic predisposition to
the disease can be seen most commonly in the following breeds: Icelandic, German Shire,
Shetland Ponies, Quarter Horses, and Thoroughbreds. Clinical signs are typically seasonal;
most commonly seen in the spring, summer and fall. Normally, the condition worsens with
age and clinical signs are more evident morning and evening when the insects normally
feed. Dorsal distribution of lesions is the most common manifestation in the horse. It starts
with itching usually beginning at the mane, croup, and base of tail. It is typically referred to
as a “buzzed mane” and/or “rat tail.” It can extend to other areas of the body. Itching and
chronicity leads to erosions, ulcers, variable hair loss, and pigmentary changes.
Diagnosis of IBH is usually based on history. The combination of seasonality with the
distribution pattern of the skin lesions and the presence of the insect breeding ground
in the horse’s environment is typically enough to make a diagnosis of IBH. In some cases,
intradermal skin testing (IDST) can be used to detect which insect or group of insects that
the horse is most allergic.
The treatment of Insect Bite Hypersensitivity involves control of the insect causing the
disease and addressing the skin lesions associated with it. Controlling the insects involves
applying long-lasting insect repellents. Likewise, the owner can stable the horse during
times of high insect activity. Depending on the severity of the skin lesions, treatment may
involve systemic as well as topical treatments. Specifically, antibiotics and corticosteroids
can be given to treat skin infections and to decrease the immune reaction.
Kinetic Vet has launched a product that encompasses each area for the topical treatment of
Insect Bite Hypersensitivity. EquiShield
®
IBH Salve is the only product available specifically
formulated to address IBH in horses. It is an antiseptic (chlorhexidine), anti-inflammatory
(hydrocortisone), anti-itch (pramoxine) and insect repellent (citronella) in one formulation.
It also contains colloidal oatmeal and lanolin to soothe skin.
Insect hypersensitivity can be a very difficult disease to manage. Every effort should be
made to identify the insect causing the hypersensitivity and to reduce the exposure.
Successful treatment of the skin may involve both systemic and topical therapies.
Insect Bite Hypersensitivity (IBH)
by Stuart L. Pierce, DVM
AUTHOR
Stuart L. Pierce, DVM
received his Doctor of
Veterinary Medicine degree in 1992 from the
University of Missouri College of Veterinary
Medicine and currently owns a multi-doctor
practice with its offices in Lexington. He is a
member of the American Veterinary Medical
Association, American Association of Bovine
Practitioners and the Kentucky Veterinary
Medical Association.
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