Transcript:

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Hi everyone, welcome back to Mad Barn Academy — and if you’re new here, welcome. We hope to earn your subscription today. I’m Dr. Fran Rowe, one of the veterinary nutritionists here at Mad Barn.

With summer fully upon us, our nutrition team has seen a real uptick in diets mentioning seasonal allergies. So I thought it would be a great time to cover the most common type of allergy in horses: insect bite hypersensitivity, or IBH. Let’s get started.

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Many of you might know this condition as “sweet itch” or “summer itch.” Insect bite hypersensitivity is an allergic reaction to the saliva of midges — tiny biting insects in the Culicoides family. In affected horses, these bites cause very intense itching. Horses will obsessively rub, scratch, and even bite at themselves to get relief.

It’s not uncommon for IBH to get worse year after year, as horses become more sensitive with repeated exposure. It’s estimated that around 10% of horses worldwide are affected.

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So, what exactly is a hypersensitivity reaction? Let’s back up a bit and review the role of the immune system.

The immune system’s job is to identify something foreign — called an antigen — that could harm the body, and destroy it. Dangerous pathogens like bacteria, viruses, and parasites are all types of foreign invaders that the immune system protects us from every day.

Sometimes, however, the immune system overreacts and targets harmless antigens such as pollen, food proteins, or medications, leading to an allergy. Other times, it can mistakenly attack the body’s own cells, triggering an autoimmune reaction.

Hypersensitivity reactions are immune responses that are inappropriate or exaggerated. The immune system goes overboard or gets it wrong, ultimately causing harm to the body through inflammation, cell damage, and other effects.

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There are four types of hypersensitivity reactions:

• Type I (Immediate): An antigen triggers a rapid release of histamine and other inflammatory mediators from immune cells. This causes localized swelling, redness, and itching — think of a mosquito bite. In severe cases, it can cause a whole-body inflammatory response, respiratory distress, or even anaphylaxis. Examples in people and horses include insect bite hypersensitivity, asthma, and anaphylaxis.
• Type II (Cytotoxic): The immune system attacks and destroys the body’s own cells. Examples in humans include Graves’ disease and myasthenia gravis; in horses, neonatal isoerythrolysis and immune-mediated hemolytic anemia (IMHA).
• Type III (Immune Complex–Mediated): Antigen–antibody complexes form and deposit in tissues, causing inflammation and damage. In humans, rheumatoid arthritis and lupus are examples. In horses, examples include purpura hemorrhagica (a complication of Streptococcus equi infection, or strangles) and recurrent uveitis.
• Type IV (Delayed): Reactions occur two to three days after exposure. Contact dermatitis is a common example, seen in humans allergic to poison ivy or latex, and in animals with similar skin sensitivities.

IBH is a Type I hypersensitivity reaction to midge saliva — a harmless antigen that still triggers an extreme immune response.

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Midges are blood-feeding insects that come out during warmer weather. Only females bite. They are most active in low-light conditions such as dawn and dusk.

While any part of the body can be bitten, midges tend to focus on the belly (ventrum), tailhead, neck, and mane — areas horses can’t easily reach to remove insects.

Midges are found worldwide in a variety of climates, from deserts to high elevations and cold regions. They prefer damp breeding environments such as wetlands, marshy areas, standing water, rotting vegetation, compost, or manure piles.

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About 10% of horses worldwide are affected by IBH. Why some develop it while others don’t is linked to several factors:

• Environment: Horses living in high-midge areas are more likely to develop sensitivity.
• Exposure: Foals exposed to midge saliva early in life may be less likely to develop IBH. Relocating naïve horses into midge-heavy areas may increase risk.
• Genetics: There is evidence of heritability. Horses with affected dams or grand-dams may be more likely to develop IBH.
• Concurrent Disease: Horses with asthma appear more likely to also have IBH, and vice versa.

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IBH is usually easy to spot, especially in severely affected horses. They scratch and bite at affected areas, sometimes breaking the skin and causing wounds. They may appear agitated or restless and find creative ways to reach itchy spots like the belly, between the hind legs, or the top of the neck.

Lesions are most common along the belly, udder or sheath, groin, tailhead, and neck/mane. Depending on severity, signs include hair loss, raw or bleeding skin, thickened or crusted skin, scabs, hives, and sometimes secondary bacterial infections. Infected areas may show swelling, heat, redness, and pus.

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Diagnosis is often presumptive, based on history, seasonality, lesion distribution, and whether the horse lives in an environment with midges.

Definitive diagnosis can be made through:

• Intradermal allergy testing: Injecting small amounts of allergens under the skin and observing reactions.
• Serum testing: Measuring allergen-specific antibodies in the blood.

Combining both methods can improve accuracy, especially in mild or atypical cases.

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IBH is not curable. Management focuses on: limiting exposure, controlling itching, and supporting immune health.

Limiting exposure

• Stable horses during dawn and dusk.
• Use high-powered fans to deter insects.
• Remove standing water, compost, manure, and other breeding sites.
• Use physical barriers such as fly sheets, masks, leg covers, and belly guards.
• Apply insect repellents as appropriate.

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Controlling itch

• Work with your veterinarian.
• Medications may include steroids, antihistamines, other anti-inflammatories, antibiotics for secondary infections, medicated shampoos, and topical treatments.
• Allergen-specific immunotherapy (“allergy shots”) can desensitize the immune system over time. This requires regular injections and may take years to show full benefits.

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Nutritional support

• Omega-3 fatty acids (DHA, EPA): Support healthy inflammatory regulation and skin condition.
• Spirulina: Supports healthy immune and allergy responses.

Some horses respond to one or both. Nutrition can add support but usually won’t replace other treatments.

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Thanks for listening! Don’t forget to like and subscribe, and check the video description for links to our article on IBH and other resources on skin conditions and allergies. Until next time.