Summer eczema (insect allergy) in horses

What is summer eczema?

Summer eczema — medically insect bite hypersensitivity (IBH) — is the most common chronic allergic skin condition in horses worldwide. The prevalence is 5–18%; in Friesians this rises to approximately 18% [1][3]. It is not an infection but an IgE-mediated hypersensitivity reaction to salivary proteins of Culicoides midges (knuts). The predisposition is strongly genetically determined and the condition is incurable — only manageable.

Characteristic symptoms are intense itching, hair loss, crusty or wet patches (often on manes, tail root, belly line and ears) and skin damage caused by scratching. The restlessness associated with this has a measurable impact on the horse's behaviour and movement activity [3].

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Approach: what works?

Insect avoidance (core approach, essential)

Maximum avoidance of Culicoides midges is the basis of every treatment plan:

• Stabling at dusk and dawn, the peak hours of Culicoides activity
• Fine-mesh eczema rug that covers the body as completely as possible
• Insect repellents to supplement physical measures

Without adequate insect avoidance, all other measures have less effect.

Allergen-specific immunotherapy (AIT)

AIT with recombinant Culicoides allergens in adjuvant is currently the best-supported treatment option. In a double-blind placebo-controlled trial, 67% of treated horses achieved an improvement of >50% in lesion score in year 1, rising to 89% in year 2 (versus 14% placebo) [1]. An earlier double-blind study confirms the principle [2]. AIT requires consistent, long-term use and does not work equally quickly in every horse.

Corticosteroids

Dexamethasone and prednisolone provide short-term symptom relief and can be used as a course during acute periods. However, repeated or long-term systemic use carries real risks of adverse effects, including an increased risk of laminitis. This medication belongs under the supervision of a veterinary surgeon, not as an independent long-term approach.

Additional options: limited evidence

For both: they are not harmful when used correctly, but do not expect them to replace insect avoidance or AIT.

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Breeding

Because the genetic component is strong, it is recommended not to breed affected animals. This significantly reduces the chance of transmitting the predisposition to offspring [1][3].

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When to see a veterinary surgeon?

• For initial diagnosis: confirmation and drawing up an individual management plan
• When considering AIT: referral to a specialist for allergen testing
• If infection is suspected, in case of severe lesions or insufficient response to existing policy
• Corticosteroids always via the veterinary surgeon, never long-term without supervision

Additional measures are an addition to, never a replacement for, veterinary supervision and proven insect avoidance.