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Equine skin allergies
There are two main causes of skin allergies in horses: environmental allergens and insect bite hypersensitivity. Environmental allergens can cause hives, atopic dermatitis, and may be pruritic or not. Insect bite hypersensitivity is caused by bites from insects like Culicoides midges and causes sweet itch marked by hair loss on the mane, tail, and belly along with intense itching. Diagnosis involves ruling out other causes and doing skin or serum allergy testing to identify specific allergens. Treatment focuses on avoidance of allergens, topical therapies, antihistamines, corticosteroids, and immunotherapy.
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Equine skin allergies
- 1. EQUINE SKIN ALLERGIES CatherineJacobs DVM Loomis Basin Equine Medical Center
- 2. AN ITCHY HORSECAN BE AN UNHAPPY HORSE Two Main Causes of Skin Allergies in Horses 1. Environmental Allergens 2. Insect Bite Hypersensitvity
- 3. EQUINE SKIN ALLERGIES EnvironmentalAllergens Atopic Dermatitis Hives (Urticaria) May or may not be pruritic (itchy) May note some lethargy Insect Bite Hypersensitivity Sweet Itch Loss of mane, tail hair, hair on belly Always itchy
- 4. HIVES - APPEARANCE Flat topped wheal Doughnut shape Neck and Trunk most common May or may not ooze serum May or may not itch
- 5. HIVES - APPEARANCE FLATTOPPED COALESCING WHEALS
- 6. HIVES - APPEARANCE DOUGNUTSHAPED HIVES
- 7. HIVES - APPEARANCE HIVESWITH CRUSTING
- 8. HIVES - CAUSES Usually due to inhaled allergens in the environment Can also be due to, but less commonly: 1. Food allergy 2. Contact allergy (shavings, fly spray, laundry detergent) 3. Drug reactions 4. Infections 5. Non immunologic causes (stress, pressure, exercise)
- 9. HIVES - DIAGNOSIS Evaluateif any new bedding, topicals, medications, or feed introduced recently Skin Allergy Testing – must withdraw meds 14-28 days prior – more sensitive for allergen specific IgE levels Serum Allergy testing – no medication withdrawl needed – not as sensitive
- 10. SERUM ALLERGY TESTING– PULL BLOOD SAMPLE Idexx laboratory Regional 2 panel CA 1. Food – Barley, Beetpulp, Yeast, Corn, Oats, Flaxseed, etc. 2. Farm and Stable – Alfalfa, Orchard Grass, Grain Mill Dust, Cat Dander, red clover, Candida Albicans, etc. 3. Insects – Flea, cockroach, biting midge, culicoides, caddis fly, storage mite, house fly, stable fly, mosquito, horsefly, mayfly, etc, 4. Molds, grasses, weeds and Trees common in our area
- 11. HIVES - TREATMENT Topicalcontrol – Genesis spray (only if contact allergy) Anithistamines – Diphenydramine, Hydroxizine, Doxepin Corticosteroids – Prednisolone, Dexamethasone Omega 6/Omega 3 Fatty acids Allergen Specific Immunotherapy Move from environment Dietary trials 4-6 weeks novel food source Control insects
- 12. ALLERGEN SPECIFIC IMMUNOTHERAPY Considerif treating hives more than 4 months out of the year Lack of satisfactory response to management changes Concerns about adverse drug affects with corticosteroids (laminitis) Concerns about competing – Cannot show on Hydroxizine
- 13. ALLERGEN SPECIFIC IMMUNOTHERAPY AllergyTesting (serum or skin) used to determine specific environmental reactants These reactants are incorporated into allergen specific immunotherapy Small volume injections initially a few days apart Effects as soon as 2 months after starting injections but can take 12 months 60-70% of these horses affected by inhaled environemtnal allergens improve with Allergen Specific Immunotherapy
- 14. INSECT HYPERSENSITIVITY Insect BiteHypersensitivity is the most common cause of pruritus (itchiness) in horses
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- 16. INSECT HYPERSENSITIVITY -CAUSES Culicoides – biting midge – most common Leads to self trauma of mane, tail, underbelly Black flies Stable Flies Mosquitos Horn flies Deer flies
- 17. INSECT HYPERSENSITIVITY -CAUSES Causes of Pruritus from insect bites 1. The bite itself 2. Immediate reaction to salivary antigens of the insect 3. Delayed reaction to insect proteins
- 18. INSECT HYPERSENSITIVITY -SIGNS Seasonal – spring and summer Highly Pruritic Dorsal or ventral distribution depending on insect (Culicoides – mane, tail, ventrum) Horn Flies (ventrum) Secondary hair loss, crusting, thickening of skin over time
- 19. INSECT HYPERSENSITVITY -DIAGNOSIS Seasonality Distribution patterns Ruling out ectoparasite, bacterial, fungal causes Intradermal Skin allergy testing of insect allergen proteins – use to confirm diagnosis and to select extracts to use for therapy
- 20. INSECT HYPERSENSITIVITY -TREATMENT AVOIDANCE – reduce insect contact as much as possible Keep in at dawn and dusk Fly control in the barn with automated spray 2%Permethrin Flyspray Fipronil (Frontline)spray on trouble areas Fans Fly sheets/masks Feed through fly control
- 21. INSECT HYPERSENSITIVITY -TREATMENT Manure control and standing water control Feed through fly control
- 22. INSECT HYPERSENSITIVITY -TREATMENT Corticosteroids – topical - Genesis spray systemic – Prednisolone, Dexamethasone Antihistamines – often have little effect Allergen Specific Immunotherapy – mixed levels of success In horses with insect hypersensitivity
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