This presentation was given at the Loomis Basin Equine Medical Center's 2014 Open House.

1. EQUINE SKIN ALLERGIES
Catherine Jacobs DVM
Loomis Basin Equine Medical Center

2. AN ITCHY HORSE CAN BE AN
UNHAPPY HORSE
Two Main Causes of Skin Allergies in Horses
1. Environmental Allergens
2. Insect Bite Hypersensitvity

3. EQUINE SKIN ALLERGIES
Environmental Allergens
 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
FLAT TOPPED
COALESCING
WHEALS

6. HIVES - APPEARANCE
DOUGNUT SHAPED HIVES

7. HIVES - APPEARANCE
HIVES WITH 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
Evaluate if 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
Topical control – 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
Consider if 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
Allergy Testing (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 Bite Hypersensitivity is the most
common cause of pruritus (itchiness) in
horses

15. INSECT HYPERSENSITVITIY

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

23. QUESTIONS?