EQUINE SKIN ALLERGIESCatherine Jacobs DVM

Loomis Basin Equine Medical Center

AN ITCHY HORSE CAN BE AN UNHAPPY HORSE

Two Main Causes of Skin Allergies in Horses

1. Environmental Allergens

2. Insect Bite Hypersensitvity

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

HIVES - APPEARANCE

Flat topped wheal

Doughnut shape

Neck and Trunk most common

May or may not ooze serum

May or may not itch

HIVES - APPEARANCE

FLAT TOPPED COALESCING WHEALS

HIVES - APPEARANCE

DOUGNUT SHAPED HIVES

HIVES - APPEARANCE

Click icon to add picture

HIVES WITH CRUSTING

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)

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

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

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

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

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

INSECT HYPERSENSITIVITY

Insect Bite Hypersensitivity is the most common cause of pruritus (itchiness) in horses

INSECT HYPERSENSITVITIY

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

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

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

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

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

INSECT HYPERSENSITIVITY - TREATMENT

Manure control and standing water control

Feed through fly control

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

QUESTIONS?