Equine Pruritis

Question 1

what are the main causes of equine pruritis?

Answer 1

1. ectoparasites:
   -chorioptes
   -psoroptes
   -flies: black fly, stable fly, horn fly, horse fly, deer fly, mosquitos
2. infections:
   -bacteria
   -fungi: dermatophytosis
   -pinworms: oxyuris equi
3. hypersensitivities/allergies
   -cullicoides/sweet itch
   -adverse food reactions
   -atopic (environmental)

Question 2

describe chorioptes in equine pruritis

Answer 2

1. draft horses and other horses with feathered fetlocks are predisposed (es in winter)
2. most common on distal limbs: fetlocks, pasterns
3. severe infestation can involve hind limbs and spread to ventrum
4. diagnostics: skin scrape

Question 3

describe management of corioptes in horses

Answer 3

1. treat all animals!
2. cleaning and insecticides: organophosphates, chlorinated hydrocarbon
3. clip feathers and topical:
   -2% selenium sulfide shampoo
   -0.25% fipronil spray
   -5% lime sulfur solution
   -some clients will have issues with you clipping feathers
4. systemic
   -oral ivermectin paste
   -oral moxidectin paste

Question 4

describe scabies in llamas

Answer 4

1. pruritis frequently observed
2. historical treatment with amitraz, moxidectin/ivermectin every three weeks
3. also recommend a single oral fluraner dose (Bravecto for dogs)
4. topical chlorhexidine +/- systemic antibiotics for secondary infections

Question 5

describe scabies in pigs

Answer 5

1. pruritis frequently observed
   -ZOONOTIC TRANSMISSION
2. historical treatment with amitraz, moxidectin/ivermectin every 3 weeks
3. single oral afoxolaner dose (Nexgard for dogs)
4. topical chlorhexidine +/- systemic antibiotics for secondary infections

Question 6

what attracts the different types of flies that bother equines?

Answer 6

1. stable flies: manure, decaying bedding
2. black fly: running water
3. horse fly and deer fly: water and vegetation
4. horn fly: cow manure
5. mosquito: water

Question 7

describe insect management for horses

Answer 7

avoidance:
goal is to reduce exposure and total allergen load

1. fans
2. protective netting
3. insecticides/repellents: permethrin, DEET, fipronil, avon skin so soft, borates

symptomatic management of skin lesions (itch and inflammation)
1. topical glucocorticoids
2. systemic glucocorticoids, oral oclacitinib

Question 8

describe staphylococcal pyoderma and equine pruritis

Answer 8

1. due to staph aureus( can be methicillin-resistant)
   -methicillin resistant staphylococci are resistant to virtually all beta-lactam antimicrobials (penicillins, cephalosporins, carbapenems) thanks to the mecA gene
2. almost always a secondary problem!
   -allergies, Cushing’s, environment/management

Question 9

describe dermatophytosis and equine pruritis

Answer 9

1. mild, if any pruritis
2. due to trychophyton equinum, M. canis, T. mentagrophytes, and T. verrucosum

Question 10

describe oxyuris equi

Answer 10

1. perianal pruritis that fails to respond to classic equine IBH therapy
2. adhesive strip preparation shows topical operculate eggs of O. equi for diagnosis
3. eggs cause direct irritation to the skin or a possible immunogenic reaction
4. antihelmintic treatment is recommended

Question 11

describe equine bite hypersensitivity (IBH)/sweet itch/summer exzema

Answer 11

1. over 1000 cullicoides/biting midges species worldwide
   -multiple species can feed on the same horse
2. hypersensitivity to proteins in cullicoides saliva
3. most active dusk and dawn, do not like winds
4. seasonal disease (winter remission)
5. diagnosis is primarily by clinical signs with supportive IgE and response to insect control
   -commercial cullicoides antigens for intradermal testing are much more accurate than serological testing
6. most common lesions:
   -pruritis and papules: either mane and tail/neck, or ventral midline but could be generalized
   -secondary infections/clinical signs: alopecia, scale, crust, lichenification, ulceration, secondary bacterial infections

Question 12

describe diagnosis of equine IBH

Answer 12

1. presumptive diagnosis based on:
   -history
   -physical exam
   -clinical signs
   -ruling out other causes of pruritis
   -response to environmental managemnet
2. age:
   -uncommon in horses <1 year
   -onset usually age 2-4 years
3. usually seasonal, at least during the first few years in temperate climates
4. intradermal and serum allergy testing canNOT be used to diagnose, but can be SUPPORTIVE
5. skin histopathology:
   -nonspecific superficial to deep perivascular to interstitial dermatitis with eosinophils as the dominant inflammatory cell

Question 13

describe therapeutic management of equine IBH

Answer 13

1. prevent additional bites and decrease exposure of the horse to biting midges
   -stable at sunrise and sunset (peak feeding hours)
   -use ultrafine netting or screens placed in windows and barns
   -use fans in stalls to disrupt flying of midges (weak fliers)
   -fly control measures: draining standing water (midges depend on for breeding and larval survival)
   -permethrin-repellant products applied to the horse
2. minimizing the pruritis and inflammation to prevent secondary self trauma
   -antihistamines: poor response! but can try cetirizine
   -systemic and topical glucocorticoids (ALWAYS USE TOPICAL)
   -(review side effects of hepatopathy, muscle wasting, altered bone metabolism, hyperglycemia, PU/PD, increased susceptibility to infection, and possibly laminitis)
   -oclacitinib
   -allergen-specific immunotherapy using whole cullicoides extract
3. resolve any secondary infections
   -topical antimicrobial treatment utilizing antiseptics and/or topical antibiotics via shampoos, sprays, ointments, and conditioners

Question 14

describe food hypersensitivity in horses

Answer 14

1. sometimes also with urticaria and pruritis
2. non-seasonal (unless new ingredient)
3. substantiated food allergies that resolve on a hypoallergenic diet and subsequently recur upon rechallenge with the original feed are very uncommon in horses!!
4. serum IgE testing is a waste of client money
5. gold standard diagnosis: elimination diet and provocation tests to ID offending substance
   -feed novel dietary substance
   -diet free of additives, supplements, treats
   -get nutritionist help if needed

Question 15

describe atopic/environmental allergen hypersensitivity

Answer 15

1. environmental allergens include:
   -dust and storage mites, molds: year round symptoms

-pollens from trees, weeds, and grass: seasonal symptoms

2. pruritis with alopecia, excoriations, lichenification, erosions to ulcers, crusts, etc.
3. diagnosis:
   -presumptive: based on clinical signs and exclusion of cullicoides hypersensitivity after lack of clinical improvement with insect management
   –some horses can have both insect and atopic hypersensitivity, or atopic hypersensitivity and asthma

-intradermal and serum allergy testing with environmental allergens canNOT be used to diagnose

-skin histopath: non-specific superficial to deep perivascular to interstitial dermatitis with eosinophils as the dominant inflammatory cell

Question 16

describe treatment of atopic (environmental allergen) hypersensitivity

Answer 16

1. allergen avoidance if possible
   -rubber matting in stalls
   -decreasing loose bedding
   -feeding vacuum packed, wilted grass or pelleted concentrate food
2. anti-pruritic/anti-inflammatory agents and secondary infections
   -antihistamines: poor response
   -oral/topical glucocorticoids
   -oclacitinib
   -topical antimicrobial therapy
3. allergen immunotherapy