Equine Derm 1 Flashcards by Mckenna Maloney

Common problem list for horses

Pruritis
• Alopecia/ alteration of hair quantity or quality
• Scaling and crusting (dry dermatosis)
• Weeping and seeping (moist dermatosis)
• Pastern dermatitis
• Nodule
• Pigmentary alterations

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Diagnostic methods for equine DX

Skin scraping
•Groomings
•Tape preparation
•Needle aspirate
•Restriction/provocation test
•Serology
• Hair sampling
•Culture/sensitivity
•Biopsy
•Allergy testing
•Hematology
•Evaluate other organ systems

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Pathophys of skin problems in horses

Inflammation* main cause of itchy skin
Acute: neutrophils, mononuclear phag
Chronic: lymph, macrophages
Hypersensitivity reactions: 1-4

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Lesion location

Ventral midline
Distal limbs
Face
Trunk
Dorsal trunk
Cranial trunk
Caudal trunk

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Ventral midline

Linear, widespread, Culicoides or black flies
Focal = horn fly

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Distal limb

Vasculitis, chorioptes mites
Rare: contact allergy, atopic derm, Dermatophytes

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Face

Atopic dermatitis, black flies, stable flies

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Trunk

Dermatophyte, vasculitis, atopic dermatitis, lice, trombiculids, food allergy

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Dorsal trunk

Culicoides (mane, tail) black flies

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Cranial trunk

Stable flies (Stomoxys calcitrans)

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Caudal trunk

Culicoides, pinworms, atopic dermatitis, yeast (malassezia)

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Pediculosis

Equine lice
Damalinia equi - small, broad body, square head
Haematopinus asini - larger body, conical head
Common in abuse situations
Can Tx with permethrin or oral ivermectin

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Cluicoides hypersensitivity

Causes sweet itch in horses
Most common allergic dermatitis in horses***
Hypersensitivity due to antigens in insect saliva
Seasonal flair in warm ares

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Pathophys of Culicoides hypersensitivity

Bites from midges or gnats
Breed in stagnant water, feed in low light situations
Primary bite causes irritation in all horses which can develop an allergic reaction
Common in welsh, Icelandic, shires, Arabs

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Clinical signs of cluicoides hypersensativity

Seasonal pruritis
• Secondary alopecia, crusting and scaling
Seasonal pattern of pruritis
• Warm weather
• Temporal pattern of pruritis
• Worst in evening and early morning
Characteristic pattern of lesion distribution
• Mane
• Tail head
• Ventral midline

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Diagnosing Culicoides hypersensitivity

Seasonality
• Distribution of lesions
• History of exposure
• Response to therapy
• Intradermal Testing
• Biopsy

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Treating Culicoides hypersensitivity

Decrease insect exposure
• Do not turn affected horses out during dawn and dusk
• Keep in stable during those times – stall may even require
ultrafine insect netting and overhead fans
• Physical barriers – sheets or ’dresses’
• Insect repellent
• Oil based wipe on permethrin products seem to last longest and provide best protection
Benzyl benzoate in oil - ’Killitch’
Corticosteroids
• Topical betamethasone/triamcinolone
• Oral prednisolone

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Fly and insect irritation clinical signs

Tabanus spp. (Horse flies)
- painful bites, pruritic wheal, central bite mark with blood
Stomoxys calcitrans (Stable flies)
-Relatively large skin lesion, often several in a group • Simulium spp. (Black flies)
-Extreme irritation and painful bites, especially on ears and head
• May be associated with development of aural plaques,
hypersensitivity reactions • Haemotobia spp. (Buffalo and horn flies)
• Characteristic head-down position in groups, especially around shoulders, neck, withers, flanks and abdomen; blood may be observed at site of bite

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Tabanus

Horse flies
Painful bites, pruritic wheal

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Stomoxys calcitrans

Stable flies
Large skin lesions

Simulium spp

Black flies
Extreme irritation & painful bites - head and ears
Can cause hypersensitivity reactions

Haematobia

Buffalo and horn flies
Feed with head down, deep painful bites

Oxyuriasis

Equine pinworms
Anal pruritis - tail rubbing
DX w acetate tape prep
TX w anthelminitc therapy

Urticaria

Type I hypersensitivity reaction
Common with drug associated reactions
Results in wheals, intense pruritis ***

DX of urticaria

Vary to determine cause Intradermal allergy, ELISA/RAST - serology Food / contact allergy

TX of urticaria

Avoid exposure Acute: epinephrine or systemic corticosteroids Antihistamines Hyposensitization

Atopy

Genetically mediated type I hypersensitivity - caused by environmental antigens Recurrent pruritis /self trauma Last resort DX - ruled everything else out

TX Atopy

Allergen avoidance Hyposensitization Systemic glucocorticoids

Alopecia

Non specific derm sign Hair growth failure or loss of hair

Scaling and crusting

Dry dermatosis Excessive flaking of skin , accumulation of dried exudate

Dermatophytosis

RINGWORM- highly contagious Enters through abrasions Circular lesions w raised scars, develop alopecia with scaling

Etiology of Dermatophytosis

Trichophytosis - most common - trich. Equi equi - trich. Equi autotrophicum Microsporosis - microsporum gypseum, m. Equi, canis

DX and Tx of Dermatophytosis

Clinical signs Hair plucking - DTM culture Topical fungicides - azole, sulfur

Deramtophilosis

Rain scald - Dermatophilus congolensis Common in rainy seasons Alopecia, crusting, pruritis, paint brush lesions (scabs)

Pathophys of dermatophilosis

Clinical signs of dermatophilosis

Tx of dermatophilosis

Pemphigus foliaceus

Autoimmune disorder - type II hypersensitivity Autoantibodies to epidermal antigens - vesicle & pustules Acute inflame - coronary band, chestnuts, ergot Also causes scaling and marked alopecia

DX findings for pemphigus foliaceus

Direct impression smear - acanthocytes * indicative but also seen with other derm lesions Biopsy —> histopath - acantholysis, intraepithelial bulla formation

Tx pemphigus foliaceus

Immunosuppressive therapy w GC’s Prednisolone or dexamethasone Gold therapy - injecting gold salts

Px for pemphigus foliaceus

Poor long term prognosis Younger horses respond better Goal is remission**

Actinic dermatoses

Photosensitization Sunburn - chemical reaction to UV light Affects nonpigmented skin

Primary path of actinic dermatoses

Ingestion of photodynamic plants UV light + photodynamic agent Dermal lesions

Secondary path of actinic dermatoses

Secondary photo plants, hepatotoxic drugs, hepatic disease, hepatic damage Inhibits clearance of phylloerythrin UV light + phylloerythrin Dermal lesions

Clinical signs of photosensitive

Restless, erythema, blisters, serum exudation, scab formation Secondary self trauma & bacterial infection Large areas affected can slough off and become leathery

DX for photosensitive

Important to screen liver w chemistry for evidence of heptopathy

Offending plants for photosensitive

St. Johnswort, buckwheat, perennial rye grass, clover Rape grass, spine brush

Tx photosensitive

Remove from sunlight Remove offending plants Treat hepatic diseases +/- topical diseases to enhance comfort