Equine Derm 1 Flashcards
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
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
Pathophys of skin problems in horses
Inflammation* main cause of itchy skin
Acute: neutrophils, mononuclear phag
Chronic: lymph, macrophages
Hypersensitivity reactions: 1-4
Lesion location
Ventral midline
Distal limbs
Face
Trunk
Dorsal trunk
Cranial trunk
Caudal trunk
Ventral midline
Linear, widespread, Culicoides or black flies
Focal = horn fly
Distal limb
Vasculitis, chorioptes mites
Rare: contact allergy, atopic derm, Dermatophytes
Face
Atopic dermatitis, black flies, stable flies
Trunk
Dermatophyte, vasculitis, atopic dermatitis, lice, trombiculids, food allergy
Dorsal trunk
Culicoides (mane, tail) black flies
Cranial trunk
Stable flies (Stomoxys calcitrans)
Caudal trunk
Culicoides, pinworms, atopic dermatitis, yeast (malassezia)
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
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
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
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
Diagnosing Culicoides hypersensitivity
Seasonality
• Distribution of lesions
• History of exposure
• Response to therapy
• Intradermal Testing
• Biopsy
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
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
Tabanus
Horse flies
Painful bites, pruritic wheal
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
