Equine dermatology 2 Flashcards
What are common causes of crusting and scaling?
Infectious
- Dermatophilosis (Rain Scald)
- Dermatophytosis (Ringworm)
- Bacterial infection- Staphylococcus spp. –> follicullitis/furunculosis/pyoderma
Dermatosis of lower limb
- Leucocytoclastic vasculitis
- Pastern dermatitis
Photo dermatitis
Seborrhea
Localised keratinisation defects
- Cannon keratosis
- Linear keratosis
Immune-mediated
- Pemphigus foliaceus – RARE
- Coronary band dystrophy- RARE
Idiopathic
- Multisystemic eosinophilic epitheliotrophic disease (MEED)- RARE
- Generalised granulomatous disease (SARCOIDOSIS) – UNCOMMON
What is the disease profile of dermatophilosis?
- Dermatophilus congolensis
- G +ve facultative anaerobic actinomycete
- Thought to exist in quiescent state (no clinical signs) in chronically infected animals until conditions are favourable for proliferation
- Skin damage- other skin disease, insect bites, environmental trauma etc
- Wet skin – sweating, rain, washing
- ? Genetic susceptibility- some horses more prone
- Contagious
- Immunocompromised/malnourished animals
- Short lived immunity so can get recurrent infections
What are the clinical signs of dermatophilosis?
- Follicular/non follicular tufted papules–> rapidly coalesce–> exudative —> matted hair (= paintbrush lesions)
- When plucked leave erosions/ulcerations- may bleed or be purulent
- Commonly seen on
- rump and top line- rainfall
- Saddle area- trauma/ sweating under tack
- Face and neck- trauma/sweating under tack
- Pasterns, coronet, heels= mud fever/grease
- heel/scratches – poorly drained pasture/muddy
- Lesions may be painful e.g. Distal limb swelling, oedema, lameness
- Can be on white skin
- Rarely pruritic
- Healing stage–>dry crusts, scaling and alopecia
- Lesions smaller in summer
How is dermatophilosis diagnosed?
- History
- Clinical exam
- Impression smears- cytology
- G +ve branching, filamentous
- Chain like coccus “railway tracks”
- Culture- microaerophilic / high CO2
- Skin biopsy
What are the DDx for dermatophilosis?
- Staphylococcal follicullitis
- Dermatophytosis
- Pemphigus foliaceaus RARE
- Photo dermatitis
- Other causes of pastern dermatitis
How is dermatophilosis managed?
- Prevent wetting e.g. stable horse
- Remove rugs etc to prevent sweating
- Keep tack and grooming kit clean/individual use
- Most cases spontaneously regress within 1 month if kept dry
- Remove crusts , dispose carefully
- Topical treatment
- Chlorhexidine shampoos
- Silver sulphadiazine (Flammazine )cream
- NOT steroids because this is a infection!!
- Systemic treatment
- if horse systemically ill however horse tends not be with this infection
- If severe, generalised, chronic infection
- Antibiotics appropriate for gram+ bacteria- penicillin/ TMPS
What is the disease profile for a staphylococcus infection?
- Sporadic infection
- G +ve Staphylococcus aureus
- Common Spring and Summer- post clipping/ during coat change
- Especially fine skinned horses- TB’s
- PAINFUL (if you try and pull these scabs off it hurts)
- Contact areas of tack, saddle patch, riders legs
- Potentially contagious if shared tack, equipment
What are the clinical signs of a staphylococcus infection?
- Lesion starts as focal papule
- Hairs stick up against lie of the coat, can be glued by small crusts
- Can progress to furunculosis – nodules, draining tracts, ulcers, crusts
- Can get cellulitis, lymphatic engorgement (= runners)
How is a staphylococcal infection diagnosed and treated?
Diagnosis:
- Clinical signs
- Swab and culture and exudate
- Remember Staphylococcus aureus is a commensal – look for pure growth on selective media
DDX
- Pemphigus foliaceaus
- Other bacterial infection- Strep/ dermatophilosis
- Onchocerciasis – this is pruritic
Management
- NSAIDS –> pain
- Avoid contact with tack, rider, rugs other horses
- Topical antiseptic shampoos – Chlorhexidine/ povidone iodine based
- Systemic antibiotics
What is the clinical profile of dermatophytosis?
- HIGHLY CONTAGIOUS and COMMON
- Potentially ZOONOTIC
- Transmitted via contact with infected animals/environment- tack, rugs, grooming kit, bedding, fencing, transport vehicles, people
- 2 causes in horse
- Trichophyton equinum and verrucosum
- Microsporum gypseum and equinum
- Incubation period 1-6 weeks
- Young animals –> esp. susceptible
- Some immunity with age/post infection – unusual for a healthy horse to get dermatophytosis a second time.
- Spores very resistant , survive for long periods in environment
- Disease is endemic in many livery/racing yards
- NOTE:
- Racehorses are NOT allowed on racecourses with active lesions
- Horses may NOT be exported with lesions
What are the clinical signs of dermpatophytosis?
- Common at sites of tack contact-
- face, neck, dorsolateral thorax, girth ( legs- rarely)
- multiple lesions
- Initially change in angle of hairs –> small often circular patches
- Amongst hairs- amounts of finely keratinised squames (=Cigarette ash!)
- Fungus produces keratolytic enzymes –> weakening hairs –> easily broken / epilated
- Focal areas coalesce –> extensive scaling and flaking
- Healing occurs from the centre
- most active fungal growths at margins of the lesion- imp for sampling
- Variable pain
- Variable pruritus
- Difficult to tell which fungal spp. is involved just by clinical presentation
How is dermatophytosis diagnosed and managed?
Diagnosis
- Hair plucks at periphery of lesions
- Microscopy
- Culture ( can take up to 30days) sabouraud’s medium + red phenol dye agar turns red if +ve
- Microsporum spp. Add drop vit B to culture as tricky to grow
- Woods lamp NOT useful in horse
- Skin punch biopsy- fungal spores within hair follicles
Management
- ID of species not critical for treatment
- Most infections are self-limiting (5-10 weeks)
- Wear gloves to tx as potentially ZOONOTIC
Two main principles:
- Treat active infection to decrease spore formation
- Eliminate infective spores from environment
- Topical/ systemic drugs
- Disinfectants – anti-fungal action
Discuss the disease profile of pastern dermatitis?
COMMON! Often winter! Often multifactorial! Chronic wetting of the skin! White legs but not exclusively!
- INFECTIOUS – bacteria, fungus, virus, parasite
vs
- NON-INFECTIOUS- trauma, immune mediated, neoplastic
DDX:
- Dermatophilosis- crusts on top of pus, not that painful
- Staphylococcal dermatitis – extremely painful
- Pastern and cannon leukocytoclastic vasculitis-not painful
- Other autoimmune disease eg. SLE , immune mediated necrotising vascultis
What are the clinical signs of pastern dermatitis?
Clinical signs:
Mild- alopecia, erythema, mild serum exudation
Progression to – papules, significant serum exudation -> crusts -> scabs
+/- pain on palpation
+/- lameness
+/- cellulitis
How is pastern dermatitis diagnosed?
- Clinical signs
- Coat brushings
- Skin scrapes
- Swabs from exudate – culture/sensitivity
- Skin biopsy – often poor return, may help in recurrent or refractory cases
- Eliminate other causes e.g. Chorioptes spp.
What is this?
Pastern leukocytoclastic vasculitis
- Follows the blood vessels
- Cause unknown ? Associated with bacterial infection
Clinical signs:
- in almost all cases affects white limbs, often follows BV’s Lat and med limb
- Firmly attached crusts on distal limbs
Diagnosis: skin biopsy
- See vasculitis, karryorrhexis of neutrophils
Treatment:
- Topical
- Systemic steroids
- eg, prednisolone/dexamethasone
- Avoid sun
Discuss the disease profile of photosensitisation?
Occurs following normal light exposure
Indirectly caused by photodynamic agents in skin due to
- Ingestion of plants containing photodynamic agents –>direct absorption into blood eg. UK Hypericum perforatum – St. Johns Wort
- failure of the liver to de-toxify phlloerythrin (by- product of chlorophyll digestion) hepatotoxic plants eg. Senecio jacobea= Ragwort
How can you diagnose and manage photosensitisation?
- Check paddocks –> ID plants
- Ragwort –> usually unpalatable when alive BUT when cut palatability ꜛ eg. In hay
- Toxic effects –> not seen –> months after ingestion
- Can affect multiple horses in a group
- Not all horses have liver failure BUT its prudent to rule out
Clinical signs: erythema, oedema, pain, vesicles, serum exudation, skin necrosis, ulceration, sloughing, possible other signs of liver disease, secondary bacterial infection
Management : sun avoidance ( stable in day, turnout at night), UV masks, high factor sun screens, avoid grazing with toxic plants. use topical creams to remove crusts and soothe eg. Dermisol/aloe vera .
- evidence of severe liver disease have guarded prognosis.
What rare condition is seen here?
Pemphigus foliaceus – RARE
- Antigen in horse not known
- Lesions often start on face –> generalised over several months
- Early lesions –> papules and crusts
- Annular thick crusts, annular erosions with/without epidermal collarettes, annular alopecia, oozing, matted hair coat, scaling.
Diagnosis:
- Skin biopsy – acantholysis, neutrophils, eosinophils
- Direct smear of pustules/erosions- cytology
- Immunohistochemistry
Discuss coat colour changes in the horse?
Most coat colour changes go to white
Leukotrichia/Leukoderma:
- acquired loss of coat colour
- without loss of skin pigment e.g. Freeze brand
- bandage rub
- patches of white hair
- non progressive
Vitiligo- gradual appearance of non-pigmented skin without other changes e.g. Pink peri-ocular areas of Arabs
Spotted Leukotrichia
- Shire, TB, Arab
- Non-inflammatory white haired spots on normal skin
- Get increased number of static spots
Reticulated Leukotrichia
- White hair patterns
- Can be painful
- Quarter horse , TB, SB
- Cause unknown
All 4 conditions can be differentiated by clinical signs or histopathology of biopsies.
No treatment
What is seen here?
Linear keratosis
- A little patch of hyperkeratosis that goes alopecic
- Relatively common
- All ages/breeds, TB and Quarter horses, rare in ponies
Clinical signs :
- Initially small areas hyperkeratosis–> develop alopecia
- Lesions develop in a linear direction
- Neck, chest, quarters
- No pain, pruritus
Diagnosis:
- Clinical presentation
- skin scrapes to eliminate other diseases
- skin biopsy- regular/irregular hyperplasia
- Hyperkeratosis
- lymphocytic follicullitis
- Management:
- No treatment/ not required
- Permanent/progressive
