Equine skin disease Flashcards
How are equine skin diseases categorised?
Infections or non-infectious
List infectious equine skin diseases
- ectoparasite (infestation)
- dermatophilosis
- folliculitis
- fungal (dermatophytosis)
- viral (aural plaques)
Non-infectious skin diseases
- allergies
- immune-mediated
- endocrinopathies
- miscellaneous
- neoplastic
What ectoparasites can affect horses?
- Chorioptes spp
- Psoroptes spp
- Neotrombicula autumnalis, Demanyssus gallinae
- RARE: scabies, demodex
- Ticks, lice, fleas, flies
Where are chorioptes found?
limbs and tail (pastern dermatitis)
Where are Psoroptes spp found?
head and ears
What causes equine chorioptic mange?
Chorioptes bovis, especially feathered horses
CS - chorioptic mange
pruritus, erythema, crusts, papules,
- peaks in WINTER
Tx - chorioptic mange
- challenging, often recurrent
- clipping (especially feathered)
- fipronil spray (repeat after 1 month)
- avermectins (controversial efficacy)
- permethrins/pyrethroids - flumethrin is acaricidal
CS - lice infestation
pruritus variable, very host specific
Tx - lice infestation
- fipronil spray (2tx, 10 days apart)
- synthetic pyrethroids
- systemic ivermectin
Dx - lice infestation
ID parasites
How can flies be a problem to horses?
- bites and stings
- hypersensitivity (culicoides - sweet itch)
- larvae (myasis)
- disease transmission (Habronemiasis, Ochocerchiasis)
What fly species can affect horses?
- Tabanus (horse fly)
- Stomoxys (stable fly)
- haematobia spp
- Muscids
- Culicoides spp
- Hyrotea spp.
- Hippobosca equina
- Simulium spp.
What causes itchy bottom?
Pinworm infestation (oxyuriasis): Oxyuris equi adult worms migrate from terminal parts of intestines out of anus to lay eggs –> tail rubbing, self-trauma around tail base, restlessness
Dx - pinworm infestatin
- handheld lens OR
- acetate tape and microscope to ID eggs
Tx - pinworm infestation
anthelmintics
What is the commonest skin allergy in horses?
sweet itch / culicoides bite hypersensitivity
CS - sweet itch
- seasonal pruritus
- excoriations
- alopecia
- SECONDARY LESIONS: papules, crusts, skin thickening, alopecia (primary lesions not well described)
- Dorsal or ventral midline
- restlessness and weight loss
2 forms of sweet itch
- dorsal distributed - commonest
- ventral biting Culicoides
Where is sweet itch common?
- culicoides spp regions
- wet fields, little wind
- animals > 6 months
Ddx - sweet itch
- Oxyuris equi
- other insects
- other allergies
Dx - sweet itch
- clinic
- midges
- (intradermal/ serology testing of little value since they only indicate exposure)
Management - sweet itch
- ) AVOIDANCE - stable 4pm-8am, rugs and hoods, fans, fly screens and traps, windy, dry grazing
- ) REPELLANTS AND LONG TERM INSECTICIDES: synthetic pyrethroids (cypermethrin, flumethrin, deltamethrin. Frequent administration essential)
- ) ANTI-INFLAMMATORIES/ANTI-PRURITIC - antihistamines and GCs (severe)
What bacteria infect equine skin?
- Staphylococci
- Dermatophilus congolensis
- Many others
How are equine bacterial skin infections diagnosed?
As in small animals - cytology (pathognomic railroad tracks seen)
What type of bacteria is Dermatophilus?
branching filamentous actinomycete
mainly affects ruminants and horses
varied clinical presentations
Describe Dermatphilus congolensis in cattle.
significant economic importance in central and west affrica - severe form in cattle infested by Amblyomma variegatum tick
What is Dermatophilus associated with in temperate climes?
moisture and skin trauma
Colloquial names - Dermatophilosis
Fleece rot - sheep
Mud fever - horses (also mud rash, greasy heal, pastern folliculitis)
Rain scald - horses
Where on the body is mud fever common?
lower limb very common –> irritation, foot stamping, chewing. Often chronic with scarring + secondary lesions
What does papillomavirus infection cause in horses?
aural plaques
Describe aural plaques
- hyperkeratotic plaques
- concave aspect of pinnae
- common
- not self-limiting (as other spp)
- yearling +
- Simulium spp as vectors
- Tx = observation (doesn’t bother)
What causes equine ringworm ?
- Trichophyton equinum var equinum
- T. mentagrophytes
- M. equinum
- M. gypseum
Describe ringworm
- Healthy host - spontaneous resolution in 5-6 wks
- can be pruritic
- unsightly
Dx - ringworm
- same as smallies
- CS - patchy alopecia, easy epilation, hair stands on tufts
- NOT wood’s lamp
- hair pluck and coat brush –> fungal culture
Tx - ringworm
- Nothing licensed
- topical (griseofulvin, potassium iodide)
- isolation
- hygiene
List 4 horse allergies
- Culicoides hypersensitivity
- Food
- AD
- (Contact hypersensitivity)
List equine immune-mediated/ autoimmune diseases - 5
- PF
- Erythema multiforme (not a diagnosis but an inflammation pattern)
- ADRs
- Vasculitis including purpura haemorrhagica - including purpura haemorrhagica (also not a diagnosis but an inflammation pattern)
- Alopecia areata
What may erythema multiforme look like?
urticaria (differentiate by histopath. also urticaria should pit on pressure then return to original shape slowly. Eryhthema multiorme conditions can be pressed down but ‘pop back up quickly’ when pressure is released.
Causes of vasculitis and erythema multiforme
- ADR
- infection
- neoplasia
Define PPID
= pituitary pars intermedia dysfunction = cushing’s disease
CS - PPID/Cushing’s
- hirsutism
- laminitis
- secondary infections
- supraorbital fat deposits
- hyperhydrosis
Tx - PPID/ Cushing’s - 2
- pergolide - controls ACTH output
- trilostane - stops production of cortisol in adrenals
What is systemic granulomatous disease/ chronic eosinophilic enteritis?
- RARE, dramatic disease
- skin + GIT involved
- both grave prognosis
- aka Equine sarcoidosis (nothing to do with sarcoids)
- aetiology unknown
Tx - systemic granulomatous disease/ chronic eosinophilic enteritis
- change feed
- systemic GC (months)
Prognosis - systemic granulomatous disease/ chronic eosinophilic enteritis
grave (spontaneous recovery described)
Skin signs - systemic granulomatous disease/ chronic eosinophilic enteritis
exfoliative dermatitis = generalised scaling. often crusting, alopecia or nodules
Systemic signs - systemic granulomatous disease/ chronic eosinophilic enteritis
- severe wasting
- fever
- lymphadenopathy
- icterus
- diarrhoea
Diagnosis - systemic granulomatous disease/ chronic eosinophilic enteritis
- hx
- cs
- leukocytosis
- anaemia
- abnormal liver/ kidney function
- skin histopath
- organ biopsy = granulomatous +/- eosinophils
What test should you always perform in cases of unexplained pruritus in horses?
Liver and kidney function (in systemic granulomatous disease/ chronic eosinophilic enteritis these results will be abnormal)
3 factors required for photosensitisation
UV + poorly pigmented skin + photodynamic agent in skin
Types of photosensitisation
- PRIMARY - St. John’s wort ingestion
- SECONDARY - liver problem and phylloerythrin
What happens in leucocytoclastic vasculitis?
accumulation of WVCs around BV wall –> BV destruction
CS - leucocytoclastic vasculitis
- nonpigmented lower limbs
- acute onset erythema, oozing, crusting, painf
Dx - leucocytoclastic vasculitis
biopsy (good sedation because pain)
Tx - leucocytoclastic vasculitis
High dose immunosuppressive therapy
3 categories of nodular disease
- STERILE (often harmless)
- MICROBIAL/PARASITIC
- NEOPLASTIC
List sterile nodular diseases
- collagenolytic granuloma
- cutaneous mastocytosis
- axillary nodular necrosis
- unilateral papillomatosis
List 4 microbial /parasitic nodular diseases
- Botryomycosis
- Habronemiasis
- Dermatophilosis
- Dermatophytosis
Describe collagenolytic granuloma
- aetiology unknown
- saddle area, neck, flanks
- spring and summer mostly
- single/ multiple dermal lesions, firm, well circumscribed
- variable diameter
- NOT alopecic, ulcerative, painful, pruritis
- Chronic - lesion mineralisation
Hx - collagenolytic granuloma
- age
- speed of onset
- season
- recent tx
- systemic disease
Diagnostics - collagenolytic granuloma
- fungal and bacterial culture
- FNA cytology
- often histopath (definitive diagnosis)
Ddx - collagenolytic granuloma
THIS IS NOT AN EXHAUSTIVE LIST!:
- hypoermiasis
- papular dermatitis
- staph folliculitis and furunculosis
- dermatophytosis
- dermatophilosis
- neoplasia
- calcinosis circumscripta
- cutaneous amyloidosis
Tx - collagenolytic granuloma
- leave alone
- Sx excision (single/few lesions
- GCs (systemic, intralesional or sub-lesional injections
Prognsosis - collagenolytic granuloma
- may resolve spontaneously
- recurrence common
- GCs probably ineffective in later stages after mineralisation
- Tx unlikely to produce permanent cure
Name the 6 types of equine sarcoid
- occult
- nodular
- verrucous
- malevolent
- mixed
- fibroblastic
Ddx - occult sarcoid
- dermatophytosis
- burn trauma
Ddx - nodular sarcocid
- fibroma
- melanoma
- collagenolytic granuloma
- warble fly cysts
Ddx - verrucous sarcoid
- papillomatosis
- chronic sweet itch
- SCC
Ddx - fibroblastic sarcoid
- GT
- botryomycosis
- habronemiasis
- neurofibroma
- SCC
Ddx - mixed sarcoid
- easy to recognise
- GT
- habronemiasis
Ddx- malevolent sarcoid
- lymphangitis
- glanders
- lymphosarcoma
- SC mycosis
