Common skin conditions in horses

what is pruritus?

unpleasant sensation that provokes the desire to scratch or itch

what are the main causes of pruritus?

1. parasitic skin disease

2. hypersensitivities (allergies)

what parasites can cause pruritus in horses?

• lice

• mites

• ticks

• nematodes

What is Werneckiella (previously known as Damalinia equi)?

• biting louse in horses

• feeds on epidermal debri

• mainly on dorsolateral trunk, neck and face

What is Haematopinus asini?

• sucking louse in horses

• feeds on blood

• mainly found on mane and tail, fetlock and pastern

how can lice be transmitted?

• directly between horses

• indirectly - e.g. sharing rugs

when are lice more common?

• more common in winter

• more common in young or old animals (immunocompromised or immunonaive)

• no breed or sex predilection

how severe are lice infections?

• may be asymptomatic in some horses

• may cause severe debilitation in others

what is the diagnosis for lice?

• coat brush

• hair pluck

what are the treatments for lice in horses?

• pyrethrins

• pyrethroids

• permethrin

• fipronil

what should we do when treating horses?

• clip hair first

• product needs to get to the skin

what louse is this?

Werneckiella (biting louse)

what louse is this?

Haematopinus asini - sucking louse

what parasite is likely to be affecting this horse?

lice

What is Chorioptes equi?

• mite of horses

• mainly on distal limbs

• causes intense pruritus with stamping / scratching / chewing of feet

• if affected shave feathers when treating

When is Chorioptes equi more common?

• in horses with feathers (long hair on bottom on legs) e.g. Cobb, Shire

• more common in winter (but happens all year round)

what other condition is common in horses with feathers?

chronic progressive lymphadema (CPL)

What is Sarcoptes scabiei?

• mite affecting whole body - entire body will be pruritic

• zoonotic

• difficult to see on skin scrapings

What is Psoroptes equi?

• scab mite

• affects forelock, main and tail, trunk

• if affecting ears may cause headshaking

What is Trombiculidiasis?

• infection with larvae of free living adult Harvest mites

• causes papules with small orange or red larvae in centre

• affects face, distal limbs, ventral thorax and abdomen

What is Dermanyssus gallinae?

• poultry mite

• affects head and legs of horses

• remove birds if horse is affected

what is the diagnosis of mites?

skin brushings

what is the treatments for mites?

• inject macrocylic lactones (cascade)

  • 2 injections 2 weeks apart (subcutaneous)

• topical macrocylic lactones (cascade)

  • once every 4 weeks

• topical shampoo - lime sulphur shampoo, selenium sulphate shampoo, topical ivermectin

what mite is this?

Harvest mite - larvae cause trombiculidiasis

what mite is this?

Dermanyssus gallinae (poultry mite)

what mite is this?

sarcoptes scabiei

what mite is this?

Psoroptes equi

what mite is this?

Chorioptes equi

What is Oxyuris equi?

• pinworm in horses (nematode)

• seen on perianus

• causes perianal pruritus

how is Oxyuris equi diagnosed?

• clinical signs

• cellophane tape

how is Oxyuris equi treated?

anthelmintics

What are the types of hypersensitivities?

• insect hypersensitivity

• food allergy

• contact allergy

• atopy

• urticaria

what causes insect bite hypersensitivity?

• Culicoides spp - sweet itch

• affects main, back, tail and ventrum

• seasonal

• risks - standing water, dawn and dusk

what is treatment for insect bite hypersensitivities?

• avoid midge contact

• improve skin integrity

what can food allergies cause in horses?

• pruritus

• diarrhoea

• respiratory signs

(food allergies rare in horses)

what is diagnosis for food allergies?

diet elimination

what is atopy?

sensitivity to multiple allergens

what is the diagnosis for atopy?

exclusion

intradermal skin testing can help identify allergens

what is the treatment for atopy?

• avoid allergen

• immunotherapy

• cortiosteroids / antihistamines

• improve skin barrier function - using shampoos, conditioners and emolients

what do we see with urticaria / hives?

• wheals = raised bumps on skin

• oedema

• pruritus

what do we need to do when diagnosing urticaria / hives?

• easy to recognise, can be itchy

• cause is difficult to determine

• rule out food and insect / contact allergy

what is the treatment for urticaria / hives?

• corticosteroids

• antihistamines

what skin condition is shown here?

urticaria (hives)

what is scaling?

dry flaky dandruff appearance of skin

what is crusting?

yellow, red or brown, wet / damp, oozing on skin, like a scab

what is the difference between erosion and ulceration?

• erosion is superficial

• ulceration is deeper

what is this?

scaling

what is this?

crusting

what conditions cause crusting, scaling, erosion or ulceration?

• dermatophilosis (rain scald)

• bacterial folliculitis

• dermatophytosis (ringworm)

• photosensitisation

• leukocytoclastic vasculitis

• pastern dermatitis

• pemphigus foliaceous

what is Dermatophilosis (rain scald)?

• caused by dermatophilus congolensis (gram positive, facultative anaerobe)

• causes chronic moisture and skin damage

• see crust and moist mats of hair at the lesion

• affects the gluteal area, face, neck and extremities

how is Dermatophilosis diagnosed?

cytology (smear pus onto a slide)

what is the treatment for dermatophilosis?

• topical - mild cases

• systemic antimicrobials - severe cases

what skin condition is shown here?

dermatophilosis (rain scald)

what is bacterial folliculitis?

• caused by staphylococcus and streptococcus

• painful lesion

what is the diagnosis of bacterial folliculitis?

cytology, culture

what is the treatment of bacterial folliculitis?

• topical - mild cases

• system antimicrobial - severe cases

what is dermatophytosis (ringworm)?

• highly contagious fungal skin infection

• caused by trichophyton and mycrosporum

• see circular patches of alopecia

what animals is dermatophytosis (ringworm) common in?

young and immunocompromised animals

what is the diagnosis of dermatophytosis?

fungal culture, PCR, microscopy

what is the treatment of dermatophytosis?

topical antifungals

• natamycin

• enilconazole

• miconazole

what skin condition is shown here?

dermatophytosis (ringworm)

what are the two causes of photosensitisation?

1. hepatogenous

2. ingestion or application of photodynamic agent

where are photosensitisation lesions common?

in white areas

what is the diagnosis of photosensitisation?

clinical signs and blood tests

what is the treatment of photosensitisation?

• treat liver disease

• removal of agent

what is leukocytoclastic vasculitis?

• common disorder that affects non-pigmented areas on distal (or lateral) limb

• can be painful

what is the diagnosis of leukocytoclastic vasculitis?

• clinical signs

• skin biopsy

what is the treatment of leukocytoclastic vasculitis

• avoid exposure to light

• (corticosteroids - not always affective)

what skin condition is shown here?

leukocytoclastic vasculitis

what is pastern dermatitis?

• very common disorder on back of horses distal leg (pastern)

• a syndrome rather than a disease

when is pastern dermatitis seen commonly?

in winter (also when more wet) and in white limbs

what can cause pastern dermatitis?

• infectious conditions

• inflammatory conditions

• chronic disease

what skin condition is shown here?

pastern dermatitis

what is pemphigus foliaceous?

• rare, autoimmune disease

• causes severe crusting

• no age or sex predilection

what is the diagnosis of pemphigus foliaceous?

skin biopsy

what is the treatment of pemphigus foliaceous?

immunosuppressive drugs

what is the prognosis of pemphigus foliaceous?

guarded - prognosis is better in younger horses, older horses tend to not respond to medication

what skin condition is shown here?

pemphigus foliaceous

what cutaneous swellings, nodules and tumours do we see in horses?

• viral papillomatosis

• warbles

• genetic / developmental

• eosinophilic granuloma

• tumours

what is viral papillomatosis?

• grass warts - seen on muzzle and face of young horses

• pinnal acanthosis or aural placks

• no need to treat

what skin condition is shown here?

viral papillomatosis - grass warts on muzzle

what skin condition is shown here?

viral papillomatosis - pinnal acanthosis / aural placks

what are warbles?

• larval stages of Hypoderma bovis and lineatum

• notifiable but very rare due to use of ivermectin

• nodules with central pore

• painful

what is the treatment of warbles?

• enlargement of pore to remove central grub

• surgical removal

what skin condition is shown here?

warbles

what genetic / developmental cysts / nodules do we see?

• dentigerous cyst

• atheroma

• dermoid cyst

• vascular hamartoma

what skin condition is shown here?

what skin condition is shown here?

what skin condition is shown here?

what skin condition is shown here?

what is eosinophilic granuloma?

• collagen necrosis

• seen very frequently

• caused by insect bites or trauma

• not painful and not pruritic

what is the appearance of eosinophilic granuloma?

• may have single or multiple

• 0.5 to 10cm

what skin condition is shown here?

eosinophilic granuloma

what are the most common skin tumours that we see in horses?

• sarcoids

• melanoma

• squamous cell carcinoma

• mast cell tumour, lymphoma, etc.

what are sarcoids?

• most common skin tumour in horses

• seen with bovine papillomavirus 1 and 2

• genetic predisposition - no sex or breed predisposition

• can be seen with flies

what are the 6 clinical presentations of sarcoids?

• occult sarcoid

• verrucose sarcoid

• nodular sarcoid

• fibroblastic sarcoid

• mixed sarcoid

• malignant sarcoid

would we biopsy sarcoids?

• not always - as dangers of exacerbation

• if we have a positive diagnosis - be ready to treat

what are the treatments of sarcoids?

• surgery / laser removal

• immune therapy - BCG injections

• cytotoxins (topical and injection)

• antimitotics (topical)

• photodynamic therapy

• brachytherapy - most successful but not always available

what is the prognosis of sarcoids?

• variable

• the more they have the more they will get

• they multiply over summer and grow over winter

• a single sarcoid implies genetic susceptibility

  • this remains for life

what type of sarcoid is shown here?

occult sarcoid