Equine dermatology Flashcards
What are the causes of allergic dermatitis in the horse?
- Insect hypersensitivity e.g. Culicoides, fy bites
- Atopy (rare)
- Contact allergy (tack, tack cleaning products, creosote on fences, shampoos)
- Food allergy (very rare)
What is the main cause of pruritus on the ears in horses?
Black flies
What are the main causes of pruritus on the mane of horses
- Culicoides
- Lice
- Psoroptes
What are the main causes of pruritus on the tail of horses?
- CUlicoides
- Other insects
- Lice
- Pinworm
- Food allergy
- Psoroptes
What are the main causes of pruritus on the legs of horses?
- Chorioptes
- Habronemiasis
- Dermatophytosis
What are the main causes of pruritus on the ventrum of horses, that is a: diffuse and b: focal
A: Culicoides, lice, dermatophytosis, other insects, onchocerciasis
B: horn fly dermatopphytosis
-Dermatophytosis as focal or diffuse depends on the individual
What are the potential causes of generalised pruritus in horses?
- Food allergy
- Dermatophytosis
- Culicoides
- Lice
- Other insects
- Urticaria
- Drugs/drug reactions
What are the main causes of pruritus of the head/face in horses?
- Culicoides
- Other insects
- Lice
- Sarcoptes
- Onchocerciasis
- Dermatophytosis
- Habronemiasis
What are the common, re-emerging, and other parasitic infection causes of pruritus in horses?
- Common: lice, mites
- Re-emerging: Habronema spp, pinworms (Oxyuris equi)
- Other: ticks, Onchocerca spp.
Name the biting and sucking lice of horses
- Biting/chewing: Weneckiella equi equi
- Sucking: Haematopinus asini
Name the mites that may affect horses, identifying those that are commonly seen
- Common: Chorioptes equi, Trombicula autumnalis
- rare/rarely cause pruritus: Psoroptes spp., Sarcoptes scabiei, Demodicosis, Dermanyssus gallinae (if housed with poultry)
Outline the importance of ticks in horses
- Seen occasionally, mainly head, distal limb, groin and tail
- Most common in spring/summer
- Important re. disease transmission
- Often geographical distribution
How does Onchocerca cervicalis cause disease in horses?
- Nematode that lives in nuchal ligament
- Produces microfilariae that migrate to skin where they are ingested by intermediate host Culicoides
When is onchocerciasis usually seen in horses?
- Usually spring when vector present in high numbers
- Horses >4yo
Name the parasites that cause habronemiasis in horses
- Habronema muscae
- Habronema majus
- Drashia megastoma
How does habronemiasis occur?
- Nematodes deposited on wounds by flies (house and stable fly, intermediate hosts)or near mouth of horse then swallowed
- Adult nematodes live in stomach, produce larvae, passed in faeces and ingested by maggots o fintermediate hosts
Describe the disease profile of pediculosis (life cycle, transmission, environmental survival, seasonality)
- Highly host specific
- Entire life cycle on horse
- Transmission direct or indirect, contagious
- Can live in right environment for 2-4 weeks
- More common autumn/winter
- Associated with debilitated, stress, diseased animals,, poor nutrition and overcrowding
In what group of horses is pediculosis most commonly seen?
Rescue cases
How is pediculosis diagnosed?
Easy to identify eggs with naked eye
Describe the disease profile of Chorioptes equi (life cycle, transmission, environmental survival, seasonality)
- Surface mite, feeds on epidermal debris
- Heavily feathered breeds most commonly affected, but can also be short coated
- Adults survive of host 2 months
- Transmission direct or indirect
- Mite populations greatest in winter during cold weather
Describe the clinical signs of Chorioptes equis
- Moderate to severe pruritus, usually on limbs, but also ventrum and dorsum
- Crusting, scaling, exudation, blood staining, hair matting, skin thickening
- Secondary infection
- Stamping on hind limbs
- Rubbing heels on gates/fences
- Chewing limbs
- Draggin belly on floor
- Shorthaired breeds less stamping, generalised “moth-eaten” appearance
Which limbs are typically more affected by Chorioptes equi?
Typically hind more than fore
Describe the diagnosis of Chorioptes equi
- Superficial coat brushings/superficial scrapes
- Tape strips of distal limb
- Visualisation of mite
Describe the clinical signs of Trombicula autumnalis infestation
- Intense pruritus
- Orange/brown sticky patches of serum
- Typically distal limbs, face, neck, thorax of horses at pasture
How is Trombicula diagnosed?
- Unstained tape strip, skin scrapes
- Larvae only have 6 legs and are orange
Describe the appearance of tick lesions
- Local reaction or general hypersensitivity
- Papular or pustular area, resulting in erosions, ulcers, hair loss at site
Describe the clinical signs of onchocerciasis
- Lesions on face (annular lesions on forehead very suggestive), neck, ventral abdomen, chest
- Start as thinning haircoat then generalised alopecia, scaling, crusting plaques
- May look severely excoriated ulcerated oozing, lichenified
- Leukodermadevelops and is irreversible
- Ocular lesions
Outline the diagnosis of onchocerciasis
- Skin biopsy
- Mince preparation or histopath to demonstrate presence of microfilaria
Describe the clinical signs of cutaneous habronemiasis
- Ulcerative nodules spring and summer
- Lesions on legs, urethral process of penis, prepuce, medial canthus of eye, conjunctiva, commissures of lips or any traumatised area of skin
- Mild to severe pruritus
- Lesions single or multiple, characterised by rapid development of granulomatous inflammation, ulceration, haemorrhage, exuberant granulation
- Small yellow granules may be seen within diseased tissue
- Is a differential for lesions that do not fit any other condition
Which horses are predisposed to habronemiasis?
- Young horses
- Arabs,
- Grey, palomino and dun horses
List the differential diagnoses for cutaneous habronemiasis
- Bacterial or fungal granuloma
- Eosinophilic granuloma
- Squamous cell carcinoma
- Sarcoid
- Exuberant granulation tissue
Outline the diagnosis of cutaneous habronemiasis
- Deep scrapings or smears from lesions to identify nematode larvae
- Biopsy: eosinophils,mast cells, coagulation necrosis, nematode larvae
Describe the general treatment of pediculosis
- Topical insecticides e.g. permethrins
- Ktreat all in contacts at same time, steam clean rugs
- Treatment 3x at 10-14 day intervals to cover life cycle length
- Licensed products for horses: permethrin, cypermethrin, piperonylbutxide +pyrethrum
What stages of the louse life cycle are killed by topical insecticides?
Only adults
What treatment can be used for sucking lice?
Ivermectin 02mg/kg q14 days
Describe the non-medical management for Chorioptes equi
- Pressure wash
- Jayes fluid
- Move horses outside
- Clean stables/barn thoroughly
- Clip hair
Describe the medical management of Chorioptes equi
- No licensed products
- Treat all in contacts at same time, 3x 1 week apart, then monthly
- Selenium sulphide shampoo, fipronil spray, lime sulphur dip/spray, doramectin injections, oral ivermectin past all suggested
Describe the use of fipronil spray in the treatment of Chorioptes equi
- Skin/hair must be saturated
- Expensive
- Must clip feathers, otherwise ineffective
Discuss the use of doramectin in the treatment of Chorioptes equi
- Depot injection
- Off licence
- 0.3mg/kg DC q14 days 3 treatments
- Need informed consent
Describe the treatment of Trombicula autumnalis
- Self limiting
- No licensed products, treat as for Chorioptes if needed
- Occasional need for systemic glucocorticoids
What is the suspected reason for pruritus with cutaneous habronemiasis?
Allergy to parasite
Describe the treatment for ticks in horses
- Mechanical removal or kill tick topically
- Oral ivermectin 200ug/kg
Describe the treatment for onchocerciasis
- Ivermectin 200ug/kg PO single dose causes remission of clinical signs within 2-3 weeks
- Repeat at monthly intervals 2-3 times if no remission
- Concurrent treatment with oral prednisolone 0.5mg/kg PO
Why is the use of prednisolone suggested in the treatment of onchocerciasis?
Death of microfilaria can lead to ventral oedema of pruritus 1-10 days post treatment, pred can reduce this problem
Discuss the treatment and management of habronemiasis
- No single optimal treatment, depends on lesion size, type, position etc.
- Combination of topical and systemic treatments
- Surgery/debulking may be required
- Cryotherapy
- Ivermectin/moxidectin 2 doses 21 day interval
- Glycocorticoids e.g. pred, dex, intralesional triamcinolone
- Cream mixtures: steroids + antibiotic +/- DMSO
- Fly control
- Removal of faeces from environment
What is sweet itch?
Hypersensitivity reaction to female Culicoides salivary proteins
Describe the disease profile of Culicoides hypersensitivity (predisposed individuals, seasonality, importance)
- Possible genetic basis, Icelandic pony, Shires and Welsh pony predisposed
- Starts 2-4yo
- Seen late Spring - late autumn
- recurrent seasonal pruritus,often worsens with age
- Significant welfare and management problem
What may be seen in chronic cases of Culicoides hypersensitivity?
Patchy mane and tail ridges suggesting lichenification from chronic itching and trauma
List the differential diagnoses for Culicoides hypersensitivity
- Mite infestiation
- Pediculosis
- Dermatophilus congolensis
- Dermatophytosis
- Onchocerca cervicalis
- Mane and tail dystrophy syndrome
- Fly, midge, mosquito worry
Describe the diagnosis confirmation of Culicoides hypersensitivity
- Clinical signs on mane, tail, rump,, ventral midline
- Papules, crusts, ulcers, thickened skin
- seasonality of clinical signs
- Intradermal testing can support diagnosis
- Skin biopsy, but is non-specific
What are the main aspects of management of Culicoides hypersensitivity?
- Elimination of exposure to biting midges
- Topical insecticides
- Control of itching
- Treatment of secondary infections
- Long term management
Outline how exposure to biting midges can be avoided
- Insect proof stable: line with netting, fine mesh screens, fans
- Stable horse mid afternoon to mid morning
- Total body covers, permethrin impregnated rugs
- Topical insecticidals e.g. pyrethryms, permethrin pour on, fly tags, citronella
Outline how itching due to Culicoides hypersensitivity can be controlled
- Systemic or topical corticosteroids
- Cavalesse cream and oral treatment (nicotinamide vit B3, marmite)
- Soothing shampoos e.g. aloe, oatmeal
- Benzyl benzoate (care, can be irritant)
Which corticosteroid would be best in the control of itching due to Culicoides and why?
Cavalesse - hydrocortisone topical, not systemically absorbed so reduces risk of laminitis
Outline the long term management of Culicoides hypersensitivity
- Essential fatty acid supplementation
- Vaccines in development
- De-sensitisation using Allergen Specific Immunotherapy (ASIT)
- Avoid breeding from affected animals
- Relocate to windy hillside or breezy coastal location
- Guarded prognosis
Describe the disease profile of atopic dermatitis in horses (prevalence, seasonality, common indoor and outdoor factors, concurrent disease)
- Very common
- Any breed, any age
- Seasonal depending on trigger
- Indoor: dorage/dust mites, moulds
- Outdoor: grass, tree, weed pollens
- Can have more than one allergy occuring in one horse at any one time
- Some evidence of inheritance
Describe the clinical signs of atopic dermatitis in horses
- Pruritus +/- urticaria
- Generalised or localised lesions
- Perennial or seasonal
Outline the diagnosis of atopic dermatitis in horses
- Rule out other potential causes
- Elimination/provocation testing
- Intradermal skin testing
- Serological testing of little or no value
When is the use of intradermal skin testing indicated in horses?
- If owner wants to pursue desensitisation programmes
- Helps define what animal is allergic to but long haul process
What are the aspects of atopic dermatitis treatment in horses?
- Allergen avoidance
- Symptomatic treatment
- Allergen specific immunotherapy
Outline allergen avoidance methods in the management of atopic dermatitis in horses
- Dust-free environment
- Keep at pasture if indoor allergen or total stabled if outdoor allergen, or move to new location
- Rubber matting in stable only
- Regular vacuuming/pressure washing of stable
- Store food in sealable containers to avoid contamination with mites
- Regular washing of tack, equipment and rugs at high temperatures ad use gentle non-bio cleaners where poss
- Can use anti-dust mite covers under rugs for barrier
What are the options for symptomatic treatment of atopic dermatitis in horses?
- Antihistamines
- Steroids
- Doxepin
- Topical spray
- Shampoos
- Cavalesse
Discuss the use of anti-histamines in the treatment of atopic dermatitis in horses, and give examples of drugs
- Alone/to reduce steroid dose needed
- Side effects incl. drownsiness or nervous/jittery behaviour
- Not licensed in horses
- e.g. hydroxyzine hydrochloride, chlorpheniramine, diphenylhydramine, cetirizine
Discuss the use of steroids in the treatment of atopic dermatitis in horses
- Anti-inflammatory doses e.g. pred 0.5-1mg/kg PO q24h until clinical signs controlled, then EOD reduced dosing
- No injectable pred but have injectable dex if needed immediately
Discuss the use of doxepin in the treatment of atopic dermatitis in horses
- Tricyclic antidepressant
- Well tolerated in horse
- Second choice if hydroxyzine doesn’t work and concerned re. steroid use
- 300-600mg per 500kg q12h, unlicensed
Discuss the use of topical steroid sprays in the treatment of atopic dermatitis in horses
- Hydrocortisone aceponate (cortavance)
- Unlicensed in horses
- ONly penetrates superficial dermis and not absorbed systemically, reduced risk of laminitis
Discuss the use of shampoos in the treatment of atopic dermatitis in horses
- To remove allergens and soothe etc
- Oatmeal or aloe vera effective
- Need 10 min contact time
- Mechanism of action unknown
Discuss the use of allergen specific immunotherapy in the treatment of atopic dermatitis in horses
- Based on IDST
- Aim to cause Ig switch so Ag exposure leads to normal IgG synthesis not IgE and reduce reaction with dermal mast cells
- Requires frequent subcut injections of increasing allergy concentration
- Protocols can take 1-2 year period
Discuss food allergy in horses
- Very rare
- Diagnose/treat with hypoallergenic diet for 8 weeks
List the common skin lumps and masses of horses
- Urticaria
- Sarcoid
- Melanoma
- Viral papilloma
- Eosinophilic granuloma
- Squamous cell carcinoma
List possible causes of urticaria in horses
- Insect bite/sting
- Atopic dermatitis
- Drug reactions
- Dermatographism (pressure induced)
- Exercise induced
- Cold induced
- Dermatophytosis
- Idiopathic
- Autoimmune disease
Describe the appearance of gyrate urticaria
Doughnut shape - ring with flat centre
Describe the clinical appearance of urticaria
- Multiple, raised oedematous papules, wheals and plaques
- Variable size and distribution
- Lesions pit on pressure
- Can be diffuse and ooze serum (angioedema)
- Variable pruritus
Describe the diagnosis of the cause of urticaria
- Full history
- Clinical signs: contact e.g. drip patterns, progressive lesions where O keeps applying topical treatment
- Eliminate other problems by skin scrape, coat brushings, tape strip etc.
- Skin biopsy in persistent cases (rule out causes)
- Dermatographism: write on skin with blunt object, wheal develops in few mins
List the differentials for urticaria in horses
- Dermatophytosis
- insect bites
- Erythema multiforme (central haemorrhagic focus in wheal, v rare)
- Contact hypersensitivity (rare, no wheals)
- Infectious/immune mediated vasculitis
Describe the appearance of infectious/immune mediated vasculitis
- Purpura haemorrhagica
- Cutaneous necrosis
- Diffuse angioedema
Discuss the treatment/management of urticaria in horses
- may resolve spontaneously if acute onset
- Remove contactant with warm water wash
- Avoidance of allergens
- Steroids: IV dex 0.05-0.1mg/kg
- In case of anaphylactic shock, combination of adrenaline NSAID/steroid may be needed
- Low dose steroisd, then decrease over 1-2 weeks
- Omega 3 fatty oilds
- Pentoxyphilline
Discuss the use of pentoxyphylline in the treatment of urticaria in horses
- concerns re. steroid use
- 10mg/kg BID PO has anti-inflammatory effect
- Side effect of hyperexcitability
- Off licence
- Only for use in serious cases
What are sarcoids? Prevalence?
- Common (35-90% of all skin neoplasms in horses)
- Fibroblastic tumour which may be locally aggressive and typically on-regressive
What is associated with increased susceptibolity to sarcoids in horses?
Certain equine leukocyte antigens (ELAs)
What are the predilection sites for sarcoids?
- Ventrum
- Inguinal region
- axilla
- Periocular region
- May occur at wounds
What are the 2 main things to consider with chronic, non-healing wounds in horses?
- Habronema
- Sarcoids
Outline the development of sarcoids
- BPV-1 suspected, transmission likely through biting/rubbing, fomites or insect vectors
- Genes expressed in sarcoids capable of neoplastic transformation, but whole viral particles not produced
List the different types of sarcoid
- Occult
- Nodular
- Verrucose
- Fibroblastic
- Malevolant
- Mixed
Describe the appearance of occult sarcoids
- Flat, very superficial
- foten just ring of altered pigment with focal alopecia extendig to scaly/hyperkeratotic kin
Describe the appearance of nodular sarcoids
- Well circumscribed within dermis or subcutis
- Overlying skin appears normal initially but can become ulcerated or traumatised
Describe the appearance of verrucose sarcoids
- Warty
- Raised hyperkeratotic and resembling papilloma
- Generally slow growing
Describe the appearance of fibroblastic sarcoids
- Proud flesh-like
- Raised, ulcerative, generally aggressive and extensive
- Often on chest, can be pedunculated
Describe malevolent sarcoids
- Malignant
- Often occur at sites of wounds or trauma
- Aggressive and deeply invasive with lymphatic spread and ulcerated nodules
Describe mixed sarcoids
Two or more different types in one lesion
Describe the appearance of viral papillomas
- Common in young horses only (<3yo)
- Warts/verrucae/grass warts often on muzzle or lips
- Less commonly on eyelid, external genitalia and distal limbs
- Initially small 1mm diameter raised grey/white papules followed by rapid growth to multiple hyperkeratotic lesions up to 2 cm diameter
- Numerous keratinous projections
Describe the aetiology of viral papillomas and the importance of this
- Viral - equine papillomavirus
- Contagious, so appropriate isolation of affected individuals required
Describe the treatment for viral papillomas
- Typically resolve spontaneously
- Other treatments include autogenous tumour vaccines
Describe aural plaques
- Common ear disease of adult horses
- Ear papillomas
- Almost always incidental findings
What is the cause of aural plaques?
Papilloma virus, probably due to fly transmission
Outline the treatment of aural plaques
- Rarely regress spontaneously, but only a cosmetic problem
- Do not attempt treatment
- Extremely variable and generally results in localised pain and discomfort
What are the 3 forms of cutaneous viral papilloma?
- Viral papillomas
- Aural plaques
- Equine genital papilloma
Describe equine genital papillomas
- Older horses
- Do not regress
- Probably precursor to some genital squamous cell carcinomas
Where do melanomas occur in horses?
- All grey horses will get melanomas
- But can happen in non-greys on non-pigmented skin
- Commonly perianal region, parotid salivary gland, sheath, guttural pouch
How do melanomas develop?
Altered melanin metabolism resulting in hyperplasia then subsequent malignancy
