Equine dermatology 1 Flashcards
What are the d/dx for pruritis in the horse?
Parasite Infestation-
- common causes: lice, mites
- re-emerging causes: Habronema spp., pinworms (oxyuris equi)Seeing that more often due to worming resistance.
- other causes: Ticks, Onchocera spp., bacterial and fungal infections
Allergic dermatitis-
- Insect hypersensitivity- Culicoides spp., fly bites
- Atopy
- Contact allergy (substances rugs and tack may have been washed in)
- Food allergy (RARE!)
Which 2 lice are common causes of pediculosis in horses?
Biting/chewing- Werneckiella equi equi (previously Damalinia equi) LEFT
Sucking- Haematopinus asini RIGHT
What is the disease profile of pediculosis?
- Highly host specific
- Entire life cycle is spent on the horse
- Transmission à direct or indirect
- Contagious
- Can live off host à right environment à 2-4 weeks
- Seasonal- more common autumn/winter
- Associated with
- Debilitated
- stressed
- diseased animals
- poor nutrition
- overcrowding
What are the clinical signs of pediculosis?
- Really itchy
- Lice love heat so if you shine a light or put hands on horse lice will crawl towards it
- Evidence –> self trauma
- Variable hair loss –> horses bite/ rub
- flanks, jaw, outer limbs
- Broken hairs, excoriation, scaling
- Mature lice + eggs = visible to naked eye
- mane, tail, forelock
- Occasionally with haematopinus asini –> anaemia, hypoproteinaemia
How is pediculosis diagnosed?
- Tape strips / coat brushings best way to get samples
- Also warm hands! And bright light
- Easy identification under light microscope
What is the treatment for perdiculosis?
- Topical insecticides – permethrins licensed in horses
- Kill adults BUT not eggs
- Treat all in contacts at the same time, steam clean rugs
- Treatment at 3 x at 10-14 day intervals à allow for egg hatching and incubation period
- Note: a lot of louse powders are for environment not horse eg. Battles
- Sucking lice: ivermectin 0.2mg/kg q 14days x 3
- Licensed products
- permethrin ( Switch, Coopers Fly Repellent Plus )
- Cypermethrin ( Deosect)
- piperonylbutoxide+pyrethrum (dermoline shampoo)
What is the disease profile for Mites (Chorioptes equi)?
- Surface mite –> feeds on epidermal debris
- Heavily feathered breeds
- eg. cobs, shires, Clydesdales
- BUT can be seen in short coated horses
- Adults can survive off-host –> 2 months
- Transmission –> direct or indirect contact
- Mite populations often greatest in winter during periods of cold weather
What are the clinical signs of Chorioptes equi mite?
- Moderate –> severe pruritus
- usually on limbs ( hind limbs >forelimbs) but NOT exclusively (can be ventrum and dorsum)
- Particularly –> heavy horses-crusting, scaling, exudative lesions,
- blood staining, hair matting, skin thickening (due to self trauma)
- Secondary infection common
- Stamping of hind limbs
- Rubbing heels against gates and fences
- Chewing limbs
- Dragging belly a long floor
- In short haired breeds , often no stamping but more generalised “moth-eaten” appearance
Chorioptes equi – diagnosis and treatment?
Identification:
- Superficial coat brushings/ multiple scrapes eg. With medical spatula
- tape strips- distal limb
- Visualisation of mite –> light microscope / naked eye on a black background
Treatment :
- Environment- pressure wash, jayes fluid, move horses outside
- Treat ALL in contacts at same time, even if do not seem affected x3 times 1 week apart , then monthly
- Can be VERY difficult to eliminate
- Clip hair!!
- No UK veterinary licensed products
- There are publications describing the use of
- Selenium sulphide shampoo- q 14 days 3 applications
- Fipronil spray- skin/hair must be saturated
- Lime sulphur dips/sprays- q48h for 6 weeks (stains yellow)
- Doramectin injections- 0.3mg/kg SC q 14 days 3 treatments (depot injection under the skin NEVER GIVE IV)
- Oral ivermectin paste – 0.2mg/kg PO q 14days 3 treatments
What mite is this and what may an infestation with this look like?
Mites- Trombicula autumnalis
- “harvest mite”- adults are free living in vegetation occurs in UK at harvest time Jul-Aug
- in areas where chalk soil
- Sometimes present in hay/straw
Clinical signs:
- Intense pruritus
- Orange/brown sticky patches serum
- Distal limbs, face, neck, thorax of horses at pasture
Diagnosis:
- ID parasite on tape strip/skin scrapes
- Larvae –> 6 legs, orange colour
Treatment:
- Self-limiting infection
- No licensed products – tx as for Chorioptes
- Occasional need for systemic glucocorticoids to break the itch cycle
Ticks are seen occasional what should you do if you see them on a horse?
TX: mechanical removal, kill tick topically, oral ivermectin 200µg/KG
Discuss the culicoides hypersensitivity – disease profile?
“Sweet itch”
- Has two phases Type I ( within 6h of the bite) and Type IV Hypersensitivity reaction to salivary proteins –> females Culicoides spp. Only
- Evidence for possible genetic basis and breed predisposition(Icelandic pony, shires, welsh pony)
- Starts at 2-4 y.o
- Seen late spring- late autumn
- Recurrent seasonal pruritus –> often progressive (as they get older the problem/reaction gets worse)
- Significant welfare and management problem
What are the d/dx for culicoides hypersensitivity?
DDX:
- Mite infestation
- Pediculosis
- Dermatophilus congolensis
- Dermatophytosis
- Onchocerca cervicalis
- Mane and tail dystrophy syndrome
- Fly, midge, mosquito worry
How is culicoides hypersensitivity diagnosed?
Clinical signs
- Mane, tail, rump, ventral midline
- Papules, crusts, ulcers, thickened skin
- Seasonality and clinical signs
- Intra-dermal testing can support diagnosis
- Skin biopsy non-specific
How is culicoides hypersensitivty managed?
- Elimination of exposure to biting midges!
- Insect proof the stable- line with netting, fine mesh screens, fans as midges are not strong fliers
- stable horse from mid-afternoon to mid-morning when midges most active
- Total body covers eg. Boett blankets, permethrin impregnated rugs
- Topical insecticidal – don’t forget belly
- Pyrethrums- coopers fly repellent, Switch pour on, fly tags, citronella
Control of itching
- systemic or topical corticosteroids (cortavance- hydrocortisone) have to be careful with laminitis
- cavalesse cream and oral treatment – nicotinamide vit B3 (marmite)
- Soothing shampoos- aloe/oatmeal
- Benzyl benzoate – care as can be irritant
- Tx of any secondary infection – abi, medicated shampoos
- ??Essential fatty acid supplementation
- Vaccines- Benchmark/Evax AG – Swiss biotech companies-currently making a vaccine for release 2020-2021
- –De-sensitisation using allergen specific immunotherapy (ASIT)
- So far trials unsuccessful but anecdotal evidence
- ?? Should we breed from affected animals
- Beware at vettings
- GUARDED PROGNOSIS these don’t get better
- Re locate to windy hillside or breezy coastal location or long-term control management. These horses can be a lot better in different environments
Discuss Cutaenous Habronemiasis?
- Nematodes Habronema muscae, H. Majus, Draschia megastoma- deposited on wounds by flies (house and stable fly).
- Adults live in the stomach –> produce larvae, these are passed in faeces and ingested by maggots of the intermediate hosts.
- Intermediate hosts deposits larvae near mouth of horse –> swallows them
- Ulcerative nodules seen spring and summer
- A recent study suggests young horses, Arabs, grey, palomino, dun horses may be predisposed
- Lesions commonly on legs, urethral process of penis, prepuce, medial canthus of eye, conjunctiva, commisures of lips or any traumatised area of skin
- Pruritus most likely due to allergy to parasite , mild –> severe
- Lesions single or multiple, characterised by rapid development of granulomatous inflammation, ulceration, haemorrhage, exuberant granulation
- Small yellow granules may be seen within diseased tissue
What are the d/dx for cutaneous habronemiasis?
DDX:
Bacterial or fungal granuloma
Eosinophilic granuloma
Squamous cell carcimoma
Sarcoid
Exuberant granulation tissue
How is cutaneous habronemiasis diagnosed and treated?
Diagnosis:
- Deep scrapings or smears from lesions- nematode larvae
- Biopsy- eosinophils, mast cells, coagulation necrosis, nematode larvae
Treatment:
- No one optimal tx , depends on lesion size, type, position etc
- Combination of topical and systemic tx
- Sx/de-baulking
- Cryotherapy
- Ivermectin or moxidectin 2 doses at 21 day interval
- Glucocorticoids: prednisolone PO 1 mg/kg, dexamethasone 0.04mg/kg PO, intralesional triamcinolone
- Cream mixtures- steroid + abi+/- DMSO
- Fly control
- Removal of faeces from environment
Discuss atopic dermatitis in equine medicine?
- Allergic skin disease VERY commonly seen in equine practice
- Hypersensitivity –> environmental trigger
- Any breed
- Any age
- ? Seasonality
- “indoor” related factors eg. Forage/dust mites, moulds
- “outdoor” related factors eg. Grass, tree, weed pollens
- Note can have more than one allergy going on in one horse at same time eg. Culicoides and atopy
- Lesion distribution in the horse not well defined
- Some evidence of familial inheritance? Do not breed from affected animals
What are the clinical signs of urticaria?
Clinical signs
- Multiple, raised oedematous papules, wheals, plaques
- Variable size
- Variable distribution- commonly head, neck, trunk
- Lesions pit on pressure
- Doughnut shape = gyrate form but appearance doesn’t correlate with underling cause!
- Can be diffuse and ooze serum = angioedma
- Variable pruritus
What kind of sarcoid is this?
Occult (flat): very superficial, often just a ring of altered pigment with focal alopecia extending to scaly/hyperkeratotic skin
What kind of sarcoid is this?
Nodular: well circumscribed within the dermis or subcutis. Overlying skin appears normal initially but can become ulcerated or traumatised.
What kind of sarcoid is this?
Verrucose (warty): raised, hyperkeratotic and resembling papilloma (but any “wart” on a horse is a sarcoid unless proved otherwise). Generally slow-growing.
What kind of sarcoid is this?
Fibroblastic (“proud flesh”-like): raised, ulcerative, and generally aggressive and extensive. Can be pedunculated. Can be bleeding. Only one that does not have a dermal covering over it, it is ulcerated.
What kind of sarcoid is this?
Malevolant (“malignant”): often occur at the sites of wounds or trauma. Aggressive and deeply invasive with lymphatic spread and ulcerated nodules/ Extension of sarcoid under skin surface
What kind of sarcoid is this?
Mixed: two or more different types
What is the treatment for sarcoids?
Surgical removal
Sharp excision - smaller sarcoids (e.g. nodular) but failure rate high
Laser excision –> higher success rate –> now widely available
Ligation
Some owners will use hair tails – NOT a good plan!
DON’T use unless you are sure there is no root
Elastrator rings useful for some nodular and pedunculated fibroblastic sarcoids
Cryosurgery
Only useful for small superficial tumours (need to freeze/thaw tissues
Time-consuming, and high-recurrence rate if not used effectively
Immuno-therapy
BCG injection into the lesions can be effective for peri-ocular nodular or fibroblastic lesions
Does not work for verrucose or occult lesions
Not currently available to vets in UK
Chemotherapy
Intra-lesional injection of cytotoxic drugs –> cisplatin, mitomycin C, 5-fluoro-uracil
Can be effective but significant dangers to surgeon: not recommended
Topical 5-FU can be effective
Photodynamic therapy
Application of chemical to lesion —-> significant cell damage when exposed to a certain wavelength of light
Poor penetration - only applicable to very small, superficial lesions, side-effects when animal exposed to sunlight
Topical cytotoxic therapy
AW5-LUDES (“Liverpool cream”) contains 5-FU and other heavy metals
Reasonably effective in certain circumstances, requires repeated topical application every 48-72 hours
Only available through Derek Knottenbelt
Health and safety concerns
Vaseline over the normal skin before application
Everything else (imiquimod, acyclovir, bloodroot ointment, bleomycin, topical mitomycin C, tazarotene….)
Radiotherapy
Iridium wires no longer available in UK
High dose rate brachytherapy - very high activity iridium 192 source, emits primarily gamma radiation – catheters implanted into lesion; source driven through catheters by remote afterloader, treatment takes only a few minutes and is delivered in two fractions a week apart – horse not radioactive between treatments, no operator exposure
Excellent cosmesis and success around 95%, but expensive (£3800 -£4800 dependant on lesion size , available at AHT only for periocular lesions
Treat early for best results!
What is this?
- Common, but only seen in young horses (<3 years old)
- 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 2cm in diameter
- Numerous keratinous projections
- Typically respond spontaneously
- Other treatments included autogenous tumour vaccines
- Viral aetiology (equine papillomavirus, a DNA papovavirus)
- Is contagious and therefore appropriate isolation may be required
- Potentially contagious as it is a virus
What are these?
Aural plaques
- Common disease of adult horses
- Ear papillomas
- ? Fly transmission
- Almost always an incidental finding
- However, rarely, if ever, regress
- Cosmetic problem only
- DO NOT attempt treatment
- Many anecdotal/isolated case reports have been attempted
- Extremely variable and generally result in localised pain and discomfort
What is this?
Melanoma
-
A grey horse disease?
- Any skin mass could be a melanoma
- Any unexplained disorder could be a melanoma
- All grey horses will get them eventually! (Reassure owners they are not the same as human melanomas but they can/will become pathologically malignant)
- Common sites include perianal region, parotid salivary gland, sheath…. and guttural pouch
- Altered melanin metabolism results in hyperplasia then subsequent malignancy
- Typically, but not exclusively grey or white horses
- Middle aged to older horses
- Do not confuse with rarer melanocytoma (melanocytic nevi)
- Benign and no coat predilection, surgical excision curative
- Usually young horses
What is the treatment for melanomas?
- Benign neglect/monitor
- Standard approach but all lesions will progress
- Cimetidine?
- Evidence is contradictory
- Surgical removal
- Wide surgical excision required for larger lesions
- Intra-lesional treatments
- Cisplatin, mitomycin C (health and safety concerns)
- Vaccines/immunotherapy??
- Vaccine-based therapy available but expensive (approx.£2000 for initial course, then £500/vaccine thereafter and unproven although reports of 50% success rates
What is this?
Eosinophilic granuloma
- Nodular lesions commonly in the saddle area
- Precise cause and pathogenesis unknown
- Often occur in spring and summer so often attributed to fly hypersensitivity or atopic dermatitis
- Other authors suggest trauma
- Often called collagen necrosis or similar names although not entirely accurate histopathologically
Treatment
- Intra- or peri-lesional steroids (methylprednisolone or triamcinolone)
- Systemic steroids (prednisolone or dexamethasone)
- In an annoying place on dorsum under saddle
What is this?
Squamous cell carcinoma
- Malignant neoplasm of keratinocytes
- Can spread either along lymphatic chains or by direct transplantation
- Sites: face, eyelids/cornea/globe, genitalia
- Can occur anywhere but typically at mucocutaneous junctions
- Risk factors: susceptibility to UV light, smegma?
- Second most common cutaneous tumour
- Most common tumour genitalia
- Also common periocular lesion, esp third eyelid
- Common in pink skinned horses
- Smeg is risk factor.
Melanoma rostral, Squamous Cell Carcinoma caudal and top lid a nodular sarcoid.
