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Dermatology 2 > Equine dermatology > Flashcards

Equine dermatology Flashcards

1
Q

What are the causes of allergic dermatitis in the horse?

A
  • Insect hypersensitivity e.g. Culicoides, fy bites
  • Atopy (rare)
  • Contact allergy (tack, tack cleaning products, creosote on fences, shampoos)
  • Food allergy (very rare)
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2
Q

What is the main cause of pruritus on the ears in horses?

A

Black flies

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3
Q

What are the main causes of pruritus on the mane of horses

A
  • Culicoides
  • Lice
  • Psoroptes
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4
Q

What are the main causes of pruritus on the tail of horses?

A
  • CUlicoides
  • Other insects
  • Lice
  • Pinworm
  • Food allergy
  • Psoroptes
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5
Q

What are the main causes of pruritus on the legs of horses?

A
  • Chorioptes
  • Habronemiasis
  • Dermatophytosis
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6
Q

What are the main causes of pruritus on the ventrum of horses, that is a: diffuse and b: focal

A

A: Culicoides, lice, dermatophytosis, other insects, onchocerciasis
B: horn fly dermatopphytosis
-Dermatophytosis as focal or diffuse depends on the individual

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7
Q

What are the potential causes of generalised pruritus in horses?

A
  • Food allergy
  • Dermatophytosis
  • Culicoides
  • Lice
  • Other insects
  • Urticaria
  • Drugs/drug reactions
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8
Q

What are the main causes of pruritus of the head/face in horses?

A
  • Culicoides
  • Other insects
  • Lice
  • Sarcoptes
  • Onchocerciasis
  • Dermatophytosis
  • Habronemiasis
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9
Q

What are the common, re-emerging, and other parasitic infection causes of pruritus in horses?

A
  • Common: lice, mites
  • Re-emerging: Habronema spp, pinworms (Oxyuris equi)
  • Other: ticks, Onchocerca spp.
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10
Q

Name the biting and sucking lice of horses

A
  • Biting/chewing: Weneckiella equi equi

- Sucking: Haematopinus asini

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11
Q

Name the mites that may affect horses, identifying those that are commonly seen

A
  • Common: Chorioptes equi, Trombicula autumnalis
  • rare/rarely cause pruritus: Psoroptes spp., Sarcoptes scabiei, Demodicosis, Dermanyssus gallinae (if housed with poultry)
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12
Q

Outline the importance of ticks in horses

A
  • Seen occasionally, mainly head, distal limb, groin and tail
  • Most common in spring/summer
  • Important re. disease transmission
  • Often geographical distribution
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13
Q

How does Onchocerca cervicalis cause disease in horses?

A
  • Nematode that lives in nuchal ligament

- Produces microfilariae that migrate to skin where they are ingested by intermediate host Culicoides

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14
Q

When is onchocerciasis usually seen in horses?

A
  • Usually spring when vector present in high numbers

- Horses >4yo

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15
Q

Name the parasites that cause habronemiasis in horses

A
  • Habronema muscae
  • Habronema majus
  • Drashia megastoma
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16
Q

How does habronemiasis occur?

A
  • 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
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17
Q

Describe the disease profile of pediculosis (life cycle, transmission, environmental survival, seasonality)

A
  • 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
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18
Q

In what group of horses is pediculosis most commonly seen?

A

Rescue cases

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19
Q

How is pediculosis diagnosed?

A

Easy to identify eggs with naked eye

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20
Q

Describe the disease profile of Chorioptes equi (life cycle, transmission, environmental survival, seasonality)

A
  • 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
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21
Q

Describe the clinical signs of Chorioptes equis

A
  • 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
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22
Q

Which limbs are typically more affected by Chorioptes equi?

A

Typically hind more than fore

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23
Q

Describe the diagnosis of Chorioptes equi

A
  • Superficial coat brushings/superficial scrapes
  • Tape strips of distal limb
  • Visualisation of mite
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24
Q

Describe the clinical signs of Trombicula autumnalis infestation

A
  • Intense pruritus
  • Orange/brown sticky patches of serum
  • Typically distal limbs, face, neck, thorax of horses at pasture
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25
Q

How is Trombicula diagnosed?

A
  • Unstained tape strip, skin scrapes

- Larvae only have 6 legs and are orange

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26
Q

Describe the appearance of tick lesions

A
  • Local reaction or general hypersensitivity

- Papular or pustular area, resulting in erosions, ulcers, hair loss at site

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27
Q

Describe the clinical signs of onchocerciasis

A
  • 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
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28
Q

Outline the diagnosis of onchocerciasis

A
  • Skin biopsy

- Mince preparation or histopath to demonstrate presence of microfilaria

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29
Q

Describe the clinical signs of cutaneous habronemiasis

A
  • 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
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30
Q

Which horses are predisposed to habronemiasis?

A
  • Young horses
  • Arabs,
  • Grey, palomino and dun horses
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31
Q

List the differential diagnoses for cutaneous habronemiasis

A
  • Bacterial or fungal granuloma
  • Eosinophilic granuloma
  • Squamous cell carcinoma
  • Sarcoid
  • Exuberant granulation tissue
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32
Q

Outline the diagnosis of cutaneous habronemiasis

A
  • Deep scrapings or smears from lesions to identify nematode larvae
  • Biopsy: eosinophils,mast cells, coagulation necrosis, nematode larvae
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33
Q

Describe the general treatment of pediculosis

A
  • 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
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34
Q

What stages of the louse life cycle are killed by topical insecticides?

A

Only adults

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35
Q

What treatment can be used for sucking lice?

A

Ivermectin 02mg/kg q14 days

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36
Q

Describe the non-medical management for Chorioptes equi

A
  • Pressure wash
  • Jayes fluid
  • Move horses outside
  • Clean stables/barn thoroughly
  • Clip hair
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37
Q

Describe the medical management of Chorioptes equi

A
  • 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
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38
Q

Describe the use of fipronil spray in the treatment of Chorioptes equi

A
  • Skin/hair must be saturated
  • Expensive
  • Must clip feathers, otherwise ineffective
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39
Q

Discuss the use of doramectin in the treatment of Chorioptes equi

A
  • Depot injection
  • Off licence
  • 0.3mg/kg DC q14 days 3 treatments
  • Need informed consent
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40
Q

Describe the treatment of Trombicula autumnalis

A
  • Self limiting
  • No licensed products, treat as for Chorioptes if needed
  • Occasional need for systemic glucocorticoids
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41
Q

What is the suspected reason for pruritus with cutaneous habronemiasis?

A

Allergy to parasite

42
Q

Describe the treatment for ticks in horses

A
  • Mechanical removal or kill tick topically

- Oral ivermectin 200ug/kg

43
Q

Describe the treatment for onchocerciasis

A
  • 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
44
Q

Why is the use of prednisolone suggested in the treatment of onchocerciasis?

A

Death of microfilaria can lead to ventral oedema of pruritus 1-10 days post treatment, pred can reduce this problem

45
Q

Discuss the treatment and management of habronemiasis

A
  • 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
46
Q

What is sweet itch?

A

Hypersensitivity reaction to female Culicoides salivary proteins

47
Q

Describe the disease profile of Culicoides hypersensitivity (predisposed individuals, seasonality, importance)

A
  • 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
48
Q

What may be seen in chronic cases of Culicoides hypersensitivity?

A

Patchy mane and tail ridges suggesting lichenification from chronic itching and trauma

49
Q

List the differential diagnoses for Culicoides hypersensitivity

A
  • Mite infestiation
  • Pediculosis
  • Dermatophilus congolensis
  • Dermatophytosis
  • Onchocerca cervicalis
  • Mane and tail dystrophy syndrome
  • Fly, midge, mosquito worry
50
Q

Describe the diagnosis confirmation of Culicoides hypersensitivity

A
  • 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
51
Q

What are the main aspects of management of Culicoides hypersensitivity?

A
  • Elimination of exposure to biting midges
  • Topical insecticides
  • Control of itching
  • Treatment of secondary infections
  • Long term management
52
Q

Outline how exposure to biting midges can be avoided

A
  • 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
53
Q

Outline how itching due to Culicoides hypersensitivity can be controlled

A
  • 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)
54
Q

Which corticosteroid would be best in the control of itching due to Culicoides and why?

A

Cavalesse - hydrocortisone topical, not systemically absorbed so reduces risk of laminitis

55
Q

Outline the long term management of Culicoides hypersensitivity

A
  • 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
56
Q

Describe the disease profile of atopic dermatitis in horses (prevalence, seasonality, common indoor and outdoor factors, concurrent disease)

A
  • 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
57
Q

Describe the clinical signs of atopic dermatitis in horses

A
  • Pruritus +/- urticaria
  • Generalised or localised lesions
  • Perennial or seasonal
58
Q

Outline the diagnosis of atopic dermatitis in horses

A
  • Rule out other potential causes
  • Elimination/provocation testing
  • Intradermal skin testing
  • Serological testing of little or no value
59
Q

When is the use of intradermal skin testing indicated in horses?

A
  • If owner wants to pursue desensitisation programmes

- Helps define what animal is allergic to but long haul process

60
Q

What are the aspects of atopic dermatitis treatment in horses?

A
  • Allergen avoidance
  • Symptomatic treatment
  • Allergen specific immunotherapy
61
Q

Outline allergen avoidance methods in the management of atopic dermatitis in horses

A
  • 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
62
Q

What are the options for symptomatic treatment of atopic dermatitis in horses?

A
  • Antihistamines
  • Steroids
  • Doxepin
  • Topical spray
  • Shampoos
  • Cavalesse
63
Q

Discuss the use of anti-histamines in the treatment of atopic dermatitis in horses, and give examples of drugs

A
  • 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
64
Q

Discuss the use of steroids in the treatment of atopic dermatitis in horses

A
  • 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
65
Q

Discuss the use of doxepin in the treatment of atopic dermatitis in horses

A
  • Tricyclic antidepressant
  • Well tolerated in horse
  • Second choice if hydroxyzine doesn’t work and concerned re. steroid use
  • 300-600mg per 500kg q12h, unlicensed
66
Q

Discuss the use of topical steroid sprays in the treatment of atopic dermatitis in horses

A
  • Hydrocortisone aceponate (cortavance)
  • Unlicensed in horses
  • ONly penetrates superficial dermis and not absorbed systemically, reduced risk of laminitis
67
Q

Discuss the use of shampoos in the treatment of atopic dermatitis in horses

A
  • To remove allergens and soothe etc
  • Oatmeal or aloe vera effective
  • Need 10 min contact time
  • Mechanism of action unknown
68
Q

Discuss the use of allergen specific immunotherapy in the treatment of atopic dermatitis in horses

A
  • 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
69
Q

Discuss food allergy in horses

A
  • Very rare

- Diagnose/treat with hypoallergenic diet for 8 weeks

70
Q

List the common skin lumps and masses of horses

A
  • Urticaria
  • Sarcoid
  • Melanoma
  • Viral papilloma
  • Eosinophilic granuloma
  • Squamous cell carcinoma
71
Q

List possible causes of urticaria in horses

A
  • Insect bite/sting
  • Atopic dermatitis
  • Drug reactions
  • Dermatographism (pressure induced)
  • Exercise induced
  • Cold induced
  • Dermatophytosis
  • Idiopathic
  • Autoimmune disease
72
Q

Describe the appearance of gyrate urticaria

A

Doughnut shape - ring with flat centre

73
Q

Describe the clinical appearance of urticaria

A
  • Multiple, raised oedematous papules, wheals and plaques
  • Variable size and distribution
  • Lesions pit on pressure
  • Can be diffuse and ooze serum (angioedema)
  • Variable pruritus
74
Q

Describe the diagnosis of the cause of urticaria

A
  • 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
75
Q

List the differentials for urticaria in horses

A
  • Dermatophytosis
  • insect bites
  • Erythema multiforme (central haemorrhagic focus in wheal, v rare)
  • Contact hypersensitivity (rare, no wheals)
  • Infectious/immune mediated vasculitis
76
Q

Describe the appearance of infectious/immune mediated vasculitis

A
  • Purpura haemorrhagica
  • Cutaneous necrosis
  • Diffuse angioedema
77
Q

Discuss the treatment/management of urticaria in horses

A
  • 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
78
Q

Discuss the use of pentoxyphylline in the treatment of urticaria in horses

A
  • concerns re. steroid use
  • 10mg/kg BID PO has anti-inflammatory effect
  • Side effect of hyperexcitability
  • Off licence
  • Only for use in serious cases
79
Q

What are sarcoids? Prevalence?

A
  • Common (35-90% of all skin neoplasms in horses)

- Fibroblastic tumour which may be locally aggressive and typically on-regressive

80
Q

What is associated with increased susceptibolity to sarcoids in horses?

A

Certain equine leukocyte antigens (ELAs)

81
Q

What are the predilection sites for sarcoids?

A
  • Ventrum
  • Inguinal region
  • axilla
  • Periocular region
  • May occur at wounds
82
Q

What are the 2 main things to consider with chronic, non-healing wounds in horses?

A
  • Habronema

- Sarcoids

83
Q

Outline the development of sarcoids

A
  • 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
84
Q

List the different types of sarcoid

A
  • Occult
  • Nodular
  • Verrucose
  • Fibroblastic
  • Malevolant
  • Mixed
85
Q

Describe the appearance of occult sarcoids

A
  • Flat, very superficial

- foten just ring of altered pigment with focal alopecia extendig to scaly/hyperkeratotic kin

86
Q

Describe the appearance of nodular sarcoids

A
  • Well circumscribed within dermis or subcutis

- Overlying skin appears normal initially but can become ulcerated or traumatised

87
Q

Describe the appearance of verrucose sarcoids

A
  • Warty
  • Raised hyperkeratotic and resembling papilloma
  • Generally slow growing
88
Q

Describe the appearance of fibroblastic sarcoids

A
  • Proud flesh-like
  • Raised, ulcerative, generally aggressive and extensive
  • Often on chest, can be pedunculated
89
Q

Describe malevolent sarcoids

A
  • Malignant
  • Often occur at sites of wounds or trauma
  • Aggressive and deeply invasive with lymphatic spread and ulcerated nodules
90
Q

Describe mixed sarcoids

A

Two or more different types in one lesion

91
Q

Describe the appearance of viral papillomas

A
  • 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
92
Q

Describe the aetiology of viral papillomas and the importance of this

A
  • Viral - equine papillomavirus

- Contagious, so appropriate isolation of affected individuals required

93
Q

Describe the treatment for viral papillomas

A
  • Typically resolve spontaneously

- Other treatments include autogenous tumour vaccines

94
Q

Describe aural plaques

A
  • Common ear disease of adult horses
  • Ear papillomas
  • Almost always incidental findings
95
Q

What is the cause of aural plaques?

A

Papilloma virus, probably due to fly transmission

96
Q

Outline the treatment of aural plaques

A
  • Rarely regress spontaneously, but only a cosmetic problem
  • Do not attempt treatment
  • Extremely variable and generally results in localised pain and discomfort
97
Q

What are the 3 forms of cutaneous viral papilloma?

A
  • Viral papillomas
  • Aural plaques
  • Equine genital papilloma
98
Q

Describe equine genital papillomas

A
  • Older horses
  • Do not regress
  • Probably precursor to some genital squamous cell carcinomas
99
Q

Where do melanomas occur in horses?

A
  • 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
100
Q

How do melanomas develop?

A

Altered melanin metabolism resulting in hyperplasia then subsequent malignancy

Dermatology 2 (23 decks)

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