Skin disease 1 Flashcards
What is pruritus?
Unpleasant sensation that provokes the desire to scratch
- C-polymodal receptor units with C axons localised around hair follicle
Local release of vasoactive substances stimulates
* Histamine
* Eicosanoids
* Serotonin
* Kallikrein
* Bradykinin
What are the 3 broad causes of pruritus?
Ectoparasites
* Mites
* Lice
* Biting flies/insects
* Oxyuris equi
Hypersensitivity
* Culicoides-induced
* Atopic dermatitis
* Food allergy
* Contact allergy
Drug reactions
* Trimethoprim/Sulfonamides
* Macrocyclic lactones
* Vaccines
* Shampoos/ creams
Where is the pruritus most likely to be located depending on the cause?
Trombicula autumnalis
- distal limbs
- dorsum and neck
- face
Chorioptes mites
- distal limbs
- face
Oxyuris equi
- tail head/rump
Atopic dermatitis (food allergy & drug reactions)
- ventral midline
- distal limbs
- dorsum and neck
- tail head and rump
- trunk/body/flanks
- face
Culicoides hypersensitivity
- ventral midline
- dorsum and neck
- tail head/rump
Louse infestation
- dorsum and neck
- tail head/rump
- trunk/body/flanks
- face
What are the most common mites in the horse? What season are they most common in? What clinical signs are associated?
Chorioptes equi
* Distal limb +++
* Groin/abdomen
* Winter
* (asymptomatic horses as carriers)
* Draft breeds with dense feathering
* Rubbing distal limbs, biting, stamping
* Exudation, matting of the hair, alopecia, scabs, secondary bacterial infections
Trombicula autunnalis
* Head and legs (+++)
* Autumn/winter
* (contaminated hay/straw bedding)
* All, dense feathering most likely
* Biting, stamping,
* Small papules pastern, nose
Psoroptes equi
* Head, tail
* ears
* All year around
* All horses
* Tail rubbing, broken tail hairs, scaling of ears, ear discharge
Dermanyssus gallinae
* Legs, face, and abdomen
* Contact with poultry
* All horses
* Small orange/red mite.
* Biting/stamping legs
* Small papules/crusts
Identify these ectoparasites
- chorioptes
- psoroptes
- trombicula
How can you control and treat chorioptes equi?
Control
- Clip feathers/hair and burn the hair subsequently
- highly infectious: treat all horses on the property might be necessary, dinsinfecting stables and allowing them time to rest (At least 70 days = ideally)
- extensive disinfection of tack
- re-occurence frequent: regular treatments in affected horses
Treatment
- Doramectin injections SC/IM single injection or 2 injections 2 weeks apart (ivermectin is not recommended due to high incidence of side effects)
- 0.25% fipronil spray daily application for 1 week, then weekly for 4 weeks
- 5% lime sulphrur solution applied weekly for 1 month
How can you control and treat trombicula autumnalis?
Control
- remove straw bedding
- avoid infected tall grass or woods
- normally self-limiting but migh need some local treatment
Treatment
- lime sulphur solution
- pyrethrin spray daily application for 1 week, then weekly for 4 weeks
- 0.25% fipronil spray daily application for 1 week, then weekly for 4 weeks
- if severe pruritus, short term steroid therapy might be required to avoid self trauma
How can you control and treat psoroptes equi?
Control
- Remove organic debris from the stables
- make sure the stable is dry and well ventilated
- disinfection of stable is required and resting period around 70 days
- disinfection of tack required
Treatment
- otitis is responsive to oral macrocytic lactones (ivermectin or moxidectin)
- lime sulphur solution every week for 1 month
- pyrethrin spray every week for 1 month
Where is pruritus located with louse infestations? When are they most common? What clinical signs are associated? How can you differentiate the 2 types of louse?
- More common in winter months
- Crowed barns
- “Moth-eaten” “Snow flake” appearance coat
- Mane, base of tail and dorsum most common
- Severe pruritus, self-mutilating, biting, rubbing
- Alopecia, excoriation, serum exudation
Biting lice: small, yellowish, broad flatted head feeds on scales
Sucking Lice: dark colour blood sucking, narrow head, slightly bigger
How can lice be controlled and treated?
Control
- Clean the stable and disinfect with diluted bleach (10%), rinse and let it dry
- treatment of in contact horses might be required
- wash tack (particularly rugs, saddle pads) 60 degree washing and/or permethrin application
Treatment
- permethrin pour on
- 0.25% fipronil spray
- 1% Se sulphide shampoo q 10 days (3 times)
Where do oxyuris equi settle in the horse? What signs are associated? How is it treated?
- The female worms are large, grey worms (>10cm in), with a long pointed tail. The male worms are smaller (<1cm)
- Live attached to caecum and colon mucosa
- Once the female is fertilised migrates to anus to lay eggs>intense pruritus
- Rubbing tail, broken hair on tail head, abrasions on perineum
- More common in young horses never treated with ivermectin
- Treatment: Ivermectin (some resistance documented), pyrantel, fenbendazole by mouth
What type of hypersensitivity is associated to sweet itch? When does it develop? What season of the year is worst for it?
- Insect-Bite (Culicoides hypersensitivity) AKA Sweet-itch
- Salivary antigens of Culicoides gnats, flies (black and stable)
- Type I: immediate and late phase response
- Type IV: delayed response
- Most common allergic and pruritic condition in the horse
- Increase risk in some breeds: genetic predisposition?
- Icelandic, German shire horses, Welsh, Shetlands, Connemara..
- Develops early in live (3-4yo) but worsen with age
- Seasonal presentation: Spring-early autumn
- Wet areas, riverside, marshes…
Where are lesions located with sweet itch? What other clinical signs are associated?
- Dorsal or ventral distribution , or a combination
- Rubbing against object, chewing dorsum
- Crusted papules: mane, rump, base of the tail that extend to face, pinna, neck
- Chronic cases: excoriation, alopecia, lignification, secondary bacterial infections (superficial folliculitis)
How can culicoides hypersensitivity be managed?
- Keep horses away from premises near water sources, decaying vegetation, and manure
- Keep horses in stables at night with fly-screen (32-mesh) on windows, and/or use middle stables: Gnats/midges feed at dusk/dawn:
- if no stable available fly –sheet should be maintained all day
- Clean regularly water troughs
- Keep fly-shit cover while on pasture (Spring- Autumn)
- Time-operating insecticide spray system in the barn
- Stall window fans (20 inches)> midges are poor fliers
- Apply permethrin pour-on (++) or any other fly repellent
- Short course of steroids might be required : pruritus
Alternative and novel therapies
* Insol vaccine: manufactured for control of ringworm in horses, but recognised as an off-licence treatment option. Promising results: Significant reduction in clinical signs when the vaccine is given before the midge season (Feb)- 2 weeks apart
* Allergen-specific immunotherapy: Intradermal consecutive injections
* Immunotherapy with IL-5 blockers: Three subcutaneous injections at monthly intervals, followed by an annual booster. Still experimental
What feeds are most commonly associated with food allergies? What type of hypersensitivity is associated?
- Alfalfa, barley, beet pulp, bran, clover
- Feed additives and supplements
type 1
What lesions are associated with contact dermatitis? What type of hypersensitivity is it?
Erythema, oedema, oozing leading to alopecia and lichenification
Type 4 hypersensitivity
What is urticaria?
- Immunologic reaction against allergens in contact with the skin, inhaled, ingested or injected and dermal pressure
- nettle, daisy, dandelion, horse chestnut, Hair: cat, cattle, sheep and pigeon
- stimulus causes histamine release which increases vascular permeability and forms angioedema and oedematous papules/plaques
How can urticaria be managed?
- Identify trigger: very important to avoid relapse
- Wash skin if environmental trigger or contact reaction suspected
- Cold hosing might improve clinical signs
- Steroids 0.05-1mg/kg IV (1-2 doses)
- Cetirizine at 0.2–0.4 mg/kg bwt PO q. 12 h 3-4 days
- Hydroxyzine hydrochloride/ pamoate
- Omega fatty acids
What are the 2 types of hypopigmentation?
Vitiligo & alopecia areata
What is vitiligo? Where is it usually present? How is it treated?
- Idiopathic depigmentation
- Most common in grey horses
- Andalusian
- Arabs
- Around eyes and lips
- No treatment=permanent change
What is alopecia areata? How can you confirm its diagnosis?
- Auto-immune disease
- Non-pruritic progressive thinning mane and tail
- Areas of alopecia
- Leukotrichia
- Exclamation shape hair bulb but
- Biopsy for confirmation
