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