LA Dermatology

Question 1

Is non-pigmented skin more prone to issues than pigmented skin in horses?

Answer 1

Yes.
The probability of suffering from sunburn and hoof of lesser quality was increased in animals with an elevated white marking index. Those with lighter skin have an increased risk of suffering pastern dermatitis.

Question 2

What ectoparasites typically affect the distal limb of the horse?

Answer 2

Chorioptes bovis.
Ixodes (and muzzles).
Thrombiculids.

Question 3

Clinical presentation of pastern dermatitis.

Answer 3

Owner reports pain, stamping, rubbing, biting, resents touch locally.
You find lameness, swollen limb, local oedema, crusting, hyperkeratosis.
Feathers may obscure lots!
Feathers may cause an ideal and sweaty environment for mites to thrive.

Question 4

Name factors contributing to pastern dermatitis, other than chorioptes.

Answer 4

Humidity, lack of hygiene, bacterial infection (staph.), mud, wet ground, environmental irritants.

Question 5

Main skin allergy seen in horses?

Answer 5

Culicoides hypersensitivity (sweet itch).

Question 6

1. What is pastern dermatitis?
2. Non-contagious causes of pastern dermatitis?
3. Contagious causes of pastern dermatitis.

Answer 6

1. Inflammation of the skin in the pastern region. Wetting often makes worse.
2. Vasculitis.
   Photosensitisation - primary (ingestion), secondary (liver failure).
3. Dermatophilus congolensis - “mud fever”.
   Staphylococcus - “folliculitis”.
   Chorioptic mange - “feather mites”.
   Trobicula autumnalis - “harvest mites”.

Question 7

Management and treatment of pastern dermatitis - appropriate to aetiology.

Answer 7

Clip limbs.
- may need sedation and/or analgesia to achieve.
- sterilise clippers after.
Movement to stop swelling/oedema - ideally in clean environment.
Medicated shampoo - chlorhexidine (S. aureus), Seleen (parasites), sebolytic (if hyperkeratosis).
Silver sulphadiazine (Flamazine) (can help make ulcerated areas under crusts more comfortable - anti-inflammatory and antimicrobial).
Lime and sulphur (Lime plus).
Sunblock (if photosensitisation).
Analgesia (NSAIDs - oral butorphanol – 4.4mg/kg down to 2.2mg/kg).
Doramectin-Dectomax (if mites).
ABX - topical or systemic.

Question 8

Common cause of pruritus in horses that may be seen in field mates (not solo horse).

Answer 8

Culicoides and hypersensitivity to their bites (sweet itch).
Lice/pediculosis.
Mud fever (Dermatophilus congolensis).

Question 9

Equine pruritus causes.

Answer 9

Infectious - S. aureus (Dermatophilus).
Parasites - flies, lice, mites.
Photosensitisation.
Allergy - hypersensitivity, atopy.
Contact reaction - “scalding” (cold be iatrogenic).
Primary or secondary cause?
- PPID (Pituitary Pars Intermedia Dysfunction) may lead to chronic skin infections.

Question 10

Common cause of alopecia in horses?

Answer 10

Dermatophytosis (primary).
Lice&raquo_space; pruritus&raquo_space; rubbing&raquo_space; alopecia.
Sweet itch&raquo_space; rub&raquo_space; alopecia.
Sweat rub/rug rub.
Self-trauma.
Pruritus.
Folliculitis.
Pemphigus (very rare).

Question 11

Distinguishing between sucking lice and chewing lice?

Answer 11

Sucking lice = pointy head.
Chewing lice = blunt head.

Question 12

Clinical presentation and diagnosis of lice in horses.

Answer 12

Present with:
- alopecia – moth-eaten pattern.
- pruritus.
- scale (scurf).
- ill thrift? – more prone as lice opportunistic.
Diagnosis:
- visible to naked eye – adult lice and eggs stuck on hair shafts.
- migrate away from cold (rug, remove and look).
- microscopy? – only tells what family of lice they are but not much more than that.

Question 13

1. Management of lice?
2. What treatments for lice are licensed for horses?

Answer 13

1. Clip, wash/bath, clean equipment - wash rugs, headcollars, grooming kit (50 degrees C sufficient to kill lice).
2. Cypermethrin (in Deosect).
   - 10ml soltion in 500ml water, delivered as a fine mist at 500ml per horse or 125ml per pony.
   - repeat at <14d intervals to kill hatchlings.
   - has a withdrawal period.
   - not to be used in animals intended for human consumption.

Question 14

What sampling may be taken in sheep with variable wool loss and some showing severe pruritus?

Answer 14

Skin scrape.
To view under microscopy.
Likely to be psoroptic mites (Psoroptes ovis causes sheep scab).

Question 15

Tx of sheep scab?

Answer 15

Challenging.
Reinfection common - from environment (handling facilities, fences etc.) and other sheep.
Important to take a blanket approach to eradicate.
Macrocytic lactones:
- Ivermectin – 2 injections 7d apart, care w/ resistance, SCOPS principles e.g. weighing to accurately dose, dosing gun calibration, treating the right animals. /Moxidectin/Doramectin).
Plunge dips - organophosphates (OP).
- highly toxic.
- certificate of competence needed – “mobile dippers” –> correct disposal.

Question 16

Overweight sheep, isolated, laying down a lot, full fleece in May, high RR, high HR, normal rumen turnover, normal temperature.
Large area wet fleece, many flies nearby, fly strike suspected.
Treatment?

Answer 16

Clip away fleece / completely shear animal.
Cleanse with Hibiscrub.
Pour-on permethrin.
Injectable antibiotic.*
Topical antibiotic.*
*may or may not be needed.
NSAID.

Question 17

Prevention of fly strike in sheep.

Answer 17

Blowfly tracker.
Prompt shearing.
Scour prevention.
Client education.
Duration of action must be considered in preventative products e.g. Crovect (short-acting – 6-8w), Clik (much longer lasting).
Crovect will be used before shearing so wears off and not as nasty for shearer to handle the sheep.

Question 18

1. Diagnosis of skin lesions on post-wean calves.
2. Treatment?
3. Prevention?

Answer 18

1. Based on clinical signs.
   - Multiple animals affected.
   - Does not appear to be pruritic.
   - Circular areas of alopecia.
   No diagnostic tests needed.
   It is ringworm.
2. Lesions self-resolve - quicker w/ UV.
   Can’t go through market w/ these lesions.
   Zoonotic.
3. Vaccines available but uptake is slow (Trichoben AV).