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Ectoparasitic skin disease - mites INTRODUCTION Mites belong to the group Acari within the class Arachnida. Adults have two body segments and four pairs of legs. Mite larvae have only 3 pairs of legs, but can be differentiation from insects by their small size and lack of body segments.
Mites may be burrowing or surface mites. Surface mites are found within the skin or hair and can be detected using skin scrapes. They have longer legs. The terminal part of the leg (pedicel or pretarsus) is often important in surface mite identification. Burrowing mites are found deeper within the skin or hair follicles and require a deep skin scrape or hair pluck to be seen. They have shorter legs - the 3 rd and 4th pair of legs are so short they are often not visible.
DEMODECOSIS (DEMODECTIC MANGE) Demodecosis is caused by Demodex mites. These are burrowing mites with an elongated, cigar-shaped body.
Canine demodecosis Species: D. canis., D. injai
- Often seen in young dogs around the head (from suckling).
- <6 multifocal lesions that are well-circumscribed
- Possible erythema
- Usually non-pruritic.
- Occasional secondary malassezia infection. Generalised
- >12 lesions over the entire body region and one or more feet.
- Secondary bacterial infection common. Pododermatitis
- Demodecosis of the feet.
Pathogenesis??Demodex is a common and normal inhabitant of canine skin. Demodecosis is caused by excessive multiplication of demodex mites in hair follicles and sebaceous glands. Demodecosis usually occurs in immunocompromised animals, such as in young dogs <1 year of age or dogs with systemic disease such as hypothyroidism, Cushings or neoplasia. It is not contagious. D. injai particularly affects the dorsal trunk of adult dogs, in particular West Highland White Terriers.
Diagnosis?Deep skin scrapings using liquid paraffin and coverslip. Hair plucks from feet or face. Skin biopsy.
In young dogs, localised demodecosis usually resolves. Generalised demodecosis requires use of acaricide
-?Amitraz (Aludex) o Potentially toxic product with atipamezole being the antidote. o Given weekly alongside prior clip and degreasing bath. o Risk of hypothermia.
- 10% Imidacloprid/2.5% moxidectin spot on (Advocate)
- Metaflumizone/amitraz spot on (Pro-Meris Duo)
- Unlicensed treatment include milbemycin daily PO, ivermectin or moxidectin daily PO (risk of fatal side effects especially in Collies). Treatment of secondary infections. Treatment should be monitored by regular monthly skin scrapes, and continued until two negative skin scrapes are obtained a minimum of one month apart. Glucocorticoids are CONTRAINDICATED.
In adults, prognosis is poor without treatment of underlying immunosuppressive condition. In young dogs, prognosis is good - most localised demodecosis will self resolve.
Feline demodecosis Species: D. cati, D. gatoi
Pruritis - D. gatoi Alopecia - focal or generalised. Crusting Potential secondary pyoderma Waxy otitis externa. Underlying immunosuppression.
Demodecosis is uncommon in cats. It is a generalised disease usually associated with underlying immunosuppression, such as FIV, FeLV or diabetes mellitus. D. cati is a normal inhabitant of feline skin. Demodecosis caused by D. gatoi is contagious.
Diagnosis??Deep (D. cati) and superficial (D. gatoi) skin scrapings using liquid paraffin and coverslip. Hair plucks from feet or face. Skin biopsy. Check for viral immunosuppression if not already diagnosed. For D. gatoi, response to treatment is often diagnostic.
No licensed treatment products for D. cati. 2% lime sulphur weekly dips for D. gatoi
- Also treat in-contact animals as it is contagious.
Treatment is often unrewarding. Unpredictable due to associated with underlying disease.
Hamster demodecosis Caused by D. criceti (superficial) or D. aurati (follicular).
Equine demodecosis Caused by D. equi (body) or D caballi (eyelids and muzzle). Demodecosis is rarely seen in horses and is usually caused by underlying immunosuppression. It is characterised by patchy alopecia and scaling or nodules and is non-pruritic. There is no effective treatment.
Bovine demodecosis Caused by D. bovis. Demodectic mange usually passes unnoticed in ruminants. It is characterised by non-pruritic follicular papules and nodules. Impacts of continued demodectic mange may include reduced food intake and production due to stress. Recovery is usually spontaneous. It can be treated with organophosphorous pouron products and ivermectins. Preventative treatment in December/January can improve herd health.
Ovine demodecosis Caused by D. ovis and D. caprae. Characterised by non-pruritic nodules or papules. In goats, these may contain a thick, waxy greyish exudate that contains the mites. Localised lesions in coats can be excised. Ovine demodecosis can be treated with trichlorfon.
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