31 (328)

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A Practical Guide to Feline Dermatology

Sarcoptic mange

Sarcoptes scabiei var canis (Table 3:1) (Fig. 3 : b) is extremely rare in the cat, causing pruritus, alopecia, erythema, scaling and crusting on the face, neck and distal limbs. The parasite can spread to people causing a pruritic rash

Otodectic mange

Aetiopathogenesis

Otodectic mange, also referred to as otoacariasis or ear mite infestation, is the most common mite infestation in the cat, accounting for up to 25% of consultations in feline dermatology. It is caused by Otodectes cynotis, a mite from the family Psoroptidae (Table 3:1). Otodectes lives mainly in the extemal ear canal and morę rarely, on the face (around the ears and on the lateral pinnae), neck and body (dorsolumbar region and taił base) \ Transmission is by direct contact and occurs mostly in the neonatal period. Young animals are, therefore, most susceptible ^U4. Otodectic mange is endemic with a high morbidity. This mite is not host-specific and also causes otitis in the dog and ferret. Transmission to humans may cause pruritus on the arms and trunk ^l\

Otodectes cynotis causes disease through its irritant effects (mechanical and Chemical) and also by induction of hypersensitivity reactions.

Clinical features

Otodectic mange is characterised by otitis, usually bilateral and erythemato-ceruminous, with dry blackish, brown cerumen (Fig. 3 : 5). Pruritus is severe. Self-induced erosive lesions around the ears and aural haematomas are often seen ^U4. If the tympanic membranę is ruptured, vestibular syndrome is sometimes observed. Non-specific pruritic lesions on the face, neck and dorsolumbar region, presenting as miliary dermatitis or symmetrical alopecia, are typical (Figs 3 : 6-8) ^UM7. Sometimes, the body is affected without involvement of the ear canals⁸.

Diagnosis

Microscopical examination of ear wax, mounted in liquid paraffin or chloral lactophenol reveals the presence of numerous Otodectes mites - adults and immature stages (eggs, larne and nymphs)¹ (Table 3:1) (Figs 3 : c,d).

Skin scrapings, when the body is affected, reveals far fewer Otodectes cynotis ⁶-\

Treatment

Amitraz* (0,5%o in propylene glycol) can be applied twice weekly into the ear canals for 6-8 weeks, following ear cleaning'.

Fipronil** in spot-on formulation is a very effective treatment for otodectic mange⁹. Two drops should be applied into each ear canal, on two occasions, two weeks apart, without prior cleaning. The rest of the pipette should be placed on the body to avoid wider cutaneous involvement. This treatment is extremely well tolerated.

hermectin * (200-400 pg/kg), given once or twice (2 weeks apart), by subcutaneous injection, gives excellent results⁵. It should not be given to cats less than 4 months old.

Selamectin (6 mg/kg) is very effective in the treatment of otodectic mange. It is applied, once, as a spot-on onto the neck. Transient alopecia and local irritation at the application site have, in rare cases, been seen in cats.

Acaricidal treatment of the whole body is necessary \ Treatment will sometimes fail due to reinfestation of the ears by mites present on the skin surface ⁷. Current treatment involves either applying fipronil spray or spot-on over the body or subcutaneous injection of ivermectin at the dose given above.

When groups of cats are affected, ivermectin is the treatment of choice.

* This product is not licensed for use in the cat and responsibility for its use falls on the prescribing veterinary surgeon.

** This product is not licensed for this indication in the cat and responsibility for its use falls on the prescribing veterinary surgeon.

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