Demodicosis (Demodex Mange)

Demodicosis is skin disease caused by Demodex mites — cigar-shaped microscopic parasites that live head-down in the hair follicles and sebaceous glands. A small population of these mites is a normal part of healthy skin, kept in check by the immune system. Disease develops only when that balance breaks down and the mites multiply out of control.

In cats, unlike dogs, demodicosis is uncommon, and its appearance is clinically important because it so often points to something else going on. Two species are involved. Demodex cati behaves as an opportunist: it flourishes when a cat is immunosuppressed or ill, so a diagnosis prompts the vet to search for underlying feline leukaemia virus, feline immunodeficiency virus, diabetes, or thyroid disease. Demodex gatoi is different — it lives more superficially, spreads readily between cats, and typically causes intense, self-inflicted itching and hair loss.

Owners usually notice patches of thinning fur, most often around the face, eyelids, head and neck, sometimes with scaling, crusting or reddened skin. With D. gatoi the cat may over-groom to the point of barbering large areas of coat. Ear involvement can produce a dark, waxy discharge that mimics ear-mite infection.

The diagnosis is confirmed by taking skin scrapings and examining them under a microscope for the characteristic mites, though the superficial D. gatoi can be frustratingly hard to find and is sometimes diagnosed by response to treatment. Weekly lime-sulphur dips are a traditional and effective therapy; several of the newer flea-and-tick isoxazoline products are also highly effective when used under veterinary guidance. Alongside treating the mites, resolving any underlying illness is essential for a lasting cure.