Our veterinarian said our cat has a mite infection that is sometimes called walking dandruff. What is this? Also, we've been using a flea spray for two weeks and things don't seem to be getting any better. Can you give us any advice?

A contagious skin disease caused by a large mite.

Cheyletiellosis, or "walking dandruff," is a contagious, parasitic disease caused by several species of Cheyletiella, a genus of large mites. Various species of Cheyletiella may infect the skin of dogs, cats, rabbits and humans. Some species of this genus of mites can be transmitted from dogs and cats to humans. This disease causes itchy skin and scaling of the haircoat. This mite is very contagious and fairly common.

Cheyletiella mites reside in the keratin coat of the skin's epidermis, or outer skin layers. (Keratin is a protein and the principal constituent of the outer part of the skin.) The mites' eggs attach to the hair shafts of the affected animal until hatching. These mites are obligate parasites, which means they need to infect a host to survive. Cheyletiella mites are large relative to other mites and are visible under a hand-held magnifying glass.

The signs of infection with these mites vary according to the specific species of the infecting mite and the species being infected. In general signs range from mild scaling and itching (dogs and cats) to intense itching (rabbits) and skin vesiculation, or small blister formation (humans). Skin plaques may also be seen. The mites typically infect the back and spinal areas of dogs, cats and rabbits.

Cheyletiellosis can be diagnosed by obtaining a sample of the mites by flea combing the hair and looking for eggs, by skin scraping or by collecting the mites on tape and looking at the collected debris under the microscope. Cheyletiella mites have a characteristic appearance. Other causes of scaling and itching must be ruled out. These include seborrhea, fleabite allergy, scabies and other mites, food allergy, inhalant allergy and other itch-and-scratch syndromes.

Eliminating the Cheyletiella mites requires treatment of the affected animal, all of its contacts and the environment. Your veterinarian can recommend an appropriate environmental insecticide for this latter purpose. Fomites (anything in the environment, such as bedding, clothes, and the like, that may act as a transfer point for the mites from animal to animal or to people) must be disinfected or thrown away. Traditional flea sprays and powders may or may not be effective in killing these mites. Mites in some parts of the country seem to be more resistant to these products than in other geographic areas. Cases resistant to traditional treatments may require alternative medications and prolonged therapy. Sometimes resistance to treatment occurs when the mites migrate and hide in the nasal passages of the affected animal.

I recommend that you talk to your veterinarian about your pet's progress or lack of it. He or she will likely change the treatment regimen. With Cheyletiella mite infection, persistence and patience are essential.

01/29/09