DEMODECTIC MANGE IN THE CAT
Demodectic mange mites live in the hair follicles of all species as normal skin residents. They live in balance with their host’s immune system but if the balance shifts in favor of the mite, skin disease results. The nature of the skin disease can be quite variable ranging from over-grooming ( also called "fur mowing") to raw weepy eosinophilic granuloma complex lesions to the dry seedlike scabs commonly referred to as "miliary dermatitis."
Demodectic mange in the dog is extremely common, especially in puppies. Demodicosis in the cat is much more unusual and this article will feature the differences.
THERE ARE THREE TYPES OF DEMODEX MITES IN THE CAT
Demodex cati and Demodex gatoi are the two main demodex mites of the cat with a third species recently described buy yet unnamed. (The dog has only Demodex canis to address.) Demodex cati is long and slender like the “alligator-esque” canine mite and lives inside hair follicles also like the canine mite while Demodex gatoi is short, stubby with hardly has any tail at all, and lives more superficially in the skin. Demodex cati is felt to be a normal resident of feline skin while Demodex gatoi is more likely an infectious agent. The new unnamed mite is of a size in between that of the other two species and lives on the skin surface like Demodex gatoi.
(Graphics courtesy of Dr. Carol Foil. Used with permission)
A skin scraping is usually necessary to detect Demodex mites though it is important to note that mites can be elusive even with multiple skin scrape samples. Since treatment for Demodex cati is different from treatment for the other two mite species, scrapes are done to not only confirm the presence of mites but also determine their type. Demodex gatoi tends to reside superficially in the skin and is readily licked away by an itchy cat so a cat with a negative scrape cannot be assumed to be free from infection. In lieu of scraping, sometimes a strip of cellophane tape is used to collect a superficial skin sample but, similarly, the cat may have licked away the majority of the mite population making the diagnosis tricky. Skin biopsy, unless the sample is lucky enough to contain an actual mite fragment, may only show a non-specific hypersensitivity response so it is generally not helpful. Occasionally, mites that have been licked away and swallowed are found on a fecal parasite exam so it is important not to forget to check stool under the microscope when skin samples are negative. Still, a trial course of treatment may be the only way to be confident that demodicosis has been ruled out. Demodex cati lives deeper in the skin (inside hair follicles) so is not as easily licked away by the patient and is somewhat more amenable to detection in scrapings.
TREATMENT FOR DEMODEX CATI
The series of dips described above should be effective against Demodex cati but the good news is that Demodex cati is not contagious; it is a normal resident of the feline skin. This means that the other cats in the household do not need to be dipped. For a normal resident of the skin to overgrow, there may be an immune problem altering the patient's natural balance (recent steroid use, stressful change at home, a second disease afoot etc.) so some attention should be given to determining what might have led to the overgrowth of the mite.
Oral ivermectin or topical moxidectin or selamectin is effective against demodicosis in the dog but has been unreliable in the cat so it is not recommended. Occasionally, a Demodex infection is limited to the ear canals where the dip cannot reach. Topical ivermectin or milbemycin (see our page on Ear Mites) can be used in this situation which is more difficult to clear than mites on the skin.
TREATMENT OF CATS TESTING NEGATIVE FOR MITES
It is not unusual for cats to test negative for mites for the reasons already described. For these cats, dipping can be performed on a trial basis. Dips are given once a week for three weeks. If the cat is notably improved after this time frame, then three more weekly dips should be performed the other cats in the home should be dipped for six dips each as well.
Page last updated: 6/25/2016