Demodex mites are normal residents of the skin in virtually all mammal species. They live inside hair follicles and cause no trouble for the most part. They do not spread from host to host in a contagious way. This peaceful scenario could easily change if something happens to the immune system, allowing the mites to proliferate. An itchy, scabby skin disease could erupt.

This itchy condition is called demodectic mange, and in the cat, it is caused by a mite called Demodex cati.

Unfortunately, there is another form of demodectic mange in cats, which does not depend on anything happening to the immune system and is instead a contagious disease. Contact with an infected cat commonly leads to a new infection in a new cat.

Both conditions can cause itching, over-grooming, raw, weepy, eosinophilic granuloma complex lesions, or dry, seed-like scabs commonly called "military" dermatitis. Basically, there are two types of demodectic mange in cats, with similar skin lesions but different vulnerable cat populations.

Demodectic mange in dogs is extremely common, especially in puppies. Demodicosis in cats is much more unusual.

Two Types of Mange, Three Types of Mange Mites

Demodex cati and Demodex gatoi are the two main Demodex mites of cats, with a third species recently described but yet unnamed. Demodex cati is long and slender, resembling a short-nosed alligator, while Demodex gatoi is short, stubby, and hardly has any tail at all. The unnamed mite is slightly bigger than the Demodex gatoi but is also short-tailed. 

Demodex cati, as mentioned, lives inside hair follicles while Demodex gatoi and the unnamed mite live more superficially in the skin. For all intents and purposes, the unnamed mite has biology similar to that of Demodex gatoi and appears to respond to the same therapies. This article discusses feline demodicosis as either the "cati" type or the "gatoi" type.

Demodex cati. Courtesy of Dr. Carol Foil

Demodex gatoi. Courtesy of Dr. Carol Foil

Diagnosis

Most of the time, diagnosis is confirmed with a skin scraping or similar skin sampling technique. Occasionally, mites are found during examination of a fecal sample because itchy cats will groom and swallow their skin mites (especially in the event of Demodex gatoi infection, where the mites are superficial in the skin and readily licked away). If skin scrapes are negative for an itchy cat, a fecal sample is a good way to cover all bases. It is important to determine which mite is present, as the treatment and consequences will be very different.

When disease is caused by Demodex cati, the mites are fairly easy to find. With Demodex gatoi, a small number of mites can lead to a great deal of inflammation. The smaller numbers make them harder to find. 

Recently, a PCR DNA test for Demodex gatoi has been developed so as to detect mite presence in a skin scrape. Response to treatment is sometimes used to diagnose Demodex gatoi, as they are elusive.

Treatment for Demodex cati

Because Demodex cati lives deeper in the hair follicle, it is sensitive to treatment in a way that Demodex gatoi is not. Effective treatments include topical fluralaner (Bravecto®). Other flea products of the isoxazoline class (such as Revolution Plus®) may also be effective. Still, the Bravecto product uses a uniquely high dose so that a single dose can last 3 months, which may be important. Daily oral ivermectin or milbemycin may be used. The moxidectin topical product Advantage Multi® can be effectively used at the off-label frequency of every two weeks against Demodex cati. Historically, lime sulfur dips once or twice weekly for six dips have been used, but since dipping a cat in a stinky chemical solution is no fun for any of the parties involved, the topical products currently dominate the recommendations. The good news regarding treatment is that since Demodex cati does not create a contagious disease, only the affected cat needs to be treated. This is not so for Demodex gatoi.

The bad news is that a Demodex cati infection suggests a problem with the cat’s immune system and it is important to seek a second disease that might result in immune suppression. Expect further testing to be needed.

Treatment for Demodex gatoi

This species of mite is considered contagious among cats, so if it is confirmed or strongly suspected in one cat, then all the cats in the household must be treated.

The good news is that the isoxazoline insecticide class mentioned above for Demodex cati also works on Demodex gatoi. The advent of the isoxazoline class has been a great blessing in treating many parasitic diseases. That said, the previous "treatment of choice" also works in case an isoxazoline is not an option for some reason. This previous treatment of choice involves a series of six dips of two-percent lime sulfur given at weekly intervals. The cat must soak in the dip, which regrettably stinks of rotten eggs, for at least five minutes and must air dry afterwards. The dip smells bad and will stain fabric and jewelry, and can temporarily impart a yellow tinge to white fur. Because of these unpleasant factors and because many cats are not amenable to being quietly bathed, these dips are frequently performed in the veterinary hospital. It should be noted that the dips are also very drying to the skin, so special conditioners may be needed by the third week to prevent dandruff. It is easy to see why an isoxazoline-based flea product would be a simpler choice.

As noted, if Demodex gatoi has been confirmed or is strongly suspected, all cats in the home must be treated. There is a temptation not to treat cats that are not showing symptoms, but it is possible for cats to carry Demodex gatoi without showing symptoms, so they all must be treated to avoid the potential for a carrier cat reinfecting the others. 

If no response in the skin condition is seen three weeks into treatment and Demodex gatoi is never actually confirmed, this would suggest that another disease is causing the problem, and a different approach to the skin problem should be pursued.

Treatment of Cats Testing Negative for Mites

Demodex cati is relatively easy to find when it is present so a negative scrape largely rules out this infection. If there is any question, one of the topical treatment plans above can be used to take care of any undetected mites. 

Demodex gatoi, however, is a bit of a trickster and can be difficult to find when it is present. To cover this situation, all cats can be treated with an isoxazoline product, or the affected cat can be treated with lime sulfur dip on a trial basis before deciding if the entire household must be treated. It should be noted that ringworm, a fungal skin disease, also responds to lime sulfur, so response to dipping treatment might still leave the true diagnosis unclear.