Demodex mites are normal residents of the skin in virtually all mammal species. For the most part, they live in peace in our hair follicles and are not able to spread to another host, much less cross to another species. The cat is no different and provides a home to Demodex cati, which does not cause skin disease unless the host becomes immune-compromised and the mites proliferate unchecked.
Unfortunately, the cat is also host to two other Demodex mite species that are very much contagious to other cats and readily cause skin disease. The nature of the skin disease with either type of mite infection can be quite variable ranging from over-grooming (also called fur mowing) to raw weepy eosinophilic granuloma complex lesions to the dry seed-like scabs commonly referred to as miliary dermatitis. Feline demodicosis is usually itchy.
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 Demodex gatoi but 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 so from here on out we will discuss feline demodicosis as either of the "cati" type or the "gatoi" type.
Demodex cati. Courtesy of Dr. Carol Foil
Demodex gatoi. Courtesy of Dr. Carol Foil
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. Sometimes we must go by response to treatment 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 but the Bravecto product uses a uniquely high dose so as that a single dose can last 3 months, and this 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 6 dips has 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 to be contagious among cats so if it is confirmed or strongly suspected in one cat, then all the cats in the household must be treated. 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 not only smells bad but 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 that conditioners may be needed by the third week to prevent dandruff.
As noted, if Demodex gatoi has been confirmed or is strongly suspected, all cats in the home must be treated. There is 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 after three weekly dips, however, and Demodex gatoi was never actually confirmed, this would suggest that another disease is causing the problem and dipping may be abandoned.
Dipping is labor-intensive and unpleasant for all the reasons noted above. It would be great if an oral treatment such as ivermectin could be used. Unfortunately, because Demodex gatoi lives on the surface of the skin, ivermectin cannot reach it and it is not a reliable treatment. Fluralaner (Bravecto®) and other isoxazoline flea products have been miraculous for canine demodectic mange and it is hoped that they will be useful for the feline situation, but research is lacking at this time and dipping remains treatment of choice.
Treatment of Cats Testing Negative for Mites
Demodex cati is relatively easy to find when a cat has it, 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 there. As mentioned, the systemic treatments may not be reliable for this mite as it lives so superficially in the skin. 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. Response to lime sulfur dip is seen in conditions other than demodicosis, so you cannot necessarily infer demodicosis from results. That said, other conditions that might respond, ringworm for example, would likely necessitate lime sulfur treatment of the entire household cat population anyway.