DEMODECTIC MANGE IN THE CAT

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 causes no 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 an itchy disease.

Demodex mites may or may not be contagious depending on which type of Demodex mite we are dealing with.

TWO TYPES OF MANGE, THREE TYPES OF MANGE MITE

Demodex cati and Demodex gatoi are the two main Demodex mites of the cat 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. Why do we care which type? It matters because mites living protected inside hair follicles are not vulnerable to the same treatments as mites living on the skin surface. Knowing the type of mite tells us what to do.

(Graphics courtesy of Dr. Carol Foil. Used with permission)                                                                                                         

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 very 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 as there must be a moderate number of mites present to create disease. On the other side, it takes only a few gatoi mites to generate a lot of inflammation. This means gatoi mites may be rare, even with a lot of skin disease. 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 flea products of the isoxazoline class (see flea product comparison chart). These products are the newest on the insecticide scene and are licensed to kill both fleas and ticks and it turns out they will kill Demodex cati as well. Typically, a three month course of one of the topical feline isoxazolines is recommended. Bravecto, one of the commercial isoxazoline products, is commonly recommended as it employs a very high dose of its isoxazoline (fluralaner) so as to work against fleas and ticks for a 3 month period. This means that a single dose ought to take care of a Demodex cati infection whereas the monthly isoxazolines, such as Revolution Plus, must be repeatedly dosed. One of the moxidectin-containing topicals, such as Advantage Multi, has also been found effective against Demodex cati in similar repeated doses. Traditionally lime sulfur dips once or twice weekly for 6 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.

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 special 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 re-infecting 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.

(original graphic by marvistavet.com)

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 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. 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 one 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.

Page last updated: 7/24/2023