Demodectic Mange in Cats
Demodectic mange mites are normal skin residents in the hair follicles of all species. 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 the raw, weepy lesions of eosinophilic granuloma complex, to the dry seed-like scabs commonly referred to as miliary dermatitis.
Demodectic mange in dogs is extremely common, especially in puppies. Demodicosis in cats is much more unusual.
Cats have Two Types of Demodex Mites
Demodex cati and Demodex gatoi are the two Demodex mites of cata. (Dogs have only Demodex canis to address.) Demodex cati is long and slender like the alligator-esque canine mite and like the canine mite lives inside hair follicles. Demodex gatoi is short and stubby with hardly 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.
Because this is not a common condition, only a limited number of cases have been published, and it’s necessary to extrapolate from the canine condition. Some sort of immune suppression appears to be a pre-requisite to infection for both mites (as is the case with dogs). Unlike the canine situation, there is some reason to think that Demodex gatoi may be transmissible between individuals. Demodex gatoi infection appears to be slightly more common than infection with Demodex cati, and is noted for extreme itchiness.
A skin scraping is necessary to detect these mites, though they are not as easily seen nor present in obviously large numbers as the canine mites are. Part of the problem is that Demodex gatoi mites reside superficially in the skin and are readily licked away by an itchy cat. The fact that this condition is so rare (and thus unexpected) is probably the chief impediment to making the diagnosis.
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 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 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 in cats as it is used in dogs. Unfortunately, treatment failures have been known to occur with ivermectin so rather than risk one cat being able to re-infect the whole lot because of a treatment failure, it is best to go with dipping if at all possible.
Treatment for Demodex cati
Because Demodex cati lives deeper in the hair follicle, it is sensitive to ivermectin in a way that Demodex gatoi is not. This allows for a daily oral alternative to dipping, though weekly dipping as described above is also effective. Further good news is that since Demodex cati does not create a contagious disease, treating all the cats in the home is unnecessary.
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 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. 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.
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