Demodectic mites are normal skin residents in the hair follicles of all species. They live in balance with their host’s immune system, but if something shifts the balance and mites proliferate, skin disease occurs.
Two Types of Demodex Mites in Cats
Demodex cati and Demodex gatoi are the two Demodex mites of cats. Demodex cati is long and slender and lives inside hair follicles. Demodex gatoi is short and stubby with hardly any tail 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, we extrapolate from the disease in dogs. Some sort of immune suppression is thought to be involved in over-proliferation. It is also thought that Demodex gatoi may be transmissible between cats. 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.
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.
While no studies have been performed, there are many anecdotal and single case reports of the mite being cleared using the topical spot-on product Bravecto®, Merck Animal Health. In a case report of an adult cat with generalized demodicosis secondary to chronic glucocorticoid administration, a single dose of 28 mg/kg Bravecto was administered orally.43 Negative skin scrapings were obtained within one month and clinical cure within two months.
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. The product Bravecto as well as Advantage-Multi has also proven efficacious for this demodex mite.
Also, 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. Additionally, treatment with the topical Bravecto might also be considered and is far less stressful for the cat.
Urban Animal Veterinary Hospital
1327 Yale St
Houston, TX 77008