What is demodicosis?
Demodicosis is a parasitic skin condition caused by Demodex mites. These microscopic mites can be found on the skin of all animals but, in some cases, they multiply to excessive levels and cause clinical signs. This increase is often associated with a suppressed immune system, although this is not always the case.
While demodicosis is more common in dogs than in cats, there are two species of Demodex mites that can affect cats: Demodex cati and Demodex gatoi. D. cati is typically found within the hair follicles, while D. gatoi is more likely to live on the surface of the skin. Cats of all breeds and ages can be affected by Demodex mites.
"Demodex mites are species-specific."
Demodex mites are species-specific. Each species of Demodex mite only has one host species on which it can survive. This means that an infected dog cannot transmit Demodex mites to a cat, and vice-versa. Additionally, Demodex mites found on cats and dogs do not spread to humans.
What are the clinical signs of demodicosis?
Demodex mites can be associated with localized or generalized disease. Signs vary, depending on the species of mite involved.
D. cati is frequently associated with hair loss, skin inflammation, and crusting. The skin lesions may be itchy, though this is not always the case. In some cases, cats may have only localized skin issues, commonly on the face, head, and neck. In other cases, lesions may spread to involve the entire body. D. cati can also be a cause of recurrent ear infections.
D. gatoi frequently causes severe itching, inflammation of the skin, and crusts along the trunk and limbs. In some cases, cats may develop ulcers on the lips or small scabs (military dermatitis) across the entire body. In most cases, the skin issues associated with D. gatoi are clinically indistinguishable from allergic skin disease. Therefore, demodicosis should be considered a possibility in any cat suspected of having allergic skin disease. Some cats infected with D. gatoi may be completely asymptomatic with no visible skin lesions.
How is demodicosis diagnosed?
Diagnosing demodicosis typically requires a test known as a skin scrape. In this test, your veterinarian will use a scalpel blade to scrape off some of the outer layers of skin cells, removing Demodex mites that may be living on the surface of the skin or in the hair follicles. The samples obtained via the skin scrape will be examined under a microscope to assess for the presence of Demodex mites.
Other tests that may be used to assess for the presence of Demodex mites include an acetate tape preparation, in which a piece of transparent tape is applied to your cat's skin to lift off any parasites that may be living on the surface. This piece of tape is then examined under a microscope for the presence of Demodex mites. Hair pluck samples may also be examined under a microscope, to look for Demodex mites that may be found within the hair follicle. Less commonly, more invasive tests, such as skin biopsy, may be required to visualize the Demodex mites within the hair follicle.
In cases of ear infections caused by Demodex mites, the mite may be discovered while using a microscope to examine debris sampled from the ear canal.
"As Demodex can be difficult to find using the above tests, your veterinarian may recommend a trial of medication that will kill the parasite..."
As Demodex can be difficult to find using the above tests, your veterinarian may recommend a trial of medication that will kill the parasite, such as fluralaner (Bravecto®) or sarolaner (Revolution Plus®).
How did my cat become infected with Demodex mites?
D. cati is not contagious and cannot be spread between cats. Cases of localized infection do not necessarily indicate an underlying cause, however, generalized infection may indicate underlying immunosuppression that is allowing the mite to multiply out of control. In cases of generalized D. cati infestations, your veterinarian may recommend testing for feline leukemia virus, feline immunodeficiency virus, or other immunosuppressive conditions. Additionally, D. cati may be associated with medications that can suppress the immune system; your veterinarian will take a thorough history to ensure that your cat is not receiving any medications that may lead to this condition.
D. gatoi is contagious to other cats. Because some cats may remain asymptomatic even if infected, it is important to consider the possibility of asymptomatic carriers if you have a multi-cat home and issues with D. gatoi in one cat. These cats may spread Demodex mites to other cats in the home, even if they are not showing signs of skin disease.
How is demodicosis treated?
The treatment of feline demodicosis depends upon which specific Demodex species is involved.
With D. cati, successful treatment depends upon identifying and addressing the underlying cause of immunosuppression. Although not all infected cats have a suppressed immune system, many cats do, and these cats cannot be successfully treated until immunosuppression is addressed. As immunosuppression is addressed or ruled out, antibiotics are given to address secondary bacterial skin infections and medication will be administered to kill the Demodex mites. The options for addressing D. cati mites include topical treatments (lime sulfur dips), oral medications, such as ivermectin (Heartgard®) or milbemycin (Interceptor®), as well as other, newer topical medication options. Each treatment has a unique set of benefits and side effects, so your veterinarian will work with you to determine the best treatment for your cat.
"In cats with D. gatoi, successful treatment relies on treating all cats in the household."
In cats with D. gatoi, successful treatment relies on treating all cats in the household. The treatments used to treat D. gatoi are similar to those used for D. cati, including lime sulfur dips, ivermectin, milbemycin, or other treatments. This particular species, however, can be more difficult to clear up than D. cati.
What is my cat’s prognosis with treatment?
In most cases, demodicosis in cats can be successfully treated. The prognosis for cats infected with D. gatoi is very good if all in-contact cats can be treated to prevent reinfection. The prognosis for cats infected with D. cati depends on the ability to manage any underlying immunosuppressive conditions, but treatment is typically effective when underlying immunosuppression is ruled out or eliminated.