What is demodecosis?
Demodecosis 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 proliferate 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 demodecosis is more common in dogs than cats, there are two species of demodex mites that can affect cats: Demodex cati and Demodex gatoi. Demodex 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, although Burmese and Siamese cats do appear to be overrepresented.
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 demodecosis?
Demodex mites can be associated with localized or generalized disease. Signs vary, depending on the species of mite involved.
Demodex 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. Demodex cati can also be a cause of recurrent ear infections.
Demodex 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 Demodex gatoi are clinically indistinguishable from allergic skin disease. Therefore, demodecosis should be considered a possibility in any cat suspected of having allergic skin disease. Some cats infected with Demodex gatoi may be completely asymptomatic with no visible skin lesions.
How is demodex diagnosed?
Diagnosing demodex 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 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 the microscope, looking 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, the mite is often discovered while attempting to the find the cause of recurrent ear infections. This workup frequently involves taking swabs of otic debris from the ear canals, then examining this debris under a microscope. If a cat is infected with demodex, demodex mites may be seen during microscopic examination of the otic debris.
Image via Wikimedia Commons / Joel Mills (CC BY-SA 3.0.)
How did my cat contract demodex?
"Demodex cati is not contagious and cannot be spread between cats. Demodex gatoi, however, is contagious to other cats."
Demodex 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 Demodex cati infestations, your veterinarian may recommend testing for Feline Leukemia Virus, Feline Immunodeficiency Virus, or other immunosuppressive conditions. Additionally, Demodex 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.
Demodex gatoi, however, is contagious to other cats. Because some cats may remain asympomatic even if infected, it is important to consider the possibility of asymptomatic carriers if you have a multi-cat home and issues with Demodex 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 demodex treated?
The treatment of feline demodecosis depends upon which specific demodex species is involved.
"Although not all infected cats have a suppressed immune system, many cats do and these cats cannot be successfully treated until the immunosuppression is addressed."
With Demodex 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 the 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 Demodex cati mites include topical treatments (lime sulfur dips), oral medications (ivermectin or milbemycin), as well as other 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 Demodex gatoi, successful treatment relies on treating all cats in the household. The treatments used to treat Demodex gatoi are similar to those used for Demodex cati, including lime sulfur, ivermectin, milbemycin, or other treatments.
What is my cat’s prognosis with treatment?
In most cases, demodecosis in cats can be successfully treated. The prognosis for cats infected with Demodex gatoi is very good, if all in-contact cats can be treated to prevent re-infection. The prognosis for cats infected with Demodex cati depends on the ability to manage any underlying immunosuppressive conditions, but treatment is typically effective if underlying immunosuppression is ruled out or eliminated.