Yeast (Malassezia) Infections
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Malassezia pachydermatis is a yeast that is commonly found on the skin of most cats. This yeast normally exists without creating any problems; however, in some cases, it can grow, reproduce in abnormal numbers and cause disease.

Where is Malassezia found?
Malassezia can be found on the skin of cats living throughout all of North America. Its presence is not considered abnormal in healthy cats. It is commonly found in the ear canal, anal sacs, vagina, and rectum. Malassezia can infect cats of all ages and breeds.

Why do cats get Malassezia yeast infections?
Any hereditary or infectious disease that weakens the skin's immune system can allow a Malassezia infection to begin. Cats that have an underlying condition such as a bacterial infection, allergy, or seborrhea can produce irritated skin that is then susceptible to an infection with Malassezia. It should be noted, however, that infections with this yeast are rare in cats.

What are the symptoms of a Malassezia yeast infection in cats?
The most common symptom of Malassezia infections in cats is alopecia (hair loss). Chin acne, redness, and seborrhea can also occur.

How is a Malassezia yeast infection in cats diagnosed?
The best way to diagnose Malassezia is with a positive identification of the organism under the microscope. The lesion can be scraped, swabbed, or transparent tape can be applied to and removed from the infected area to obtain a sample. Most infections will have a large number of yeast present that will confirm the diagnosis. Laboratory cultures can also be performed to identify the organism. Keep in mind that because Malassezia can be present on the skin of a healthy animal, there may always be some doubt as to whether or not it is the causative agent of the symptoms. Therefore, diagnosis is usually confirmed by the cat's response to treatment.

How are Malassezia yeast infections in cats treated?
Treatment can be approached in several different ways. For a long-term solution to the problem the underlying condition must be properly diagnosed and treated. Once the underlying conditions are addressed, then either localized or generalized treatment can begin.

To provide an inhospitable environment for Malassezia, lipids (fats) on the cat's skin need to be removed. Chlorhexidine shampoos that are 1% or stronger, and shampoos containing benzoyl peroxide and sulfur can be used. Human shampoos containing ketoconazole have also been used.

For localized treatment of very small areas, miconazole cream is applied twice daily for several weeks.

For cats with more severe cases, or in those that are resistant to topical treatment, oral ketoconazole, fluconazole or itraconazole can be administered for several weeks. A response is generally seen within 1-2 weeks, however, therapy needs to continue for an additional 3-5 weeks. These oral antifungal drugs are very effective, but because of their potentially toxic side effects and expense, they should only be used under direct veterinary supervision.

Conclusion
Malassezia is a yeast commonly found on the skin of most cats. In high numbers, it is almost always associated with hair loss and is often misdiagnosed as a skin allergy; although infections in cats are rare. The organism can be readily identified and treatment is usually successful. If your cat has hair loss and has failed to respond to conventional treatments, make sure your veterinarian checks her skin for the ever-present Malassezia.

 
References and Further Reading

Ackerman. Skin and Haircoat problems in dogs. Published by Alpine Publications; 1994.

Greene, CE. Malassezia dermatitis. In Greene, CE (ed): Infectious Diseases of the Dog and Cat. W.B. Saunders Co. Philadelphia, PA; 1998;547-548.

Griffin, Kwochka, Macdonald. Current Veterinary Dermatology. Published by Mosby; 1993.

Scott, Miller, and Griffin. Small Animal Dermatology. Published by W.B. Saunders Co. Philadelphia, PA; 1995.  

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