Malassezia pachydermatis is a yeast that is commonly found on the skin of most dogs and cats. The presence of yeast normally causes few problems, however, in some cases, Malassezia can grow and reproduce in abnormal numbers.

Where is Malassezia found?

Malassezia is commonly found in the ear canal, anal sacs, vagina, and rectum of healthy dogs and cats. Disease-causing infections with Malassezia can occur in dogs of all ages and breeds, but are not as common in cats. There are several dog breeds that appear to have an increased susceptibility to developing Malassezia infections including the Silky, Australian, Maltese, and West Highland White Terriers, Chihuahuas, Poodles, Shetland Sheepdogs, and German Shepherd Dogs.

Why do dogs get Malassezia infections?

Any hereditary or infectious disease that weakens the skin's immune system can allow a Malassezia infection to begin. Animals that have an underlying condition such as a bacterial infection, allergy, or seborrhea can have irritated skin that is then susceptible to becoming infected with Malassezia. Some animals, particularly of those breeds listed above, may have a weakened immune system, specifically with a type of cell called the T lymphocyte. These are the cells which help control Malassezia.

What are the signs of a Malassezia infection?

The signs of a Malassezia infection often appear in the high-humidity months of summer and will persist into the fall. Itchy skin is almost always present with these infections. Because of the scratching, the dog may further traumatize the skin. The yeast may be localized on the ear, muzzle, toes, anal area, or may be generalized, covering most of the body. Dogs with the generalized form will often have an offensive, greasy smell and may suffer from oily, scaly skin. Dogs with localized muzzle infections may rub their face or have episodes of intensely scratching their face. Dogs with infections on their toes may lick their feet constantly. Hair loss, redness, hyperpigmentation (blackening of the skin), and thickening of the skin may also be present.

Many ear problems in dogs are also associated with Malassezia. As with skin infections with Malassezia, the yeast start to grow when the environment in the ear canal changes due to another disease condition such as allergies or a bacterial infection. If the yeast infection is in the ear, the dog may shake his head and scratch at his ears.

How is a Malassezia infection diagnosed?

The best way to diagnose a Malassezia infection is with a positive identification of the organism under the microscope. The lesion can be scraped, swabbed, or scotch tape can be used 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. However, because Malassezia can be present on a healthy animal, there may always be some doubt as to if it is the causative agent of the signs. Therefore, diagnosis is usually confirmed by response to treatment.

How are Malassezia infections treated?

Treatment can be approached in several different ways. For a long-term solution to the problem the underlying condition must be properly treated, whether it is a bacterial infection, allergy, or seborrhea.

To provide an inhospitable environment for Malassezia, lipids on the skin need to be removed. Chlorhexidine shampoos that are 1% or stronger, and shampoos containing benzoyl peroxide and sulfur can be used. Selsun Blue shampoo for people also has a good effect against Malassezia in some dogs, although it can be irritating. 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 dogs with more severe cases, or in those that are resistant to topical treatment, oral ketoconazole 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. Both of 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.

Ear infections with Malassezia are treated by cleaning the ears 1-2 times daily. Ear cleaners containing acids such as acetic or boric acid help to maintain a pH that inhibits the growth of yeast. After cleaning and allowing the ear to dry, appropriate topical medications containing nystatin, thiabendazole, or clomitrazole can be used. Again, the underlying condition must also be treated or treatment for the yeast infection will be unsuccessful.

Conclusion

Malassezia is a common yeast found on almost every dog. Infections with Malassezia are almost always associated with severe itching in dogs, and are often misdiagnosed as skin allergies. The organism can be readily identified with a skin scraping and treatment is usually successful. If your dog has itchy skin or hair loss and has failed to respond to conventional treatments make sure your veterinarian checks her for the ever-present Malassezia.