Treating Continual Yeast Infection in Canines
What is yeast dermatitis?
Yeast dermatitis or Malassezia dermatitis is caused by the fungus Malassezia pachydermatis. It is an extremely common cause of skin disease in dogs. This yeast is normally found on the skin, but its abnormal overgrowth can cause dermatitis, or inflammation of the skin.
What are the clinical signs of a yeast skin infection?
The most common clinical signs of yeast dermatitis are:
- itching and redness
- musty odor
- scales and crusty, flaky skin
- thickened skin ('elephant skin')
- hyperpigmentation (darkly pigmented skin)
- chronic or recurrent otitis externa or ear infections
How does a dog get a yeast skin infection?
The skin is host to innumerable bacteria and fungi. Under normal circumstances, these organisms do not cause a problem and are kept under control by the immune system. If conditions on the skin change or if the immune system is suppressed, these bacteria and fungi can cause infection. These types of infections are termed opportunistic infections. If the number of yeast organisms on the skin increase, a yeast skin infection results.
"Yeast dermatitis is not contagious."
A common cause of a yeast skin infection is an increase in the amount of oils produced on the skin. This is most frequently associated with allergic skin disease. Another common cause of excess skin oils is seborrhea oleosa (see handout "Seborrhea in Dogs" for information on this condition).
Some dogs have an immune deficiency making them ineffective at fighting yeast infections resulting in chronic infection. Dogs that receive immunosuppressive drugs such as corticosteroids (steroids) may also be unable to effectively prevent yeast infections, so may develop a chronic yeast infection.
Yeast dermatitis is not contagious; your dog did not get this infection from another dog. Opportunistic yeast infections often recur unless the underlying allergy or skin condition is controlled.
There are certain breeds thought to be genetically predisposed to developing yeast infections. These breeds include West Highland White Terrier, Basset Hound, Cocker Spaniel, Silky Terrier, Australian Terrier, Maltese Terrier, Chihuahua, Poodle, Shetland Sheepdog, Lhasa Apso, and Dachshund.
How is yeast dermatitis diagnosed?
There are several techniques used to collect samples for diagnosing yeast dermatitis: 
- Skin scraping - scraping the skin with a blade to collect yeast organisms
- Impression smear - pressing a microscope slide on the skin to collect yeast organisms.
- Cotton swab sample - rubbing a moistened swab on the skin to collect yeast organisms.
- Acetate tape preparations - applying a piece of clear tape to the skin to collect yeast organisms.
- Skin biopsy - obtaining a small piece of skin with a biopsy punch. This is the most invasive diagnostic test, but provides the most complete diagnostic information.
Once the sample is obtained, it is examined by a veterinary pathologist under the microscope.
How is yeast dermatitis treated?
Treatment for yeast dermatitis may be topical, oral, or a combination of both, and is based on the severity of your dog's condition.
Topical treatment. Treatment with medicated shampoos is a vital part of treating yeast dermatitis. Many dogs with greasy or oily skin will require an initial 'degreasing' cleansing with a shampoo containing selenium sulfide or benzoyl peroxide. After the initial bathing is complete, bathing with an anti-fungal shampoo containing chlorhexidine, miconazole, or ketoconazole is performed. It is important the anti-fungal shampoo remain in contact with the skin for at least ten minutes. To be effective, this topical treatment is required every 3-5 days for two to twelve weeks. If the infection is in the ears or in only one or two spots on the skin, a topical ointment may be prescribed for daily use.
Oral treatment. In more severe, chronic, or persistent cases of yeast dermatitis, the use of oral or systemic anti-fungal medications is often required. Many dogs with yeast dermatitis will also have a bacterial skin infection (pyoderma) and will require antibiotics to treat the bacterial infection for typically four to twelve weeks. Oral anti-fungal medications include ketoconazole, itraconazole, and fluconazole.
Although these medications are highly effective, they must be given for prolonged periods of time (often several months). Because these drugs have potential side effects, particularly involving the liver, close monitoring with routine blood tests is necessary. If the dog has a relapse of the fungal infection after an initial successful treatment, a higher dose of the antifungal medication will usually be required. Most dogs with advanced or chronic yeast dermatitis are treated with a combination of oral and topical treatment.
What is the prognosis for yeast dermatitis?
The prognosis for yeast dermatitis is generally good. While the condition usually requires long-term treatment, the majority of cases respond favorably and the itching is reduced within a week of beginning therapy.
"In cases with underlying allergies or immune compromise, the prognosis is based on the ability to control those conditions."
In cases with underlying allergies or immune compromise, the prognosis is based on the ability to control those conditions. It is not uncommon for dogs with severe skin allergies to have recurrent secondary yeast or bacterial skin infections, sometimes two or three times a year. Your veterinarian will discuss a diagnostic and treatment plan for your dog to help you manage this condition.
Source: https://vcahospitals.com/know-your-pet/yeast-dermatitis-in-dogs
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