Yeast Infection in Dogs: Symptoms, Causes and Treatment

Medically reviewed by: Kinga Wojtczak, Doctor of Veterinary Medicine, specialist in canine and feline diseases

A yeast infection in a dog—that sounds scary! The first thing that comes to mind with this condition is nasty-looking skin lesions that may also be dangerous to humans. Is that really the case? Not quite. The yeasts most often found on dogs' skin are those of the genus Malassezia. Specifically, the species most often isolated from canine skin is Malassezia pachydermatis. They are commensals, which means that under normal conditions they live on dogs' skin, even in healthy animals, and cause infection only under certain conditions. In small numbers, these yeasts are found around the mouth, in the external ear canal and around the anus in healthy dogs. They are opportunistic pathogens—when immunity drops or the epidermis is damaged, Malassezia multiplies rapidly and may complicate an existing infection.

Which dogs are prone to yeast infections

Dogs of any breed can develop skin infections caused by Malassezia yeasts, but these infections are particularly common in:

• Basset Hounds,
• Dachshunds,
• Cocker Spaniels,
• Poodles,
• Shar-Peis,
• Bulldogs,
• West Highland White Terriers.

Dogs are not the only ones that can be infected—in cats, Malassezia is found particularly often in Sphynx cats. As I mentioned, Malassezia usually complicates an existing infection or tissue damage. It is very often found in skin scrapings and cultures, accompanying external parasite infestations. General ill health, loss of immunity, or a weakened immune system, e.g., in older dogs, can lead to Malassezia overgrowth.

Causes of yeast infection in dogs

When heavy yeast overgrowth is found on a dog's skin, an underlying primary cause should be sought and other skin diseases should be ruled out. Most often these are:

• atopic dermatitis,
• food hypersensitivity,
• contact allergy,
• hormonal disorders,
• skin diseases such as disorders of epidermal keratinization or seborrheic dermatitis,
• metabolic diseases,
• steroid therapy, or chronic diseases that impair immunity.

Symptoms of yeast infection in dogs

Malassezia should be suspected when you notice redness on your dog's body, often combined with greasy skin, in the following areas:

• the inguinal (groin) folds,
• the axillary (armpit) folds,
• the face,
• the abdomen,
• between the toes.

Signs of the fungal infection also include affected claws and ears. In the chronic form of the disease, the skin shows discoloration and darkening, and lichenification (thickening of the skin) may develop. The hair becomes weak and breaks; the dog loses hair. Hyperkeratosis, often described as "elephant skin," is also characteristic of this infection. When the process involves the claws, a brown buildup is seen around the nail bed, and the claw itself may become brittle and break easily.

Very often these signs of fungal infection are accompanied by inflammation of the external ear canal (otitis externa)—with redness, scaling of the skin and a strong odor along with a brown or yellowish waxy discharge.

Diagnosis of yeast infection

Yeast on your pet's skin is confirmed by collecting a sample from the affected skin and examining it under a microscope (cytology). The most commonly performed test is a tape preparation (tape cytology)—a piece of adhesive tape is pressed onto the skin, which picks up a layer of skin cells and the microorganisms on them. An impression smear also works well for detecting and identifying yeast overgrowth.

Zawsze warto przeprowadzić także badanie hodowlane, aby upewnić się, że to właśnie Malassezia jest przyczyną infekcji. Zarodniki grzybów znajdowane są też często w zeskrobinie, wymazach z ran i uszkodzeń skóry. Uważa się, że jeśli w materiale, pobranym ze zmienionej w jakikolwiek sposób tkanki zostaną znalezione drożdżaki, w ilości 5 komórek w polu widzenia w preparacie, powinna zostać wprowadzona terapia przeciwgrzybicza.

Malassezia in the ear canal relatively rarely causes primary otitis. Most often it is a factor that complicates an existing infection. The fungal spores isolated from the ear canal are not only those of Malassezia pachydermatis, which I mentioned earlier. In some cases, Malassezia furfur and M. obtusa can also be found there. Candida is another yeast that can cause yeast dermatitis.

These are yeasts that normally colonize mucous membranes—they are present, for example, on the oral mucosa. Their overgrowth on the skin has causes similar to those of Malassezia—they colonize tissues that are damaged, affected by chronic inflammation, or moist. Immunosuppressive diseases and surgical wounds that are not properly cared for are also factors predisposing to yeast growth.

Skin lesions complicated by Candida look somewhat different from those complicated by Malassezia yeasts. The skin is red and moist, with erosion-like lesions and exudate. The lesions are covered with scaly crusts, and the epidermis is clearly lifted at their edges. Hair loss is seen in the infected areas of the dog's body. The skin lesions resemble superficial pyoderma (pus-forming skin infection).

Candidiasis can also appear on mucous membranes, in the form of:

• thrush,
• erosions,
• shallow ulcers.

Most often the lesions are located at the junction of the skin and mucous membranes (mucocutaneous junctions). Their appearance is characteristic—the edges of the lesions are red and slightly raised above the surface of the tissue, while the center is covered with a whitish coating that cannot be removed from the damaged tissue. Candidiasis is diagnosed exactly the same way as Malassezia infection—it is also necessary to collect material for examination under a microscope.

If characteristic budding yeasts and pseudohyphae are found, it is a good idea to send the collected sample for fungal culture to confirm the suspicion.

Treatment of yeast infection

Treatment of yeast dermatitis can be divided into two types—topical and systemic. Today, veterinarians try to choose products that are as effective as possible with as few side effects as possible. That is why topical products are increasingly used in dermatologic therapy, especially when the infectious agent is located in the superficial layers of the skin, which a topically applied product can reach.

For Malassezia and cutaneous candidiasis, rinses, compresses and medicated baths with antifungal shampoos are used, depending on the location and size of the area where the infection has developed.

The main active ingredients in antifungal products are:

• miconazole,
• clotrimazole,
• posaconazole.

Additional antibiotics also help control secondary bacterial infection (bacterial infections are the ones that most often coexist). When an ear infection involving the ear canal and part of the external ear canal has been diagnosed, careful hygiene of this area and cleaning of the dog's ears are recommended. It is important to use appropriate ear cleaners, preferably with a specific pH that is unfavorable to yeast growth and will limit it.

As for systemic therapy, antifungal treatment may be recommended by a veterinarian if the yeast infection is very severe, the signs of fungal infection are advanced, or there are contraindications to topical therapy.

The drugs recommended for systemic therapy are:

• ketoconazole,
• fluconazole,
• terbinafine,
• itraconazole.

Therapy should last at least three weeks, and after it ends a follow-up test should be performed to check whether the infection has resolved. When the infection is located in the claws, oral therapy alone may not be enough; only a combination of topical therapy with systemically administered medication gives satisfactory results. Candidiasis of the mucous membranes may require long-term treatment—therapy should last at least 4 weeks.

Therapy should be continued for a week after the signs resolve. Remember that it is essential to have your pet thoroughly diagnosed. As I mentioned earlier, Malassezia and Candida rarely cause a primary infection; most often they complicate an existing infection, taking advantage of epidermal damage caused by external parasites or of decreased immunity. If the primary cause is not identified and treated, the yeast infection will keep coming back. Therefore, the prognosis depends on the patient's general condition, on the stage of the underlying disease and the options for treating it, and on accurate identification of the complicating factor.

As for supportive care during antifungal treatment, a very important part of therapy is a properly balanced diet. It must contain good-quality, easily digestible nutrients and must not lead to deficiencies. Any ingredients that may cause a food allergy must be excluded. It is a good idea to add products that boost immunity, such as beta-glucan, to your dog's daily routine.

Daily omega-3 and omega-6 fatty acid supplementation with a suitable product is also a good idea. Polyunsaturated fatty acids support regenerative processes in the body and also have a significant effect on skin healing. With this condition, it is a good idea to seek the advice of a veterinary nutritionist, who will plan your dog's diet.

Preventing yeast infection

When it comes to preventing yeast infection, there are a few important rules to always follow:

1. Above all, you should avoid places where your dog may become infected.
2. Contact with sick animals should be significantly limited.
3. You should not bring home a dog that has not been examined first.
4. Every skin lesion or coat discoloration that appears should be thoroughly investigated.

Keep in mind that yeast dermatitis can be a zoonosis—that is, it can also cause infections in people with immune deficiencies—so it is a good idea to practice especially careful hygiene when handling an infected pet. Washing your hands after every petting and play session is an absolute must.

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