Identifying and Treating Fungal Infections in Dogs


By Reyna Gobel


Bacteria and viruses are what typically spring to mind hen pet parents think “infection,” but fungi can also be to blame. While not as common as bacterial or viral infections, fungal infections can be just as serious. Dogs can contract fungal infections from other animals, from the environment, or as a result of the overgrowth of fungi that are naturally present on their own bodies. Every pet is potentially at risk for contracting a fungal infection, and an accurate diagnosis is necessary before appropriate treatment can begin. Read on to learn more about fungal infections in dogs.


Fungal Skin Infections


When your dog starts scratching himself more than is normal, it can be hard to tell whether it’s because of an allergy, flea bites, infection, or something else. Excessive itching can be quite worrisome, especially if your dog develops bald spots or damages his own skin as a result.


One telltale sign of fleas is the presence of flea dirt (small black clumps of flea feces) on your dog’s skin and fur. If you see flea dirt or actual fleas, treat him right away. But if fleas or ticks aren’t to blame, “don’t self-diagnose or rely on Dr. Google,” warns Dr. John DaJong, a veterinarian at Newton Animal Hospital in Massachusetts. After performing a complete physical exam, your veterinarian can conduct specific tests to help diagnose the problem and identify whether a fungal infection is to blame.


Let’s look at two common types of fungal infections that affect the skin of dogs and how to treat them.



Ringworm is a common fungal infection in pets. It can affect a dog’s skin, fur, and also the nails. Common symptoms include hair loss, itching, flaky or crusty skin, and misshapen or brittle nails. While you should treat any infection as soon as possible, time is of the essence with ringworm because it can easily spread to other household animals and humans, says Dr. Andrew Rosenberg, a veterinarian at Riverdale Veterinary Dermatology clinic in Riverdale, New Jersey.


To diagnose ringworm, your veterinarian will perform a fungal culture of hair or skin cells or a microscopic examination of a hair sample. Depending on the severity of the infection, ringworm may be treated with medicated baths and dips and/or oral antifungal medications. Vacuuming and disinfecting the house will also help lessen the chances that ringworm will spread between pets and people.


Yeast Infection

Overgrowth of yeast on a dog’s body can lead to irritating yeast infections, commonly affecting the skin, paws, and ears. These infections can be extremely uncomfortable for dogs, says Rosenberg. They’re generally secondary to allergies or other conditions that disrupt the skin’s ability to control the yeast that normally live there.


“If I suspect a dog might have a yeast infection, I take an impression smear of the area that might be infected and look at it under a microscope,” Rosenberg says. “When the slide is stained, the yeast look like little purple peanuts.”


Treatment normally involves an antiseptic or antifungal drug applied to the skin. Oral medications may be necessary in severe cases. Unlike ringworm, yeast infections aren’t contagious to other pets or people. To prevent yeast infections from recurring, it’s important to treat any underlying conditions as recommended by your veterinarian.


If your pet is constantly itching and scratching, schedule an appointment with your veterinarian. Unfortunately, not all conditions can be solved with one visit. Sometimes it could take several visits to pinpoint the cause of your dog’s itching or require a visit to a veterinary dermatologist, Rosenberg says.


Systemic Fungal Infections


Fungal infections on the surface of the body are bad enough, but those that invade deeper structures can have even more serious consequences. Let’s look at several common types of systemic fungal infections in dogs and how to treat them.



Blastomycosis is most commonly diagnosed in dogs that have spent time in Mississippi, Ohio, Missouri, Tennessee, the St. Lawrence River valley, the mid-Atlantic, and around the Great Lakes because the types of soil that are typically found in these areas support the growth of the fungus. “Dogs that spend time sniffing around in the dirt are at risk for inhaling fungal spores, which can lead to a lung infection,” says Dr. Jennifer Coates, veterinarian and author of Dictionary of Veterinary Terms, Vet-Speak Deciphered for the Non-Veterinarian. From there, the organism can travel almost anywhere in the body. According to Coates, common symptoms include poor appetite, weight loss, coughing, difficulty breathing, limping, eye problems, skin lesions (particularly around the toenails), enlarged lymph nodes, and fever. If the disease is caught early enough, treatment with an oral anti-fungal medication can be curative.



While cats are more commonly infected with the fungus Cryptococcus, Coates says dogs tend to develop a more severe form of the disease. The fungus is present in soils world-wide but may be especially prevalent in areas where pigeons and other birds congregate. As is the case with blastomycosis, dogs typically inhale the Cryptococcus fungus, leading to a lung infection. It can then spread almost anywhere in the body, which can cause symptoms ranging from lethargy, coughing, nasal discharge, eye problems, skin lesions, and even seizures and other neurologic abnormalities.  Coates warns that treating cryptococosis can be difficult. Oral antifungal medications may need to be given for a year or more and some dogs will still succumb to the disease.



Dogs can get coccidioidomycosis (also known as Valley Fever) from inhaling dust or dirt that contains coccidioides fungal spores, says Dr. Carol Hillhouse, a veterinarian in Panhandle, Texas. “It tends to grow in desert areas with little rain and sandy soil, such as California, Nevada, Arizona, New Mexico, and Texas,” she says. “Strong winds, earthquakes, construction areas, and even crop harvesting can stir up the spores into the air.”


Once the spores are inhaled, the fungus may simply cause a chronic cough, Hillhouse says. “In other cases, especially if immunosuppressed, the dog may develop pneumonia or the fungus can spread to other areas in the body, such as bone or the eyes,” she says. “It can be difficult to diagnose, and usually requires radiographs, blood, and cell testing.” Valley fever requires long-term treatment with oral antifungal medications, but the prognosis is pretty good if caught early, she says.



Another soil-borne fungus, Histoplasma, prefers the temperate climates of Ohio, Mississippi, and Missouri River Valleys, Hillhouse says. This fungus grows best in nitrogen-rich soil, such as bird and bat excrement, and is usually acquired by inhalation of the organism from the environment. “Infected dogs can show weight loss, fever, cough, eye inflammation, vomiting, and diarrhea,” she says. “Often, a combination of blood and urine tests, as well as radiographs, are used to make the diagnosis. Sometimes biopsies are required as well.” Treatment involves long-term fungal medication, but prevention is best by restricting access to soil that is contaminated with bird or bat droppings.



Infections with Aspergillus fungus are usually limited to a dog’s nasal passages. Aspergillosis can affect dogs residing in almost any part of the country since the fungus is present in most soils. Treatment typically involves anesthetizing the pet and infusing his nasal passages with a liquid anti-fungal medication. Most dogs will recover if treated appropriately, although a second treatment may be necessary in some cases.


Preventing Fungal Infections in Dogs


Fungal infections in dogs range from localized annoyances to potentially fatal systemic diseases. Prevention is not always possible, but common sense measures can help. If you live in an area where a certain type of fungal infection is endemic, avoid high risk environments. Pets with ringworm should be isolated to limit the spread of the disease to people or other animals. Finally, appropriately manage any underlying health problems that increase your dog’s risk for developing a fungal infection.