Dog digging in sand on a beach
Blastomycosis is caused by a type of fungus that grows in moist soils andis often found in southern Saskatchewan and Manitoba. Photo:

Digging up danger

As dogs dig holes and sniff their surroundings during their daily walks, owners should be aware of a potentially fatal fungal disease that could infect their pets.

By Cat Zens

Blastomycosis is a disease caused by Blastomyces dermatitidis, a type of fungus that lives in moist soils often found in eastern North America. The fungus is often found in the Prairie provinces — most commonly in southern Saskatchewan and Manitoba.

Dr. Mathieu Paulin (DVM) is a small animal internal medicine resident and PhD student at the Western College of Veterinary Medicine (WCVM) who has ample experience working with prairie-based blastomycosis cases in the college’s Veterinary Medical Centre (VMC) on the University of Saskatchewan campus.

“People call me the magnet for fungal diseases,” he quips.

He adds that B. dermatitidis is particularly active in dust-producing regions, especially during periods of rainfall. Although blastomycosis is relatively uncommon on the Prairies, dog owners should be aware of the disease — especially when they’re in high-moisture areas.

Dogs with blastomycosis typically get infected by digging soil or breathing dust in the air affected by the fungus. While the disease is most common in the lungs, it can affect almost any part of the dog’s body such as its eyes, brain, prostate, liver or spleen. If not treated quickly enough, the disease can spread to multiple body parts at once, making treatment even more difficult.

Paulin adds that blastomycosis isn’t likely to be transmitted from dog to dog nor from a dog to a human. However, localized Blastomyces infections have occurred in health care workers when sampling lesions in dogs and working with fungal culture in the lab. 

Because most dogs spend a lot of time outside surrounded by dust and soil, preventing them from becoming infected with blastomycosis is nearly impossible.

“You would have to forbid your dog to sniff outside, which is pretty hard to do,” Paulin says. He adds that dog owners’ best option is to act as soon as they first see signs of illness in their pet.  

But the clinical signs of blastomycosis are challenging to identify since the disease can affect almost any part of a dog’s body. For example, signs such as coughing, heavy breathing, decreased appetite, fatigue and weight loss could all be caused by this illness — as well as many other conditions. If a dog is showing any of these symptoms, Paulin recommends taking the pet in to a veterinarian for an examination. 

“All positive cases of blastomycosis should be treated,” he says. “You need to treat [the dogs] as soon as possible.”

Paulin says the VMC typically sees between five and 10 blastomycosis cases in canine patients every year. However, this number is likely higher as many cases go undiagnosed due to the disease's highly complex nature and the costs associated with diagnosis and treatment.

The process of diagnosing blastomycosis alone can range from $1,500 to $5,000. Once the disease is diagnosed, veterinarians will treat blastomycosis with antifungal medications that cost about $200 per month, with fungal therapy usually lasting at least two to three months.

Paulin explains that veterinarians usually make a definitive diagnosis based on the combined results from X-rays, blood tests, urine tests and sampling of the lesions.

“In a blastomycosis case in the lungs, usually we do chest radiographs and then we see some nodules in the lung, and we can aspirate with a needle in those nodules. Then hopefully we can get an answer through cytology testing,” says Paulin.

“Another way to [diagnose blastomycosis] is to collect urine samples and measure the antigen of the blastomycosis on the urine sample.”

Dogs with blastomycosis must be treated with an anti-fungal drug (usually itraconazole), for at least two to three months. This medication stops the formation of a constituent (ergosterol) of fungal cell membranes (such as the skin surrounding the fungus) and causes the fungus to die. 

“With a case of blastomycosis in the lungs, you stabilize the patient first, provide oxygen if needed, and then treat them with anti-fungal medication,” Paulin says. 

Sometimes, surgery is also required to overcome blastomycosis. For instance, if the fungus is affecting the patient’s eyes, veterinarians may need to remove one or both eyes to save the dog’s life.

According to Paulin, blastomycosis therapy has a success rate of 70 to 80 per cent, and most dogs respond positively to treatment. However, relapses are possible despite appropriate therapy.  

“The earliest the dogs get treatment, the better chance they will have to survive,” he says.

If you suspect that your dog has potential clinical signs of blastomycosis, contact your local veterinarian or call the VMC’s Small Animal Clinic (306-966-7126).

Cat Zens of North Battleford, Sask., worked as a research communications intern at the Western College of Veterinary Medicine (WCVM) in 2023.

Click here to read more articles in the Spring 2024 issue of Vet Topics, newsletter for the WCVM's Companion Animal Health Fund.