What is Blastomycosis in Dogs?

If your dog has been coughing for weeks, losing weight, or developing strange skin sores after spending time near a lake or wooded area, blastomycosis might be on your radar. It’s a serious systemic fungal infection caused by inhaling microscopic spores of a fungus called Blastomyces dermatitidis, and it can affect your dog’s lungs, skin, eyes, lymph nodes, and bones all at once. The good news: caught early, many dogs recover fully.

The key is knowing what to look for and asking the right questions.

What causes blastomycosis in dogs

Blastomycosis is caused by a fungus called Blastomyces dermatitidis that lives in the soil, particularly in moist, sandy, or decaying organic matter near bodies of water. It’s not a bacteria, virus, or parasite. It’s a fungus, and it spreads through the environment, not between animals or people.

When a dog digs, sniffs the ground, or runs through disturbed soil, they can inhale the microscopic spores. Those spores travel into the lungs, where they convert into a form that can multiply and spread through the bloodstream to other organs. That’s why blastomycosis is called a systemic fungal infection: it rarely stays in one place.

Dogs in regions where blasto is common are most at risk. Those include the Mississippi, Missouri, and Ohio River valleys, the Great Lakes region, and parts of the mid-Atlantic states. Hunting dogs and sporting dogs that spend time near water or in wooded areas are disproportionately affected, but any dog with outdoor access in these areas can be exposed.

Symptoms of blastomycosis in dogs

One of the things that makes blasto so tricky is how many different symptoms it can cause. Because the infection can spread to multiple organ systems, what you see depends on where it’s taken hold. Early signs of blastomycosis in dogs often look like a respiratory illness or general malaise, which is part of why it gets missed.

Respiratory symptoms

The lungs are usually the first place the infection sets in. You might notice a dry, persistent cough that doesn’t respond to antibiotics, difficulty breathing, rapid or labored breathing, or exercise intolerance (your dog tires more quickly than usual). Chest x-rays of an infected dog often show a diffuse, hazy pattern in the lungs that can look remarkably similar to cancer.

Skin lesions and draining sores

Blastomycosis skin lesions in dogs are a common sign of disseminated blastomycosis, meaning the infection has spread beyond the lungs. These appear as raised, crusty, or ulcerated sores, often on the face, nose, and nail beds. Some lesions drain fluid. If you’re seeing unusual skin sores alongside a cough or weight loss, that combination should raise a flag.

Eye problems

Blastomycosis in dogs’ eyes is more common than people expect. Ocular involvement, meaning the infection has reached the eyes, can cause redness, cloudiness, swelling, or even blindness if left untreated. This is one of the more urgent complications because eye damage can be permanent even after the infection itself is treated.

Other signs to watch for

• Swollen lymph nodes (lumps under the jaw, in front of the shoulders, or behind the knees)
• Unexplained weight loss and decreased appetite
• Fever that comes and goes
• Lameness or swollen joints (when the infection spreads to bones)
• General lethargy or weakness

Why blastomycosis gets misdiagnosed

This is where a lot of dogs lose critical time. Blastomycosis mimics several other conditions so convincingly that even experienced vets can initially head in the wrong direction. The two most common look-alikes are lung cancer and bacterial pneumonia.

On a chest x-ray, a blasto-infected lung can look nearly identical to lung cancer in dogs, with nodular masses or widespread hazy infiltrates that suggest a tumor. Dogs are sometimes referred to oncologists before a fungal infection is even considered. Similarly, the cough, fever, and labored breathing of blasto can look exactly like bacterial pneumonia, leading to rounds of antibiotics that do nothing to treat a fungal infection.

If your dog is in an endemic region and the antibiotics aren’t working, or if lung cancer is being discussed before a fungal disease has been ruled out, here are specific questions to ask your vet:

• “Has a blastomycosis urine antigen test been run?” This is one of the fastest and least invasive ways to flag the infection.
• “Could this be a fungal infection given where we live or where my dog spends time?” Geography matters. If you’re in the Great Lakes region or a river valley, bring it up explicitly.
• “Can we do cytology before pursuing cancer diagnostics?” Cytology, which means examining a sample of cells under a microscope, can sometimes identify the fungal organisms directly and is less invasive than a biopsy or advanced imaging.
• “Is there any reason not to test for blasto given the x-ray findings?” A simple antigen test is inexpensive compared to the cost of pursuing the wrong diagnosis.

Advocating for your dog in the exam room isn’t overstepping. It’s one of the most useful things you can do.

How vets diagnose blastomycosis in dogs

There’s no single test that confirms blastomycosis on its own, so vets typically use a combination of tools.

• Urine antigen test: This test looks for a protein released by the fungus in your dog’s urine. It’s fast, minimally invasive, and highly sensitive, making it a great first step, especially in endemic regions.
• Cytology: A vet collects a small sample from a skin lesion, lymph node, or lung fluid and examines it under a microscope to look for the distinctive round, thick-walled fungal cells. A positive cytology result can confirm the diagnosis quickly.
• Chest x-rays: X-rays show how much of the lungs are affected and help gauge severity. They’re essential for monitoring treatment progress, too.
• Blood work and urinalysis: These give the vet a broader picture of how the infection is affecting your dog’s overall health and organ function.
• Fungal culture: Growing the organism in a lab can confirm the species, but it takes weeks and is usually reserved for unclear cases.

Treatment for blastomycosis in dogs

The primary treatment is a long course of antifungal medication. Itraconazole is the most commonly used antifungal for blasto in dogs. It’s taken orally, usually once a day, and treatment typically lasts anywhere from 60 days to 6 months depending on the severity of the infection and how your dog responds.

Your vet will likely recheck urine antigen levels throughout treatment to track whether the fungal load is decreasing. Medication shouldn’t be stopped early, even if your dog looks better, because the infection can come back and be harder to treat the second time around.

Dogs with severe lung involvement may need hospitalization and oxygen therapy to support their breathing while the antifungals begin working. Some dogs with ocular blastomycosis may also need eye-specific treatment to reduce inflammation and try to preserve vision.

Survival rate and prognosis

The honest answer: blastomycosis is a serious disease, and outcomes vary. With treatment, survival rates are generally estimated between 60 and 75%, though dogs with severe lung disease or central nervous system involvement have a more guarded prognosis. Dogs that are diagnosed early and tolerate antifungal therapy well often recover fully and go on to live normal lives.

Eye involvement, even when the dog survives, can result in permanent vision loss in the affected eye. The blastomycosis in dogs timeline from diagnosis to recovery is usually several months, with some dogs requiring a year of monitoring to confirm the infection is fully cleared.

How to prevent blastomycosis in dogs

There’s no vaccine for blastomycosis, and there’s no practical way to completely eliminate your dog’s risk if they spend time outdoors in endemic regions. But there are some reasonable steps you can take to reduce exposure.

• Avoid letting your dog dig in moist, sandy soil near rivers, lakes, or swamps, particularly in areas where blasto is known to be present.
• Keep hunting dogs and sporting dogs out of heavily wooded, waterlogged areas when possible, or at least be aware of the risk and watch for symptoms afterward.
• Know your region. If you live in or near the Great Lakes, Mississippi River valley, or other endemic regions, make blastomycosis part of your annual vet conversation.
• See your vet promptly if your dog develops a persistent cough, unexplained weight loss, or skin sores. Early diagnosis makes a significant difference in outcomes.

Does pet insurance cover blastomycosis in dogs?

Treating blastomycosis isn’t cheap. Between the diagnostic workup (urine antigen tests, x-rays, cytology), weeks or months of itraconazole, and potential hospitalization with oxygen therapy, blastomycosis in dogs treatment cost can run into the thousands of dollars, sometimes significantly more for severe cases.

Lemonade pet insurance can help cover those costs when blastomycosis isn’t a pre-existing condition. That includes diagnostics, antifungal medication, hospitalization, and specialist visits, depending on the plan you choose. The catch, as with any insurance, is that coverage only applies to conditions that develop after your policy starts, and after your 14-day illness waiting period has passed. A dog diagnosed with blasto before or shortly after enrollment typically won’t be covered for that specific condition.

If you live in a region where blasto is common and your dog spends time outdoors, getting a quote before something happens is the move. You can’t predict when your dog will inhale a spore, but you can make sure you’re not facing a multi-thousand-dollar vet bill without a safety net.

Before we go

Blastomycosis is one of those conditions that’s easy to miss and hard to reverse if treatment starts too late. If your dog has been coughing, losing weight, or showing skin sores or eye problems, especially after spending time near water or wooded soil in an endemic region, don’t wait it out. Get to a vet, mention blastomycosis specifically, and ask about the urine antigen test. Being informed and specific in that conversation could be the difference between an early diagnosis and a much harder road.

And if you’re not yet covered, it’s worth looking into Lemonade pet insurance now, before you need it.

Frequently Asked Questions

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