Blastomycosis in Dogs: Fungal Infection Guide
- See your vet promptly if your dog has a persistent cough, fast or labored breathing, fever, eye redness, vision changes, or draining skin sores—blastomycosis can worsen quickly.
- Blastomycosis is a systemic fungal infection caused by inhaling Blastomyces spores from soil, especially near rivers, lakes, wetlands, and disturbed ground in the Mississippi, Missouri, and Ohio River valleys and the Great Lakes region.
- Most dogs need months of antifungal treatment. Itraconazole is commonly the first-line medication, while fluconazole may be considered in some eye or nervous system cases because it penetrates those tissues better.
- Clinical cure is possible, but relapse can happen. Published veterinary references report about 70% of treated dogs achieve clinical cure, and about 1 in 5 may relapse months to years later.
- Typical total cost range in the U.S. is about $1,500 to $5,000+, with higher costs if your dog needs hospitalization, oxygen support, specialist care, or prolonged monitoring.
What Is Blastomycosis?
Blastomycosis is a serious fungal infection caused by Blastomyces dermatitidis (and closely related Blastomyces species). Dogs usually become infected after inhaling fungal spores from the environment. Those spores settle in the lungs, change into a yeast form inside the body, and may then spread to other organs.
The lungs are affected most often, but the infection can also involve the eyes, skin, lymph nodes, bones, and sometimes the brain or spinal cord. That is why one dog may come in for coughing and breathing trouble, while another shows eye pain, draining skin lesions, or lameness.
This disease is seen most often in parts of North America near waterways and moist soil, including the Mississippi, Missouri, and Ohio River valleys and the Great Lakes region. Dogs that hunt, dig, hike, or spend time around riverbanks and disturbed soil have more exposure opportunities. Any dog can be affected, but young, active, medium-to-large dogs are overrepresented in many case series.
Blastomycosis is not usually spread from dog to dog or from dogs to people. In most cases, each infected person or animal was exposed directly to the same environment. If your dog is diagnosed, it does not mean your family caught it from your pet, but it does mean the fungus may be present in your local area.
Symptoms of Blastomycosis
- Coughing, which may start mild and become persistent
- Rapid, labored, or noisy breathing—an urgent sign if worsening
- Fever, often with low energy and reduced interest in food
- Weight loss and poor appetite over days to weeks
- Lethargy, exercise intolerance, or seeming unusually tired
- Eye changes such as redness, cloudiness, squinting, pain, dilated pupils, or sudden vision loss
- Draining skin nodules or sores, often on the face, nose, or nail beds
- Limping or bone pain if the infection has spread to the skeleton
- Enlarged lymph nodes, especially with widespread disease
Blastomycosis can look different from one dog to the next because it may affect several body systems at once. Respiratory signs are common, but some dogs first show eye disease, skin lesions, or lameness. Eye involvement is especially important because vision can be lost quickly if inflammation is severe.
See your vet immediately if your dog is struggling to breathe, breathing faster than normal at rest, seems weak or collapsed, or develops sudden eye pain or blindness. Even when signs seem mild at first, this infection can become serious fast, so early evaluation matters.
What Causes Blastomycosis?
Blastomycosis is caused by exposure to Blastomyces fungi in the environment. The mold form lives in soil and decaying organic material, especially in moist areas near rivers, lakes, marshes, and wooded sites. When contaminated soil is disturbed by digging, construction, hunting, or trail activity, spores can become airborne and be inhaled.
After a dog inhales the spores, they convert to a yeast form in the lungs at body temperature. From there, the organism may stay mostly in the lungs or spread through the lymphatic system and bloodstream to other organs. This spread is what makes blastomycosis a systemic disease rather than a simple lung infection.
Not every exposed dog becomes sick. The amount of exposure, the dog’s immune response, and where the spores settle all seem to matter. Dogs are diagnosed more often than people, likely because they spend more time close to the ground, sniffing and digging in high-risk areas.
The incubation period is variable. Some dogs become ill within a few weeks, while others may not show obvious signs for longer. That delay can make it hard for pet parents to connect symptoms with a hike, hunting trip, or yard work from earlier in the season.
How Is Blastomycosis Diagnosed?
Diagnosis usually starts with your dog’s history, physical exam, and chest imaging. Dogs with lung involvement often have chest X-ray changes that raise strong suspicion for fungal pneumonia, but X-rays alone cannot confirm blastomycosis. Your vet may also recommend pulse oximetry or blood-gas testing if breathing is a concern.
The most direct way to confirm the disease is to identify the yeast organism in samples from affected tissue or fluid. That may include cytology from a skin lesion, lymph node aspirate, transtracheal wash, or other sample. When the organism is seen under the microscope, diagnosis is much more straightforward.
A urine antigen test is widely used because it is noninvasive and highly sensitive. It is also helpful for monitoring response during treatment. One limitation is cross-reaction with some other fungal infections, especially histoplasmosis, so your vet interprets the result alongside symptoms, imaging, and other test findings.
Most dogs also need baseline bloodwork before and during treatment. A CBC and chemistry panel help assess overall health, hydration, inflammation, and liver values before starting antifungal medication. If your dog has eye signs, an ophthalmic exam is important. If there are neurologic signs, advanced imaging or referral may be discussed. A practical diagnostic cost range is often $500 to $1,500+, depending on how many tests are needed and whether emergency stabilization is involved.
Treatment Options for Blastomycosis
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Outpatient antifungal care for stable dogs
- Exam and baseline diagnostics to confirm likely blastomycosis and assess severity
- Oral itraconazole as first-line antifungal therapy for several months
- Recheck bloodwork to monitor liver values and overall response
- Urine antigen testing at intervals to track treatment progress
- Follow-up chest X-rays as needed based on symptoms and response
- Home monitoring of appetite, breathing rate, cough, weight, and energy
Hospital-supported medical management
- Initial hospitalization for dogs with dehydration, fever, poor appetite, or moderate respiratory compromise
- Oxygen support if breathing effort is increased
- Oral itraconazole or, in selected cases, fluconazole when eye or central nervous system penetration is a priority
- Repeat chest imaging and urine antigen monitoring
- Ophthalmic evaluation and eye medications when ocular inflammation is present
- Nutrition support, anti-nausea medication, and pain control as indicated
Critical care and specialist-directed therapy
- ICU-level hospitalization for severe respiratory distress or low oxygen levels
- Continuous oxygen therapy and intensive monitoring
- Amphotericin B in selected life-threatening cases, often alongside an azole antifungal
- Fluconazole when central nervous system involvement is suspected or confirmed
- Advanced imaging such as CT or MRI for neurologic disease
- Specialist care from internal medicine, critical care, or veterinary ophthalmology
- Procedures such as enucleation if an eye is blind and painful
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Blastomycosis
Bring these questions to your vet appointment to get the most out of your visit.
- Which organs seem affected in my dog right now? Lung-only disease is managed differently from cases that also involve the eyes, skin, bones, or nervous system.
- Do you recommend itraconazole, fluconazole, or another antifungal for my dog’s specific pattern of disease? Different medications have different strengths, tissue penetration, side effects, and cost ranges.
- Does my dog need hospitalization or oxygen support, or is home care reasonable? The first days of treatment can be the riskiest in dogs with significant lung involvement.
- How will we monitor treatment response over time? Urine antigen testing, bloodwork, weight checks, and chest imaging can help your vet decide whether treatment is working and when it is safe to stop.
- What side effects should I watch for with antifungal medication? Loss of appetite, vomiting, diarrhea, lethargy, skin changes, and liver-related problems may require a treatment adjustment.
- Should my dog have an eye exam even if vision seems normal at home? Ocular blastomycosis can be present before a pet parent notices obvious changes, and early treatment may help preserve comfort and function.
- What signs would mean I should bring my dog back immediately? Knowing the emergency signs—especially worsening breathing, collapse, or sudden eye pain—helps you act quickly.
- What total cost range should I plan for over the next several months? Blastomycosis care often involves repeated rechecks and long-term medication, so a realistic budget discussion helps avoid interruptions in care.
How to Prevent Blastomycosis
There is no vaccine for blastomycosis, and prevention is not perfect because the fungus lives in the environment. Still, you can lower risk by being thoughtful about where your dog spends time, especially if you live in or travel through an endemic region.
Try to limit access to disturbed soil near rivers, lakes, marshes, wooded trails, excavation sites, and piles of decaying organic material. Dogs that dig, hunt, or run through muddy shoreline areas may have more exposure than dogs that stay on maintained paths. After outdoor activity, watch for coughing, eye changes, or unusual fatigue over the next several weeks.
Early recognition matters as much as prevention. If your dog develops a persistent cough, fast breathing, draining skin lesions, or eye inflammation after spending time in high-risk environments, let your vet know about that exposure history. That detail can help move fungal disease higher on the list sooner.
Blastomycosis is not considered a routine contagious disease between pets in the home. Even so, if one dog is diagnosed, it is reasonable to stay alert for similar signs in other pets that shared the same outdoor environment.