Blastomycosis Vet Guide 2025 🧫🐾

Greetings from Dr Duncan Houston BVSc! In this detailed, easy-to-read 2025 update, we’re exploring blastomycosis—a lung-based fungal infection that can affect dogs and cats. You’ll learn where it arises, how it spreads through the body, how we find and treat it, and what recovery looks like. Let’s get started! 😊

🌍 What Is Blastomycosis?

Blastomycosis is a systemic fungal infection caused by Blastomyces dermatitidis. It’s found mainly in wet, sandy, acidic soil rich in organic matter—commonly in river valleys and lakes. While dogs and cats inhale spores and become infected, the fungus doesn’t spread from animal to animal or to people under normal circumstances.

📍 Where Does It Occur?

• Mississippi River Valley
• Ohio & Missouri River Valleys
• Tennessee Valley
• St. Lawrence River Valley
• Provinces: Quebec, Ontario, Manitoba
• Also reported: Africa, India, Europe, Central America

Spore growth is favored in warm, moist soil near bodies of water—common hunting/play areas for pets. Those environments put dogs and cats at higher risk.

🐶 Who Gets Infected?

Dogs are much more likely—10× more so than people, and 100× more than cats. Annually, 1–2% of dogs in endemic areas get infected. Young male large breeds (like hounds or pointers) are often most affected, probably due to activity levels and time outdoors. However, it can affect any age, breed, or sex.

🔁 How Does It Spread in the Body?

Infection starts when spores are inhaled into the lungs, where they convert into yeast forms. This typically takes 5–12 weeks. From the lungs, the fungus can spread through the bloodstream and lymph system to involve:

• Lungs (primary sign)
• Skin (draining lesions, nodules)
• Eyes (redness, blindness)
• Bones and joints (lameness, swelling)
• Brain (neurologic signs like seizures)
• Lymph nodes, nasal passages, testicles, liver, heart

⚠️ What Are the Clinical Signs?

Symptoms vary by organ system and may include:

• Coughing/difficulty breathing (lungs)
• Skin lesions—ulcerated or draining nodules
• Ocular signs—inflammation, vision loss
• Bone pain or limping (bones/joints)
• Fever and weight loss (nonspecific)
• Neurologic issues—seizures, ataxia
• Nasal discharge or bleeding
• Swollen lymph nodes, testicles

Signs depend on which organs are affected. Dogs commonly have lung or bone signs, while cats show more skin or neurological involvement.

🔍 Diagnosing Blastomycosis

Clinical Exam

We check lungs, skin, eyes, bones, lymph nodes, nose, and overall condition.

Bloodwork

• Complete blood count (CBC): may show anemia or inflammation
• Biochemistry panel: assess organ function)

Imaging

• Chest radiographs or Ct: lung masses, nodules
• Bone/limb/brain imaging: detect lesions or neurologic damage

Urinalysis & Antigen Testing

Enzyme immunoassay for B. dermatitidis antigen in urine (93.5% sensitivity) or serum (87%). Cross-reactivity with related fungi can occur.

Cytology / Culture / Biopsy

Definitive diagnosis is seeing or culturing yeast forms from:

• Sputum or lung wash fluid
• Skin lesion material or lymph node aspirate
• Bone aspirate or biopsy
• Eye fluid or nasal samples

Serology

Antibody tests are unreliable (false negatives possible). Culture or cytology remains most reliable.

🛠️ Treatment Options

Oral Antifungals

• Itraconazole – first-line choice, many owners treat at home
• Fluconazole & Ketoconazole – alternative options
• Amphotericin B – used in severe cases, given IV in hospital

Combined Therapy

Severe cases may need amphotericin initially followed by itraconazole orally.

Supportive Care

• Restricted exercise for respiratory cases
• Hospital care: IV fluids, oxygen therapy, nutritional support
• Skin wounds: cleaning, debridement, pain relief
• Eye involvement: systemic & topical antifungals±corticosteroids or surgery

Treatment Duration

Expect to treat 6–12 months, depending on severity. Regular checkups should include:

• Every 4 weeks: physical exam, bloodwork, possibly imaging
• Urine antigen tests to track treatment response

📉 Prognosis & Relapse

• Good outcomes: 50–75% recovery with itraconazole, fluconazole, or amphotericin combos
• Early survival matters: surviving first 7–10 days improves long-term outlook
• Severe lung or neurologic cases: caution advised, higher risk
• Cats and eye involvement: vision may be permanently affected
• Multisystem cases: worse prognosis
• Relapse risk: 18–22%—most within 6 months. Requires additional treatment

🔎 Monitoring & Follow-Up

• Antigen levels checked at 1, 3, 6 months post-treatment
• Physical exams and imaging as needed
• Restart therapy if relapse occurs

🚫 Prevention

• No vaccine available.
• Best prevention: avoid endemic areas or restrict outdoor exposure in those zones.
• Remove and treat wet soil near homes if possible.

🧼 Zoonotic Risk & Safety

Blastomycosis isn’t contagious between pets or to people. Humans get infected from environmental spores—not from their animals. Immunocompromised individuals should handle infected pets with care (wear gloves when cleaning wounds).

📋 Owner’s Checklist

• ✔️ Monitor for persistent coughing, skin sores, eye changes, lameness, or neurologic signs.
• ✔️ Seek vet care if symptoms arise—early diagnosis boosts outcomes.
• ✔️ Prepare for long therapy—at-home oral antifungals, monthly labs.
• ✔️ Keep recheck appointments for bloodwork, antigen tests, imaging.
• ✔️ Use gloves for skin lesions; practice hygiene when handling bedding or urine.
• ✔️ Avoid walking pets near marshlands or river edges in endemic zones.

📱 Ask A Vet Service

Need help with blood sample collection, antifungal side effects, or environmental hygiene measures? Our Ask A Vet team offers on-demand advice—including lab guidance, dosing tips, and recovery monitoring. 💚

🔚 Final Thoughts

Blastomycosis can be a serious but treatable disease in dogs—and to a lesser extent, cats. With accurate diagnosis, long-term antifungal therapy, and supportive care, many pets can recover fully. Stay vigilant, act early, and partner with your veterinarian to ensure the best care. Reach out anytime through AskAVet.com or our app.

— Dr Duncan Houston BVSc