Veterinary Guide to Histoplasmosis in Dogs 2025 🩺🍄🐶

By Dr. Duncan Houston BVSc

🧬 What Is Histoplasmosis?

Histoplasmosis is a systemic fungal infection caused by Histoplasma capsulatum, which thrives in soil enriched with bird or bat droppings, especially in river valleys like the Mississippi & Ohio in North America. Dogs inhale or ingest spores, leading to pulmonary or gastrointestinal disease, or widespread dissemination to other organs.

🌍 Why It Matters in 2025

• • Often overlooked due to vague symptoms like fever, weight loss, and lethargy.
  • Potentially fatal if untreated—but treatable with timely antifungal therapy.
  • Dogs act as sentinels; awareness helps protect both pet and owner health.

🚩 Who’s at Risk?

• • Age: Most dogs under 4–5 years old.
  • Breed predisposition: Brittany Spaniels, Pointers, Weimaraners, working dogs.
  • Location: River valley regions; exposure to caves, roosting birds/bats.

👀 Clinical Signs & Variability

Symptoms depend on the organ systems involved; commonly include:

• • General signs: Fever, weight loss, anorexia, lethargy.
  • GI signs (most common): Chronic diarrhea (often bloody/mucoid), straining, vomiting.
  • Respiratory signs: Coughing, tachypnea, nasal discharge.
  • Hepatic/lymphatic: Hepatomegaly, splenomegaly, lymphadenopathy, jaundice.
  • Other: Draining skin lesions, ocular inflammation, lameness from bone/joint involvement; rare neurologic signs.

🔬 Diagnosis: Multi-layered Approach

1. 1. Signalment & history: Young working dogs in endemic areas.
   2. Baseline tests: CBC (anemia, thrombocytopenia), biochemistry (hypoalbuminemia, elevated liver enzymes).
   3. Imaging: Thoracic X-rays—interstitial/nodular patterns; abdominal ultrasound—organ enlargement, mucosal thickening.
   4. Cytology/Histopathology: FNA or biopsy from lymph nodes, lungs, GI tract—looking for yeast inside macrophages.
   5. Antigen testing: Urine antigen ELISA—noninvasive and sensitive.
   6. Lavage techniques: BAL or TTW for pulmonary involvement.

🩺 Treatment Protocols

Antifungal Therapy

• • Itraconazole: 5–10 mg/kg daily; well tolerated and effective.
  • Fluconazole: Alternative; similar remission rates (~64–71%).
  • Severe cases: Amphotericin B (IV), often followed by azole maintenance.
  • Duration: Continue treatment at least 1 month beyond clinical resolution—typically 6–12 months.
  • Supportive medications: Corticosteroids (short course) for lymph node inflammation; appetite stimulants; antiemetics.

Supportive Care

• • IV fluids for dehydration.
  • Nutritional support or feeding tubes if anorexic.
  • Manage secondary infections.
  • Monitor liver/kidney function during prolonged azole therapy.

📊 Monitoring & Prognosis

• • Recheck antigen levels, bloodwork, and imaging every 2–3 months.
  • Most dogs (<70%) enter clinical remission.
  • Negative prognostic indicators: dyspnea, icterus, anemia, thrombocytopenia, organomegaly.
  • Early detection and treatment yield best outcomes.

🏡 At-Home Care Guide

• • Administer antifungals consistently and monitor for side effects.
  • Track appetite, feces, drinking, and energy levels.
  • Provide soft bedding and gentle exercise.
  • Ensure follow-up diagnostics and antigen testing.
  • Equip with cooling pads or e-collars for skin lesions.

📱 Ask A Vet Integration

• • Telehealth check-ins: Review diagnostics, adjust treatment plans.
  • Medication reminders: Scheduled dosing alerts via the app.

🎓 Case Spotlight: “Ranger” the Brittany

“Ranger,” a 3‑year‑old Brittany, presented with chronic diarrhea and weight loss. FNA confirmed Histoplasma in lymph nodes; urine antigen was positive. Treated with itraconazole for 9 months plus supportive care, Ranger regained energy, weight, and antigen levels became negative after 7 months. Owner says: “He’s back to his bird dog self!” 🐾

🔚 Key Take-Aways

1. 1. Histoplasmosis is a treatable systemic fungal disease—early suspicion is crucial.
   2. Diagnosis relies on imaging, antigen testing, and cytology.
   3. Itraconazole and fluconazole are effective; amphotericin B is used for severe cases.
   4. Long-term therapy, monitoring, and supportive care yield good outcomes.
   5. Ask A Vet offers ongoing remote support—from dosing to nutrition and comfort tools.

Dr Duncan Houston BVSc, Ask A Vet founder. Don’t forget to download the Ask A Vet app for expert fungal infection guidance anytime—your pup deserves a healthy future! 🐶❤️