Blastomycosis in Horses

Blastomycosis in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
Blastomycosis in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What are Blastomycosis?

While Blastomycosis is typically found in dogs and cats, it can also be found in horses (though cases are extremely rare). Because of this, diagnosing Blastomycosis can be difficult. Skin lesions may be the only presenting symptoms; however, other signs such as dry cough, fatigue, weight loss and lethargy can be present and alternately point to a myriad of different conditions. 

Although limited documentation is available, studies do show that equines have been affected by cutaneous Blastomycosis, and in addition, fatal disseminated Blastomycosis, whereby no obvious symptoms were present but lung involvement was found. Primarily, infection is seen in the lungs. Evaluation by your equine veterinarian is essential to the correct treatment and recovery of the condition.

Blastomycosis is a condition that results from contact with the fungus Blastomycosis dermatitidis. Systemic infection and cutaneous lesions are characteristic of this condition and are found after examination of the tissue of the animal

Symptoms of Blastomycosis in Horses

Equines may be asymptomatic or present with skin lesions alone. Symptoms may vary but may include:

  • Dry cough 
  • Fever
  • Heavy sweating
  • Fatigue
  • Pain
  • Eyes may appear infected
  • Skin changes – Your horse can develop skin bumps that turn into blisters filled with pus; the blisters burst and create abscesses that will not heal. 
  • Lethargy
  • Anorexia
  • Weight loss 
  • Anemia
  • Nasal discharge
  • Respiratory distress – Your horse may begin to develop labored breathing due to the impact on his lungs 
  • Pneumonia – This may be secondary to the actual fungal infection 


Causes of Blastomycosis in Horses


  • North America: Mississippi, Missouri, Tennessee, Ohio River Basin, Great Lakes and St. Lawrence Seaway, Pacific Northwest, Northwestern Wisconsin
  • Southern Canada
  • Central America
  • Moist, acidic, and rich decaying vegetation
  • Beaver dams


  • Your horse comes into contact with this fungus when he inhales the spores
  • Once your horse inhales the fungus, it can spread to his skin, bones, and other organs 
  • Upon inhaling the spores, they cause inflammation of the lungs
  • Yeast forms can be found in pleural and peritoneal fluid
  • This is an airborne condition making it difficult to eradicate


Diagnosis of Blastomycosis in Horses

Documentation of Blastomycosis in equines is limited. Typically, the clinical examination may show respiratory issues. 

Tests can include x-rays of the lungs and ultrasounds of the chest and abdomen to check for lesions. Microscopic examination will be performed on samples taken from nasal discharge or a swabbing of your horse’s throat or mouth. 

A biopsy may be done on your horse’s lungs with the help of ultrasound guidance. This will allow the veterinarian to test the tissue directly from your horse’s lungs to determine what is causing his symptoms. Stains used to test for Blastomycosis are special as typical stains tend to not show the fungus. These will be the most common tests your veterinarian may suggest. Blood tests could show a high white blood cell count. Differential diagnosis may be pneumonia, uveitis, and neoplasia.



Treatment of Blastomycosis in Horses

Treatment options for Blastomycosis will vary, depending on your veterinarian’s suggestions. Antifungal medications are one option and alternative treatments are the second option. 

Antifungal Medications

  • Amphotericin B (Given via IV, many more side effects than Ketoconazole and will most likely require hospitalization for administering and monitoring side effects)
  • Ketoconazole (Found to be about 75% effective)
  • Itraconazole 
  • Fluconazole
  • Voriconazole
  • Enilconazole

Alternative Treatments

  • Creating an environment that will not support continued fungus growth
  • Low dairy, low sugars, no honey diet
  • Vitamins A plus, B, C and E can also help

Most studies show euthanization of the horse due to a poor prognosis. However, a horse who does have a positive response to the treatment may recover, although 20% of cases show a relapse months to even years after the initial infection.



Worried about the cost of Blastomycosis treatment?

Pet Insurance covers the cost of many common pet health conditions. Prepare for the unexpected by getting a quote from top pet insurance providers.

Recovery of Blastomycosis in Horses

It has been noted that horses have required a lifetime of treatment in order to stay ahead of a return of the fungus. The initial treatment may need to be repeated in order to eradicate the fungus. Many animals succumb to the condition as a result of the strain on the respiratory system, In endemic regions a vaccination may be warranted once developed.



Blastomycosis Questions and Advice from Veterinary Professionals

Need pet insurance?
Need pet insurance?

Learn more in the Wag! app

Five starsFive starsFive starsFive starsFive stars

43k+ reviews


© 2022 Wag Labs, Inc. All rights reserved.