Fungal Infection (Blastomycosis) in Dogs

4 min read

Blastomycosis in Dogs

Blastomycosis is a systematic yeastlike fungal infection caused by the organism Blastomyces dermatitidis, which is commonly found in decaying wood and soil. Blastomycosis occurs most frequently in male dogs, but female dogs are also susceptible.

Dogs that are frequently exposed to environments where Blastomyces dermatitidis exists are at increased risk.

This is particularly so with large-breed dogs weighing at least 55 lbs (25 kg), and especially sporting breeds. The Blastomyces fungus thrives in wet environments, such as riverbanks, lakes and swamps, where damp soil lacking direct sunlight fosters growth of the fungus. It is also present in areas that are rich in decaying matter, such as wooded areas, forests, and farms. It is a naturally occurring North American fungus, with the highest prevalence of infection taking place in geographic areas located near water -- such as the Mississippi, Ohio, Missouri, and Tennessee River basins. Studies have concluded that most affected dogs live within at least 400 meters of a body of water.

The condition or disease described in this medical article can affect both dogs and cats. If you would like to learn more about how this disease affects cats, please visit this page in the PetMD health library.

Symptoms and Types

  • Fever
  • Loss of appetite (anorexia)
  • Weight loss
  • Eye discharge
  • Eye inflammation, specifically the iris
  • Difficulty breathing (e.g., coughing, wheezing and other unusual breathing sounds)
  • Skin lesions, which are frequently filled with pus


Blastomycosis typically occurs when the dog inhales the airborne fungal spores of the genus Blastomyces dermatitidis after the contaminated soil has been disturbed. This can be from an activity as benign as digging in the dirt or following a scent trail. The spores can also enter through the skin. Exposure to areas with water, decaying matter, or recently excavated areas increase the risk of exposure to the fungus and consequent development of the disease.


Care must be taken to test properly for this condition, since it is commonly misdiagnosed, which can lead to permanent or fatal damage. It may be mistaken for cancer and mistreated, or it may be mistaken for a lung infection of bacterial origin and treated with antibiotics, which puts your pet at greater risk. If your pet has been in an environment where the Blastomyces fungus may have been present, at any time in the six weeks previous to the onset of symptoms, you will want to ask your veterinarian to test for fungal infection.

The best methods for diagnosing blastomycosis is an examination of the cells in the lymph nodes, an analysis of fluid drained from skin lesions, a tracheal wash for collecting trachea (windpipe) fluids, and an examination of lung tissues. Tissue samples may also be taken to check for the presence of fungal organisms, especially if there is no productive cough (productive, meaning that fluids are produced). Other tests that may help diagnose blastomycosis include a urine analysis, and an X-ray of the dog's lungs.

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