Fungal Infection (Blastomycosis) in Cats

Blastomycosis in Cats

Blastomycosis is a systematic yeastlike fungal infection caused by the organism Blastomyces dermatitidis, which thrives in wet environments, such as riverbanks, lakes and swamps, where damp soil lacking direct sunlight fosters growth of the fungus. The fungus 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.

Symptoms and Types

  • Difficulty breathing
  • Skin lesions


Blastomycosis typically occurs when a cat 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 cat at greater risk. You will want to ask your veterinarian to test for fungal infection if your cat has been in an environment where the blastomyces fungus might have been present at any time in the six weeks previous to the onset of symptoms.

The best methods for diagnosing blastomycosis is through examination of the cells in the lymph nodes, an analysis of fluid drained from skin lesions, a tracheal (windpipe) wash for collecting tracheal 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 your cat's lungs.

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