Fungal Infection (Blastomycosis) in Cats

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Last updated on
5 min read

Key takeaways

Blastomycosis is a fungal infection in cats caused by the fungus Blastomyces dermatitidis, which is commonly found in soil around bodies of water.

  • Cases are most commonly identified around the Ohio, Mississippi, Tennessee, and St. Lawrence rivers
  • When fungal spores are inhaled, symptoms such as difficulty breathing, coughing, fever, blindness, draining skin sores, and seizures can develop
  • Diagnosis involves a physical examination, bloodwork, urinalysis, diagnostic imaging, and specific testing for the fungus
  • Treatment involves a long course of antifungal medications
  • The prognosis of blastomycosis is guarded, as severe organ damage can occur due to the infection
  • Cats that develop severe lung infections or infections of the nervous system have the poorest prognosis
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A closer look: Fungal Infection (Blastomycosis) in Cats

The fungus Blastomyces dermatitidis is found throughout Eastern North America near waterways. It is a difficult fungus to identify in nature but appears to prefer areas of high moisture, near water, with abundant decaying organic matter. Inhalation of aerosolized spores is the primary method of infection.

Blastomycosis typically affects the lungs, causing difficulty breathing.** Any cat showing symptoms of respiratory distress requires immediate veterinary care.** Other forms of blastomycosis include draining skin sores or abscesses, swollen lymph nodes, and seizures. Cats showing these symptoms require prompt veterinary attention, as rapid treatment can improve the prognosis.

Blastomycosis can infect humans through inhalation of spores. Direct spread of infection from an animal to a human is unlikely, but has been reported in association with bite wounds.

Risk factors

Blastomycosis is an uncommon infection that primarily affects outdoor cats. Areas where blastomycosis is most common include the river basins of the Mississippi, Tennessee, Ohio, and St. Lawrence rivers. Cats that have access to wet environments, such as streams, lakes, or swamps, may also have a higher risk.

Blastomycosis may affect the skin, eyes, and nervous system of cats.

Blastomyces infection of the skin can also cause abscesses, leading to draining or oozing sores or lumps on the skin.

Possible causes

The causative agent of blastomycosis is the fungus Blastomyces dermatitidis. Blastomyces is typically found in the soil, where it produces fungal spores. Cats inhale the spores, resulting in infection of the lungs. From there, the infection can spread throughout the body via the bloodstream.

Blastomyces is most common in wet environments, such as near streams, lakes, swamps, or rivers. Outdoor cats living near bodies of water are most at risk of developing infection. Cats that are exposed to soil that has been recently uncovered are also at risk.

Main symptoms

Most cases of blastomycosis primarily affect the lungs.

Testing and diagnosis

Diagnosis of blastomycosis involves identifying the fungal organism, and identifying organs that are affected. Diagnostics include:

  • Physical examination
  • Bloodwork
  • Urinalysis
  • Diagnostic imaging, including X-rays
  • Identification of fungal proteins in the blood or urine
  • Cytology of lymph nodes, tracheal wash fluid, or skin lesions
  • Biopsy of affected tissue

Steps to Recovery

Treatment initially focuses on stabilizing the patient with supplemental oxygen, particularly if they present with difficulty breathing. Once stabilized, long-term antifungal treatment is required to control the infection. Other treatments may include:

  • Surgical removal of affected lung lobes
  • Surgical removal of affected eyes

Antifungal therapy can have serious side effects, particularly liver failure. Repeated bloodwork is required to monitor for organ damage. Repeated X-rays and fungal testing are also used to monitor treatment progress, and ensure that the infection is resolved before treatment stops.

Blastomycosis is difficult to treat, and many treatment protocols require several months of antifungal therapy. Cats that are treated early in the infection have the best prognosis, as minimal damage to organs has occurred. Cats that have severe lung disease or neurologic signs have an extremely poor prognosis.


The precise locations where Blastomyces grows are unknown, so avoiding exposure is difficult. For cats, keeping them indoors offers the best protection, as they are unlikely to be exposed to spores within a household environment.

Blastomycosis is generally not considered directly contagious from animal to animal, or from animal to human, although there have been reports of dog bites spreading infection. Infected cats within a household may indicate that humans have been exposed to fungal spores.

Is Fungal Infection (Blastomycosis) in Cats common?

The prevalence of blastomycosis depends on the geographic area. Cases are most common along the Ohio, Tennessee, Mississippi, and St. Lawrence rivers.

Typical Treatment

Antifungal medication


No Author - Writing for Cornell University College of Veterinary Medicine
Tamara Gull, DVM, PhD, DACVM, DACVIM (LA), DACVPM - Writing for Merck Veterinary Manual
Smith, F.W.K., Tilley, L.P., Sleeper, M.M., Brainard, B.M. - Writing for Blackwell’s Five-Minute Veterinary Consult: Canine and Feline. Seventh Edition.

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