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Blastomycosis in Cats

By: Dr. Rosanna Marsalla

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Blastomycosis is a systemic disease caused by a fungus present in the soil of certain regions, such as Mississippi, Missouri and Ohio River Valley. The organism is present in the soil and infection occurs by inhalation of the fungus. Once infection is established in the lung, the fungus changes its characteristics by converting from the mycelial form into the yeast form and spreads to other organs causing a disseminated infection.

This fungus exists in two different forms:

  • Mycelial form. This form is present in the environment and is contagious.
  • Yeast. This form is found in the tissues and is not contagious.

    Hunting cats that spend a lot of time outdoors and live in endemic areas are at risk for inhaling this organism and developing the disease.

    Some animals may be infected but not show clinical signs for a long time. These animals are not a risk for contagion of other animals and people because the stage of the organism present in the animal's tissues is not that of an infectious stage.

    If left untreated, these cats can become seriously ill. Cats may develop infection in the kidneys, eyes, brain and bones. According to the organ that is affected, the clinical signs may vary. They may have ocular problems or neurological signs like seizures and head tilt. In some cats lameness may be the primary complaint due to infection in the bones.

    What to Watch For

  • Coughing
  • Difficulty breathing
  • Fever
  • Loss of appetite
  • Weight loss


    Suspicion of blastomycosis comes from the history of living in an area at risk for this infection, especially in animals that hunt or spend a lot of time outside. Clinical signs may not be very specific.

  • There are some tests that can be run to see if the animal has been exposed to the organism and has produced antibodies against it. This type of test (serology) requires a blood sample and is not 100 percent reliable. It could be falsely negative in the early stage of the disease.

  • The definitive diagnosis comes from the identification of the fungus in the tissues. This is possible when skin lesions are present in the form of nodules that drain purulent material. In those cases a biopsy is taken and sent to the laboratory for microscopic examination and for culture.


  • Affected animals require many months of antifungal therapy.

  • Some drugs are given intravenously (amphotericin B) while others are given orally (e.g. ketoconazole). Depending on the severity of the disease a combination of drugs may be selected.

  • These drugs have the potential to cause kidney and liver damage, thus it is very important that your pet is closely monitored and that blood work is repeated frequently to check for signs of toxicity.

  • The prognosis (outcome) depends on the severity of the lung disease, and how extensive is the infection in the body. It is important to take chest radiographs and evaluate the extent of the lung involvement.

    Home Care and Prevention

    It is important that you administer the medications as instructed by your veterinarian and that you monitor the appetite and bowel movements of your pet. Some drugs may induce nausea and vomiting. If your pet stops eating, your veterinarian needs to be notified immediately.

    There is no vaccine or effective way of disinfecting the contaminated soil.

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