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Blastomycosis in Cats

By: Dr. Rosanna Marsalla

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Diagnosis In-depth

Certain diagnostic tests must be performed to confirm the diagnosis of blastomycosis and exclude other diseases that may cause similar symptoms. Tests may include:

  • A complete medical history and physical examination, including auscultation (listening with a stethoscope) of the lungs, careful examination of the eyes and nervous system, and evaluation of the skin for draining nodules

  • A complete blood count (CBC or hemogram) to evaluate the severity and chronicity of inflammation, detect the presence of non-regenerative anemia, and check platelet count. The clinical presentation of animals with some diseases associated with low platelet count (Ehrlichiosis, Rocky Mountain spotted fever) can resemble blastomycosis.

  • Serum biochemistry tests to determine the effect of blastomycosis on other organ systems, and to evaluate the health of other organ systems, especially the liver and kidneys, before treatment with anti-fungal drugs that can be toxic for the liver and kidneys. Rarely, high blood calcium concentration (hypercalcemia) is found in animals with systemic fungal infection and hypercalcemia can occur in diseases that can be confused with systemic fungal infection like lymphosarcoma. Certain blood proteins may be increased in the blood of animals with systemic fungal infection and in those with other chronic infectious diseases.

  • Urinalysis to identify urogential involvement, evaluate kidney function and check for bacterial urinary tract infection.

  • X-rays of the chest to evaluate the severity of lung involvement and to check for enlarged lymph nodes in the chest. Bone involvement also may be identified on X-rays of the chest.

  • X-rays of the abdomen to evaluate vital organs, especially the liver and kidneys. Bone involvement also may be identified on X-rays of the abdomen.

  • Serologic tests for heartworm disease, brucellosis, and rickettsial infection as well as the agar gel immunodiffusion test to identify blastomycosis. The agar gel test is very reliable but may be negative early in the course of infection.

  • Finding the blastomyces organism during microscopic examination of material collected from draining skin nodules results in a definitive diagnosis.

  • Microscopic examination of a biopsy specimen from affected tissue by a veterinary pathologist can also lead to a definitive diagnosis, but this method is more invasive, and results take longer to return from the laboratory.

    Treatment In-depth

    Treatment of blastomycosis must be individualized based on the severity of the condition and other factors that must be evaluated by your veterinarian. Therapy is aimed at relief of specific symptoms (e.g. difficulty breathing, coughing, eye problems) and elimination of the fungus from the body. Treatment may include one or more of the following:

  • Antifungal drugs. Those effective against blastomyces include amphotericin B and the imidazole derivatives (e.g. ketoconazole, itraconazole, fluconazole).

  • Amphotericin B is often administered intravenously followed by oral administration of ketoconazole, one of the imidazole derivatives. Then it is administered three times per week until a sufficient cumulative dose has been achieved. Amphotericin must be given in relatively small amounts over time because it is very toxic to the kidneys. Kidney function tests must be monitored during the course of amphotericin B therapy. Amphotericin B is given diluted in a 5 percent dextrose solution, and the intravenous administration of the fluid also serves to protect the kidneys from toxicity.

  • Ketoconazole is an imidazole drug that can be administered orally (often after a course of amphotericin B). Ketoconazole is well absorbed from the gastrointestinal tract and has reasonable activity against blastomyces. Treated animals should be watched for loss of appetite, vomiting, or diarrhea because these symptoms may indicate drug toxicity. Ketoconazole is potentially toxic to the liver, and liver function tests should be monitored in treated animals. Ketoconazole has the potential to produce adverse reactions when used in combination with some other drugs, and other medications being administered to the animal should be reviewed before beginning therapy with ketoconazole. Unfortunately, treatment with ketoconazole usually does not completely eliminate the fungus from the animal's body.

  • Itraconazole is another imidazole effective against blastomyces that has less potential for liver toxicity than does ketoconazole. It usually produces a more rapid response than does ketoconazole. Itraconazole must be administered for two to three months, and approximately 20 percent of treated cats ultimately experience a recurrence of disease. Adverse effects include loss of appetite, vomiting, and diarrhea.

  • Fluconazole is an imidazole derivative active against blastomyces that has good penetration into the nervous system, eyes, and urinary tract. It is especially useful in animals with urogential infections because ketoconazole and itraconazole are not excreted into the urine in any appreciable amount. The dosage of fluconazole should be adjusted in animals with poor kidney function. In general, however, fluconazole is less toxic than ketoconazole. Also, it is not associated with the adverse drug interactions occasionally observed with ketoconazole use. Like the other imidazole derivatives, it must be administered for a minimum of 60 days and recurrence may occur in up to 20 percent of treated animals.

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