Fungal Infection (Coccidioidomycosis) in Cats

Key takeaways

Coccidioidomycosis in cats is a systemic infection caused by inhalation of dust-borne fungal spores of Coccidioides immitis or Coccidioides posadasii. Coccidioides is endemic in dry, desert areas and outbreaks commonly occur after dust storms.

  • General symptoms include fever, lack of appetite, and weight loss
  • Other symptoms vary with organs affected, and include skin masses/abscesses, cough, lameness, and seizures
  • About half of affected cats have the disseminated form of the disease, meaning the fungus has infiltrated multiple organ systems
  • Immunosuppression may be a predisposing factor, but the common immunosuppressive diseases FIV and FelV are not thought to contribute to susceptibility
  • Diagnosis is through imaging (x-rays, MRI), blood work, and fungal identification in tissue biopsy
  • Treatment is long-term antifungal drugs
  • Prognosis is generally good with treatment and if the drugs do not cause unacceptable side effects
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A closer look: Fungal Infection (Coccidioidomycosis) in Cats

Coccidioides is a genus of fungus that is found primarily in dry desert climates. When inhaled, it can cause infection leading to coccidioidomycosis. Inhalation is most common when the soil has been recently disturbed and aerosolized. Coccidioidomycosis is rare in cats. Many of the potential symptoms are painful and warrant veterinary attention. Early intervention may improve prognosis.

While a pet parent cannot contract a Coccidioides infection from an infected cat, the fungus can infect humans. When a pet is infected it can be an indication that associated humans may also be infected.

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Risk factors

The coccidioides fungus is primarily found in the Western hemisphere and is endemic in the Southwestern United States. As it thrives in dry, desert-like environments, pets in areas with that type of climate are at higher risk of infection.

Symptoms can depend on which organs are affected by this systemic disease.

In cats, the skin is most commonly affected. Dermatological conditions include draining skin lesions (abscesses) that appear as subcutaneous skin tumor-like masses that may drain or ooze from the skin.

Cats with coccidioidomycosis can also develop pneumonia which overlap with respiratory-related clinical signs above.

Symptoms of coccidioidomycosis can vary from very mild and self-limiting to fatal.

Possible causes

Infection occurs by inhalation of the spores of Coccidioides immitis or Coccidioides posadasii. It is unclear why approximately 40% of exposed cats get sick after inhaling Coccidioides spores, but rick factors may include:

  • Living in dry, arid, or semi-arid areas
  • Outdoor roaming
  • Immunosuppression (though FIV and FelV are not thought to predispose)

Main symptoms

Testing and diagnosis

Diagnosis of coccidioidomycosis can be difficult, because it is rare and the signs mimic those of many other disease processes. Diagnosis begins with a physical exam, and is often followed by tissue biopsy, imaging (x-rays, MRI), and blood work (including possible antibody and/or antigen tests to detect the fungus). It is best if diagnosis is confirmed by more than one test.

Steps to Recovery

Treatment is antifungal drugs. Duration of treatment is generally long-term and ranges from less than 1 week to over 3 years. Blood work is needed during treatment to monitor for disease clearance and side effects of medication. Prognosis is generally good with proper compliance and in the absence of unacceptable side effects. Relapse is seen in 15-20% of cases.


Coccidioidomycosis is not contagious. Prevention relies on not being exposed to the organism, therefore avoiding Coccidioides-endemic areas and not allowing cats to go outdoors may be helpful. These preventatives are especially important in immunosuppressed cats, such as those prescribed steroids.

Is Fungal Infection (Coccidioidomycosis) in Cats common?

Coccidioidomycosis is rare in cats.

Typical Treatment

Long-term antifungal drugs.


Tamara Gull , DVM, PhD, DACVM, DACVIM (LA), DACVPM - Writing for Merck Veterinary Manual
Wendy Brooks, DVM, DABVP - Writing for Veterinary Partner
J.S. Renschler, DVM, PhD, Dipl ACVP and L.J. Wheat, MD - Writing for MiraVista Veterinary Diagnostics
No Author - Writing for The Center for Food Security and Public Health
Greene RT, Troy GC. - Writing for Journal of Veterinary Internal Medicine

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