Blastomycosis in Cats

Published Nov. 14, 2022
tabby cat walking outside

In This Article


What Is Blastomycosis in Cats?

Blastomycosis, sometimes called blasto, is a disease caused by the fungus Blastomyces dermatitidis. The condition more commonly occurs in dogs, although it also occurs in cats. Blasto primarily affects the lungs of cats, but it can also progress to the brain and spinal cord, lymph nodes, skin, eyes, or gastrointestinal system.

The fungus is commonly found in soil near wet environments, such as riverbanks, lakes, and swamps, or around decomposing organic matter, such as wooded areas and forests. Many cases of blastomycosis have occurred in the Mississippi, Missouri, Tennessee, and Ohio river basins; near the Great Lakes; and in Canada’s Manitoba and Ontario provinces.

Cats can acquire these infections by ingesting or inhaling the blasto organism or by the microbe entering the skin through a wound or cut (it cannot penetrate intact skin). The time between exposure to this organism to when a cat starts to show clinical signs ranges from 5-12 weeks. Blastomycosis is not contagious between animals and people. Unfortunately, it can be fatal to those infected.

Symptoms of Blastomycosis in Cats

The symptoms of blastomycosis vary, depending on which organ system is involved. Below is a list of blasto symptoms, ordered from most to least common in cats.

These symptoms can also be non-specific, meaning they are not directly related to the fungal lesion but are related to a general feeling of illness. It is important to bring your cat to a veterinarian as quickly as possible if they have any signs of blastomycosis.

  • Weight loss

  • Lethargy

  • Coughing

  • Decreased or lack of appetite (anorexia)

  • Difficulty breathing

  • Nasal discharge, especially bloody discharge

  • Eye issues or ocular changes, such as inflammation, redness, swelling, or blindness

  • Enlarged lymph nodes, lumps under the skin

  • Lameness, limping

  • Skin lesions, abscesses

  • Fever

  • Neurologic changes

  • Bloody urine

  • Difficulty urinating

Causes of Blastomycosis in Cats

The most common way for cats to contract blastomycosis is by ingesting or inhaling the fungal spores, but it can also be transmitted directly into a cat’s circulation through a skin wound. While infectious fungal spores are found only in soil near waterways, both indoor cats and cats with access to the outdoors can be infected, since the spores live and spread in the air.

Once the fungal spores are inhaled or ingested, the warmth of the cat’s body allows the spores to transform into budding yeast. The yeast establishes lesions in the lungs or broken skin, and from there it can spread to the bloodstream and infect other organs. Though fungal infections can cause disease in healthy cats, those with a compromised immune system or those weak or sick with other illnesses commonly become infected more readily. Cats that are provided antibiotic drugs or immunosuppressive agents long-term also appear to be more susceptible to fungal infections.

How Veterinarians Diagnose Blastomycosis in Cats

An important aspect of diagnosing a blasto infection is knowing if your cat frequents the type of place that harbors the fungal organism, so providing your veterinarian with a detailed history of your pet’s activities is crucial.

Your veterinarian will probably do a complete physical examination and order bloodwork (chemistry panel, complete blood count, and electrolyte panel) to assess body function and to rule out other conditions that might cause similar signs. A urine and blood test specifically for blastomycosis is only reliable for dogs, so the diagnosis in cats is generally made through visualization under a microscope of fungal organisms in infected tissues.

If your cat has lesions on the skin or other body organs, a biopsy will be recommended to collect cells or remove a piece of abnormal tissue that will then be tested for the blasto organism. These lesions can be seen during a physical examination as skin abscesses, on radiographs as lung nodules, or on advanced imaging such as a CT scan or MRI as advanced lung disease or other body systems being affected.

In coughing cats, with or without lung disease evident on initial chest x-rays, an airway wash (tracheal wash or tracheal lavage) is typically ordered. This procedure requires your cat to be heavily sedated so that lung fluid samples can be collected for analysis. It is possible that your vet can see the fungal spores in this analysis, which would confirm the diagnosis.

Treatment of Blastomycosis in Cats

Treatment is highly dependent on how severely affected your cat is. Cats that are having breathing issues or those not eating are more likely to be hospitalized. Treatment for feline blastomycosis consists of a prolonged course of oral antifungal medications. Itraconazole is the treatment of choice for both cats and dogs with blasto. Combination therapy with other antifungal medications is sometimes needed for advanced cases or those not responding to itraconazole alone.

If the fungus has infected the respiratory system, your veterinarian will also work to stabilize your cat’s condition and treat any severe symptoms. Supportive care to help with symptoms may include oxygen therapy for those having trouble breathing, IV fluids, anti-inflammatories, appetite stimulants, and liver protectants.

Antifungal medications have the propensity for side effects on the liver and gastrointestinal system. For this reason, it is important that your vet monitor your cat’s liver enzymes and other body functions with routine bloodwork and urine testing during and after treatment.

The prognosis for feline blastomycosis is guarded, but treatment is improving with the availability of newer antifungal medications. Unfortunately, the death rate in cats with severe respiratory infections is high, even after treatment begins.

Recovery and Management of Blastomycosis in Cats

Antifungal medication is given daily for two to six months. Once cats have made it through the first two weeks of treatment, the prognosis for recovery improves. It is critical to give all medications as directed. Working closely with your veterinarian and following all medication instructions will increase your cat’s chance of survival and reduce the likelihood of relapse and returning symptoms.

To know when treatment can be discontinued, routine x-rays of the lungs will likely be done to ensure that the lesions are healing. Medications are usually continued for at least a month after clinical signs have dissipated and lung lesions are no longer visible on x-rays. Relapse can occur in cats with very severe cases of blastomycosis or those in which treatment was stopped too soon.

Prevention of Blastomycosis in Cats

There is no way to prevent blastomycosis except keeping your cat away from areas that have a high risk for fungus, such as riverbanks and decaying organic material. If your cat spends time outside in environments that are damp and wet with minimal sunlight and you see symptoms that may indicate a fungal infection, contact your veterinarian immediately. While there is no vaccine currently available to prevent blastomycosis, studies are ongoing to formulate an effective and safe vaccine against this fungal disease.

Featured Image: iStock/aryutkin photo

Barri J. Morrison, DVM


Barri J. Morrison, DVM


Barri Morrison was born and raised and currently resides in Ft. Lauderdale, Florida. She went to University of Florida for her...

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