Fungal Lung Infection in Cats: Signs and Treatment

A fungal lung infection in cats occurs when fungal spores are inhaled and infect the lungs. The infection can cause coughing, rapid or labored breathing, fever, and discomfort.

Fungal lung infections in cats are rare but can be fatal if left untreated.

Here’s what pet parents should know about the types, symptoms, causes, diagnosis, and treatment of fungal lung infections in cats.

What Is a Fungal Lung Infection in Cats?

A fungal lung infection in cats occurs when a cat breathes in fungal spores that enter the lungs and cause a pulmonary infection.

Fungus includes any of a group of organisms that produce spores and feed on organic matter, including molds, yeast, mushrooms, and toadstools.

The spores typically enter through the nose and make their way to the lungs, eventually growing into a yeast form.

The presence of the fungal organism in the lungs triggers the body’s defenses to form lesions in the lungs. This leads to symptoms such as coughing, rapid and labored breathing, fever, and discomfort.

Fungal infections in cats are rare, but they can be fatal if not treated.

What Are the Types of Fungal Lung Infections in Cats?

The four most common types of fungal lung infections in cats are blastomycosis, coccidioidomycosis, cryptococcosis, and histoplasmosis.

Blastomycosis

• Caused by a fungus known as Blastomyces dermatitidis
• It is most common in the river basins of Mississippi, Missouri, Tennessee, and Ohio, but is also found around the Great Lakes and St. Lawrence Seaway.
• The fungus is native to Africa, India, Europe, Central America, and a few Canadian provinces.
• Coughing and difficulty breathing are the most common symptoms.

Coccidioidomycosis

• Caused by the Coccidioides fungal species
• This type of fungus prefers arid and semi-arid environments of the U.S. Southwest, Mexico, and Central and South America.
• Coccidioidomycosis has many symptoms, ranging from being asymptomatic (no visible symptoms) to severe symptoms, such as trouble breathing.

Cryptococcosis

• A fungal infection caused by Cryptococcus neoformans or Cryptococcus gattii
• C. neoformans is found worldwide, while C. gattii is native to Australia, New Zealand, Canada, the Pacific Northwest, and Central and South America.
• Cats acquire the fungus by inhaling the spores from the soil, decayed wood, or bird guano, especially from pigeons.
• Upper respiratory symptoms are most common, such as:
  • Sneezing
  • Hard swelling over the bridge of the nose
  • Polyps in the nasal passages
  • Nasal discharge
  • Difficulty breathing
• Lower respiratory disease is less common, but if the fungus infects the lungs, cats will have coughing as well as rapid and labored breathing.

Histoplasmosis

• Caused by Histoplasma capsulatum
• This fungus is a common inhabitant of soil that contains fecal matter from birds and bats. It can be found globally, and in the U.S. it is predominantly found along the Mississippi and Ohio River valleys.
• The spores spread primarily to the lungs, as well

What Are the Symptoms of a Fungal Lung Infection in Cats?

Symptoms of a fungal lung infection in cats include coughing, difficulty breathing, increased respiratory rate, discomfort, decreased appetite, lethargy, and fever.

Common symptoms include:

• Coughing
• Difficulty breathing
• Increased respiratory rate
• Discomfort
• Decreased appetite
• Lethargy
• Fever

What Causes Fungal Lung Infections in Cats?

A fungal lung infection in cats develops when a cat breathes in airborne fungal spores that invade the lungs and other areas of the body.

The environment plays an important role as to where certain fungi flourish.

Blastomycosis fungi prefer areas where there is natural water and acidic soil that is sandy and moist. Cryptococcosis and histoplasmosis fungi grow best in guano or decaying wood. Coccidioidomycosis fungi grow best in arid and semi-arid areas after a dust storm.

How Veterinarians Diagnose Fungal Lung Infections in Cats

Veterinarians can diagnose a fungal lung infection in cats using cytology, radiography (X-rays), antigen and antibody testing, fungal culture, PCR testing, and histopathology.

• Cytology: A veterinarian gathers tissue samples from a cat, which will then be analyzed with a stain that highlights the fungal organism. Urine, nasal swabs, cerebral spinal fluid (CSF), or fluid obtained from the lungs can also be examined.
• Radiography: While X-rays cannot provide a definite diagnosis, they are helpful in determining if a fungal infection is possible, leading to further testing. If a fungal infection is present, the lungs may contain nodules and have a "snowstorm" appearance or have other various abnormal lung patterns.
• Antigen and antibody tests: These tests are very sensitive and highly specific, as they test for the antigen or antibody levels for the specific fungus in specimens. False positive and negative test results may occur, so the results of these tests are often interpreted with other diagnostic tests to reach a definitive diagnosis.
• Fungal culture: Using urine, CSF, joint fluid, tissue, or fine needle aspirates, a culture can grow the fungus so it can be examined. Fungal cultures are not done to test for histoplasmosis, blastomycosis, or coccidioidomycosis because these fungal organisms would be harmful to laboratory workers.
• Polymerase chain reaction (PCR) assay: This test can detect and identify a fungus in a deep pharyngeal or nasal swab, fluid from the lungs or trachea, aspirate, or biopsy of infected tissue. It takes one to four days to obtain test results.
• Histopathology: Biopsy samples from an infected tissue or organ or necropsy specimens can be sectioned and stained to scan microscopically for the presence of fungi.

How Veterinarians Treat Fungal Lung Infections in Cats

Treatment for a fungal lung infection in cats typically involves antifungal medication for several months. The type of medication used and the length of treatment depend on the type and severity of the infection.

Commonly prescribed antifungal medications include:

• Itraconazole: This oral anti-fungal medication is the preferred treatment for histoplasmosis.
• Fluconazole: This oral anti-fungal medication is often the treatment of choice for cryptococcosis, blastomycosis, and coccidioidomycosis.
• Ketoconazole: This oral anti-fungal medication is less effective compared to itraconazole or fluconazole and can be toxic to the liver. This medication is typically used if other treatments are too costly.
• Amphotericin B (AMB): This medication is often prescribed when a cat has a severe fungal infection in the lungs and other areas of the body. Amphotericin B is given as an injection, usually three days a week for three to four weeks. It can be the sole therapy or given along with an oral anti-fungal medication.
  
  Amphotericin B can cause toxicity to the kidneys, so cats on this medication should have blood work and a urinalysis test done periodically to monitor their kidney function.

Recovery and Management of Fungal Lung Infections in Cats

Recovery from a fungal lung infection in cats depends on the type and severity of the infection. Treatment may require ongoing monitoring with antigen titer tests to check for relapse.

The length of treatment for any of the above anti-fungal medications is based on antigen titers (tests). When the titer reaches zero, treatment is discontinued. Titers are usually conducted every three to six months to check for a relapse of infection. 

If the titer is unchanged after two months of treatment, then a different treatment plan is prescribed. If a cat has a relapse of infection, they are treated again.

How To Prevent Fungal Lung Infections in Cats

Keeping cats indoors can help reduce their exposure to harmful fungal spores, although indoor cats can still develop fungal lung infections.

Indoor cats should be kept away from house plants, as the soil in the pots could contain fungus. Unfinished basements should also be off limits to cats because they commonly have dirt floors that may contain fungi.