What actually happens when a cat inhales fungal spores?

Fungal pneumonia in cats begins when airborne spores from organisms such as Blastomyces dermatitidis, Histoplasma capsulatum, Coccidioides species, or Cryptococcus are inhaled through the nose and settle deep in the lung tissue, where they convert into a yeast-like form and begin to multiply. The Merck Veterinary Manual describes this process as triggering a granulomatous immune response, meaning the body walls off the organism into small nodules rather than clearing it outright, which is part of why these infections can smolder for weeks before an owner notices anything wrong (Merck Veterinary Manual, 2023). Because the fungus can also travel through the bloodstream to the eyes, skin, bones, and central nervous system, a case that starts as a cough can eventually look like an entirely different disease if it isn't caught early.

Cryptococcus neoformans and Cryptococcus gattii are considered the most commonly diagnosed systemic fungal pathogens in cats in North America, according to the Cornell Feline Health Center, and they are typically acquired from soil contaminated with pigeon droppings or from decaying eucalyptus and other trees (Cornell Feline Health Center, 2021). Unlike some of the other regional fungi, cryptococcosis more often produces nasal swelling and sinus involvement alongside or instead of classic lung disease, which is one reason veterinarians run a broader diagnostic panel rather than assuming pneumonia from cough alone.

Which parts of the country put cats most at risk?

Geography matters enormously with these infections because each fungus favors a specific soil and climate niche. Blastomyces dermatitidis is concentrated along the Mississippi, Missouri, and Ohio River valleys and around the Great Lakes and St. Lawrence Seaway, where it thrives in moist, acidic soil enriched by decaying leaves and animal waste (CDC, 2024). Coccidioides immitis, the cause of Valley Fever, is instead endemic to the arid soils of the southwestern United States, particularly Arizona and the San Joaquin Valley of California, with the CDC estimating tens of thousands of human cases diagnosed annually in Arizona alone — a signal of how much fungal material is circulating in that region's dust (CDC, 2024). Histoplasma capsulatum overlaps with blastomycosis geographically but is specifically associated with soil enriched by bat or bird droppings, such as caves, old barns, and chicken coops.

Indoor-only cats are not automatically protected, since spores can be tracked inside on shoes or carried through open windows, though the highest-risk cats are typically those with regular access to riverbanks, wooded areas, construction sites, or barns in an endemic region. A cat's outdoor lifestyle combined with living in or having recently traveled through one of these river valley or desert regions should raise a veterinarian's suspicion index considerably when respiratory signs appear without an obvious viral or bacterial explanation.

What are the first signs an owner is likely to notice?

Early signs of fungal pneumonia are frequently mistaken for a run-of-the-mill upper respiratory infection or asthma, which delays diagnosis. Owners most often report a persistent dry or moist cough, increased respiratory rate or effort, lethargy, reduced appetite, and an intermittent low-grade fever that doesn't resolve with rest, according to Merck's veterinary reference on systemic mycoses (Merck Veterinary Manual, 2023). Weight loss over several weeks is common as well, since chronic granulomatous inflammation in the lungs raises the body's energy demands while simultaneously suppressing appetite.

Because blastomycosis and histoplasmosis in particular can disseminate beyond the chest, some cats present first with skin lesions that won't heal, draining nodules, or eye changes such as cloudiness and inflammation rather than obvious breathing problems. A veterinarian evaluating a cat with a chronic, non-healing skin wound in a Blastomyces-endemic area is often advised to consider systemic fungal disease even if the cat's lungs sound relatively clear on auscultation.

How do veterinarians confirm a fungal lung infection?

Diagnosis typically starts with thoracic radiographs, which often reveal a diffuse nodular or interstitial pattern throughout the lung fields rather than the localized consolidation seen with bacterial pneumonia. From there, veterinarians usually pursue cytology or histopathology from a fine-needle aspirate of an affected lymph node, skin lesion, or lung tissue, since visualizing the actual yeast organisms under the microscope remains one of the fastest ways to confirm the diagnosis. Blood or urine antigen testing is also widely used, and the Cornell Feline Health Center notes that a serum cryptococcal antigen test is both sensitive and specific enough to be considered a first-line diagnostic for suspected cryptococcosis (Cornell Feline Health Center, 2021).

Fungal culture can confirm species identification but may take one to several weeks to grow, so vets often begin treatment based on cytology and antigen results rather than waiting on culture confirmation, particularly in cats that are already showing respiratory distress. A CBC and chemistry panel are typically run alongside imaging to check for anemia, elevated globulins, or organ involvement that would indicate the infection has already disseminated beyond the lungs.

What does treatment actually involve, and how long does it take?

Systemic antifungal medication is the backbone of treatment, with itraconazole and fluconazole the most commonly prescribed drugs in cats due to their relatively favorable side-effect profile compared with older antifungals like amphotericin B (Merck Veterinary Manual, 2023). Fluconazole is often preferred for cryptococcosis specifically because it crosses into the central nervous system and eye more effectively, which matters when infection has spread to those tissues. Treatment courses are long by necessity — typically a minimum of two to six months, and sometimes up to a year — because antifungal drugs only slow fungal replication rather than killing the organism outright, meaning the cat's own immune system has to finish clearing the infection over time.

Cats with severe respiratory compromise at diagnosis may need supplemental oxygen, hospitalization, and supportive care such as IV fluids and appetite stimulants before oral antifungal therapy can even take full effect. Regular bloodwork to monitor liver enzymes is standard during treatment, since azole antifungals are processed through the liver and can cause elevations that require dose adjustment; veterinarians typically recheck liver values roughly every four to eight weeks during the treatment course.

How is a cat with fungal pneumonia cared for at home during recovery?

Once a cat is stable enough to continue treatment outside the hospital, consistent daily dosing of the prescribed antifungal is the single most important factor in a good outcome, since missed doses allow the fungal population to rebound. Owners are generally advised to keep affected cats strictly indoors during treatment, both to limit re-exposure to environmental spores and to reduce exertion while the lungs are healing. Monitoring respiratory rate at rest — counting breaths per minute while the cat is sleeping or calm — gives owners an objective way to track whether the lungs are improving, with a resting rate consistently above 30 to 40 breaths per minute generally considered a reason to contact the veterinarian.

Follow-up radiographs and antigen titers are typically repeated at intervals determined by the treating veterinarian to confirm the infection is actually resolving rather than just quieting down clinically, and many veterinarians continue antifungal therapy for a period after clinical signs resolve to reduce the chance of relapse. Cats should also be kept away from other high-exposure situations, such as excavation sites or barns, throughout the treatment period and beyond if they live in an endemic region.

What's the long-term outlook once treatment starts?

Prognosis depends heavily on how early the infection is caught and how far it has spread before treatment begins. Cats diagnosed while the infection is still confined to the lungs generally have a fair to good chance of full recovery with several months of antifungal therapy, while cats with disseminated disease involving the central nervous system, bones, or multiple organs carry a more guarded prognosis. The Merck Veterinary Manual notes that untreated systemic fungal infections in cats can be fatal, which underscores why early veterinary evaluation of a persistent, unexplained cough matters so much (Merck Veterinary Manual, 2023).

Relapse is possible even after a cat appears clinically normal, particularly if antifungal therapy is stopped too early, so many veterinarians recommend a final round of imaging and antigen or titer testing before fully discontinuing medication. Cats that recover from one systemic fungal infection do not appear to develop lasting immunity against re-exposure, so ongoing environmental precautions remain relevant for cats living in or traveling through endemic regions.