What exactly is valley fever and how does a cat catch it?

Valley fever is caused by inhaling airborne spores of Coccidioides fungi, which live in soil across arid and semi-arid regions of the southwestern United States, particularly Arizona's Sonoran Desert and California's San Joaquin Valley, and have also been documented in south-central Washington State (U.S. Geological Survey, 2023). A cat does not catch it from another animal; the infection begins when soil is disturbed by wind, digging, or construction, releasing microscopic arthroconidia that lodge in the lungs after inhalation (Centers for Disease Control and Prevention, 2024). Once inside the lungs, the spores convert into spherules, a structural form unique to this fungus that allows it to evade the immune system and establish a localized respiratory infection.

Cats are infected far less frequently than dogs, and the reasons are not fully understood, though reduced outdoor roaming and different digging behavior likely play a role (University of Arizona Valley Fever Center for Excellence, 2023). Indoor-outdoor cats in endemic counties, including Pima, Maricopa, and Pinal counties in Arizona, carry the highest documented exposure risk. The disease is not contagious between pets or from pets to people, since transmission requires direct inhalation of spores from contaminated soil or dust rather than contact with an infected animal (CDC, 2024).

What are the first signs an owner might notice at home?

Early respiratory infection often looks unremarkable at first: a mild cough, low-grade fever, or a cat that seems more tired than usual and eats less over several days. Because these signs overlap with common upper respiratory infections, valley fever is frequently missed during the first one to three weeks of illness, which is the typical incubation window before symptoms appear (Merck Veterinary Manual, 2024). Weight loss despite normal food availability is one of the more telling early clues owners report.

When the fungus escapes the lungs into the bloodstream, it produces what veterinarians call disseminated disease, and this occurs in roughly half of all diagnosed feline cases, a notably higher proportion than seen in dogs (Merck Veterinary Manual, 2024). Disseminated infection can cause draining skin lesions that will not heal, swollen or painful joints and limping, eye inflammation, or neurologic signs like seizures if the fungus reaches the central nervous system. Any non-healing sore or sudden lameness in a cat from an endemic region deserves veterinary attention rather than a wait-and-see approach.

Which cats are most at risk of getting infected?

Geography is the single biggest risk factor. Cats living in or recently traveling through the Lower Sonoran life zone of Arizona, the San Joaquin Valley, parts of northern Mexico, and pockets of Central and South America with comparable dry climates face the highest exposure (University of Arizona Valley Fever Center for Excellence, 2023). Seasonal weather patterns matter too, since spore counts in the air rise after dust storms and during dry periods that follow rain, when disturbed soil releases more arthroconidia into circulation.

Outdoor access is the behavioral factor that most directly predicts risk, since cats that dig, hunt, or spend extended time outside inhale far more airborne dust than strictly indoor cats. Age and immune status also influence severity: kittens and cats with concurrent illnesses such as feline immunodeficiency virus infection appear more likely to develop severe or disseminated disease once infected (Merck Veterinary Manual, 2024). There is no breed predisposition documented for cats, unlike some patterns seen in dog breeds.

How do veterinarians confirm a valley fever diagnosis in cats?

Diagnosis typically starts with a serology blood test that detects antibodies against Coccidioides, most commonly an immunodiffusion or enzyme immunoassay test, though titers can take several weeks to become positive after initial infection and may need to be repeated (University of Arizona Valley Fever Center for Excellence, 2023). Chest radiographs are standard for cats with respiratory signs and often reveal a distinctive pattern of lung nodules or enlarged lymph nodes near the airways.

For cats with skin lesions, joint swelling, or draining tracts, veterinarians frequently pursue cytology or biopsy of the affected tissue, since spherules can sometimes be identified directly under a microscope, giving a faster answer than waiting on serology (Merck Veterinary Manual, 2024). In cases involving neurologic signs, advanced imaging such as MRI along with cerebrospinal fluid analysis may be recommended to determine whether the fungus has reached the brain or spinal cord, which changes both prognosis and drug choice.

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

Treatment centers on oral antifungal medication, most commonly fluconazole or itraconazole, chosen for their ability to penetrate tissues including bone and the eye (Merck Veterinary Manual, 2024). Unlike a typical course of antibiotics, valley fever treatment in cats is measured in months rather than weeks; mild respiratory-only cases may need six to twelve months of therapy, while disseminated disease involving bone, eyes, or the nervous system often requires a year or longer, sometimes lifelong management if relapse occurs.

Cats generally tolerate azole antifungals reasonably well, though liver enzyme elevation is a known side effect, so veterinarians typically recheck bloodwork every four to eight weeks during treatment to catch problems early (University of Arizona Valley Fever Center for Excellence, 2023). Dosing is adjusted based on clinical response and repeat titers rather than a fixed calendar, and medication is not stopped simply because symptoms improve, since premature discontinuation is a leading cause of relapse.

What does day-to-day home care look like during treatment?

Most cats undergoing valley fever treatment can stay at home rather than hospitalized, but owners should expect a long-haul routine: giving oral medication consistently at the same time daily, since erratic dosing undermines the sustained blood levels antifungals need to control the fungus (Merck Veterinary Manual, 2024). Cats with joint or bone involvement may need restricted activity and a quiet, low-stress environment while lesions heal, and any draining skin wounds should be kept clean and covered to prevent secondary bacterial infection.

Nutrition support matters more than owners expect, since chronic illness and reduced appetite during flare-ups can lead to significant weight loss; a palatable, calorie-dense diet recommended by the treating veterinarian helps cats maintain condition through months of therapy. Routine rechecks, typically including physical exams and periodic titer testing every two to three months, track whether the infection is responding, so keeping every follow-up appointment is as important as the medication itself (University of Arizona Valley Fever Center for Excellence, 2023).

What is the long-term outlook, and can valley fever come back?

Prognosis depends heavily on how early the disease was caught and whether it disseminated. Cats treated for localized respiratory infection generally have a good prognosis with appropriate antifungal therapy, while disseminated cases involving the central nervous system carry a more guarded outlook (Merck Veterinary Manual, 2024). Relapse can occur even after apparently successful treatment, which is why many veterinarians continue monitoring antibody titers for a period after medication is discontinued rather than declaring a cure the moment symptoms resolve.

There is currently no vaccine approved for cats, though research into a canine Coccidioides vaccine has been underway through the University of Arizona's Valley Fever Center for Excellence, and any future feline application would likely follow years behind (University of Arizona Valley Fever Center for Excellence, 2023). For now, prevention rests on limiting outdoor exposure to disturbed soil and dust in endemic regions, particularly during construction, digging, or dust storms.