Valley fever, a disease caused by the soilborne fungus Coccidioides, is spreading across California’s Central Valley and other arid regions of the western United States. The illness affects both humans and animals, particularly dogs, and has seen rising case numbers in recent years.
Rex Dangerfield, a 56-year-old resident of Stockton, recounted his experience with valley fever meningitis after being exposed to the fungus while gardening in Patterson in 2013. “I don’t feel normal anymore,” Dangerfield said through tears. “I used to be able to play basketball. I used to love to bowl. I can’t do that anymore.” He now requires lifelong antifungal medication and regular medical care.
The disease develops when spores from disturbed soil become airborne and are inhaled. People who work outdoors or are frequently exposed to dust—such as agricultural workers, construction workers, and firefighters—are at higher risk. Many infected individuals may not develop symptoms, but for some, like Dangerfield, the consequences can be severe and long-lasting.
Dr. George Thompson, an infectious disease physician who co-directs the UC Davis Center for Valley Fever at UC Davis Health, noted that valley fever often presents with common respiratory symptoms such as cough, fever, chills or fatigue. “Patients with uncomplicated respiratory disease are often given multiple courses of antibiotics erroneously, but eventually they feel better,” Thompson said. “They’re never diagnosed definitively or accurately.”
Thompson emphasized the importance of considering valley fever in persistent cases: “If you’ve driven through the valley and you’ve got a cough or an illness that doesn’t seem to be going away for weeks or even a month, think about valley fever,” he said. “You only have to breathe in one spore once to acquire the infection.”
In California’s Central Valley alone, experts estimate up to one in four pneumonia cases may actually be valley fever. In 2024, California reported nearly 12,500 cases—the highest on record—with more than 5,500 new infections in just the first half of this year. Arizona also experienced its highest caseload in over a decade.
Misdiagnosis is common among patients like Kyleigh Cooyar of Sacramento who spent weeks hospitalized before doctors identified her condition as valley fever rather than an autoimmune disorder. She described her ordeal: “I even remember times when I felt like maybe it would be better if I were dead because I felt so terrible.” Cooyar credits Dr. Thompson with stabilizing her health: “He’s the one that got it under control,” she said. “I think he saved my life.”
Dogs are also susceptible to valley fever due to their tendency to dig in contaminated soil. Dr. Jane Sykes of UC Davis Veterinary Medicine has treated numerous canine cases referred for persistent respiratory symptoms initially misattributed to kennel cough.
Omar and Rosemary Rios brought their dog Cooper—a boxer mix—to UC Davis after he developed serious complications from valley fever including heart damage requiring surgery and ongoing antifungal treatment at home.
Researchers at UC Davis are studying how tracking dog infections could help predict human outbreaks since dogs tend not to travel far from where they live and play outdoors frequently. According to Sykes’ research using almost a decade’s worth of dog antibody tests nationwide, nearly 38% were positive for exposure—and patterns matched those seen in human cases across states like California and Arizona.
“There are lots of dogs, and they don’t travel as much as people,” Sykes said. “They dig in soil… They’re potentially good sentinels or signs that humans might also be getting infected in a region.” Positive canine test results have also appeared in states not previously considered endemic for valley fever such as Texas, Montana, Idaho, Oregon, Washington and Colorado.
Climate change is believed to contribute significantly by creating favorable conditions for fungal growth—periods of heavy rain followed by droughts increase spore dispersal via windstorms or wildfire smoke carrying spores over long distances.
“We think it’s probably already in some of these Midwest states,” Thompson said regarding newly affected areas beyond traditional hotspots.
Antifungal medications can manage but not cure valley fever; some patients require lifelong therapy while awaiting advances from ongoing research collaborations involving institutions such as UC Davis Health and veterinary partners working on new drugs and vaccines for both humans and animals.
“We’re really at the pinnacle of science right now,” Thompson said about prospects for breakthroughs within months ahead.
For survivors like Dangerfield and Cooyar—and pets like Cooper—the impact remains personal yet shared across communities increasingly affected by this emerging threat.
