Valley fever, a disease caused by the soilborne fungus Coccidioides, is spreading across California and other arid regions of the western United States, affecting both people and animals. The illness is contracted when spores from disturbed soil become airborne and are inhaled.
Rex Dangerfield, 56, of Stockton, described how his life changed after he developed the most severe form of valley fever—meningitis—after gardening in Patterson in 2013. “I don’t feel normal anymore,” Dangerfield said. “I used to be able to play basketball. I used to love to bowl. I can’t do that anymore.” His condition requires lifelong treatment with antifungal medication.
The number of valley fever cases continues to rise in California and other states. In 2024, California reported nearly 12,500 cases—the highest on record—with another 5,500 infections documented in the first half of this year. Arizona also experienced its highest caseload in more than a decade.
UC Davis is among the few institutions where both human and animal cases are treated side by side. Researchers at UC Davis are collaborating to improve detection and treatment for valley fever and are investigating whether monitoring dogs can help predict outbreaks among humans.
Symptoms of valley fever often resemble those of pneumonia or other respiratory illnesses, making diagnosis difficult. Dr. George Thompson, infectious disease physician and co-director of the UC Davis Center for Valley Fever at UC Davis Health, explained: “Patients with uncomplicated respiratory disease are often given multiple courses of antibiotics erroneously, but eventually they feel better,” he said. “They’re never diagnosed definitively or accurately.” He added: “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. You only have to breathe in one spore once to acquire the infection.”
Estimates suggest as many as one in four pneumonia cases in California’s Central Valley may actually be valley fever. In severe instances like Dangerfield’s, the fungus can spread beyond the lungs.
Kyleigh Cooyar sought care at UC Davis Health after her own misdiagnosis delayed appropriate treatment for her valley fever infection that had spread throughout her body. She said: “I had never heard of valley fever… I thought it was something that was simple to cure.” After receiving care from Dr. Thompson she noted: “He’s the one that got it under control… I think he saved my life.”
Dogs are also vulnerable; Cooper, a boxer mix owned by Omar and Rosemary Rios from Farmersville, suffered heart complications due to valley fever before being treated at UC Davis Veterinary Medical Teaching Hospital.
Dr. Jane Sykes at UC Davis noted dogs could serve as sentinels for tracking disease spread because they dig in soil and tend not to travel far distances like humans do: “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.” A study analyzing nearly a decade’s worth of dog antibody tests found almost 38% were positive for exposure.
Mapping these canine cases alongside human infections revealed significant overlap not only in known hotspots like California and Arizona but also in states not previously considered endemic such as Texas, Montana, Idaho, Oregon, Washington and Colorado.
Experts believe climate change is contributing to the wider spread by creating conditions favorable for fungal growth—heavy rains followed by droughts increase risk—and wildfire smoke may transport spores over long distances.
Antifungal drugs can suppress but not cure valley fever; some patients require lifelong medication management at specialized centers like UC Davis Health’s Center for Valley Fever. New drugs showing promise against resistant fungi are under development while researchers pursue vaccine options for both humans and animals.
“We’re really at the pinnacle of science right now,” Thompson said. “We’re hoping to see some big breakthroughs and advances just over the next six months.”
Cooper has regained much of his health after surgery and ongoing treatments; his owners credit his resilience through recovery: “He is a miracle for sure,” Rosemary Rios said. “He’s a fighter.” Both Dangerfield and Cooyar continue their treatments at UC Davis.
The efforts at UC Davis reflect ongoing attempts by researchers and clinicians to understand this unpredictable disease—one that affects individuals regardless of age or species—and develop new ways to diagnose, treat or prevent its spread.
