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, with recent years seeing a notable increase in reported cases.
The infection occurs when fungal spores are released into the air after soil disturbance and then inhaled. Those at highest risk include agricultural workers, construction crews, and firefighters due to their frequent exposure to dust. While many exposed individuals do not develop symptoms, others can experience severe or even life-threatening illness.
Rex Dangerfield of Stockton was diagnosed with valley fever meningitis after first experiencing headaches 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 following surgeries for complications related to the infection.
Symptoms of valley fever often resemble common respiratory illnesses such as pneumonia, making diagnosis challenging. 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. They’re never diagnosed definitively or accurately.” He advised those who have traveled through affected areas and experience persistent cough or illness to consider valley fever as a possible cause: “You only have to breathe in one spore once to acquire the infection.”
Estimates suggest that up to one in four pneumonia cases in California’s Central Valley may actually be valley fever. In rare instances—about 1% to 3%—the fungus can spread beyond the lungs and affect other organs.
Kyleigh Cooyar described her own struggle with misdiagnosis before being treated at UC Davis Health: “I had never heard of valley fever,” she said. After weeks of debilitating symptoms and incorrect diagnoses, she was finally tested for valley fever when her condition worsened. She credits Dr. Thompson for stabilizing her health: “He’s the one that got it under control… I think he saved my life.”
Animals are also susceptible; dogs are commonly affected because they dig in contaminated soil. Dr. Jane Sykes, a small animal veterinarian at UC Davis specializing in infectious diseases, noted: “I’ve had dogs that have been referred to me because they’ve been diagnosed with chronic kennel cough, when in fact they have valley fever.” Cooper, a boxer mix owned by Omar and Rosemary Rios from Farmersville, required emergency surgery at UC Davis Veterinary Medical Teaching Hospital after developing severe complications from the infection.
Researchers believe dogs can serve as sentinels for tracking the spread of valley fever among humans because their movements are more localized than people’s and they frequently interact with contaminated soil. An analysis led by Sykes found nearly 38% positivity among dog antibody tests over almost a decade nationwide; mapping these results showed strong overlap between canine and human cases—even identifying potential hotspots outside traditional endemic areas such as Texas, Montana, Idaho, Oregon, Washington, and Colorado.
Climate change is contributing to an expansion of regions where Coccidioides thrives due to patterns like heavy rains followed by droughts and wind events that disperse spores widely—including via wildfire smoke particles traveling long distances.
Drugs currently available suppress but do not cure valley fever; some patients require treatment indefinitely. However, new medications showing promise against fungal pathogens are under development according to Dr. Thompson: “We’re really at the pinnacle of science right now… We’re hoping to see some big breakthroughs and advances just over the next six months.” Collaborative research involving patient blood samples aims to uncover genetic factors influencing susceptibility while veterinary studies focus on similar questions in dogs—a preventive vaccine for dogs is reportedly nearing approval.
UC Davis remains central both clinically—treating complex human and animal cases—and scientifically through ongoing research collaborations aimed at improving detection methods and advancing treatments or vaccines for this persistent disease.
