The Spread of Valley Fever in the Western U.S.: Risks to People and Dogs

Valley fever, also known as coccidioidomycosis, is rapidly spreading across the arid regions of the Western United States, posing health threats to both humans and animals, particularly dogs. This disease is caused by a soil-dwelling fungus that releases microscopic spores into the air when disturbed, which can then be inhaled. Exposure is common during activities that disturb the soil, including farming, construction, and firefighting.

In recent years, cases of valley fever have surged, with California reporting nearly 12,500 infections in 2024—the highest in history—and thousands more affected in other states like Arizona. The disease’s symptoms often mimic those of pneumonia or other respiratory illnesses, including cough, fever, chills, and fatigue. Due to the nonspecific symptoms, many cases are misdiagnosed or overlooked, leading to delayed treatment.

The severity of valley fever varies among individuals. While many experience mild or no symptoms, others can develop severe complications such as meningitis, which can be fatal without lifelong antifungal treatment. The disease can also attack multiple organs, making diagnosis and management complex. Dogs, especially those that dig or sniff in contaminated soil, are also susceptible and can serve as indicators of environmental exposure.

UC Davis is a leading center for the treatment and research of valley fever. Veterinarians and physicians collaborate to better understand the disease, develop early detection methods, and explore potential vaccines. Researchers are also studying genetic factors that influence the severity of infection in both humans and dogs.

The spread of valley fever is exacerbated by climate change, which creates ideal conditions—heavy rains followed by drought and wind—for the fungus to flourish and disperse. Wildfires further contribute by sending fungal spores aloft, allowing them to travel long distances.

While current antifungal medications can suppress the disease, there is no cure yet. However, promising new treatments and vaccine developments offer hope for more effective prevention and management in the future. Increased awareness, early diagnosis, and ongoing research are essential to controlling the spread and impact of valley fever among people and animals.