A mysterious lung infection, long associated with arid soil and dusty winds, is spreading across the western United States. And the latest clues aren’t coming from air monitors or satellite data—they're coming from dogs.

Valley fever, also known as coccidioidomycosis, is caused by inhaling fungal spores from *Coccidioides* species that live in the soil. While human cases have surged in recent years, a groundbreaking study by researchers at UC Davis and UC Berkeley has uncovered that dogs may be early indicators of where this disease is gaining ground.

“Dogs are sentinels for human infections,” Jane Sykes, professor of small animal internal medicine at UC Davis, told ScienceDaily. “They can help us understand not just the epidemiology of the disease but they’re also models to help us understand the disease in people.”

From Backyard Dust to Dangerous Spores

Dogs often dig, sniff, and romp in the dirt—precisely where *Coccidioides* spores hide. When drought dries the soil and wind kicks up the dust, these spores become airborne. Once inhaled, they settle deep in the lungs.

Infections in dogs mirror those in humans, often starting with coughing and lethargy. In both species, the disease can escalate. In rare but severe cases, it spreads to bones, skin, or the brain, sometimes requiring lifelong treatment with antifungal medications.

As Sykes explains in Earth.com, “some dogs become so sick that they die.”

Tracking a Silent Surge

The UC Davis-led study analyzed nearly 835,000 canine antibody tests collected between 2012 and 2022. What they found was staggering: Valley fever in dogs expanded from just 2.4% of U.S. counties to 12.4% over the decade. The disease was prevalent not only in known hotspots like Arizona and California but also appeared in Oregon, Idaho, Washington, and other states where human cases aren’t always tracked or reported.

As noted in USA TODAY, many of these states lack mandatory reporting of human Valley fever cases. That’s why researchers say dogs may be our best early warning system.

“We are also finding cases in states where valley fever is not considered endemic by the CDC,” Sykes said. “We should be closely watching those states because there could be under-recognition.”

Dogs exposed to Valley fever often show symptoms before humans in the same region.

A Climate-Driven Threat

Valley fever thrives in extremes—drought, followed by heavy rains. These conditions promote fungal growth and dust formation, ideal for spores to spread. Climate models suggest this pattern is becoming more common across the western U.S.

Simon Camponuri of UC Berkeley emphasized to The Mercury News that dog testing fills crucial gaps in human health surveillance.

“We have this kind of incomplete picture… dogs fill that gap really well,” he said. And with over 60 million dogs living in U.S. households, their health may provide one of the most comprehensive datasets available.

Dogs and humans contract Valley fever the same way—by breathing airborne spores.

Canine Cases as Public Health Tools

Dogs don’t just mirror our exposure—they also give public health officials a head start. In areas where human testing is rare or delayed, spikes in canine infections may signal hidden outbreaks.

Public health researcher Peter Rabinowitz told The Mercury News that vet-reported dog cases could help communities take proactive steps, like using masks during dust storms or avoiding certain outdoor activities.

And it’s not just about preventing illness. According to UC Davis Health News, these findings could lead to better diagnostics and treatments. If dogs develop Valley fever in similar ways, they might hold answers to human treatments still on the horizon.

The disease can spread from dogs’ lungs to their bones and brain.

Connecting the Dots Between Species

The study’s implications go far beyond veterinary clinics. With human cases potentially underreported by a factor of 33, according to Sykes, tapping into dog health records could fill in critical blind spots.

“The study findings present an important advance for both public health and animal health,” said Cornell’s Renata Ivanek, who was not involved in the research but praised the study's methodology in The Mercury News.

As Valley fever pushes into new regions, dog data could shape smarter, faster responses. The disease isn’t contagious between animals and humans—but our shared environments mean we face the same risks.

Veterinary medicine may now play an unexpected role in public health forecasting. As Sykes told USA TODAY, “They’re not just our companions—they’re our partners in detecting threats we can’t see.”