For man’s best friend, pet owners often go to great lengths — whether that’s doggy daycare and specialty pup chow, or late nights at the vet running tests that drain bank accounts.

Now, a new study by researchers from UC Davis and UC Berkeley has found a way our canine companions can help us, offering a unique glimpse into Valley fever — a disease that has been growing steadily throughout California and the American West.

Knowing when and where dogs got sick with Valley fever can help pinpoint the geographical areas where humans might also contract the disease, according to a paper recently published in The Journal of Infectious Diseases. The study may offer another tool for public health workers to spread awareness and bolster prevention, helping make life a little healthier for humans and their precious pups.

“Understanding the distribution has been really challenging,” said Simon Camponuri, a coauthor of the study who researches Valley fever at UC Berkeley. “We have this kind of incomplete picture … dogs fill that gap really well.”

Valley fever is a disease with a foothold in the American Southwest and Washington caused by a fungus that takes root in the lungs, where it can cause pneumonia. While those who get sick generally get better on their own, some require special treatment, and in rare cases, the disease can spread to the bones, skin, and even the brain. The disease is not contagious; instead, it spreads when humans and other animals inhale tiny spores from the fungus Coccidioides that are hidden in dust particles and carried in the air.

Since the start of the millennium, cases in California have ballooned from around 1,400 cases in 2001 to over 9,000 cases in 2023, according to data from the California Department of Public Health, disproportionately affecting those who work in the soil like farmworkers and construction workers.

Often the disease is misdiagnosed, and delays in diagnosis can make treatment more difficult. All these factors mean that tracking the disease, spreading awareness, and taking preventative measures where it takes root are  essential to keeping people safe. But the fungus is tough to track by testing in the soil or the air.

That’s where dogs come in.

Humans and dogs hang out a lot. A little less than half of households in the U.S. have a dog, and these curious creatures tend to root around in the dirt and dust, making them more likely to come in contact with the disease. They also get the disease in ways that are similar to us, contracting pneumonia that in rare occasions can spread beyond the lungs.

Because of this, the researchers decided to see whether Valley fever in dogs lined up with where the illness showed up in humans. The team started with more than 2 million tests submitted by vets to labs that tested for Valley fever, and homed in on tests of dogs from 2012 to 2022. The tests represented more than 800,000 hounds across the country.

They found that the cases in dogs spread over time, with most centered in Arizona, followed by California in a distant second. When they looked at how the disease grew over time in those two states, they found that when more dogs got sick, humans also saw an uptick in Valley fever. When comparing the spread of the disease, they also noticed that hotspots for Valley fever in dogs were likely to also be hotspots for humans.

“The study findings present an important advance for both public health and animal health,” said Renata Ivanek, a professor at Cornell University who studies human and animal infectious disease and was not involved with the study. While she notes that the correlation between dog and human cases was “not perfect,” she argues that the method benefits by using information that is already out there. “The elegance of this approach is that diagnostic testing is already done,” she said.

While this could help public health researchers in places where Valley fever has already taken root, it also might tell us where to look next. In states like Texas and Idaho that don’t regularly report cases of Valley fever in humans, the tests from dogs showed significant cases. This means that the study, and the canine data, could serve as a warning sign for where humans should look out for the illness.

“I think this really suggests that there’s public health value in knowing what’s going on with the dogs in the area,” said Peter Rabinowitz, who researches public health at the University of Washington and was not involved in the study. He does note that the data may not be a perfect picture of Valley fever in dogs: the study only looked at dogs who were tested by vets, which means the dog was likely rather sick and the vet had to know to test for Valley fever.

Even so, he suggests that asking vets to report cases to public health authorities could offer a clearer picture of the extent of the disease, raise awareness for clinicians who treat animals and humans, and help public health officials alert communities when to take precautions like wearing masks to block out dust. “It shows the power of bringing in clinical data from both animals and humans.”

Jane Sykes, the veterinary researcher at UC Davis who led the study, holds that the research serves as a reminder of how connected human health is to that of animals and the environment, pointing out that the spread of Valley fever may be sped up by climate change and even wildfires.

Given this, she argues that narrow approaches to health won’t be enough to solve “increasingly complex problems” in health and the environment. Instead, she said, the study serves as an invitation to a wider view of health that could mean better outcomes for humans, their environment, and their furry friends.

“We need to have that very broad lens,” said Sykes.