John Taylor has spent years studying valley fever and the fungus that causes it across the Central Valley and the Southwest.

The sometimes-fatal disease is increasing, and the UC Berkeley professor has grim advice for people doing outdoor manual labor in those arid regions: Wear a full face mask hooked up to a HEPA-filtered air supply.

“Anything else, you are playing with a dangerous situation that could make you sick for the rest of your life,” he said.

Some 40% of people infected with the fungus will come down with respiratory symptoms, and a small number develop serious lung problems. The disease can spread throughout the body and be fatal.

Rodent burrows, in particular, Taylor said, are something people should watch out for. His research is increasingly pointing to them as home for the deadly fungi.Two new studies his team published expand understanding of the fungus. For the first time, they found it in urban areas, in the burrows of rodents living along rivers and streams. And his colleagues have found that Kern residents who live near new oil and gas wells are at increased risk.

Valley fever is caused by the Coccidioides fungus. The incidence of the disease has increased in recent years as its footprint has expanded across the western U.S.

Much has been made of the fungi’s relationship to drought, precipitation and climate, but Taylor’s work over the past three decades shows the fungus may have a particular taste for rodents.

People get valley fever when they breathe in dust laden with the cocci spores. So do rodents and other mammals.

When the spores hit the lungs, they “persuade” the host’s immune system to coat them with cells that are usually harnessed to kill pathogens. Instead of being killed by them, the spores use the cells as a protective shield — creating an object called a granuloma.

For most people — and probably for 99% of rodents that get it — “they never get sick. It’s in them. It’s just sitting there,” he said.

The fungus plays the long game, said Taylor, who conveys his deep knowledge and love of biology with a dark, humorous relish. It waits for the host to die by natural causes, then consumes the corpse, assuming it wasn’t cremated, embalmed or eaten by a scavenger.

Upon feasting, the fungus will multiply, reproduce and send out spores to start the cycle over again.

Taylor, who’s been infected, said he’s no longer a good candidate for a green burial. The spores inside him are alive and well and ready to spread should his unpreserved body be interred in the soil.

While the fungus will infect any mammal it crosses, it seems to have a special relationship with rodents, said Taylor.

Because rodents don’t get sick, they’ll reproduce. This provides the fungus with new morsels of meat. In addition, because rodents often die in their burrows, and new rodents move in to set up camp, the fungus capitalizes on a steady stream of mammal flesh.

People, wildlife and domestic animals get valley fever when the soil in these burrows is disturbed, by a dog digging, a kick of the boot, a shovel, construction equipment, wind or wildfire.

Taylor said when he sees dust devils whirling up dirt west of Highway 33, he makes sure the air in his car is recirculating. If outside, time to mask up; dust devils pull the spores high up into the airstream, enabling them to spread for miles.

One of the new studies, led by Lisa Couper, a postdoctoral fellow at UC Berkeley, found that living within three miles of new oil and gas drilling in Kern County increases the risk of valley fever by 12.5%.

When crews put in new wells, they level sites with heavy equipment, pour well pads and drill the well — all disturbing soil and aerosolizing dust, she said.

About 72% of Kern County residents lived within roughly three miles of an oil and gas well being built during those years, Couper said.

Other types of construction have also been linked to the infection — including a recent outbreak associated with construction of a solar farm in Monterey County.

All of this is concerning, said Taylor, because for many people, the disease can be very serious.

In 10% of the symptomatic cases, people develop serious lung problems that require medical care plus antifungal medication. And in 3% to 5% of those cases, it affects the brain and spine, in what’s known as disseminated disease — which can lead to death if untreated.

It’s not totally clear who is likely to get this sick. Taylor said research shows some patients who become gravely ill have compromised immune systems. Some breathe in so much fungus it overwhelms their bodies. Others appear to have genetic variants that make them susceptible.

It boils down to whether your body can make those encapsulated granulomas.

“If you don’t make a granuloma, or if the granuloma fails for some reason, that little spore increases in volume a thousand times and then makes little spores inside of itself,” he said, creating a fungal form called a spherical. If that thing ruptures, “those little spores come out, and they get in your blood system, and they go everywhere.” Hence, the term disseminated disease.

Genetic analyses of the fungus have shown that cocci have evolved over time to eat mammal flesh, losing genes that help it digest plant cells.

Which is why identifying rodent burrows is so critical, he said, because that’s where you’ll find the fungus.

In the other new study, Taylor and his colleagues looked along the banks of rivers running through the cities of Bakersfield and Coalinga. They found higher levels of the fungus inside rodent burrows than outside, furthering his hypothesis that there’s a critical connection between rodents and the fungus.

He and his team are now looking at genetic markers in valley fever patients that could potentially show whether they got it from disturbed rodent burrows in cities, or from dust that blew in from rural areas.

But not everyone is convinced rodents are a critical piece of the valley fever puzzle.

Antje Lauer, a professor in the biology department at Cal State Bakersfield — who has also studied valley fever and the cocci virus for decades — said the focus shouldn’t be on rodents, but on the rampant construction taking place in Bakersfield.

The city is planning 450,000 new housing units by 2045. Solar farms also are spreading throughout the Mojave Desert.

Construction crews are “going into natural areas, and soils will be disturbed,” she said. The wind will blow south down the valley, and people will get sick.

She said more than a million people are expected to move into the area in the coming years — people from San Francisco and Los Angeles — who and have never been exposed to the fungus and are likely to become ill.

“I know that he likes to present the rodents as the ultimate driver of valley fever outbreaks,” she said, “but there is a lot more to say.”

She said public health officials and state regulators should be concerned about the digging and construction, not the rodents.

Taylor agreed that rooting out and killing rodents isn’t the answer. Poisoning or trapping only releases the fungus from carcasses. Better to remove food and create barriers to prevent them from moving in. And keeping people from breathing in dust is critical.

Couper, the postdoctoral researcher, said her findings signal that stronger protections are needed. That includes wetting down soil during construction — so it’s less likely to get airborne — and making sure nearby residents receive education about how to wear N95 masks. Ideally, construction that generates heavy dust should be delayed on really windy days — or even better, moved to the winter, when valley fever fungus is in its most non-infectious form, she said.

And while state law establishes a one-kilometer buffer zone between new oil and gas wells and sensitive areas such as homes, schools and hospitals, “ideally it would be extended to a further distance,” she said.