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Climate Change May Bring Valley Fever To More Of The Mountain West

Morgan Gorris
University of California, Irvine
Figure shows researchers' current estimate of where Valley fever may be endemic by the end of the century in a high climate-warming scenario.

Researchers say the fungus behind a disease called Valley fever may spread in the Mountain West as rain and temperature patterns change.

Coccidioides fungi are found in soil in dry places, and their tiny spores can get kicked up by wind and human activity. If a spore gets into a person’s lungs it can grow into a ball of other spores, which eventually bursts and makes a person sick.

According to the Centers for Disease Control and Prevention, outbreaks sometimes happen after events that disturb lots of soil -- like earthquakes, dust storms, archaeological digs and solar farm construction. In 2012, there were a few cases among a film crew shooting a TV show at a California location that reportedly had dust blowing in from a nearby mine.

“As temperatures warm across the western U.S., that could create conditions where the fungus can now grow,” says Morgan Gorris, a climate scientist who led the study while at the University of California Irvine. “And this will expose more people to this disease and could ultimately lead to more Valley fever cases.”  

Credit Centers for Disease Control and Prevention

Gorris and her colleagues wanted to know how climate change might affect the fungus' range. In the study, published in the journal GeoHealth, the researchers looked at two scenarios.

The first is a business-as-usual future, where emissions continue to climb over the next 80 years (in research lingo this scenario is called “RCP 8.5”). In that case, the fungus spreads beyond its current locations in Nevada and Utah, to locations throughout the Mountain West.

They also looked at a moderate warming scenario (also known as “RCP 4.5”), where emissions get curbed to some extent, peaking sometime around 2050 and then declining afterward.

"And if we analyze that scenario, we find that it doesn't spread as far north, " says Gorris. "So cutting down our greenhouse gas emissions could prevent the spread of Valley fever."

Credit Adapted from Gorris et al. 2019
Researchers modeled the range of Coccidioides fungi based on current conditions (top), future conditions in which emissions are curbed this century (middle) and future conditions in which emissions continue to climb throughout the century (bottom).

In most cases of Valley fever, people are symptom-free or get better on their own after experiencing flu-like symptoms. But in rare, untreated cases the fungus can spread to the rest of the body including the brain and spinal cord. According to the CDC, there were more than 14,000 diagnosed cases of Valley fever in the U.S. in 2017.

Don Natvig, a fungal geneticist with the University of New Mexico who studies Valley fever and was not involved in the research, says there are likely many more cases that go undiagnosed.

“Even in California and Arizona, where Valley fever is on the radar screen of physicians and health professionals they think that only about 35% of the cases are diagnosed because most people are either asymptomatic or they get mildly sick and then get well,” says Natvig. “There are these tragic cases I know about in New Mexico where people got really sick and at least one recent case where somebody died. They were otherwise perfectly healthy, they just didn't get treated.”

There are a lot of questions about Valley fever, including where the fungus actually exists on the landscape. Maps of its range are largely based on skin samples taken more than 50 years ago. It’s known to be present in states including Nevada, Colorado and Utah, though only some Mountain West states that report cases of the disease to the CDC. In 2015, researchers found the fungus had sickened people in Washington state; Natvig’s research in the Four Corners region also suggests the disease may already be more widely distributed than expected.

There’s also a question of whether it’s truly a soil fungus, or whether it instead lives in small mammals and only enters soil once the animal dies and decays. If true, that hypothesis might complicate the question of how climate change would impact the pathogen’s natural range.

“I think the specific take-home about this paper is that as we continue to get hotter and drier in the western United States, cocci[dioides] is going to expand its range,” says Natvig. “I don’t think there’s any question about that, regardless of whether it’s a soil fungus or a small mammal pathogen.”

More broadly, he adds, it brings up an often-overlooked notion of how changes we might not think about – like overall dustiness -- can impact human health.

“Climate change is going to bring about things that people don’t necessarily think about, including the range expansion of potentially a bunch of human diseases,” he says. “How fast and how far that range expansion occurs will still depend on how dramatic climate change is in the western U.S.” 

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Radio, Boise State Public Radio in Idaho, KUER in Salt Lake City, KUNR in Nevada, and KRCC and KUNC in Colorado.

Rae Ellen Bichell reports for the Mountain West News Bureau out of KUNC in Colorado.