The fungal disease valley fever is endemic to arid regions of the western United States, but new research suggests the areas where it’s found could rise along with global temperatures.
Coccidioides, the fungus that causes valley fever, thrives in soil in hot regions with little rainfall. Humans and animals develop the disease when they inhale fungal spores kicked up by disturbances to the ground. Most overcome the disease without ever realizing they’ve caught it, but some develop pneumonia-like symptoms and a rare minority will develop severe disease that can become disseminated throughout the body.
Today, coccidioides grows in 12 states. But a recent study in the scientific journal GeoHealth argues that by the end of the century, valley fever’s endemic area could grow to include as many as 17 states as far north and east as Montana and the Dakotas.
“It is surprising how quickly the endemic area may spread,” says lead author Morgan Gorris of UC Irvine, who blames the growth on climate change. “Overall, we find that the number of cases may increase by 50 percent by end of 21st century in response to a high climate warming scenario.”
Gorris and her colleagues used a variety of climate models to determine which counties in the future could be subject to the annual rain and temperature patterns that occur where the disease is endemic today. “In response to climate warming, these counties will start to heat up and will now become both hot and dry,” she says, “and that could allow the fungus to establish itself in the environment.”
This scenario assumes no changes to how humans emit climate-warming greenhouse gases into the atmosphere. Gorris points out, however, that the outlook could change. “If we reduce our GHG emissions and really reduce climate change, it may the limit the number of valley fever cases we see in the future,” she says.
In California, the valley fever caseload has risen every year since 2015. Preliminary reports suggest the 2019 case rate could be even higher.