Four years after COVID-19, researchers warn of a new “invisible epidemic.”
Valley fever doesn’t spread from person to person—instead, people get sick by breathing spore-laden dust on hot, windy days. While it’s almost never fatal, the infection can cause long-term health issues in some people, especially when diagnosed late. The fungus that causes Valley fever grows underground and is undetectable without a microscope. Most worrisome, the respiratory infection is on the move through the soil itself, and nobody really knows how far it’s spread.
Scientists say climate change could be to blame. Extreme temperatures and erratic weather can pose immediate dangers, but these shifting weather patterns also impact human health in more insidious ways—by changing the landscape of infectious disease.
As the climate shifts—2023 was the hottest year in modern history, and the first few months of 2024 are on track to continue the trend—new areas become welcoming environments for organisms that carry disease, like ticks that spread Lyme disease or mosquitoes that transmit malaria. Extreme weather events can also disrupt public health infrastructure, leading to disease outbreaks.
But not all disease changes are as visible as a natural disaster.
Katharine Walter, PhD, assistant professor of epidemiology at the Spencer Fox Eccles School of Medicine at the University of Utah, says that the cough, fever, and fatigue caused by Valley fever are often misdiagnosed as pneumonia, making it hard to tell which regions harbor the disease. The 25,000 cases annually reported nationwide likely underrepresent the actual infection rate by a factor of six.
People have gotten sick hundreds of miles outside the supposed borders of the fungus’s range, and shifts in climate are likely to encourage fungal growth in regions that were previously safe.
Walter sees these changing disease patterns as an urgent health justice issue. “The impacts of climate change are already being dramatically felt by everyone across the world,” Walter says, “and the consistent theme is always that the most vulnerable populations are put at highest risk.”
For Valley fever, this includes people who work outside. Construction workers, agricultural laborers, and firefighters can’t avoid spending time outside on hot, dusty days, which puts them on the frontlines for the disease in regions where the fungus can survive. But where exactly the danger zones are—and how they’ll change as the climate becomes more extreme—is an open question.
Walter is on a mission to find out. She and her collaborators—Katrina Derieg, vertebrate collections manager at the Natural History Museum of Utah; Eric Rickart, PhD, adjunct associate professor of biology at the U and curator of vertebrates at NHMU; and Kevin Perry, PhD, professor of atmospheric sciences in the College of Mines and Earth Sciences—are working to map where the Valley fever fungus can survive, predict how it will move across the landscape as the climate changes, and raise awareness for the people who are most at risk.
To track the spread of the fungus, the team is collecting soil and dust samples from a wide range of climate zones and testing them for fungal DNA. They’re also searching for traces of the fungus in rodents, like pocket mice, that burrow underground. While rodents don’t transmit the disease directly to humans, the scientists suspect that they are instrumental in moving the fungus into new areas of the soil.
The scientists are focusing their efforts on St. George, UT, the fastest-growing metropolitan area in the nation—and a hotspot for Valley fever. Rapid construction is churning up the surrounding desert at breakneck speed, raising large quantities of potentially spore-laden dust. Where others see future housing developments, the researchers see the potential for a spike in disease cases.
And increasingly extreme weather will likely support the continued spread of the fungus, according to Walter. During periods of heavy rainfall, the fungus thrives underground. Then, when severe drought hits, all that fungus-laced soil dries into infectious dust that blows on the wind.
But that doesn’t mean all hope is lost. Just like for other diseases that are on the move, human interventions have the power to slow or even reverse disease trends. For Valley fever, Walter says, “the best public health tool we have is raising awareness among individuals and health care providers.” Armed with that knowledge, people living in high-risk areas can wear filter masks when outside on dusty days, and doctors can know what symptoms to look for to start treatment early.
Walter emphasizes that combating Valley fever is part of the broader health justice picture. “This is just one piece of a much, much larger set of issues that we’re going to increasingly face because of climate change,” she says. “The urgency of this issue really can’t be overstated… Valley fever is just one component of this storm we’re all living through.”
