Plus, because valley fever is a regional disease, a physician needs regional knowledge to recognize its existence. Someone working in New York City might not consider it the way a physician in Las Vegas would. Compounding that lack of recognition, only 26 states (plus Washington, DC) rank it as something public health authorities have to be notified about. And although California is one of the most-affected states, second only to Arizona, California’s affluent tech workers rarely develop the disease. Its chief victims are people who are already immunocompromised or who work outside or are exposed to warm, windy, dusty conditions: not only farmworkers, but contractors, road crews, and excavators and homebuilders laying out subdivisions.
Others at risk: military personnel assigned to southwestern bases and winter vacationers from cold northern states, all of whom return home to places where doctors are unlikely to recognize the illness. As I wrote for Scientific American this summer, in 2018, CDC epidemiologists doing a nationwide sweep for the disease found cases in 14 states that mostly lie along the Canadian border—places so cold that the infections could not have occurred there. After unravelling the patients’ past travel, investigators recognized the individuals had been infected somewhere to the south and brought the fungus home.
“If we achieved a vaccine, definitely people who lived in the endemic area would be where to start, people who are immunocompromised,” Thompson says. “But it also might become a mainstay of travel medicine. A travel advisory before visiting certain locations would be interesting to contemplate—though I don’t envision states wanting to caution people to get vaccinations before visiting.”
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Valley fever is estimated to cost the US $3.9 billion per year, and by one estimate, a vaccine could save potentially $1.5 billion in health care costs every year. But that cost, and thus the urgency to achieve a vaccine, is almost certain to increase because climate change is expanding the locations where valley fever is an infection risk. The fungus responds to temperature and humidity: It needs a warm environment to thrive, and in damp conditions it remains quiescently in the soil. But as climate warming increases, new territory will open up for Coccidioides, and shifting rainfall patterns mean areas where it has begun to grow will dry out enough for it to break apart and drift. There is already a known area of vulnerability in the center of Washington State, a place that was previously thought to be too cold for the fungus. In 2010, three people contracted valley fever there, including a construction worker and a teen who had been roaring around on an ATV.
In 2019, Morgan Gorris, an Earth system scientist at Los Alamos National Laboratory, used temperature and rainfall data to estimate more precisely where valley fever is endemic, based on the fungus’s known behavior in ranges of humidity and warmth. Using those findings, and combining them with different climate-warming forecasts, she modeled how valley fever’s range might expand under different scenarios of greenhouse gas emissions. Under the highest-warming scenario (a global rise of almost 9 degrees Fahrenheit), the area where the disease could become endemic would double in size by the year 2100, covering 17 states, including Idaho, Wyoming, Montana, Nebraska, and the Dakotas. The number of cases, the model predicted, would rise by half. In another analysis based on that work, she estimated that by the year 2100, the cost of valley fever to the US would reach $18.5 billion per year.
That looming bill, along with the illness and death underlying it, may be the best rationale for reaching to develop a vaccine. “Climate change is going to exacerbate ongoing threats and cause new threats,” Gorris says. “We’ll need resources in the future to adequately combat emerging diseases. Having a vaccine to address the risk of valley fever will allow us to free up resources to tackle other climate change issues, especially those related to human health.”
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