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Valley fever, a fungal infection that can be life-threatening in severe cases, has been on the rise in the southwestern United States.
Hot, dry conditions in Arizona and California are ideal for spreading the disease. It thrives in dusty soil and its spore can be carried up to 75 miles by the wind.
Scientists have projected that valley fever cases could increase by up to 50% by the end of the century and spread across nearly a third of US states as a result of climate change. Its overall area of impact is expected to more than double.
Droughts and dust storms have been spreading a potentially fatal fungal infection known as valley fever across southwestern states like Arizona, New Mexico, and southern California.
A now, new data shows the disease could spread even farther than scientists thought possible in the next century, according to research published August 30 in GeoHealth.
To come to their conclusion, researchers from the University of California, Irvine, used existing data of valley fever cases to create a model of what conditions were best for the fungus. They determined the temperature and rain levels in which the disease was most likely to occur, testing their predictions against CDC data for accuracy. They then calculated how far those conditions were likely to spread, as climate change drives a trend toward hotter, drier weather.
The study predicted that valley fever cases could increase by as much as 50% by the year 2100, and the area it affects could double.
The fungus could also spread from the 12 states it currently occupies to 17, the research found, with a 113% increase in the number of counties affected. This could mean as many as 34,460 potential cases each year, 50% more than the current annual average.
Valley fever feels like the flu, and can be deadly
Coccidioidomycosis, known as valley fever, is an infection caused by inhaling spores of Coccidioides fungus, which is found in soil.
Not everyone who inhales the spores will get sick, but about 40% of people develop flu-like symptoms. Around 1 in 10 patients can have serious side effects, including permanent lung damage. In rare cases, valley fever can be fatal if it spreads to other areas of the body like the skin, joints, or spinal cord.
It isn't contagious, but the spores are spread by wind and weather, particularly in hot, dry climates.
But recently, valley fever has been discovered in unexpected places. Several illnesses were identified as valley fever in Washington, 700 miles north of the San Joaquin Valley where the fungus is endemic. Spores were found in the soil in that area as well as an Oregon, both farther north than scientists thought the fungus could travel.
"We're not sure if it's already spreading or if it's just in places we didn't know to look for it," lead author Morgan Gorris, researcher and former graduate student at UC Irvine, told Insider.
Her model found that cases of the disease are at their highest in an average temperature of 51 degrees and annual rainfall of 600 millimeters. If that doesn't seem like very hot weather, it's because the number is average over the course of days (including during the cooler evening hours) and throughout the year (even in winter months).
What it means is that areas as far north as Idaho, Wyoming, Montana, Nebraska, and the Dakotas could eventually become hosts to the fungus. More than 470 American counties would be within range of the disease, potentially exposing as many as 80 million people to the spores.
But there's still hope — even slightly slowing climate change could limit valley fever's spread
But it may not be too late to slow the increase in infections, Gorris said.
These assumptions are based on the current rate of climate change, she said. If humans are able to reduce the speed of global warming, the spread of valley fever would be much less significant, the model predicts.
"The numbers we talked about are for a high climate warming scenario, where we do not decrease greenhouse gas emmissions," Gorris said. "There are things people can do — reducing gas emissions and limiting climate change, the area endemic for valley fever won't extend as far north."
Gorris said her work is intended to help people understand and prepare for the threat of this under-studied disease. The research team also tested the model under scenarios where climate change was slowed, and found the spread of the disease was significantly reduced.
"The message that we want to send is one of awareness, not worry," she said. "You can't tell people to stop breathing."