Dust storms can carry more than soil. Scientists are investigating how drought, heat and cycles of rain followed by dry weather may increase human exposure to disease-causing fungal spores.

Climate change may be creating an unusual public health hazard in the American West: conditions capable of putting disease-causing fungal spores into the air.

BBC Science Focus reported in May that increasingly dry and dusty conditions have renewed concern about what might loosely be called “fungal storms” — dust events capable of carrying fungal spores. The magazine highlighted Valley fever, or coccidioidomycosis, a respiratory disease caused by inhaling spores of the soil-dwelling Coccidioides fungus.

The connection is more complicated than drought simply producing more infections.

According to the Centers for Disease Control and Prevention, Coccidioides is established primarily in the Southwest and parts of Washington state. Soil disturbance and windstorms can send its spores airborne, where people can inhale them. The CDC also says changes in temperature, precipitation and extreme events such as drought may alter the geographic distribution of fungal diseases.

Researchers are finding a particularly intriguing relationship between drought and Valley fever.

A peer-reviewed National Institutes of Health study of California surveillance data from 2000 through 2020 found that drought initially suppressed infections, but cases rebounded afterward. Researchers estimated 1,467 excess cases in the two years following the 2007-09 drought and 2,649 excess cases following the 2012-15 drought. Wet winters followed by hot, dry summers were associated with increased transmission.

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That pattern fits what researchers sometimes call the “grow and blow” hypothesis: moisture encourages fungal growth, after which hot, dry conditions allow spores to form and become airborne as soils dry and are disturbed. Research published on California cases has found particularly pronounced seasonal disease peaks following wetter-than-average wet seasons and drier-than-average dry seasons.

The health implications are significant. The CDC says about 20,000 Valley fever cases are reported annually, while its modeling estimates the actual number of symptomatic infections could reach 206,000 to 360,000 annually because the disease is frequently missed or unreported. About 40% of infections develop lung symptoms, and 5% to 10% of those infections develop complications.

There is an important uncertainty. Researchers have found associations between dusty conditions and Valley fever, but robust evidence that dust storms themselves are directly responsible for rising infection rates remains limited, as BBC Science Focus also noted.

What is becoming clearer is the larger pattern: climate, soil and fungal disease are interconnected. As drought, heat and precipitation patterns change, the invisible biological cargo carried on the wind may become another climate-related health risk.

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