The University of Arizona

Background | CLIMAS


Each year, an estimated 100,000 people contract valley fever (medical name coccidioidomycosis)—a lung infection caused by a soil-dwelling fungus found primarily in the desert regions of Arizona and California. Most never show any symptoms, while others experience mild cold or flu-like ailments.

Less than 10% of infections progress to more severe illnesses and in rare cases the fungus moves outside the lungs to the muscles, bones, or skin. At its worst, the disease can cause a form of meningitis—leading to between 50 and 100 deaths per year. Annual healthcare costs related to valley fever are upwards of $60 million.

Researchers in the 1950s discovered the microscopic culprit for the disease, the fungus Coccidioides immitis. They also noted links between outbreaks of valley fever and climatic conditions, with peak cases following heavy rainy seasons.

While researchers are still learning about the disease's link to climate, it is believed that the fungus grows during wet periods and then forms tiny spores as the soil dries out. The spores release into the air when windy conditions or human activities, such as construction, disturb the soil.

Hot weather may also be an important factor in the mix. It is believed that extremely high temperatures can sterilize the soil, possibly killing other microorganisms while C. immitis remains dormant in deeper layers of the soil. When conditions change, the fungus may return to the surface layer flourish in the soil with little competition.

As the population of the Soutwestern United States continues to swell, thousands of more people are exposed to the disease each year. The highest incidences of valley fever occur near Tucson and Phoenix in Arizona and near Bakersfield, Calif., but the fungus is also found in parts of Texas, Nevada, and New Mexico. If climate change makes conditions more favorable for the fungus in these areas, large cities such as Los Angeles, El Paso, and Las Vegas could be at risk.