Researchers have elucidated the seasonal and climate-driven patterns of Valley fever, a serious fungal illness that is transmitted through airborne dust.
Valley fever is a concerning fungal infection primarily found in the western United States. It usually leads to symptoms similar to the flu but can result in severe or potentially fatal complications. By examining the rise in reported Valley fever cases in California over the past twenty years, scientists from the University of California San Diego and the University of California, Berkeley, have pinpointed seasonal trends. These insights may aid individuals and public health officials in anticipating and managing future outbreaks of Valley fever. Additionally, the research highlights the significant impact of climate change on the risk of infectious diseases. The results are published in The Lancet Regional Health — Americas.
In collaboration with the California Department of Health (CDPH), the researchers reviewed all reported Valley fever cases in California from 2000 to 2021. By aligning these cases with seasonal climate data, they could trace how the disease ebbs and flows throughout different counties in California and how drought conditions influence these patterns. They discovered that while most cases peak between September and November, the seasonal timings varied across counties and years.
“Most seasonal infectious diseases show an annual peak, so we were surprised to find that some years recorded few or no peak cases of Valley fever in certain counties,” stated Alexandra Heaney, Ph.D., the lead author and assistant professor at the UC San Diego Herbert Wertheim School of Public Health and Human Longevity Science. “This prompted us to investigate what factors were causing these variations in seasonality over different years, and we suspected drought may play a significant role.”
The data revealed that counties in the San Joaquin Valley and Central Coast regions exhibited the most significant seasonal peaks, with San Joaquin Valley experiencing these peaks earlier.
“This information is crucial for timing public health communications to educate individuals about Valley fever symptoms and preventive measures,” added Heaney.
Valley fever is triggered by spores from the soil-dwelling fungus Coccidioides. Inhaling infectious spores, which become airborne when the soil is disturbed by environmental factors or human actions, results in the infection. Those frequently exposed to airborne dust, particularly outdoor workers, are at higher risk. However, it’s important to note that Valley fever is not contagious.
Though Valley fever has historically affected the American Southwest, case numbers have surged recently, tripling from 2014-2018 and again from 2018-2022, as reported by the CDPH. Due to its relative rarity and symptom similarities with other respiratory infections, including COVID-19, Valley fever is often misdiagnosed. Without proper treatment, the fungus can severely damage the respiratory system and can spread to other parts of the body, affecting organs such as the skin, bones, and possibly the brain, which can be fatal.
“Understanding when the Valley fever season commences and its potential intensity can guide healthcare providers in recognizing and addressing new cases with urgency,” remarked Justin Remais, Ph.D., a corresponding author and professor at UC Berkeley School of Public Health. “This study is significant as it pinpoints the highest disease risk periods across all endemic counties in California as well as regions where the disease is emerging.”
The researchers noted that during drought years, the intensity of seasonal peaks in Valley fever cases tends to be lower. However, upon the return of rains, these peaks can be quite pronounced. One theory posits that droughts allow heat-resistant Coccidioides spores to survive longer, allowing for robust growth when rainfall returns, as they face less competition for moisture and nutrients.
Another theory suggests that the connection between Valley fever and drought may stem from the drought’s impact on rodent populations that harbor the Coccidioides fungus. With fewer rodents during droughts, and considering that deceased rodents provide essential nutrients for the fungus, conditions during drought are likely to favor its survival and spread.
“This research is a vital demonstration of how climate conditions affect infectious diseases,” Heaney stated. “Even if droughts seem to reduce Valley fever cases in the short term, the overall effect is an increase in cases over time, especially as we face more frequent and severe droughts due to climate change.”
People can safeguard themselves from Valley fever during dry, dusty conditions by limiting outdoor activities and using face coverings to block dust. The researchers stress the importance of improved monitoring of the Valley fever fungus, which can be challenging to detect.
The research team is now broadening their analysis to encompass additional Valley fever hotspots across the United States.
“Arizona experiences more dust than California and has different climatic patterns, where around two-thirds of United States cases occur, making it our next focus,” Heaney noted. “Understanding the where, when, and under what conditions Valley fever is most prevalent is essential for public health officials, medical practitioners, and the community to take necessary precautions during times of heightened risk.”
