California's Droughts Are Boosting Cases of Valley Fever Fungus
Cases of Valley fever have increased dramatically over the last two decades, and California's droughts may be to blame.
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Valley fever is an emerging fungal disease in the western United States that most often causes flu-like symptoms, but can also cause dangerous or even deadly complications. By analyzing data on reported cases of Valley fever in California, which have increased dramatically over the last two decades, researchers from University of California San Diego and University of California, Berkeley, have identified seasonal patterns that could help individuals and public health officials better prepare for future surges in Valley fever cases. The findings also have important implications for how the changing climate can exacerbate the threat of infectious diseases. The findings are published in The Lancet Regional Health - Americas.
The researchers collaborated closely with the California Department of Health (CDPH) to analyze all reported Valley fever cases in California from 2000 to 2021. By comparing these to seasonal climate data, they discovered how the disease cycles seasonally across different California counties and identified how these cycles are influenced by drought periods. The researchers found that while most cases occur during the period from September to November, there were differences in seasonal patterns and timing between counties and years.
Another hypothesis suggests that the links between Valley fever and drought may be due to drought’s impact on rodents that host the Coccidioides fungus. Because rodent populations decline during droughts, and because dead rodents are thought to be an important source of nutrients for the fungus, it may be able to survive and spread more easily in drought conditions.
"This work is an important example of how infectious diseases are influenced by climate conditions,” said Heaney. “Even though droughts appear to decrease Valley fever cases in the short term, the net effect is an increase in cases over time, particularly as we experience more frequent and severe droughts due to climate change.”
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Subscribe for FREEIndividuals can help protect themselves against Valley fever during dry and dusty periods by minimizing time outdoors and wearing face coverings that can block dust. The researchers also emphasize the need for more thorough monitoring of the Valley fever fungus, which can be difficult to detect.
The team is now expanding the range of their analyses to include other Valley fever hotspots in the United States.
“Arizona is much dustier than California and has very different climate dynamics, and about two thirds of cases in the United States occur in Arizona, so that’s where we’re looking next,” said Heaney. “Understanding where, when, and in what conditions Valley fever is most prevalent is critical for public health officials, physicians, and the public to take precautions during periods of increased risk.”
Reference: Heaney AK, Camponuri SK, Head JR, et al. Coccidioidomycosis seasonality in California: a longitudinal surveillance study of the climate determinants and spatiotemporal variability of seasonal dynamics, 2000–2021. Lancet Reg Health – Americas. 2024;38. doi: 10.1016/j.lana.2024.100864
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