The Intersection of Climate Change and the Rise of Fungal Diseases
Published by Undark Magazine
In the early 2000s, valley fever was a little-known fungal disease in the US, with fewer than 3,000 reported cases each year, mainly in California and Arizona. Fast forward two decades, and cases of valley fever have skyrocketed, increasing by around seven times by 2019. And valley fever is not the only fungal disease experiencing this surge. Fungal diseases, in general, are appearing in new locations, and previously harmless fungi are becoming more dangerous to humans. Scientists believe that one contributing factor to this phenomenon is climate change. Shifting temperatures and rainfall patterns are expanding the range of disease-causing fungi. Extreme weather events caused by climate change can also aid the dispersion of fungi and increase their reach. Additionally, warmer temperatures create the conditions for fungi to evolve into more pathogenic strains.
Fungi have traditionally been overlooked as a group of pathogens. While researchers warned in the late 1990s that climate change would lead to the spread of infectious diseases caused by bacteria, viruses, and parasites, fungi were not considered a focus. This is because fungi have historically posed little threat to humans. Unlike other organisms, fungi struggle to survive inside warm mammalian bodies, as they thrive at temperatures ranging from about 12 to 30 degrees Celsius. However, with climate change, some fungal pathogens are finding new habitats.
Take valley fever as an example. This disease, caused by the fungus Coccidioides, can produce flu-like symptoms in individuals who inhale its spores. The climatic conditions suitable for valley fever are now present in 217 counties across 12 US states. However, modeling conducted by Morgan Gorris from the Los Alamos National Laboratory predicts that by 2100, in a scenario with continued greenhouse gas emissions, rising temperatures could facilitate the spread of Coccidioides as far north as the US-Canadian border.
Other fungal diseases, including histoplasmosis and blastomycosis, are also being reported outside their previous geographical ranges. This expansion is not limited to human diseases but is also observed in fungal pathogens affecting other species. For instance, the chytrid fungus responsible for amphibian declines is increasingly found at higher altitudes and latitudes, thanks to rising temperatures. Similarly, changing climate conditions are driving the spread of fungal pathogens affecting crops, such as those infecting bananas and wheat.
A warming climate also disrupts weather patterns, leading to droughts and intense rainfall. These climatic changes can increase the risk of fungal diseases in humans. Studies have shown that valley fever infections surge following prolonged droughts. During these dry periods, Coccidioides can outcompete other microbes and then quickly multiply when rains return, releasing spores into the air. Climate change can also contribute to the spread of fungal spores over long distances. Dust storms and wildfires can carry disease-causing fungi for hundreds of miles and introduce them to new regions, leading to infections in humans.
However, many questions remain unanswered. Researchers are still trying to determine where pathogenic fungi reside in the environment and uncover the triggers that release fungal spores from soil and transport them over long distances. Furthermore, warming temperatures can lead to the evolution of heat-tolerant fungi. Some strains of the stripe-rust fungus, which devastates wheat crops, have already adapted to higher temperatures in recent years.
This ability of fungi to evolve and adapt is concerning, particularly as global temperatures continue to rise. As the number of hot days increases, heat-resistant fungi may become more prevalent. There is even the possibility that some fungi may breach the human body’s temperature barrier, as seen with Candida auris. This dangerous fungal pathogen has shown increasing resistance to antifungal drugs and has become a leading cause of Candida infections in some regions.
The interplay between climate change and the rise of fungal diseases is a complex and evolving field of study. Understanding the mechanisms behind the spread and evolution of fungal pathogens is crucial for developing effective strategies to combat these emerging threats.
Source: Undark Magazine
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