Health
Fungal Foes: How Climate Change is Increasing Health Risks
At the dawn of the 21st century, Valley fever was a relatively unknown fungal disease in the United States, with fewer than 3,000 cases reported annually, primarily in California and Arizona. Fast forward two decades, and this disease has seen a dramatic increase, spreading to new states and affecting more people.
Valley fever is not an isolated case. Fungal diseases are emerging in areas where they were previously unseen, and fungi that were once harmless are becoming more dangerous. Scientists believe that climate change is a significant factor in this troubling trend. Changes in temperature and rainfall patterns are expanding the habitats of disease-causing fungi, while climate-related disasters facilitate their spread, reaching more people.
Arturo Casadevall, a microbiologist and immunologist at the Johns Hopkins Bloomberg School of Public Health, points out that “people were not focused at all on the fungi” until recently. Historically, fungi have not been a significant concern for humans due to our high body temperatures, which are inhospitable for most fungi. However, this is changing as the planet warms, allowing some fungi to adapt and thrive in new environments.
Valley fever, caused by the fungus Coccidioides, is an example of how climate change is altering the landscape of fungal diseases. Currently, conditions favorable to Valley fever exist in 217 counties across 12 U.S. states. However, a study by Morgan Gorris, an Earth system scientist at Los Alamos National Laboratory, predicts that by 2100, these conditions could extend to 476 counties in 17 states if greenhouse gas emissions continue unchecked. Gorris describes this potential expansion as a “wow moment” because it would expose millions more people to the disease.
Other fungal diseases, such as histoplasmosis and blastomycosis, are also expanding beyond their traditional ranges. This trend is not limited to human pathogens; fungal diseases affecting other species and crops are on the move as well. The chytrid fungus, which has devastated amphibian populations, and white pine blister rust, affecting pine forests, are spreading to higher altitudes and latitudes due to rising temperatures.
The changing climate also affects cycles of droughts and heavy rains, increasing the risk of fungal diseases in humans. A study of over 81,000 Valley fever cases in California from 2000 to 2020 found that infections surged in the two years following prolonged droughts. Gorris explains that “climate is not only going to affect where it is, but how many cases we have from year to year.”
Moreover, climate change can trigger more intense storms and fires, helping fungal spores travel greater distances. Unusually large outbreaks of Valley fever have been observed after dust storms and wildfires, with spores potentially traveling hundreds of miles. Researchers are investigating whether these events can carry viable, disease-causing fungi to new areas.
Climate change does not only help existing fungal diseases spread; it may also enable previously benign fungi to evolve into more dangerous pathogens. Rising temperatures could prompt fungi to adapt to heat, increasing their ability to infect humans. Casadevall warns, “Microbes really have two choices: adapt or die,” and many have the capacity to adapt.
An example of this adaptation is the emergence of Candida auris, a fungus that causes life-threatening infections and shows resistance to common antifungal drugs. Discovered in Japan in 2009, C. auris has since spread globally. Casadevall and colleagues suggest that climate change may have played a role in its emergence, allowing the fungus to adapt to higher temperatures.
The potential for warmer climates to introduce new fungal pathogens to humans is a serious concern. Casadevall emphasizes the need for vigilance, especially as drug-resistant fungi could adapt to grow at human body temperatures. He warns, “Then we find ourselves with organisms that we never knew before, like Candida auris.”
Doctors are already encountering new fungal infections, such as species of Emergomyces and Chondrostereum purpureum, which have appeared in various regions. While these emerging diseases have not been directly linked to climate change, they underscore the growing threat of fungal diseases. Casadevall concludes that it is crucial to pay more attention to this evolving challenge.
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