This article was first published underground magazine.
In the early 21st century, Valley fever was a little-known fungal disease in the United States, with fewer than 3,000 reported cases per year, occurring primarily in California and Arizona. Two decades later, Valley fever cases have exploded, increasing nearly sevenfold by 2019.
Valley fever doesn’t stop there. Fungal diseases commonly occur in places never seen before, making previously harmless or mildly harmful fungi more dangerous to people. One reason for the worsening fungal situation is likely to be climate change, scientists say. Changes in temperature and rainfall patterns are magnifying where disease-causing fungi occur. Climate-induced disasters can help the fungus spread and reach more people. And rising temperatures create opportunities for fungi to evolve into more dangerous pathogens.
For a long time, fungi were ignored as a group of pathogens. By the late 1990s, researchers were already warning that climate change would make infectious diseases caused by bacteria, viruses and parasites, such as cholera, dengue and malaria, more prevalent. “But people weren’t paying attention to fungi at all,” he says. arturo casadeval, a microbiologist and immunologist at the Johns Hopkins Bloomberg School of Public Health. That’s because until recently, fungi caused relatively little harm to humans.
High body temperature helps explain why. Many fungi grow best at temperatures between 12 and 30 degrees Celsius (approximately 54 and 86 degrees Fahrenheit). As a result, fungi do not typically thrive in the warm bodies of mammals, although they are more susceptible to infecting organisms that do not maintain a consistently high internal temperature, such as trees, crops, amphibians, fish, reptiles, and insects, Casadevall wrote in the brief. .of Immunity against invasive fungal diseases in 2022 Annual Review of Immunology. Some of the few fungi that can infect humans are dangerous, including: cryptococcus, Penicilliumand aspergillus, historically more commonly reported in tropical and subtropical regions than in cooler regions. This also suggests that their range may be limited by climate.
But now, the world’s warming climate may be facilitating the spread of some fungal pathogens to new regions. Let’s take volleyball fever as an example. The disease can cause flu-like symptoms in people who inhale microscopic spores of the fungus. Coccidioides. According to a 2019 study, climate conditions conducive to Valley fever may currently be occurring in 217 counties in 12 U.S. states. morgan gorisan Earth system scientist at Los Alamos National Laboratory in New Mexico.
But when Goris modeled where the fungus could live in the future, the results were sobering. By 2100, in a scenario where greenhouse gas emissions continue unabated, rising temperatures will Coccidioides Spreading north to 476 counties in 17 states. Once thought to be primarily confined to the southwestern United States, the disease could spread to the U.S.-Canada border in response to climate change, Goris said. It was truly a “wow moment,” she added. put millions more people at risk.
Several other human fungal diseases are also ongoing. histoplasmosis and blastomycosis. Both, like Valley fever, are increasingly being seen outside what was considered their historical range.
This range extension is Fungal pathogens of other species. For example, the chytrid fungus, which contributes to the decline of hundreds of amphibian species, thrives at environmental temperatures of 17 to 25 degrees Celsius (63 to 77 degrees Fahrenheit). However, this fungal problem is becoming increasingly severe at high altitudes and latitudes, perhaps in part because rising temperatures are making previously cold regions more hospitable to people. Masu. chytrid mold. Similarly, white pine blister rustThe fungus, which has wiped out some species of white pine in Europe and North America, has spread to highlands where conditions were previously unfavorable. This puts even more pine forests at risk. Changing climatic conditions are also helping to increase fungal pathogens in crops, such as those that infect bananas and plantains. wheatto new territory.
Climate warming may also change the cycles of droughts and heavy rains, increasing the risk of fungal diseases in humans. A study of more than 81,000 Valley fever cases in California from 2000 to 2020 found that: Infections tended to spike in the two years immediately following a long drought. Scientists still don’t fully understand why this happens. However, one hypothesis suggests that: Coccidioides They survive better than competing microorganisms during long droughts, grow rapidly when rain returns, and release spores into the air when the soil begins to dry out again. “So climate not only affects location, but also the number of cases per year,” Goris said.
Climate change could also cause more intense and frequent storms and fires, helping fungal spores spread over long distances. Researchers have found a spike in Valley fever infections in California hospitals after massive wildfires 320 miles away. Scientists have observed this phenomenon in other species, and sandstorms in Africa may be responsible for transporting coral-killing soil bacteria to the Caribbean.
Researchers are now sampling the air from dust storms and wildfires to determine whether these events can actually carry viable disease-causing fungi over long distances and into people, causing infections. I’ve confirmed it.Understanding this spread is key to understanding how the disease spreads, he says. Bala Choudharya fungal ecologist at Dartmouth; Overview of fungal spread in 2022 Annual Review of Ecology, Evolution, and Systematics. But there is a long road ahead. Scientists are still trying to figure out some basic questions, such as where different pathogenic fungi live in the environment or what exactly triggers fungal spores to be released from the soil and travel long distances to become established. I don’t have an answer to my question yet. A new place.
Helping existing fungal diseases reach new locations is not the only effect of climate change. Rising temperatures also help previously harmless fungi evolve resistance to heat. Researchers have long known that fungi have this ability. For example, in 2009 researchers found that a fungus, in this case a pathogen that infects insects, can evolve to grow at temperatures close to 37 degrees Celsius, about 5 degrees Celsius higher than the previous temperature limit after just four months. Indicated. More recently, researchers have grown a dangerous human pathogen. Cryptococcus deneoformans, performed in the laboratory at both 37 degrees Celsius (similar to human body temperature) and 30 degrees Celsius. He found that higher temperatures increased certain types of mutations in the fungal DNA by five times compared to lower temperatures. Researchers speculate that as global temperatures rise, some fungi may adapt rapidly and their populations may increase. ability to infect humans.
There are also real-world examples. Before 2000, the fungus stripe rust, which devastated wheat crops, favored cool, humid regions of the world. But since 2000, he says, some strains of this fungus have become able to adapt to higher temperatures. These hardier plants are replacing older plants and spreading into new areas.
Casadevall said this is concerning, especially as the days continue to get hotter and heatwaves become more frequent and intense. “Microorganisms really have two choices: adapt or die,” he says. “Most of them have some degree of adaptive capacity.” As climate change increases hotter days, evolution may select for heat-tolerant fungi more strongly.
And as fungi in the environment adapt to withstand heat, some may be able to break through the human temperature barrier.
This may have already happened. In 2009, Japanese doctors isolated an unknown fungus from the ear discharge of a 70-year-old woman.This new medicinal fungus named candida auris, which quickly spread to hospitals around the world, causing severe bloodstream infections in already sick patients.of World Health Organization adds to list candida auris among the most dangerous groups One contributing factor to the decline in fungal pathogens is the increasing resistance of fungi to common antifungal drugs.
“For India, it’s a real nightmare,” he says arunalok chakrabarti, a medical mycologist at the Graduate Institute of Medical Education and Research, Chandigarh, India.when C.Auris It was first reported in India more than a decade ago, but it was low on the list. candida According to Chakrabarti, the species poses a threat to patients and is now the main cause of the disease. candida Infection. In the United States, clinically, Cases have skyrocketed From 2013 to 2016, there were 63 cases, which increased to more than 2,300 cases in 2022.
where did it go C.Auris Does it come so suddenly? This fungus appeared simultaneously on three different continents. Each continental version of this fungus is genetically distinct, suggesting that it emerged independently on each continent. “It’s not like someone transported it on a plane,” Casadevall said. “The isolates are not related.”
Because all continents are exposed to the effects of climate change, Casadevall et al. human-induced global warming It may have played a role. C.Auris It may have always been present somewhere in the environment. It may be present in wetlands where researchers have recovered other pathogenic species. candida. Researchers argued in 2019 that climate change may have exposed the fungus to high temperatures over and over again, making some strains tolerant of high temperatures enough to infect humans, but many others. The researchers cautioned that other factors were also likely to be involved.
Later, scientists from India and Canada discovered C.Auris In the nature of the Andaman Islands in the Bay of Bengal.This “wild” version of C.Auris At human body temperature, they grew much more slowly than those developed in hospitals. “What this suggests to me is that this substance is present in the environment and that some isolates are adapting faster than others,” Casadevall said.
As with other explanations, C.AurisThe origin of Kasadevar is only a hypothesis and still needs to be proven, Chakrabarti said.
One way to establish a link to climate change is to examine older soil samples to see if the soil is contaminated, Casadevall said. C.Auris Among them. Older versions of the fungus don’t grow well at high temperatures, but if they start to grow over time, that’s good evidence that the fungus is adapting to the heat.
In any case, we need to take seriously the possibility that rising temperatures will bring new fungal pathogens to humans, especially drug-resistant fungi currently infecting insect and plant species that will be able to multiply at human body temperature. If that happens, Casadevall said. “After that, we will meet creatures we have never known before. candida auris”
Doctors are already encountering new fungal infections in people, including infections from several new drug classes. Emergo Secess It occurs primarily in HIV-infected patients on four continents and was first recorded in Cartilage stellate purpuraA plant mycologist in India was infected with a fungus that infects some plants in the Rosaceae family. Although these new diseases are not directly linked to climate change, they highlight the threat that fungal diseases can pose. For Casadevall, the message is clear. It’s time to pay more attention.
