Higher ambient temperatures can trigger mutations in fungi, leading to increased infectivity, more aggressive growth or resistance to numerous antifungals.
Microbiologist examines mold and fungal cultures in Petri dishes.
Health officials have long been concerned that rising temperatures on Earth could cause fungi to become more dangerous to humans. Of course, some people get ringworm or nail infections, and some women get repeated yeast infections, but other than those cases, fungal infections have not been particularly problematic. But that is changing.
An international team of medical researchers and infectious disease specialists based in China collaborated with a researcher from Singapore and another from Canada. Together they found disturbing evidence that fungi may actually become more dangerous to humans as the world warms.
Normally, mammals are naturally protected from most fungal infections because fungi are cold-adapted organisms that grow best at temperatures lower than those found in and on the body of mammals. Therefore, fungi cause far less disease in mammals than bacteria and viruses. However, infectious disease experts warn that fungi have the potential to adapt to rapidly rising climate temperatures and could therefore reach a point where they may live in and on the human body.
To find out whether this transition is already taking place, researchers searched for fungal infections in patients in 96 hospitals in China between 2009 and 2019. Among the thousands of pathogenic fungi they isolated and studied, they found a fungus that had never before been reported to infect humans. The pathogen, Rhodosporidiobolus fluvialiswas isolated from the blood of two unrelated patients who were being treated in intensive care units for severe underlying diseases: an 85-year-old woman from Tianjin who died in 2016 and a 61-year-old man from Nanjing who died in 2013. The pathogen was resistant to the two main drugs used to treat potentially fatal fungal infections in humans, caspofungin and fluconazole.
To further characterize this fungal pathogen and prove that it can infect mammals, the researchers injected it into laboratory mice with weakened immune systems. Surprisingly, the fungus thrived and some of the fungal cells even mutated into a more aggressive form.
When researchers discovered the cause of R. fluvialis‘ increased pathogenicity, they found that cells cultured at 37°C (human body temperature) developed mutations 21 times faster than cells cultured at 25°C. In addition, the researchers also discovered that R. fluvialis developed drug resistance much more rapidly when cultured at 37 °C and exposed to another common antifungal drug, amphotericin B.
This is extremely worrying. Given the increasing use of immunosuppressive drugs in recent decades and the ongoing HIV epidemic, there are more immunocompromised individuals in the general population who are at increased risk of fungal infections. In addition, since fungi mutate more frequently in warmer environments – including the higher body temperatures of mammals – this could trigger mutations in fungi, making them more infectious and drug resistant.
In line with this finding, epidemiologists are reporting numerous new fungal diseases in humans, at least some of which are already drug-resistant.
These are unexpected results and they suggest that further warming of the planet could have catastrophic health consequences for humans and other mammals.
Source:
Jingjing Huang, Pengjie Hu, Leixin Ye, Zhenghao Shen, Xinfei Chen, Fang Liu, Yuyan Xie, Jinhan Yu, Xin Fan, Meng Xiao, Clement KM Tsui, Weiping Wang, Yingxing Li, Ge Zhang, Koon Ho Wong, Lei Cai, Feng-yan Bai, Yingchun Xu, and Linqi Wang (2024). Pan-drug resistance and hypervirulence in a human fungal pathogen are enabled by mutagenesis induced by mammalian body temperature, Natural Microbiology | doi:10.1038/s41564-024-01720-y
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