Scientists in China have found a previously unknown fungal pathogen that can infect humans. The fungus Rhodosporidiobolus fluvialis was discovered in clinical samples from two unrelated hospital patients.
Researchers found that, at higher temperatures similar to those of the human body, the yeast exhibited resistance to several first-line antifungal drugs.
These temperatures also led to the emergence of “hypervirulent mutants” that caused more severe disease in lab mice.
The findings “support the idea that global warming can promote the evolution of new fungal pathogens,” the researchers behind the discovery wrote in a report published June 19 in the journal Nature Microbiology.
The scientists discovered this after examining fungi samples from patients in 96 hospitals across China between 2009 and 2019.
A total of 27,100 strains of fungi were collected and analysed, and only R. fluvialis had never been seen in humans before.
R. fluvialis was found in the blood of two unrelated patients who had serious underlying health conditions.
One patient, a 61-year-old, died in an intensive care unit (ICU) in Nanjing in 2013, while the other, an 85-year-old, died in 2016 after being treated in an ICU in Tianjin.
The report does not specify whether the fungal infection directly contributed to their deaths or if it was incidental.
Both patients were treated with common antifungal drugs, including fluconazole and caspofungin. Subsequent lab studies revealed that R. fluvialis is resistant to these drugs.
David Denning, a professor of infectious diseases at the University of Manchester in the UK who was not involved in the research, told Science: “This is a remarkable and truly unexpected finding, which bodes badly for the future.”
In the new study, researchers infected immunocompromised mice with R. fluvialis and found that some of the fungal cells quickly evolved to grow more aggressively.
They then examined the fungus in lab dishes maintained at human body temperature – 98.6 degrees Fahrenheit (37 degrees Celsius). At this temperature, the yeast mutated 21 times faster than it did at room temperature, around 77 F (25 C).
The heat also increased R. fluvialis’s likelihood of developing drug resistance. When exposed to the antifungal drug amphotericin B, the yeast developed resistance more rapidly at body temperature than at room temperature.
The team noted that if yeasts like R. fluvialis are more prone to becoming virulent and drug-resistant at high temperatures, global warming could potentially drive the evolution of new, dangerous fungal pathogens.
However, regarding R. fluvialis specifically, some scientists caution against jumping to alarming conclusions. Matthew Fisher, a professor of fungal disease epidemiology at Imperial College London who was not involved in the research, told Science that the yeast should not yet be considered a major emerging threat.
“My kind of first feeling here is that there are unsurveyed environments in China where these yeasts dwell and that these two patients have been unlucky enough to be exposed,” he told Science.
