Chinese scientists have uncovered a new fungal pathogen capable of infecting humans.

The fungus, named Rhodosporidiobolus fluvialis, was identified in clinical samples from two separate hospital patients. Research indicates that this yeast is resistant to several common antifungal drugs at body temperature, which also leads to the development of “hypervirulent mutants” that cause more severe disease in lab mice.

These findings support the theory that global warming could drive the evolution of new fungal pathogens, according to the researchers’ report published on June 19 in the journal Nature Microbiology.

The discovery was made after analyzing fungi from patients in 96 hospitals across China between 2009 and 2019. Out of 27,100 fungal strains collected, R. fluvialis was the only one previously unknown to infect humans.

R. fluvialis was found in the blood of two unconnected patients with serious underlying health conditions. One patient, a 61-year-old, died in an ICU in Nanjing in 2013, and the other, an 85-year-old, passed away in 2016 after ICU treatment in Tianjin. It remains unclear if the fungal infection directly contributed to their deaths.

Both patients were treated with common antifungal drugs, including fluconazole and caspofungin, to which R. fluvialis later proved resistant in lab tests.

“This is a remarkable and truly unexpected finding, which bodes badly for the future,” said David Denning, a professor of infectious diseases at the University of Manchester in the U.K., who was not involved in the research, speaking to Science.

Invasive fungal infections, which affect deep tissues, primarily impact individuals with weakened immune systems, such as those with HIV or on immunosuppressant drugs. The 61-year-old patient was immunosuppressed, and the 85-year-old had diabetes, which can impair immune function.

Rising global temperatures have prompted fungi to adapt and expand their habitats, increasing the likelihood of human contact. This has led to the emergence of new pathogens like the drug-resistant Candida auris, identified in over 40 countries since 2009. Meanwhile, the development of new antifungal drugs has slowed, leaving few options for treating resistant infections.

In their study, researchers infected immunocompromised mice with R. fluvialis and observed that some fungal cells rapidly evolved to become more aggressive. They then incubated the fungus at human body temperature (98.6°F or 37°C) and found that it mutated 21 times faster than at room temperature (77°F or 25°C). The yeast also became more likely to develop drug resistance when exposed to the antifungal drug amphotericin B at body temperature compared to room temperature.

The researchers concluded that if fungi like R. fluvialis are more prone to becoming virulent and drug-resistant at higher temperatures, global warming could potentially drive the evolution of new, dangerous fungal pathogens.

However, not all scientists believe R. fluvialis poses an immediate threat. Matthew Fisher, a professor of fungal disease epidemiology at Imperial College London, told Science that the yeast should not yet be considered a major emerging threat.

“My initial reaction is that there may be unsurveyed environments in China where these yeasts exist, and these two patients were simply unfortunate to be exposed,” he said. Currently, there is no evidence of R. fluvialis spreading widely among the population despite its concerning characteristics.