Scientists in China have discovered a previously unknown fungal pathogen that can infect humans.
The mushrooms, the so-called Rhodosporidiobolus fluvialis, was detected in clinical samples from two unrelated hospital patients. In experiments, the researchers found that the yeast was resistant to several first-line antifungal drugs at higher temperatures — about that of the human body. This temperature also produced “hypervirulent mutants” capable of causing more severe disease in laboratory mice.
The findings “support the idea that global warming may encourage the evolution of new fungal pathogens,” the researchers behind the discovery wrote in a report published June 19 in the journal Natural Microbiology.
Scientists made this discovery after examining fungi taken from patients in 96 hospitals in China between 2009 and 2019. A total of 27,100 strains of fungi were collected and analyzed; of these, only R. fluvialis has never before been observed in humans.
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R. fluvialis was found in the blood of two unrelated patients who, in addition to being infected with the yeast, had serious underlying health problems. One patient was a 61-year-old who died in an intensive care unit (ICU) in Nanjing in 2013, and the other was an 85-year-old who died in 2016 after being treated in an intensive care unit in Tianjin. The report did not note whether the fungal infection directly contributed to the deaths of these patients or whether they were simply infected at the time.
As part of the treatment, patients were given common antifungal drugs, including fluconazole and caspofungin. The team’s laboratory research later found this R. fluvialis is resistant to both drugs.
“This is a remarkable and truly unexpected finding that bodes ill for the future,” David Denningprofessor of infectious diseases at the University of Manchester in the United Kingdom, who was not involved in the research, said Science.
Invasive fungal infections that attack tissues deep in the body, affect mostly people whose immune systems are weakened, due to HIV infection or as a result of taking immunosuppressants, for example. In particular, the 61-year-old infected with R. fluvialis was immunosuppressed and the 85-year-old had diabetes, which can interfere with immune function.
However, rising global temperatures have forced fungi to adapt and expand their geographic reach, making some more likely to come into contact with humans. Thus, new pathogens have emergedincluding drug-resistant ones Candida auriswhich is established in more than 40 countries since its discovery in 2009. Meanwhile, the development of new antifungal drugs largely at a standstillleaving few options to fight resistant infections.
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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. The team then looked at the fungi in labware kept around human body temperature, 98.6 degrees Fahrenheit (37 degrees Celsius). At this temperature, the yeast mutated 21 times faster than at room temperature, about 77 F (25 C).
The heat did too R. fluvialis more likely to become drug resistant. When exposed to the antifungal drug amphotericin B, yeast develop resistance faster at body temperature than at room temperature.
If the yeast likes R. fluvialis are more likely to become virulent and drug-resistant at high temperatures, global warming could potentially spur the evolution of new, dangerous fungal pathogens, the team wrote in the paper.
But as for R. fluvialisin particular, some scientists resist jumping to alarmist conclusions. Matthew Fisherprofessor 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 first feeling here is that there are unexplored environments in China where these yeasts live, and that these two patients were unfortunate enough to be exposed,” he told Science. In short, there is no evidence for R. fluvialis spreading widely among the population, despite its alarming characteristics.
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