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Fungal Pathogens Flourish in the Pandemic’s Shadow

The World Health Organization’s first ever fungal priority pathogens list highlights the growing threat of fungal diseases and antifungal resistance.

Microscope visualization of Candida albicans in an esophageal sample from a rhesus monkey with thrush
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Christie Wilcox

Christie joined The Scientist's team as newsletter editor in 2021, after more than a decade of science writing. She has a PhD in cell and molecular biology, and her debut book Venomous: How Earth’s Deadliest Creatures Mastered Biochemistry, received widespread acclaim.

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ABOVE: Candida albicans in an esophageal sample from a rhesus monkey with thrush CDC / Arnold Kaufman

In a new list of fungal “priority pathogens,” the World Health Organization identifies 19 of these often-overlooked microbes that pose the greatest threat to human health. The report, released today (October 25), highlights the fact that “fungal infections are growing, and are ever more resistant to treatments, becoming a public health concern worldwide,” says Hanan Balkhy, the WHO Assistant Director-General for antimicrobial resistance, in a statement. The organization previously compiled similar lists for viruses and bacteria.

More than 150 million severe fungal infections are estimated to occur annually, resulting in approximately 1.7 million deaths. But those numbers are based on incomplete data, which is why the report “aims to focus and drive further research and policy interventions to strengthen the global response to fungal infections and antifungal resistance.” For instance, fungal infections currently receive less than 1.5 percent of all infectious disease research funding, the authors note. The University of Sydney Infectious Diseases Institute’s Justin Beardsley, who led a group commissioned by the WHO that aided in compiling the report, tells The Guardian that funding levels are unconscionably low considering the “huge burden of disease” of fungal infections. “They’re causing as many deaths as tuberculosis, and more than malaria.” Those diseases respectively caused approximately 1.5 million and 627,000 deaths in 2020, according to the WHO.

Some pathogens made the list because of their expanding geographic range, while others have exhibited increasing infection prevalence, especially during the COVID-19 pandemic.

In all, the list highlights 19 pathogens, each categorized as medium, high, or critical priority based on their potential impact on human health and what’s known about their resistance to antifungals. Four were placed in the critical category: Cryptococcus neoformans, an opportunistic pathogen that is the leading cause of death in people with HIV; Candida auris, a yeast that causes high-mortality-rate infections and has already caused several hospital outbreaks; Aspergillus fumigatus, a ubiquitous mold with emerging resistance to azole antifungals; and Candida albicans, a fungal member common in healthy human microbiomes that can also cause thrush and life-threatening blood infections.

According to the report, some pathogens made the list because of their expanding geographic range, while others have exhibited increasing infection prevalence, especially during the COVID-19 pandemic. Beardsley tells Cosmos that many newer pharmaceuticals for diseases including COVID-19 inadvertently aid pathogenic fungi by interfering with immune pathways involved in fighting fungal infections, and as a result, “we’re seeing suddenly tonnes more fungal infections, and that’s now got everyone’s attention.” A. fumigatus, for instance, rose in prominence as a secondary infection to SARS-CoV-2, causing a disease known as COVID-associated pulmonary aspergillosis.

See “Q&A: What to Know About the Drug-Resistant Fungus, Candida auris

Many of the listed fungi also raised red flags because of their emerging resistance to antifungals, drugs that are already limited in diversity because of the inherent challenges of targeting eukaryotic pathogens. Only four types of antifungals currently exist, Reuters reports. Unlike antibacterial agents, antifungals are seldom overused in humans; instead, their employment in agriculture and animal husbandry is driving the evolution of resistance, Beardsley tells Cosmos.

The report additionally outlines strategies for developing the infrastructure and capacities needed to tackle fungal diseases. “We need more data and evidence on fungal infections and antifungal resistance to inform and improve response to these priority fungal pathogens,” WHO Antimicrobial Resistance Department Director Haileyesus Getahun says in the organization’s statement.

“We were able to respond to COVID so quickly because . . . [t]he basic science was in place,” Beardsley tells Cosmos. “We haven’t invested in that basic science for decades in mycology research. So, it’s going from a standing start, and we really need to catch up and make up for lost time.”

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