In the real world, Cordyceps can’t infect humans (whew!). But I am more than happy to take a page out of its survival strategy and use this cultural phenomenon to hijack your brain — or at least, a few moments of your attention — to explain why you should be worried about fungi.
Before getting into the scary stuff, let us pause to praise our fungal friends. Yes, there are a few not-so-fun fungi that can be deadly to humans, but those are the outliers. In fact, genetically speaking, they are humanity’s closest relatives. They are nature’s composters, breaking down dead animals and plants and spreading nutrients around. They gave us penicillin and the cholesterol-lowering drug lovastatin. They gave us beer.
And for years, they’ve been relatively easy to ignore. Some 95% of them can’t survive on our balmy 98-degree Fahrenheit bodies. Meanwhile, our immune systems typically make tidy work of the ones that try. Fungi that linger might be embarrassing or annoying, causing an unsightly toenail infection or recurring yeast infection, but they’re not deadly. The exception tends to be for people who are immunocompromised, or have another bacterial or viral infection that renders them temporarily immunocompromised.
But climate change could alter those dynamics. In fact, there are signs it’s already happening.
As the world gets warmer, fungi could adapt in a way that would make our bodies more welcoming hosts. “The question that I’m asked all the time is ‘Could a fungal disease emerge to cause a pandemic?’,” says Arturo Casadevall, a microbiologist and immunologist at Johns Hopkins Bloomberg School of Public Health who studies how fungi cause disease. “The answer is: I don’t know. But there’s no reason that it can’t.”
Casadevall says what matters isn’t the average rise in temperatures, but the rising number of days of extreme heat each year. “When you have a really hot day, that’s a selection event.” Think about the temperature of the sidewalk or the soil when the thermometer surges past 100 degrees Fahrenheit. The organisms living there will either adapt or die, “and the fungi can adapt very rapidly,” he says.
He believes we already have an example of a fungi crossing our thermal defenses: In 2011 and 2012, dangerous infections with a yeast called Candida auris suddenly and simultaneously appeared across three continents. The fungus was disturbingly resistant to many of the available drugs and ended up killing more than half the people it infected.
That ability to get past our drug arsenal wasn’t due to misuse or overuse of antifungals in the way that overprescribing or misuse of antibiotics has led to drug-resistant bacteria. Rather, as Casadevall describes it, Candida auris came out of the ground with that design. And once these resistant fungi find their way into a hospital, they’re very hard to get rid of.
“To me, that’s a harbinger of a scary future,” Casadevall says.
And while that scary future might not come in the form of a fungus that turns your grandmother into a mushroom zombie, the real possibility of menacing fungal invasions is one we aren’t doing enough to prevent.
In October, the World Health Organization drew up its first-ever list of scary fungi and laid out a series of recommendations for combating them. Some of the more basic suggestions underscore how little attention we’ve paid to fungi. For example, the WHO would like to see better data on how and where people are affected by serious fungal infections and where resistance is cropping up.
Drug development is another area that needs more resources. Inventing drugs that can kill fungi is notoriously difficult. Remember when I told you they were our closest relatives? Sharing all those genes means it’s difficult to design drugs that kill fungi without harming us. Doctors are working with just four classes of antifungals, the “newest” of which is over 20 years old. And each of those has liabilities, such as risky side effects or limited modes of administration.
Beyond new drugs, there is a need to simply get a better handle on what’s lurking out there and what might pose the next big threat. In 2019, Casadevall and colleagues around the globe were trying to do just that, but the work was sidelined by Covid.
HBO might have helped revive it. Casadevall says one of his collaborators reached out this week to try to get the project going again. Let’s hope that’s only the first positive side effect of Last of Us. If mushroom zombies can convince more people to care more about the vast reach of climate change — even down at the microbial level — that would be a pretty good second side effect.
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This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.
Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry. Previously, she was executive editor of Chemical & Engineering News.
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