THE LAST OF US?
The future of fungal pathogens in an ever-warming world
Fungi like it cold — or at least, they used to. If they hadn’t, humans might never have evolved.
Sixty-six million years ago, Earth’s great dinosaur die-off was followed by a massive fungal bloom. Reptiles that hadn’t already gone extinct were vulnerable to invasive fungi because of their low body temperature. Warmblooded mammals, meanwhile, ran too hot to make good hosts, since most fungi prefer temperatures between 53 and 86 degrees. Our resistance to fungal infection gave mammals an evolutionary edge that helped us dominate the animal kingdom. Now that could be changing, warns science writer and former toxicologist Emily Monosson.
The culprit, in part, is climate change. As the environment heats up, fungi may evolve a higher temperature tolerance, making it more likely they’ll be able to infect our own warm bodies. And fungal infections, which can be even deadlier and more difficult to treat than viral and bacterial infections, pose as grave a threat to humans as asteroids did to the dinosaurs. But unlike the dinosaurs, Monosson notes, we can take steps to reduce our risk.
In “Blight,” Monosson traces the history of fungal pathogens — “the most devastating disease agents known on the planet” — and augurs a potentially catastrophic future. No background knowledge of fungi is required on the reader’s part. Although this is an expert’s account, grounded in exhaustive interviews with researchers at the forefront of mycology, the language is clear and plain. It’s an urgent message meant for a wide audience, and the tone is by turns alarming and reassuring.
The book is divided into two parts, the first of which documents the emergence of microbes that have decimated entire populations of plants
BLIGHT: Fungi and the Coming Pandemic
By Emily Monosson Norton, 288 pages, $28.95
and animals. The second offers hope, exploring ways we can prevent the unchecked spread of deadly fungi before they wipe out another species — and threaten our own. “Pine trees, bats, frogs, and myriad others — we save them, we save ourselves,” Monosson writes.
Already, more than 1.6 million people worldwide die from fungal infections each year. In 2016, a strain emerged in the US that some scientists consider the first new climate-enabled human fungal pathogen. Candida auris spread quickly, resisted antifungal medication, and killed between 30 and 60 percent of the people it infected: primarily immunocompromised hospital patients, including cancer survivors and transplant recipients. People with robust immune systems have so far been able to dodge the threat. But Monosson warns that other infectious fungi are coming, and one of them could cause a full-scale pandemic among humans, just as they have for other species.
Take the American chestnut, which once dominated forests throughout the Eastern United States. Some towered over 100 feet tall, with trunks more than 10 feet wide. Today, few of us have ever seen a full-grown chestnut tree except in pictures. In the early 1900s, a non-native fungus that came to be known as chestnut blight appeared in the Northeast, and it spread through Appalachian forests like wildfire, covering 25 to 35 miles a year on its path of destruction. None of the traditional fungus-fighting methods worked: not fungicide, not pruning diseased branches, not even cutting down afflicted trees to prevent the fungus from jumping to healthy ones. Within a few decades, the fungus had killed billions of trees, making the American chestnut functionally extinct.
Globalization is part of the problem, according to Monosson. Imported plants and animals can carry fungi that local wildlife have never before encountered, and to which they have no defenses. Even the movement of people around the globe carries risks. We can
Not all fungi are bad; most are harmless or even beneficial to humans.
easily pick up fungal spores on our travels and carry them home in our luggage without ever realizing it. Once in a new environment, surrounded by novel hosts, a pathogen that caused little or no harm in its native land could quickly spiral out of control.
Most of the time, of course, it doesn’t. Not all fungi are bad; most are harmless or even beneficial to humans. Our gut and skin microbiomes include friendly fungi, and our crops grow in soil enriched by fungi that turn decaying matter back into nutrients. “If it were not for fungi, the world would be piled high with the deceased and would be virtually uninhabitable,” Monosson notes. Her concern is with the rare — though increasingly common — fungi that feed on the living rather than the dead.
The solutions she proposes sound simple. They include increasing genetic diversity in our crops, limiting trade in wild animals, and enacting testing protocols to be sure we don’t accidentally import a pathogen that could drive another species to extinction. But, as she acknowledges, none of these are easy to pull off in practice. Today, much of our food is grown as monocrops with extremely narrow gene pools, thanks to decades or centuries of selective breeding for certain traits — such as sweetness and size in bananas — at the expense of others that might have conferred more fungal resistance.
Cultivated bananas, in fact, are one of the latest species under threat from an aggressive fungal pathogen. One day, they could disappear from grocery stores altogether. If that happens, the solution could be to reintroduce wild bananas. These varieties might be shorter and starchier; they might be red instead of yellow. But if they can stand up to fungal invaders, it will be something to celebrate. As Monosson writes: “Our foods’ salvation and our own is held in plants’ genes.”