As Emily Monosson points out in her new book, Blight, fungi are everywhere. There are thousands of species of yeasts, mushrooms, molds and mildews. Some estimates put the number of fungal species at more than five million. Most spend their time buried deep in dirt, water or even our own bodies.
Some of these fungi pose threats—to humans, animals or plants. Mostly traveling via spores, fungi can move from place to place easily, carried on an animal’s wing or the sole of a shoe. Then, once in the right conditions, fungi spread. They can infect a variety of species, recently causing problems for bananas, coffee and chocolate.
And we could be next.
“Over the past century,” Monosson writes, “fungal infections have caused catastrophic losses in other species, but so far [humans] have been lucky. Our luck may be running out.”
For many species of fungi, climate change is propelling their spread and aiding their ability to infect potential hosts. We spoke with Monosson about the dangers that fungi pose to humans and our food supply and what we can do about it.
This interview has been lightly edited for length and clarity.
Emily Monosson. Photography courtesy of W. W. Norton & Company
Modern Farmer: It feels like mushrooms and fungi are having a bit of a moment in pop culture, with Netflix documentaries and The Last of Us.
Emily Monosson: Talk about timing! Because of both the pandemic and The Last of Us, that’s brought a lot of attention to the dark side of fungi. There’s been a lot of good stuff about fungus and for good reason. I mean, the fungal kingdom is really important to everything—how we live, how we grow food…
MF: Right, you talk in the book about how fungus can be helpful or harmful, and one interesting example in agriculture is bananas. Can you expand on what happened with bananas and fungal infection?
EM: Well, in the 1950s or 1960s, we started eating the Cavendish banana, which is what we all think of as the banana. And yes, there are lots of different kinds of edible bananas, but we rely on the Cavendish. And before the Cavendish, there was the Gros Michel banana. That banana was impacted by a fungus that’s now called TR1, which pretty much threatened to wipe out the banana industry. And so, [the industry] turned to the Cavendish banana and started growing that.
MF: The problem is when we lost the Gros Michel, we had fields and fields and hectares and hectares of this banana that got wiped out. And now, we’ve replicated that process with the Cavendish, which is a little mind blowing.
EM: It is. So, the Cavendish was resistant to that TR1 one fungus, which is great. But, pathogenic fungi, if they are spore-producing fungi, some of those spores are really resilient, and they can live in the soil for maybe decades. So, once a plantation becomes infected, you can’t grow those kinds of bananas there anymore. The crop needs to be grown somewhere else. There’s no treatment for it except for maybe flooding the plantation.
Now, a newer fungi, TR4, is spreading to many of the banana-growing regions, and it is killing the Cavendish banana plants. I went to a place in Costa Rica that was growing bananas; Costa Rica does not have this TR4 yet, and they’re just terrified of that fungus making it into Costa Rica. And so, there’s very strict regulations about taking banana plant parts into places. When you go to the airport, there are big signs that [warn against bringing in bananas].
But scientists who study these fungi think that the reason this has spread is that bananas are cloned [meaning there’s no genetic variation or immunity to TR4 that can pop up]. It’s hard to understand how this can happen to that degree again, that it’s threatening most of the Cavendish banana industry, because of how much was known about how the fungus travels.
So, one of the solutions is to just broaden our palate, maybe think about eating other kinds of bananas, and be a little bit more open to buying a small banana or red banana or blue banana.
MF: Let’s talk about those spores that can live in the soil. As you say in the book, once a fungus shows up, there’s virtually no getting away from it. How long does that period last? Is it possible to wait out a fungus?
EM: It’s complicated. A single fungus can produce many different types of spores. Some of them are short-lived, and they have to land on their host. And if they don’t land on their host, they’ll just die. But some of them, like some of the spores from TR4, can apparently live for decades. That’s a big problem. Those will not go away, and when their favorite host returns, then they will germinate and grow.
I also wrote about bats, which are susceptible to fungal infections, too. Scientists believe that the spores that infect bats drop off onto the cave floor when the bats fly out. And then, as the bats fly around, they clear the fungus from their bodies. But when the bats return, the spores are still on the cave floor, and they get reinfected each time they return to their hibernacula.
MF: Throughout the book, you talk about different fungal pandemics, including the banana and bat examples we just talked about. You mention fruit and nut trees, row crops, frogs and salamanders. You mention that it’s a bit of luck we haven’t seen a widespread fungal pandemic in humans yet, but our luck could be running out. Why is that?
EM: That partly comes from Candida auris, a yeast that sort of emerged around 2016. It tends to infect people who are already compromised in some way; it runs through hospitals, long-term care facilities, and [it] impacts people who are immunocompromised. It also seemed to emerge around the world and many different places. There were five different strains of this fungus that seem to all emerge at once. And so, the question is, how would that happen? Why would that happen? It wasn’t like COVID, where you could trace to see how one strain evolved into others.
One of the hypotheses about how it emerged is that it was a fungus that was probably living in the environment, as most of them do, and making its living there. And then, as the environment has warmed a bit, it evolved to tolerate warmer temperatures. For humans, our body temperature tends to protect us from fungal pathogens, because they can’t tolerate it. So, what the thinking with Candida auris is, maybe it evolved to eventually be able to make the jump into humans and live in our body temperature and infect us. So, that’s one example of what could happen with the changing climate—more fungi that are living out in the environment might be able to grow in our bodies.
One thing that I would say, though, is that something like The Last of Us, a real pervasive fungal pandemic that’s everywhere and can infect humans, most scientists would say that’s probably pretty unlikely. We’re not going to suffer what bats or frogs or, you know, chestnut trees have experienced.
MF: Obviously, a show or video game like The Last of Us is fiction. But what does separate us from bats and trees and salamanders?
EM: That’s a really good question. One thing is that it’s rare for a fungus to spread from person to person; they’re not as transmissible. In The Last of Us, the fungal spores got into the food, and that’s how people were exposed. But to have a spore-producing fungus able to infect humans and be everywhere all at once, it’s harder to do.
MF: What about fungicide? How big a role could or should they play?
EM: Well, fungicide wouldn’t help soil-borne fungi, because it comes up through the roots, where you can’t apply fungicide. If it’s on the surface, then spraying a fungicide could be helpful.
MF: What about gene editing or other forms of fighting against the fungi?
EM: I did interview one scientist who has been working on modifying bananas so that they can resist the TR4 disease. He’s gone about it in two different ways: One is to insert a gene from other bananas into the Cavendish banana that can resist the fungus. That would be a cisgenic process, taking from one banana and putting it into another banana. The other thing that he’s doing is to see if those resistance genes are in the banana but they’re silent or not turned on. So, that’s where gene editing might come in, to see if you can basically flip the switch on those genes and have them activated.
MF: What about legislation or governmental policy?
EM: When plants are imported in for us to buy, there are rules, they are inspected. Some would like to see increased certifications or inspections made mandatory. But unless there’s really good rapid diagnostics, some of the diseases are hard to identify.
The ideal test would be able to take a swab of something and identify lots of different pathogens on it, and do it rapidly, because then a plant could either be certified that it’s clean and disease free. I wrote about a program in the US where nurseries are working with different state departments to ensure that the plants that they’re selling are certified as disease free as possible. So, you know, that’s something that if consumers look for that certification and encourage that kind of thing, then plant growers will be more aware of trying to do that.
I think the bigger problem is really in the animal world, because we don’t have as many regulations and certifications and even inspectors for animals in trade as we do for plants.
MF: There was a section where you were talking about just the sheer number of animals that pass in and out of the United States. With all of those animals traveling through the country, some escape is inevitable.
EM: Yeah, and the thinking is that’s how some of the fungal pathogens affecting wildlife have happened. So, there’s a movement to better control the animal trade.
For certain kinds of animals, there’s really no regulation that they need to be disease free. What some of the scientists that I talked to are trying to do is to just keep those animals from entering the country, to reduce the animal trade, but not being able to do that. They’ve been working with the Fish and Wildlife Service to figure out how best to reduce the potential for that to happen.
MF: What about the immediate big picture? You end the book by saying that looking critically at things like monocropping is our moral obligation. What do you make of that both on a community level and an individual level? How do we act within that system? Most people don’t grow bananas or have any control over the banana industry. So, how do we live within that moral obligation?
EM: It’s hard. You want to have solutions at the end of a book like this. And it’s often very hard for individuals to do something. If enough consumers demand something or are open to something, then there’s the potential that maybe the industry will respond.
Look at all the different kinds of grains we eat now. I mean, that was probably unheard of how many years ago? That is a hopeful thing. Making many types of grains available is mainstream now. That could happen in something like bananas. We could demand and be open to lots of different kinds of bananas, which might move them away from the big monocrop Cavendish that we have now.
The other thing we as individuals can do is while we travel, when you see that sign that says ‘Don’t bring banana anything into this country,’ don’t do it. Don’t shove it in your pocketbook and think that you’re getting away with something, because what you could be doing is carrying the next pandemic.