A fungal pandemic is unlikely in humans. That’s not true for other species.

Tiny Matters

A few months ago, we did a bonus Q&A about the HBO series The Last of Us, a show about a pandemic caused by a fungus that turned people into terrifying zombies. But after that bonus episode aired, we received emails from people who wanted to learn more about fungi and the fungal infections on the rise — like white nose syndrome in bats and Candida auris in humans. This episode is all about fungal pandemics, how they arise, and the fight to stop them.

Transcript of this Episode

Sam Jones: Hello Tiny Matters listeners! Sam here. A few months ago, we did a bonus episode Q&A about the HBO series The Last of Us, a show about a pandemic caused by a fungus that turned people into very terrifying zombies.

We chatted with a mycologist about fact versus fiction in the show and her take home message was: yes there are fungi that can infect and mind control insects but the chances of that happening to us is essentially zero because the fungus would have to essentially evolve into a whole new fungal species among other things, and right now bacteria and viruses passed to humans from other species like bats pose way more of a threat when thinking about the next pandemic.
But after that bonus episode aired we received some emails from people who wanted to learn more about fungi, including ones that definitely won’t turn us into zombies or even cause a pandemic but are still scary and problematic. One of our listeners, Betty from Sacramento, wrote in asking about fungal infections that seem to be on the rise in hospitals, specifically Candida auris.

Remember, fungi can be mushrooms, molds, mildew, yeasts… they’re super duper diverse. Candida auris is a yeast and once it enters a person’s body, it can cause severe organ and bloodstream infections unless your immune system fights it off. Serious Candida auris infections are most likely in people who have a weakened immune system, maybe because of a cancer or autoimmune treatment they’re on, and people with breathing or feeding tubes or IV catheters are at the highest risk of infection.

Treating fungal infections often means using an antifungal and most Candida auris infections are treatable that way, but now many strains are turning up that are multidrug-resistant, meaning the antifungals are not working and the CDC now considers Candida auris to pose a serious global health threat. Not a pandemic, but a threat.  

However, many plants and animals are under threat of a fungal pandemic all the time and Deboki and I and many of our listeners wanted to learn more about that. So we chatted with Emily Monosson, an environmental toxicologist and adjunct professor in the department of environmental conservation at UMass Amherst.

Emily just wrote a book called Blight: Fungi and the coming pandemic. In it, she details how trade, travel, and a changing climate are making us all more vulnerable to invasion. How populations of bats, frogs, and salamanders face extinction and how our national parks and food crops, coffee, bananas, and wheat are under threat.

She also covers some of the past drama surrounding regulation of plants and animals being imported across countries and continents. For example, in the early 20th century there was a lot of hubbub about Japanese Cherry blossoms. I live in DC and people come from all over the US to experience cherry blossom season every April. Cherry blossoms are not from here and actually the first ones shipped over were found to be infected and were burned. So what you’re seeing in DC today is actually the second batch.

But Deboki and my conversation with Emily is not all cherry blossom drama or doom and gloom. And neither is her book. Let’s remember, most fungi are harmless, many are helpful, and very few are deadly. Prevention of pandemics in plants and animals is a massive challenge but not impossible. There are scientists working tirelessly to protect species under threat and bring back those on the verge of extinction.

I learned so much reading Emily’s book, which we’ve of course linked to in the episode description. Now, let’s hop into our conversation with her. We hope you enjoy.

Deboki Chakravarti: So we're going to talk today about fungal epidemics, which is obviously a pretty bleak side of fungi. But we want to start off by just talking about what the importance of fungi are. What would a world look like without fungi? How do you see them fitting into this world?

Emily Monosson: I think a world without fungi, we would not be here probably. It would be a world piled up with dead stuff. Fungi are major decomposers, which also means that they contribute to nutrient cycling which is also very important.

Sam Jones: Yeah. In your book you said something like the planet would be piled high with dead bodies or something like that, which is a worrisome image. And like you mentioned in your book, most of them are really good, but some of them are not so much or not so much for humans. For many of us, I think conceiving of what a fungal pandemic in humans might look like can be tough. So I'm wondering, is there a fungal disease that you find helpful in order to make that picture a little bit clearer to people?

Emily Monosson: Yeah. So first, just need to clarify that a full on fungal pandemic we've just experienced with the COVID virus is very, very unlikely. I don't think you could find anyone who would say that that kind of thing is a possibility. And that's because they're just totally different organisms. Fungi are not communicable, usually. We don't spread them person to person, can't sneeze on somebody and give them a fungus usually. So, that's a big difference. They're just not that communicable. But if it were to happen, that would be sci-fi kind of scary. And the reason is not because we become zombies, but because in the species that I do write about, fungi that have gone pandemic, usually spread by spores. Fungi produce millions of spores.

Spores, some of them can live a very long time, they're environmental organisms, which means that they don't necessarily need the host to live in so that they can live in the environment so they don't go away. So fungal pandemics in humans probably not a concern, but fungal pandemic and other species definitely a concern. But the reason that I included humans in the book is because there are definitely emergent fungal pathogens, so new fungal pathogens.

And one of the ones that have physicians and mycologists worried about and public health workers worried about is Candida auris. And for those who are infected with it, who tend to be those who are immunocompromised or in the hospital or long-term healthcare settings, this is where that fungus spreads. It has a high mortality rate. So there are reasons to worry about emergent fungi, but fungal pandemics in humans probably not.

Deboki Chakravarti: Yeah. And I guess coming off of that, I found it super interesting the way that you were talking about how scientists and doctors will talk about yeast infections as a disease of antibiotics. Can you talk a little bit more about why antibiotics are related to our susceptibility to fungal infections?

Emily Monosson: Of course. Antibiotics are a great thing, but just like there's been a problem with the rise of certain bacterial infections stemming from taking antibiotics, the same thing can happen with fungi. And the reason for that is that we live with a microbiome of bacteria, fungi and other microbes. And so, we're this whole community of living organisms. And when antibiotics, particularly broad spectrum antibiotics knock out a bunch of bacteria, those members of the community are gone at least temporarily. And when they're gone, that gives the opportunity for other microbes to either take over or have a chance to bloom. And we definitely have many more bacteria than we have fungi in our bodies. So when we do suppress that, there's the opportunity for some fungi yeasts to emerge.

Deboki Chakravarti: So we talked about fungi developing this resistance to drugs, which is one way that our behavior and our advancements has led to our challenges now with fungi. But another thing that you'll hear about with fungal infections and just fungi in general is how they can increase or spread with global warming or become more dangerous as an effect of climate change. Can you explain more about why that is?

Emily Monosson: We've talked about the microbiome before. So that's one protection that we have against the fungi that are in us and on us. Another protection we have is our immune system. And a third thing we have is our body temperature. So we run pretty hot, mammals run pretty hot, and most fungi really don't grow at our warm body temperatures. They tend to prefer cooler temperatures. So, those that are going to infect us need to be able to tolerate our body temperatures. There are millions of different kinds of fungi and a very small proportion of those fungi are human pathogens.

And what the concern is now is that as the climate changes and fungi are out in the environment, they also produce lots of offspring. Those spore producing ones produce millions, which is a recipe for evolution. You've got the pressure of a warming environment and you've got the opportunity for mutations because you're making lots of offspring. Then there's a possibility that some of those are going to be able to survive in a warmer temperature.

And once they get to be able to live at our temperature, then there's the potential for an emergent fungal pathogen. And this is what scientists think might have happened with that Candida auris, the one that I mentioned earlier, it's a yeast, it's most likely living out there in the environment, lots of yeast do. And at some point, maybe a decade or two ago, some of those Candida auris yeasts evolved to tolerate warmer temperatures and were able to make the jump into our body and grow in our bodies.

Sam Jones: In your book, you focus on fungal infections in a number of plants and animals, of course, including us, including things like Candida auris. But I would say the majority of your book does not focus on humans. So I'm wondering if we can get into plants a little bit. All of the epidemics you write about in your book start with a fungus that was relocated from its home to somewhere else.

For instance, the fungus Cryphonectria parasitica is native to East Asia and Southeast Asia, but when it made it to Europe and then North America in the early 1900s, it wiped out almost all of our chestnut trees. So I'm wondering, why is it that chestnut trees in Asia can withstand this fungus but our trees in the US cannot?

Emily Monosson: Yeah, that's a good question. So, a lot of the fungi that I write about are not native to these places that they've been transported. And so the chestnut blight fungus, it’s native, it co-evolved with the chestnuts there. And so, they've come to some uneasy kind of probably relationship where the fungus can infect the tree and the tree can still survive and live on with the fungus. But when that fungus was transported to the US probably sometime in the late 1800s, early 1900s with probably some little seedlings or saplings from its place of origin, and they were taken here because lots of people like to grow different kinds of chestnut trees like Chinese chestnut trees and Japanese chestnut trees, they're very popular. You still can get those kinds of chestnuts here now. And then it found our American chestnut trees, which never saw it before. So it didn't have the opportunity to evolve any kind of resistance to it or any kind of immunity to that particular fungus.

And within a year or two years it killed well over a thousand trees, like just all the chestnuts were gone. And within decades it spread down the East Coast along the Appalachians and wiped out the chestnuts.

Deboki Chakravarti: And earlier we were talking, moving on to the animals. We were talking about mammals. Usually, we are not that easy to target. Fungi, they don't necessarily like that. We're super warm, but one of the sections in your book is about bats and the white-nose syndrome and how devastating fungi have been to bats. Can you talk about what white-nose syndrome is and why bats are susceptible, and also what researchers are trying to do to help bats survive?

Emily Monosson: So white-nose syndrome is caused by fungus caused by a fungus called Pseudogymnoascus destructans or PD. So bats run very hot. You know they're flying mammals. So how does the fungus infect bats? Bats also hibernate, and when bats hibernate, they go to their hibernacula or their cave or wherever they're hibernating, and their bodies drop to match the temperature of that location. So when the bats body temperatures come down, then the fungus can infect them. How that fungus got here, it's another story just like the chestnut trees. That fungus has been found in caves in Europe. There are bats that manage to survive that are infected with that fungus in Europe. But again, they've evolved probably to tolerate the fungus. So the thought is that maybe some cavers with mud on their boots or whatever, went from exploring caves in Europe, maybe... And this is a hypothesis, nobody really knows, but it seems pretty likely that somebody came here from there and went to the caves here, and was exploring caves here and probably dropped some spores of that fungus. It probably happened many times, not likely that it was just one shot, but whatever it was.

So then, the bats here had never seen that. They had no defenses to it. And so, it's been totally devastating to the bat populations. In some places, when you look at the numbers before and after the arrival of white-nose, 90% of some populations have been killed off by the fungus.

Sam Jones: But there are still some bats in the United States that are surviving. I'm wondering if you can share with listeners how it could be useful to study the bats that can survive this fungus.

Emily Monosson: There are some survivors and they find that there are small populations still surviving in the caves when they go back. One study, what they found was that those that were surviving tended to have heavier bodies, more weight, they were just generally more fit.

Some people called it the fatter bat study or the fat bat study because they had more on them and they thought maybe this has helped them to survive. I interviewed another scientist in Michigan, who was studying the genetics of surviving bats. What she found looking at the genetics was that it seemed that there were certain genes that occurred at higher frequency in the populations of surviving bats. It turns out some of them have to do with metabolism. So, it may be that there's a genetic underpinning to those bats that we're able to put on more weight. It does seem like that might be one of the hopes is that if they are allowed, like there's enough genetic diversity in the population, and they're allowed to breed, that there will be some survivors because they might have a genetic advantage.

Sam Jones: And that kind of gets into one of the more hopeful things we wanted to speak with you about. This is not a situation where people are throwing up their hands and saying, "Well, that's just what's going to happen. There's nothing we can do." There are a lot of people thinking about, how do different species, whether they be plant or animal, survive a fungal infection or epidemic within their community? And could we, with that information not only prevent animals or plants from getting sick, but maybe even resurrect some of them. So, I'm wondering if there's an example you want to share of people trying to bring back a plant from extinction.

Emily Monosson: The example of that would be the American chestnut. And there's a great effort, it's very interesting to bring that back. For years, after the disease hit and people realized that there were these Asian chestnuts that could survive the disease, they did go right to well, "Okay, those trees must have some kind of resistance. How could we capture that and get it into our American chestnut trees?"

So, a group of scientists came up with this 30-year plan to breed in the resistance gene from the chestnut tree, they thought it was a gene or two, and then breed out all of the other qualities of the Chinese chestnut trees because they grow differently, and capture all the American chestnut qualities. So in the end, after 30 years, you would have a tree that looked like an American chestnut tree, but it had some resistance genes. Unfortunately, genetics was a lot more complicated than that. And it turns out there wasn't just one gene or three genes, but several different genes. And scientists only just discovered this in the last couple of years when they could do better genetic analysis. So for 30 years, the American Chestnut Foundation has doing an amazing job of recruiting volunteers and scientists to carry out this 30 year rooting program.

At the same time, back in the '80s, another scientist, William Powell had the idea to, what if we could find a resistance gene and use genetic engineering to insert that gene into chestnut trees. So scientists did identify a gene that would provide resistance. So when the fungus infects chestnut trees, it releases a chemical to help it break in. And that gene, what it did was break down that chemical. So he said, "Well, if we take this gene from those plants and insert it into chestnuts, can we make resistant chestnuts?" And they've just gotten to that point where they've actually inserted that gene — it’s called oxo gene — into American chestnut trees. And those chestnut trees are resistant to the blight. The trees that the American Chestnut Foundation has been breeding for 30 years are not as resistant as they hoped they would be. They're all working together, William Powell and the American Chestnut Foundation because what everybody wants is to just get some Chestnut trees back into the wild.

Deboki Chakravarti: How should we be approaching balancing this tension between needing to trade, needing to live in a global economy, but also preventing to the extent that we can, a really dangerous outbreak that affects our food, that affects wildlife and affects our health?

Emily Monosson: Apparently the diet here before we brought all these plants was pretty boring. Just if we think of most of the stuff we eat, it's not native to here. There is a lot of regulations that are now on incoming plants and plants that can move across borders and even across state borders. But there's obviously not a lot. I mean, not enough. But just the rise of the late blight in tomato, that's something that just happened 10 years ago. And that's a fungus-like organism. It's called Phytophthora infestans. It's the same kind of organism that contributed to the Irish potato famine and also infects tomatoes.

And that just one season traveled up the East Coast. So even though we have regulations, it's still a problem. I spoke to Megan Romberg, who's got the title of national mycologist, which is kind of... I was like, "We have a national mycologist?" And she goes, "Yeah, but just for plants." We actually have two, but for a long time we only had one. But her job is when plants come into the ports, there are only a certain number of ports that imports can come into. There are inspectors there, but they can only see so much. They can only identify so much. In the things that get them stumped, they send over to Megan and then she has to identify them within the day. She only has a short time period to identify them before they're released. So, this is an imperfect system. What people would love I think is if anything coming into this country was first checked for disease and comes across with a certificate that this plant or animal is disease free.

Do we have that kind of capacity? Not yet. But the hopeful thing is with COVID, just think of those rapid tests that we are using all the time. Over the past decade or so, there's been some advances in tests that you could just give a sample and it can provide you with lots of DNA information on what's in that sample. And so once you start to know the genetics of your pathogen, you could be able to identify lots of different pathogens.

So, that would be a way to prevent the movement of some of these pathogens. One hopeful thing I think I did write about was the work of Karen Lips and Peter Jenkins and others. So Karen studies BD, which is the frog killing fungus, and that's a global pandemic. A cousin to that fungus called Bsal has been killing salamanders in Europe, okay? We have an amazing diversity of salamanders here, especially in the Appalachian Mountains. So there's a lot of fear that what would happen if that Bsal makes it over here. Salamanders are very popular in the animal trade. So short of having a total ban on the traded animals. Karen and Peter, they worked with the federal regulators, they worked with nonprofits. What they wanted was that certificate where, "Yep. Anything that comes into this country is disease free," but that's not really realistic. So what they did get was a ban on I think 200 different salamander species, which are most likely to carry Bsal.

I think most scientists would say that if you want to protect any species from these kinds of things, preserving genetic diversity is the most important. If you conserve the diversity in those populations, hopefully some of them are going to be resistant to whatever comes at them in the future.

Sam Jones: There was one point in the book where you said, "Wouldn't it be so great if we went to the grocery store and there wasn't just the cavendish dish banana, but you had 10 different banana varieties?" There are people who are thinking about genetically engineering the Cavendish banana to be more fungus resistant as a monoculture. But ideally you would just have tons of different species of bananas so that if one was infected, there's a good chance not all of them would be. So it's not like we're putting all of our eggs in one basket.

Emily Monosson: Yeah, exactly. I mean, yeah, there's a group that is working with bananas because a really destructive fungus that's hitting lots of banana plantations and it's a problem. To have these huge monocultures is a problem. And plantations are just huge monocultures along with other kinds of things that we grow, like wheat. Another scientist said, a monoculture is just a banquet. It's a feast for fungi because it's just fungi infect some plants in this one corner, they produce their millions of spores and they spread over the rest of the plantation. We ought to advocate for and that's one of the few things that we can do, the personal things we can do is expand our pallet and buy different kinds of bananas, different kinds of grains so that we're not just tied to certain staple crops.

Deboki Chakravarti: On that note, you talked about people becoming more aware of the challenges with fungi. For listeners maybe who are listening now, and maybe this is the first time they've thought about fungi in this way, is there anything you would want them to know in terms of how they could think about either their behavior or things they could look for in terms of advocacy?

Emily Monosson: I think awareness is important. Like I said, a lot of what will really make big changes, policy and regulations and things like that. You can support the organizations that do the wildlife organizations and things like that. And you can advocate for or support the growth of different kinds of varieties of foods. And you can take seriously when you're traveling in the airport, those signs that say, do not take any plant, any banana related material into Costa Rica. Don't do it. One of the places I did get to go to was Costa Rica, just go to a banana plantation. You get to the airport and there are signs all over the place, like don't carry banana anything. And people are just not even reading them. And it's the same thing with, if that's how the mud in your boots when you travel. Some places want you to remove your muddy shoes and have them disinfected or whatever, do it.

Sam Jones: Emily ends Blight by talking about responsibility — our responsibility to protect each other, plants, and animals from the next fungal disease, and one that should extend as we travel beyond Earth. We do sanitize what we send into space. “Sterilization techniques work well enough on ships and rovers,” writes Emily. “But humans can’t be sterilized. Wherever we travel, we will take our terrestrial microbiome with us, even to Mars.”

So what if we do make contact with life beyond Earth? Will what has happened to so many organisms on our planet happen again elsewhere? How can we prevent that now? What responsibility do we have to the rest of our solar system?

Thanks for tuning in to this week’s episode of Tiny Matters, a production of the American Chemical Society. And thank you to Emily Monosson for joining us. You can find me on social at samjscience and you can find Deboki at okidoki_boki. See you next time.