The Excerpt podcast: Climate change is making fungi a much bigger threat

On a special episode (first released on March 7, 2024) of The Excerpt podcast:

Fungi are among us more than we realize. From the backs of frogs to our own backyard, fungi, a largely neglected group of pathogens, are becoming a prevalent and widespread concern among scientists and health experts alike. The main reason? Climate change. Joining me today on The Excerpt to discuss what’s causing this explosion in disease-causing fungi is Dr. Arturo Casadevall, Chair of Molecular Microbiology & Immunology at John Hopkins Bloomberg School of Public Health.

Hit play on the player below to hear the podcast and follow along with the transcript beneath it. This transcript was automatically generated, and then edited for clarity in its current form. There may be some differences between the audio and the text.

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Dana Taylor:

Hello and welcome to The Excerpt. I'm Dana Taylor. Today is Thursday, March 7th, 2024, and this is a special episode of The Excerpt.

Fungi are among us more than we realize. From the backs frogs to our own backyard. Fungi, a largely neglected group of pathogens, are becoming a prevalent and widespread concern among scientists and health experts alike. The main reason? Climate change. Joining me today on The Excerpt to discuss what's causing this explosion in disease-causing fungi is Dr. Arturo Casadevall, Chair of Molecular Microbiology and Immunology at John Hopkins Bloomberg School of Public Health. Arturo, thank you for being on the show.

Arturo Casadevall :

Thank you for having me, Dana.

Dana Taylor:

We didn't care as much about fungi until recently. Why should we be concerned about their threat?

Arturo Casadevall :

So the reason that we need to be concerned about them is because even though fungal diseases are still relatively rare for most people, when they happen, they are of high consequence. They carry a high morbidity and mortality, and they often are very hard to treat. One has to take antifungal drugs for a very long time.

Dana Taylor:

What role has climate change played in influencing the growth of infectious fungi?

Arturo Casadevall :

For agriculture, we need to think that the fungi are the major pathogens of plants, and what climate change is doing, first, let's talk about agriculture first, is that it is expanding the range of some of these fungal pathogens. And the reason that is a major problem for us is because they threaten agriculture, they threaten our food supply. When it comes to us, what we are seeing, the role of climate change is more subtle right now, but we think it's going to be a bigger problem in the future.

And for that, Dana, what I'd like you to think about is that our temperature, we are 37 degrees centigrade, 88 degrees or so Fahrenheit, keeps out a lot of the fungi. Why? Because they live in the environment. They don't like very hot temperatures, and we are very hot relative to the environment. And the problem is that with climate change, we fear that some of these fungi in the environment may adapt to live at higher temperatures, and if that is the case where temperature won't protect us, and we may be seeing new fungal diseases. In fact, there is one known, Candida auris, which is a major new problem, and we can talk about that. There is some thought that it may have come as a result of climate change.

Dana Taylor:

As you've said, fungi are known to thrive in cooler temperatures and that they're adapting, becoming more infectious to humans. How rapidly is that occurring?

Arturo Casadevall :

Well, let's talk about Candida auris. Candida auris, as the name suggests, is related to candida, which is a well-known human pathogen. It causes diseases in baby, diaper rash, it can cause candida vaginitis, but this organism was not known to medicine up until around 2009, and then it emerged in three different continents in South America, in Africa, and in Asia at roughly the same time, and the isolates were not similar. That is, it's not like somebody took a plane from Asia to South America and brought it.

So we don't have a good explanation how this thing could have emerged, but there is a lot of circumstantial evidence that it may be the first organism to have adapted to higher temperatures as a result of climate change and global warming and does become a human pathogen. If that is the case, Canada auris is the canary in the coal mine to tell us what the future may be, and that is something that we are all watching very carefully.

Dana Taylor:

I don't know if you saw the picture, I'm sure you did, but a frog recently found in India had a small mushroom growing out of its back.

Arturo Casadevall :

Growing on it.

Dana Taylor:

Yeah, yeah. So while it was not collected and tested, why is this such a shock, and should we be worried?

Arturo Casadevall :

Well, it's a shock, because mushrooms don't usually cause disease. If you think about it, almost every fungus that causes disease is microscopic. You need a microscope to look at. So that picture was shocking simply by what we saw. I don't think that right now we are thinking of mushrooms growing on people and causing disease like that, but I want to point out that other organisms right now are suffering tremendously from the fungi. The frogs, as you mentioned, Dana, are an example, but it wasn't from that fungus. It's from a fungus known as a chitryd that is spread throughout the world and has decimated the frogs worldwide. The salamanders in Europe are in trouble. The snakes in North America and the bats, when they hibernate. In the summer, the bats are our temperature, 37 degrees, 98 degrees Fahrenheit. They're fine. However, in the winter, to get through the winter, they drop their temperature to around 12 degrees, and when that happens, a fungus can grow on them and kill them.

So I think if we look at our relatives, other animals, the frogs, the salamanders, the bats, and we see how much trouble they're in, I think that that is a warning that the fungal world has major threats that we need to be concerned about.

Dana Taylor:

I want to talk about extreme weather, and are these infectious fungus spreading more easily now because of that, things like fires and dust storms?

Arturo Casadevall :

The answer is yes. We recently published an article with one of my colleagues here, Daniel Smith, called Disaster Microbiology, and it argues that whenever you have a disaster, you change the microbes in the area, and sometimes that accentuates the damage. Let's think about an example that it was, well, I lived through Katrina. Katrina flooded New Orleans. When the waters receded, mold grew on those houses, and it was so devastating that the houses had to be demolished.

What you find is that whenever you have a calamity, a tornado in some cases, you stir up the air, and survivors can get fungal diseases. That happened at Joplin a few years ago, the Joplin tornado. So that is something to add to the worry list. But also, if we are aware of it to the preparation list, that whenever we're dealing with a calamity, one should expect changes in the microbiology, and some of those changes may bring us new diseases.

Dana Taylor:

The human body is remarkable. Can our immune systems learn to adapt to these changes?

Arturo Casadevall :

You are so right. Think about it. For most, we go through life with relatively few infectious diseases, and the reason for that is because our immune system is so effective at controlling them. We teach our immune system many ways how to prevent disease when we take a vaccine. A vaccine basically prevents one from getting the disease. And one mechanism of doing this is to develop vaccines against some of the fungi. Currently, there are no vaccines to fungi. They haven't been developed for a variety of reasons, but we have the knowhow, we have the technology. They could be made if needed.

Dana Taylor:

Blood tests are used to try to find fungal infections, but they aren't reliable. At the same time, fungal pathogens are very resistant to common therapies. How are they being detected, and what's being done to try and improve treatments?

Arturo Casadevall :

You bring up a set of very important points that are related. One of them is the problem in diagnosis and the problem in treatment. So the problem in diagnosis with fungal diseases is that we have few diagnostic tests. Consequently, they're often diagnosed late after the fungus established itself in the body. Once established, it's a lot harder to get out. So then the physicians treat.

Unfortunately, we don't have a lot of antifungal drugs. We only have three major classes, and some of the fungi are becoming resistant. So you're now treating, but you're treating late, and the fungus are, themselves, very resilient, so you have to treat for a long time. So in contrast to many bacterial diseases, where you can treat for a week, maybe two weeks, with fungal diseases, you often have to treat for months, and there is no guarantee that one will be able to clear it. So we have problems in diagnosis, and we have problems in treatment, and we have problems in relatively few drugs.

Dana Taylor:

What regions in the US are most at risk currently, and is the threat expected to spread, Arturo?

Arturo Casadevall :

The threat of fungal diseases depends whether the fungus comes from the environment or whether it comes from another host. So most fungal diseases actually come from the environment except for things like candida, which we tend to carry with us and generally it doesn't hurt us, but when we become immunosuppressed or take antibiotics or something, it could happen. So let's get to your question.

In different parts of the United States, there is a different fungal diseases. In the American Southwest, there is coccidioidomycosis, Valley Fever. It's currently restricted to the Southwest, but there is now a lot of data that it is moving into other states. So doctors, even in states where historically have not seen coccidioidomycosis, need to become aware of this, because the first step in making a diagnosis is to think about it.

In the Ohio River Valley and Mississippi River Valley, we have histoplasmosis. Again, relatively geographically limited, but it's moving into other areas. We just had a report of blastomycosis from Vermont. Blastomycosis is a very serious fungal disease that we see in the Midwest. What's it doing in Vermont? We don't know. But it is an example that things are moving, and there needs to be greater awareness both by the public that these things are moving and that they're a threat and by the medical community, because the medical community needs to think about it in order to make a diagnosis.

Dana Taylor:

So those are regions at risk. Are there certain populations that are more at risk than others?

Arturo Casadevall :

Yes. Again, a very, very important point. Invasive fungal diseases are relatively rare in humans that have what we call intact immunity, that are immunocompetent. So people that are well, if they get infected with one of these fungi can usually control it. But we have about 7 million immunosuppressed individuals in the United States, and many of this immunosuppression is that the result of medical problems. When we treat cancer, when we treat autoimmune diseases, we often do so at the price of the immune system. So these individuals are often immunosuppressed, and by being immunosuppressed, they're at risk for fungal diseases, and that's the population that we often see them in.

Dana Taylor:

Arturo is someone that studies microbes, how they cause disease. What can you suggest for us to do to help protect people? Is there hope for us?

Arturo Casadevall :

Absolutely. Absolutely. So in my life, I've seen great progress. When I was a resident in New York City in the mid-1980s learning medicine, I took care of many patients with HIV infection. We had no therapies for it. Almost everyone died. Today, we have terrific therapies for HIV, such that with treatment, people can expect to live a normal life. I am a big optimist, and I believe that science is our best insurance policy. So continued investment in science, in biomedical sciences will give the knowledge that would allow us to face any of these threats when they arrive. I point out to you we used faith through a COVID pandemic, and even though it was devastating, within one year, they developed rapid tests, antivirals, and vaccines. How was that possible? It was possible because previous generations had made investments in science.

Dana Taylor:

Arturo, thank you so much for being on The Excerpt.

Arturo Casadevall :

Thank you for having me.

Dana Taylor:

Thanks to our senior producer, Shannon Rae Green and Bradley Glanzrock for their production assistance. Our executive producer is Laura Beatty. Let us know what you think of this episode by sending a note to [email protected]. Thanks for listening. I'm Dana Taylor. Taylor Wilson will be back tomorrow morning with another episode of The Excerpt.