The Rise of Deadly Fungal Pathogens

By Angel N. Desai, Jason Lloyd

Fungi are ubiquitous in nature—in fact, you’re likely breathing in fungal spores as you read this. Most fungi are harmless to healthy people. But changes in the global climate, in human settlement patterns, and even in our own body temperatures have made fungal pathogens an increasing health threat.

On this episode, host Jason Lloyd interviews Angel Desai, an infectious disease specialist and associate professor at the University of California Davis Medical Center. Desai and George R. Thompson III cowrote “Foiling the Growing Threat of Fungal Pathogens” in the Winter 2025 Issues. Desai discusses what fungal pathogens are, why they are becoming more dangerous, and how the public health community can respond.

Resources

• Learn more about fungal pathogens by reading Angel Desai and George R. Thompson III’s Issues article, “Foiling the Growing Threat of Fungal Pathogens.” 
• Angel Desai and Maimuna S. Majumder’s October 2020 Issues article, “How Contact Tracing Apps Could Help Prevent COVID-19 Super-Spreader Events,” offers lessons about contact tracing and disease surveillance that can be applied to future outbreaks. 
• How can wildfire smoke spread disease? Read Leda N. Kobziar and George R. Thompson III’s “Wildfire Smoke, a Potential Infectious Agent” in Science to learn more. 
• Check out “Infectious Diseases in a Changing Climate” by Matthew C. Phillips, Regina C. LaRocque, and George R. Thompson III in JAMA to read more about the impact of climate change on infectious diseases.

Transcript

Jason Lloyd: Welcome to The Ongoing Transformation, a podcast fromIssues in Science and Technology. Issues is a quarterly journal published by the National Academy of Sciences and by Arizona State University. I’m Jason Lloyd, managing editor of Issues.

Not to scare you, but you’re probably breathing in fungal spores right now. Despite the ubiquity of fungi in nature, and the popularity of The Last of Us, a television series in which a fungal infection turns people into zombies, most fungal pathogens do not pose a significant threat to human health. But changes in the global climate, in human settlement patterns, and even in our own body temperatures, have made fungal pathogens an increasing health risk.

On this episode, I’m joined by Angel Desai, an infectious disease specialist and associate professor at the University of California Davis Medical Center. For Issues, Angel and George R. Thompson III co-wrote an essay titled, “Foiling the Growing Threat of Fungal Pathogens.”

I’m excited to talk to Angel to learn more about what fungal pathogens are, why they’re becoming more dangerous, and how the public health community can respond. Angel, welcome!

Angel Desai: Thank you so much for having me. I’m really excited to talk with you today.

Lloyd: So you wrote a piece for the winter 2025 Issues about combating fungal pathogens, and so, I thought a good place to start might be to just talk about what fungal pathogens are.

Desai: Yeah, fungal pathogens, or fungi, are microorganisms that are pretty ubiquitous in the environment. I think probably more colloquially, people recognize them as yeasts or molds.

More colloquially, people recognize them as yeasts or molds.

Normally, they don’t often cause problems for people. We sort of live with them all around us, but in certain situations, particularly when people may be immunocompromised, for example, they can cause infections in various parts of the body that can cause a lot of downstream effects thereafter.

Lloyd: Are the symptoms of a fungal infection, are they similar to a viral or a bacterial infection?

Desai: It really depends on the fungi, and then, the location of infection. So you can have disseminated infection, which can certainly make people really sick in the way that certain viruses or bacteria do. You can have pulmonary infection where you have respiratory symptoms. You can have cutaneous infections, so, skin lesions, bone infections. It can really affect many different parts, pretty much all parts of the body, in some ways that are similar, and some ways that are different, than bacterial and viral diseases.

Lloyd: And how does one contract a fungal infection?

Desai: Yeah, so again, it really kind of depends on the pathogen we’re talking about. Because fungi are ubiquitous in the environment, most people are exposed to these on a daily basis and don’t really have any issues, but in certain situations, particularly, when maybe their immune system isn’t competent, or they may have an illness from another reason, which makes them more susceptible, those are sort of the setups for situations in which people can become infected.

And so, many times, you can inhale the spores from fungi. Sometimes it’s through direct inoculation. So if you’re outside in the garden, things like that. Sometimes, it’s in certain situations, there’s certain yeasts where people that are in hospitals for a really long time, these kinds of fungi can colonize different tubing, and things of that nature, and so, people can get infected that way, as well.

Lloyd: One of the really shocking things that you mentioned in the article is that the mortality rate associated with fungal pathogen exceeds 40%. And I’m just curious, why are they so deadly?

We don’t have that many really effective drugs to treat these infections, and we’re seeing more resistance emerging for some of these fungi which makes them even more difficult to treat.

Desai: I would caveat this by saying that there’s certainly a range, in terms of mortality. And again, it really depends on that particular fungi that’s implicated, but also, the mechanism of how somebody became infected, and again, what their underlying health status is.

And so, that may be one reason. People that tend to get invasive fungal infections tend to be already sick, or already have some sort of compromised immune system. But the other issue is that we don’t have that many really effective drugs to treat these infections, and we’re seeing more resistance emerging for some of these fungi which makes them even more difficult to treat. So I think it’s probably multifactorial.

Lloyd: Yeah, that’s really interesting. So that’s the human aspect, but you also talk about how fungal infections can affect agriculture and crops, and I was wondering if you could talk about that a little bit, too.

Desai: Yeah, so I’ll say that I’m definitely a human infectious disease person, but what I will say is that fungi affect plants and animals in the way that they also infect and affect humans. And so, particularly crops and agriculture, can be very susceptible to certain types of fungi and can become widespread fairly easily. So this is the situation in which these sort of broad-based fungicides are used to try to combat that process, to really preserve those agricultural yields.

Lloyd: Yeah, I mean one of the things that you mention in the piece is that monoculture agriculture is really susceptible, because you have one species. And if that species falls prey to a fungal infection, you can really do a lot of significant damage.

Desai: Yes, exactly. So previously, in human history, there wasn’t necessarily this emphasis on having a large scale production of a singular type of crop. In some ways, that diversity was actually protective. But in the situation that we find ourselves in now—on a global scale, really—crops, and staple crops, particularly, we tend to grow them at large scale. They tend to be the same type of crop. And so, that lack of genetic diversity can mean that single pathogen—and a fungi, in this context—can emerge, and really spread very easily.

Lloyd: You mentioned bananas, in particular, which would be devastating in our households. My 18-month-old survives on bananas. (laughs)

Desai: Yes. (laughs) Ours as well.

Lloyd: So now that we’ve got a kind of understanding of what these are, what you point to in the piece is that there are factors that are really exacerbating the spread and impact of fungal diseases. The one that has a lot of different effects on fungal pathogens is climate change. And I was wondering if you could talk a little bit about how that is impacting fungi, and their effects on humans and crops.

Desai: Yeah, so I’ll say that we’re certainly learning more and more about this. This is an area that maybe was understudied in the past, but there’s a couple of mechanisms that have been posited as to why climate change and more specifically, alterations in temperature and precipitation over time, may be having an adverse effect on the dissemination of fungal pathogens.

And so, one possibility is that these alterations in these types of temperature patterns may be shifting the ranges of animals, such as migratory birds and bats. And these animals, in particular, are fairly effective at carrying fungal pathogens with them. So they transport them either on their feet, their fur, their feathers, sometimes in their lungs. And this is one way in which these types of pathogens can be spread.

Fungi seem to be adapting to tolerate these higher temperatures, but simultaneously, human body temperatures actually appear to be decreasing over time as well.

Similarly, climate change we know also has caused people to migrate, as well, in association with other socio-demographic drivers. But these pressures may move individuals into areas that are endemic for certain fungi that they haven’t been exposed to in the past. And then, couple that with, for example, frequent droughts or other sort of extreme weather events, this can make that environment more hospitable to the fungi, or to the particular fungus, which can then drive infections thereafter.

And another example, I think, which has become more salient in recent history, particularly in California, which is where I live, there have been many large scale wildfires, and there’s been some evidence to suggest that wildfire smoke, in particular, is associated with the proliferation of certain microbes and also their dispersion, which makes sense if you think about the way in which smoke disseminates. So inhaling those spores, coupled with, there’s a possibility, as well, that smoke may actually also interfere with our immune systems. That may be a potential driver to these illnesses.

But I think the other thing to just sort of take note, which I think is very interesting, and sobering, as well, is that some investigators have proposed that fungi seem to be adapting to tolerate these higher temperatures, but simultaneously, human body temperatures actually appear to be decreasing over time as well. And so, when you put these two together, it may be that fungi are able to infect at a more efficient rate than in previous history.

Lloyd: That is really fascinating. Yeah, so as you mentioned, people are moving into new places where they may be exposed to new fungi. I know that in the desert Southwest, Valley fever is often a concern, with construction of new developments stirring up dust in the soil, that people then inhale, and is making them ill. Is that an issue that you see where you are in Davis?

Desai: Yes, absolutely. And I’ll say that my co-author, Dr. Thompson, he’s an expert in this area, but certainly, there’s been evidence that in the Central Valley in California, which is endemic for the causative pathogen of Valley fever, which is Coccidioides, it does look like the incidence of these cases may be increasing.

This confluence of all of these different situations is really contributing to the ability for this particular fungi to be able to infect additional individuals.

Now, it’s tough, because there’s also a lot of other things going on, right? There’s construction, there’s human activity. There’s also been a lot of frequent droughts recently, too. All of these things, again, may make the area or the environment more hospitable to these fungi.

I do want to say, as well, we’ve also probably got, there’s also enhanced surveillance that goes on in certain areas, so we may be picking up more cases as well. But I do think that this confluence of all of these different situations is really contributing to the ability for this particular fungi to be able to infect additional individuals.

Lloyd: And when we’re talking about Valley fever, this goes back to something we talked about a little while ago. Is there a test for it? When you’re talking about surveillance and looking out for these pathogens, I feel like I’ve heard stories that Valley Fever is actually often, you know, you’ll go to a doctor, and get a different diagnosis.

It might take a while to be actually diagnosed with Valley fever. When you’re talking about fungal pathogens that may look like other diseases or other issues. How does surveillance work in that situation?

Desai: Yeah. So it’s really tough, honestly, and for exactly the reason that you’ve mentioned. So there are tests that we do do, to be able to detect whether their bodies have been exposed to, or have active infection, but some of these infections can really overlap, in terms of their syndromes and in terms of the symptoms, with other, maybe more commonly observed infections.

So that’s one of the reasons I think why this sometimes gets missed, or that it takes a while for folks to be able to hone in on this diagnosis. I think that actually makes surveillance very difficult, as well.

There’s also, historically, really been an emphasis in public health on surveillance of certain bacterial infections or viral infections, because we haven’t necessarily thought about fungi in that same way.

I think there’s also, historically, really been an emphasis in public health on surveillance of certain bacterial infections or viral infections, because we haven’t necessarily thought about fungi in that same way. As I said, because they’re not necessarily… they’re not communicable, for one, but for two, this is an issue, I think that’s become more and more salient, because of all these factors that we’ve already talked about.

Lloyd: Yeah, yeah. So just getting into the policy ideas for how to address this, could you just talk about the One Health approach, and what that is?

Desai: Yeah. So the One Health approach has been around for a while, but it’s essentially an idea in which we consider human health to be interlinked with animal health and environmental health. So things that affect the environment and animals ultimately will affect humans. And so, when we take this approach, I think it really broadens our ability to consider how all of these complex factors interplay with one another, to effectively have those downstream effects on human health.

I think this concept has really gained more traction in the last couple of decades, and certainly, even more recently, as we look to contemporary infections, such as avian influenza, which has been something that’s been in the news quite a lot recently. It’s this idea that the health of all of these sectors are all really intertwined, and we need to really consider working and collaborating with individuals that work in those sectors, to really be able to get a handle, and prevent some of these infections in humans down the line.

Lloyd: So what would implementing that framework… what would that look like, from your perspective, as an epidemiologist? Who would you be talking to and how would you be thinking about your approach within that framework?

Disease surveillance is one of the most important foundations of public health.

Desai: I think, as we’ve mentioned, fungi, fungal pathogens, they don’t necessarily stick to just one domain. So actually, I think this is the perfect setup to think about the One Health approach and applying it. So certainly, we want to reach out to our colleagues, and work with our colleagues in agriculture, for example, which we’ve already talked about, forestry and healthcare, as well as, we work a lot here at Davis with our veterinary colleagues as well. I think these are individuals who, certainly, we’d want to collaborate with and create teams with, to be able to address these issues.

And I think, to me, I always say disease surveillance is one of the most important foundations of public health, because we don’t know a problem until we are able to recognize it and identify it. One aspect of this One Health approach is actually extending surveillance, not only to the detection of human cases, which, honestly, some people say that once you’ve detected certain cases of infections in humans, you’ve already kind of a step behind where you want to be, right?

So this concept, I think, advocates for increasing surveillance among agriculture, increasing surveillance among wildlife or animals, as well, so that we kind of have a sense of what’s going on in the environment, so that we can be better prepared for the situation in which humans ultimately get affected.

Lloyd: And then, once you have determined that maybe there’s a fungal pathogen outbreak, or something that needs to be addressed, you talked about it a little bit… Are there effective treatments for things like Valley fever, or are there things in the works? How do we approach that, in terms of drugs and treatments?

Fungal disease is very widespread, but I think, again, there hasn’t necessarily been as coordinated of an effort to focus on them.

Desai: Yes, so there are certainly an array of treatments for certain fungal infections, for sure. One of the issues, not necessarily in the context of Valley Fever, but for other potential fungal pathogens, one of the issues is that we are always at risk for the development of antifungal resistance. And there are a lot of reasons for that, but we’re already starting from a pool that’s a little bit limited compared to bacterial infections, in which we have many antibiotics. I think, really identifying antifungal candidates and investing and developing them is very important as another area that we can think about when thinking about how we can best confront or treat these infections if they do occur. And there’s also many other issues with this.

So we do have a limited pool, but we also have regulatory issues and hurdles for research, and also, the incentives to invest in this type of research, as well. And fungal disease is very widespread, but I think, again, there hasn’t necessarily been as coordinated of an effort to focus on them, as there have been for other pathogens.

Lloyd: What are some of the regulatory hurdles that you’re seeing?

Desai: So, for antimicrobial drug development in general, we have certain last line drugs that are reserved intentionally, for situations in which there are crises, or if, when the first line treatments have failed. But these drugs are expensive to develop. They can be difficult to incentivize pharmaceutical companies to invest in them. And so, I think, trying to encourage government agencies to provide incentives, right, and to streamline any potential hurdles for this kind of research is super important, as well. And also, to working across sectors. Again, we talk about this in the piece, but certainly, there is maybe some concern that certain fungicides that are used in agriculture, may have some downstream effects for antifungal resistance.

We’ve seen some evidence of this that’s come out of studies that have been done in Europe, for example. And so, really being able to make sure we’re collaborating with our colleagues in these other sectors, to ensure that, of course, we need to be able to preserve food security and productivity. But also, trying to find that balance, with making sure that things that occur at that level are not potentially also having effects on human health that we’re not ready for, that we’re not prepared for. It’s going to be super important.

Lloyd: Yeah. So my last question. I’m wondering, when you look at the government’s approach to investing in public health, and particularly in things like disease surveillance, and the kinds of epidemiological work that you do, are we investing in the right things? Are the various government agencies that are responsible for disease surveillance and combating the effects of fungal pathogens doing a good job, as far as what you can see, from where you are?

Desai: So I think one of the issues with public health, there’s an old adage, I may not say it exactly correctly, but it’s this idea that when it’s working well, you don’t know that it’s working. And so, it’s always hard to encourage investments or support into something that you don’t realize is even doing what it’s supposed to be doing, right? And I think, also, certainly after COVID-19, I think that recognition of the importance of public health, but also just how difficult that work can be.

When it’s working well, you don’t know that it’s working. And so, it’s always hard to encourage investments or support into something that you don’t realize is even doing what it’s supposed to be doing.

I think, in the context of all the things that we’ve talked about with fungi, there’s been evidence that there’s… and there’ve been coordinated efforts to try to bring different federal agency, governmental agencies, I should say, together, those that look at human health and agricultural health, to really start thinking about these issues, which I think is a great first step. But infections, they don’t go away. And we are seeing new emerging infections all the time. So, continuing that support, and making sure that we’re investing in robust disease surveillance, and preventative measures, remains a monumental task.

Lloyd: If you would like to learn more about fungal pathogens, visit issues.org, to read Angel Desai and George R. Thompson III’s essay, “Foiling the Growing Threat of Fungal Pathogens.” And visit our show notes to find links to this and other resources. Please subscribe to The Ongoing Transformation wherever you get your podcasts. And write to us at podcast@issues.org. Thanks to our audio engineer, Shannon Lynch, and producer Kimberly Quach. I’m Jason Lloyd, managing editor of Issues. Thanks for listening.