Science Friday - Why Is Bubonic Plague Still With Us?

Episode Date: December 9, 2025

For many people, bubonic plague is an illness that seems squarely situated in medieval times. But each year, a handful of human cases pop up in the western United States. Plague can be treated successfully with modern medicine. But why does it still exist, and how should we think about it both locally and globally? Plague researcher Viveka Vadyvaloo joins Host Flora Lichtman to talk all things spread and containment.Guest: Dr. Viveka Vadyvaloo is a plague researcher and director of the Allen School for Global Health at Washington State University.Transcripts for each episode are available within 1-3 days at sciencefriday.com.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hi, I'm Flor Lichten, and you're listening to Science Friday. Have you heard this news? New Mexico, man, sick with the plague. A resident in South Lake Tahoe, California, has tested positive for the plague. The case of plague has been confirmed in a person in Colorado. What is going on with these cases of plague? I think of bubonic plague as an illness that lives in my history book, not in my feed. You know, it appears in that Middle Ages Europe chapter, 25 million people,

were killed by this horrible bacterial disease carried by fleas. And then we turn the page. But in reality, that isn't the end of plague's story. The disease is still around and still making people sick. So why are we seeing it pop up and how should we be thinking about it? Here to tell us more is Dr. Viveka Vadevalu, Plague researcher and director of the Allen School for Global Health at Washington State University. Viveka, welcome to Science Friday. Thanks, Flora. It's lovely to be here. Okay, so I think a lot of people think of plague, bubonic plague, as this historical disease that has come and gone. What should we make of these cases popping up?

Right. So the interesting thing about the bubonic plague is that after these great pandemics that killed many people in the medieval ages and during what we call the Asian plague, which was really where we saw a lot of the outbreak also in the Asian era. India, China, etc. in the late 1800s and early 1900s, and that sort of continued sporadically until probably the 1920s or 30s. This is when we thought that was the end of plague, right? But this is really a was a critical time when actually the organism, the bacteria that causes plague, Yersinia pestis, became established in reservoir rodent hosts all over the world. because it was a time, obviously, when people started to travel out. For example, in the United States, right, we were getting ships that were coming from Asia

onto the Pacific coast, places like San Francisco and Seattle and areas like that. Where you'd see raps that were infested with fleas, carrying the plague. There was even an outbreak of plague in San Francisco that really then allowed this establishment of this bacteria in rodent species that are here in the U.S. Wow. Okay, so it's been living in rodents here for the last 200 years and presumably all over the globe then. Right, and so when we think about plague, right,

it's really a disease of rodents and fleets. And humans tend to be just these incidental infected hosts at some point when they happen to run into an infected flea or a rodent that might die of plague, and then their fleas are looking for a new blood meal, right? So a human comes by, flea jumps on, and then passes the bacteria onto them. Well, this flea's blood feeding of that human. Do we have a sense of how widespread it is? Yeah, I think we know a fair amount about this.

I mean, the ecology of plague has been pretty well studied over the years. We know that the disease we say is endemic on probably practically every continent, except for probably Australia. And we have areas that are real hotspots where we know that we can do surveillance work and we can detect plague, especially when we have rodent die-offs. Like in the United States, we might see prairie dogs, etc., which actually are the main rodent species that infected with the plague. When we see die-offs of these populations, we can go out there, we can do surveillance, we can figure out if it's plague. And then we know

that the disease is around. And we see that all over the world, China, Mongolia, Madagascar, Africa, the Congo, Tanzania, places like that, South Americas, places like Peru, etc. we know where this disease, the regions where this disease is especially prominent. I mean, when this was a big problem for humans during medieval times and then, as you say, in Asia in 1800s, I mean, that's pre-antibiotics. Is it still something we need to worry about? Right. So it can be easily treated with antibiotics.

That's correct. And I think in areas where we have these. robust public health systems, and that's usually in our places like the United States, right? We have resources. But when we have outbreaks in poor countries, like Madagascar and, you know, the Democratic Republic of the Congo, we usually have a situation where these are really resource poor countries, right? They don't necessarily have the resources to be able to go out there and treat people with

antibiotics very easily. So this is where we see disease outbreaks as a bigger problem. So apparently, yes, there are treatments for it. Whether everyone has access to that treatment is a different question. How many people are killed by plague every year? So not many in the United States. We often see five to ten human cases. We usually can manage those cases when we get them early.

So the fatalities from that are fairly low. at least this year in June, there was a fatality from plague in the Arizona area. And then we see human fatalities in places like Madagascar, where you have annual seasonal outbreaks of the plague, places like DRC in Africa also. The numbers can vary a few years ago. There were quite a few people, over 200 people in Madagascar that died. But now probably less than that, but really a higher burden of disease and case fatalities in these areas than other areas with, again, robust public health systems. What don't we understand about plague?

In terms of what? Good question. Good follow up to me. I guess I'm interested in why you're studying it and what there's left to learn about it. Okay, when I think about the plague and I think about all the unknowns, and I actually like to compare this to what we know about other, what we call vector-borne diseases. So there are a large number of diseases that are transmitted by arthropods, right? Like Lyme disease that's transmitted by ticks, right?

Like malaria that's transmitted by mosquitoes. So there's a lot more known about these diseases in terms of how the vector populations or the fleas in the case of plague are actually really important in the transmission process. But a lot more is known about those vectors and how they function in order to transmit the disease. Less is known about fleas. And for me, that's where my interest lies, because the way we manage plague really all over the world is through managing flea populations using insecticide spring. That's our primary. Kill the host. Yes.

Kill the host, exactly. Is there a better way, do you think? I don't know if there's a better way. I mean, I think that one of the concerns, though, with that particular management strategy, is that more and more we see that there's insecticide resistance building up. So what we really want to understand is are there any other vector-based, right, or flea-based solutions that we can come up with with doing more research in understanding, for example, what I do is understand the interaction between the bacterium

and the flea host, right? What happens to the bacterium once it gets into the flea? How does it overcome some of the blood-feeding processes of the flea, which can be quite harsh? How does it overcome the immune system of the flea? Is there some way that we can actually, once we do that research, figure out a way to be innovative with that research in finding a solution to manage, you know, flee populations during outbreaks? because obviously that's the way to manage or decrease transmission of the disease. From a public health perspective, is the goal eradication? I think it would be very difficult to eradicate the plague just because it's obviously something

that's inherent or innate to flee populations in the wild. So I think eradication might not be a feasible solution for us, but I think management definitely is something that could be. be feasible and easy to implement. So that's, I think, really what the best solutions are right now. Do we have to be worried about how climate change might affect plague, for example? I think we could be worried about that. One very discerning feature of the plague in some areas, and there have been studies done on this, is that plague outbreaks usually follow a very wet period, or, you know, a period of high rainfall in some areas.

We don't know what underlies that. But, you know, if we see shifts in climate in endemic areas that might result in probably flooding or heavy rainfall, etc., we might want to be cautious or we might want to consider that that might result in maybe an exacerbated period of plague in the environment. And so, you know, risk of human infection becomes greater in that scenario. When people see news of a case popping up here or there, what do you want them to think? You know, what should their takeaway be? I think, depending on where the area is, to be cautious, right? That there are things that you can do to minimize getting bitten by an infected flea, especially if you live in areas where the disease is endemic.

And so you should have your head up and be putting in some of those practices, right? Because often people in these areas where the disease is endemic might have a cat or dog that will bring back these fleas that are infected. And unknowingly, they get bitten. And they might then obviously contract the disease. And so if people are aware, I think that helps. It's really hard, I think, in the beginning for people to make the connections that it's plagued also because some of the symptoms are very typical, you know, fevers and chills and tiredness, things that you would maybe experience with, you know, the flu or some other infection that can be less fatal. Thank you, Vaveca.

Thank you, Flora. Dr. Vivekha Vallev, Plague researcher and director of the Allen School for Global Health at Washington State University. Thank you so much for listening. This segment was produced by Kathleen Davis, and we'll see you tomorrow.