Episode 100 - How Pathogens Shaped History

Brad: 00:00:00

What is up, Brad fans? How you doing? How you living today?

We're talking about disease, a favorite topic on the show, but we're not talking about any particular disease or any particular pathogen. We're not even really talking about biology, what these pathogens do to our body.

Instead, we're taking a bigger picture view of diseases and how they impact and are impacted by human behavior, human society, human history. Throughout history, pathogens and disease have played an outsized role in the outcomes of human affairs. Things like war, immigration, colonization.

And in turn, those human activities and the political decisions, the societal decisions that we make impact disease, give diseases opportunities to spread, produce outbreaks, and also prevent outbreaks.

And joining me to discuss this topic are two experts in this field, John McNeill, an environmental historian at Georgetown University, and Elizabeth Blackmore, who is a disease ecologist trained as a historian. She'll unpack all of this a little bit for you in the episode, but who is now doing her PhD work at Yale University.

Now, John's work I've been familiar with for a long time now. I was first introduced to his book Mosquito Empires when I started grad school probably like 10 years ago.

And this book is really famous in the epidemiology, environmental historian, disease ecology world. And he'll explain a little bit what that book is about in the episode.

My first introduction to Elizabeth's work was her paper Transoceanic Pathogen Transfer in the Age of Sail and Steam, in which she questions the narrative that pathogens brought over by Europeans to the New World spread like wildfire. I wrote an article about this for the publication Nautilus, and for that article I interviewed both John and Elizabeth.

And after that conversation, after those interviews, I was desperate to get them both here on the podcast to discuss these topics further.

In this episode, we're going to try and unravel this complicated web of interactions between humans and our pathogens, and we discuss the importance of telling accurate stories about these events because as much as we focus on the big picture of.

Brad: 00:02:21

Disease and its impacts, these things are.

Brad: 00:02:24

Very personal and often very terrifying when individuals go through them.

And as Elizabeth points out in this conversation, if we're not telling accurate stories about these events and how they unfolded, well, we're not going to be prepared for the inevitable future run ins humans will have with disease.

So with that, I want to make one quick programming note, because I referred to the author of the book the Hot Zone in this episode as Dan Reston, which is my brain, I don't know, substituting the first name of some other author and giving it the last name of the Ebola strain, the Reston Ebola strain that the book is about, when in fact the author of the Hot Zone is Richard Preston. So my apologies to Richard Preston. It's a great book. Everyone should check it out.

So now let's enjoy the conversation, like subscribe all of that good stuff. If you enjoy conversations like this, you. Here we go.

Brad: 00:03:27

Welcome both of you. John and Elizabeth, thank you so much for being here, for taking time on this Friday morning.

Scheduling two busy academics at one time can be challenging. So I really appreciate you both putting some time in your schedule here to join me for this conversation.

Elizabeth: 00:03:44

Thank you, Brad. It's a pleasure to be here with you.

John: 00:03:48

Likewise.

Brad: 00:03:49

Yeah, great. So we're going to be talking about disease today.

And for listeners of my show, they know that this is a favorite topic of mine, diseases, outbreaks, pandemics, all of these terms. And I thought it would be a good place to start as talking about why we find this so interesting.

You know, this is one of those topics that can be quite macabre. You know, it involves death, some, some, some painful death in some cases.

But I, maybe a good place to start is, I'll give you my, my take why I got interested in it.

And I don't know if anyone remembers the movie from the 90s outbreak starring Dustin Hoffman and Morgan Freeman, kind of a cheesy, you both shaking your head because it was a bit of a cheesy sort of action movie. But the main villain in that movie was an Ebola virus. And I watched this.

I was born in 85, so I was probably too young to watch an R rated movie when I saw this film and it scared the pants off me. But it also piqued an interest and led me to books like the Hot Zone by Dan Reston and others. And really that was it.

From this early moment, you know, about 10 years old or something like this, I just found outbreaks, diseases, both terrifying and totally intriguing.

You know, there was whether it's the human stories behind it or just the sinister idea of a microbe being able to cause such devastation and such harm, I was hooked.

I then went on to study the parasites, the helminth parasites, which we were talking a little bit about off air, but there's a whole myriad of infectious agents out there. And as we're going to discuss today, a lot of different ways in which these things propagate and affect society.

So with that in mind, I think maybe, John, I'll start with you because in your Biography, you're labeled as an environmental historian, and to me this my understanding of your background and your career. Maybe disease isn't the only thing that you look at, although we'll focus on that today.

Maybe it's more the Anthropocene and human environmental interactions in general. But why don't you start and you can give us a quick version of what an environmental historian is and then why diseases?

Why have you found this topic so fascinating?

John: 00:06:17

Sure. So there are many different flavors of environmental historian.

I am the sort who pays attention primarily to changes to the environment that result from human activity and what that has meant for human societies.

But environmental historians also pay attention to the realm of policy, law, administration, how humans have sought to regulate their relationship with environments over the decades and sometimes centuries.

And a large proportion of environmental historians are interested in the cultural and intellectual side of the relationship between humans and environments. That is, they pay attention to what people have written and thought and more rarely painted or filmed or danced.

That refers to nature or the relationship between societies and the natural world. So there's a whole lot of different kinds of environmental history.

But because a lot of human disease is embedded in environments, a goodly share of environmental historians, including myself at least from time to time, pay attention to that subset of diseases that circulate through the environment, whether it's mosquito borne disease or diseases that are peculiar to certain kinds of micro environments. Myself, most of my disease related work has been about mosquito borne disease, malaria and yellow fever in particular.

But I have a sort of general interest in the topic of the history of human disease.

my father wrote a book in the: 1970

Brad: 00:09:05

Interesting. I mean, that's quite the endeavor for your, for your father to try to try and categorize or put into, you know, the scope of human disease. That's.

Wow, good on it.

John: 00:09:17

It's still a good book. It's outdated in some respects, overtaken by new knowledge in some respects, but it still has its merits.

Brad: 00:09:26

Excellent, excellent. I'll have to look for that one at the library. So Elizabeth, buy it Bread? Oh, yep, okay, that too. Does the family still get royalties or.

John: 00:09:37

Yeah.

Brad: 00:09:38

Okay, well then I'll be sure to look for it at my bookstore.

Elizabeth, jumping over to you, I think, again, you can correct me if I'm wrong here, but looking at sort of your background, your bibliography, it seems that maybe you're a bit more of a classical epidemiologist.

Let's say, again, correct me if I'm wrong, but why don't you give us, again, same sort of thing, the scope of what it is that you like to research or study. And then, yeah, maybe whether it was a book or a movie that you watched that got you into this topic of diseases.

Elizabeth: 00:10:12

I mean, I smile when you describe me as a classical epidemiologist because this has been. This has been something I'm working out, and it's been a question for me. I originally trained as a historian.

I am now in a graduate program in ecology and evolutionary biology where I'm training as a disease ecologist. And so, yeah, so I think I would call myself a disease ecologist in training at this point who is interested in the history of infectious disease.

I mean, just purely as a scientific question, I find infectious disease really fascinating. It is.

It's a problem of biology, and then at the same time, it's a problem about humans and how humans interact and how humans move and how humans behave with each other.

In order to understand the pattern of infectious disease, you need to understand both the basic biology of what's going on inside somebody, and you need to understand what's happening at a broader social level. So those kind of. That mix of challenges is something that I found very attractive.

But then at the same time, disease isn't just a scientific question. It is a really important humanistic question. And the way that we tell stories about infectious disease is really important.

I mean, disease makes people feel vulnerable, and when people feel vulnerable, they have a tendency to resort to telling stories that maybe aren't so constructive or helpful. We blame people for catching infectious diseases.

We characterize diseases as coming from particular populations or from particular parts of the world in a way that is inaccurate, in a way that can be deeply prejudicial. And it's really important that we tell, because diseases, the way we talk about disease can often be discriminatory.

It's really important to be telling accurate stories about what disease is, where it comes from, how it spreads.

Brad: 00:12:47

Well, I mean, that's great because it's kind of exactly, sort of that speaks to why I'm interested in these things as well, these human stories, you know, how populations or individuals react to disease, because it is this, you know, can be this terrifying, unknown thing. And we don't necessarily always have, you know, the right tools to deal with that.

So how we react is a big part, but then the other, you know, interest. And what I was hoping to.

My hope for the audience for this episode is to sort of get a picture of how everything's sort of outside of the biology of the organism and the immune system and stuff that impacts these outbreaks or the movement of disease or something like that. But then again, just what you said, how that in turn affects our society and stuff.

So it's this wheel and I was actually trying to think about the best way to sort of approach this. And maybe you guys can help me if I stumble a little bit, but because it's almost like a feedback loop, right?

Human behaviors and politics and things influence disease. And then disease turns back and causes another ripple in that chain.

So my idea, my thought about trying to unpack this for an audience so that they can get a sense of some of these factors, these human factors that go both ways would be to sort of maybe look at the historical eras that you both study.

John, you mentioned mosquito borne diseases, and I know your book Mosquito Empires, focusing on the period of kind of colonization, early colonization of the Caribbean. So maybe we can start with you if you want to take it to another period, of course.

But in this era, what are some of these factors that would be unique to that time period that would play a role in sort of the unfolding of the disease dynamics, the mosquito borne diseases that had such an impact on that process of colonization, that era? I'll let you kind of take it from there. If my question, my proposition to you makes sense.

John: 00:15:01

It makes sense, although I wouldn't use the word unique to this era. I might say distinctive.

I'm not sure that any of the stories that I tell in Mosquito empires should be understood as unique, although I do think that they are rare. Here's the quick background for your listeners.

The book that you referenced, Mosquito Empires, is about yellow fever and malaria in the Caribbean in the 17th, 18th and 19th centuries, when, in my judgment, at least these two diseases plays outsized roles in shaping human affairs, particularly political and military affairs.

And they could play these outsized roles because of strange, not quite unique, but strange circumstances that, so to speak, temporarily empowered these two diseases.

The strange circumstances were that ecological changes were underway in the Caribbean that were very favorable to the two main species of mosquito that carried yellow fever and malaria. And most of those ecological changes had to do with the installation of plantation economy, a sugar plantation economy.

Sugar plantations are fantastic. Incubators of the Aedes aegypti mosquito, for example. And so that's one unusual circumstance.

Changes in mosquito ecology and then changes in the population profile bringing humans to this part of the world, some of whom brought infections with them, such as falciparum malaria from West Africa, probably imported in the bodies of enslaved Africans taken to these plantations in the Caribbean.

All of this set up a circumstance that allowed yellow fever and malaria to wreak havoc in military situations, when new populations, recruited mainly from Western Europe, came as armies and navies to the Caribbean, trying to conquer territory primarily from the Spanish empire. These populations were recruited mainly in Britain, to a lesser extent in France.

And they were entirely naive in terms of the preparation of their immune systems for falciparium malaria and particularly for yellow fever. Had they grown up somewhere else, where these diseases were always present, endemic, then their immune systems would have been better prepared.

And with respect to the yellow fever virus, they would have been typically immune, because all evidence suggests that surviving yellow fever once is enough to make you immune for life. But these people were naive, unprepared, and the recorded mortality from these military expeditions was gigantic. 50%, 75%, 85%.

This made it comparatively easy for Spain to defend its empire in the Caribbean.

which they began to do in the: 1770

And in that circumstance, these two diseases were in service of liberation because the locally born and raised populations enjoyed an immunological advantage over populations sent from Britain, France or Spain to try to prevent independence in the Caribbean. And I extended the argument to the American Revolution in South Carolina and Virginia, which has convinced a minority of readers, I think.

Brad: 00:19:46

Right. So there's, in this scenario, it's really, you see, the dynamics of conquest.

This, you know, a very human thing that we experience, you know, empire, this kind of thing, people striking out into new lands and, you know, in the worst possible circumstances, enslaving, conquering other people, setting about this mixing of diseases, then changing the environment to promote those diseases.

John: 00:20:15

And that inadvertently and unknowingly.

Brad: 00:20:17

But yes, right, yes, exactly. Because I mean, at this point too, I mean, I wonder what the.

Maybe you can enlighten, but the sort of knowledge of malaria and yellow fever at this time, would they have known that it's a mosquito borne disease or.

John: 00:20:30

No, not at all. They had entirely different ideas.

It was only between: 1885

Brad: 00:20:48

Right. So, I mean, this is a very. And you see how it cuts both ways.

It first allows the Spanish to hold their conquest, and then in that, like you said, that fight for liberation, you know, these people have an immunological advantage. I mean, we see this in numerous conflicts throughout history.

I remember learning the Second World War, malaria, what it did in the Pacific theater, and other diseases. And war itself seems to create a breeding ground for disease.

John: 00:21:19

It does for a couple of reasons, and I'll touch on those in a sec.

But what I want to say first is that, yes, there are many, many examples of this kind of thing throughout history, but there are very few examples in which diseases were as sovereign as they were in the early modern Caribbean, even in, let's say, the Second World War in the southwest Pacific, where malaria, again, falcipara malaria, was an important infection and was really hard on the Japanese Imperial army in New guinea and the Solomon Islands campaigns. But there's no logical argument to say that malaria was decisive to the outcome of the Pacific War.

The Americans and the Australians were going to win anyway. They won a little faster because of malaria. But in the Caribbean, at least in my judgment, these diseases were much more powerful.

The mortality rates were much higher, and the political consequences frequently decisive in a way that is comparatively rare. But you're right that war creates momentary circumstances for the flourishing of infectious disease.

There are many reasons for this, and I'd be interested in Lizzie's take on this.

But in my guesstimate, the most important reason for that is bringing together large agglomerations of people from very different backgrounds, places, disease environments, and then smushing them together where they get to share infections.

Elizabeth: 00:23:11

Yeah.

John: 00:23:12

But every war. Every war until the First World War featured larger disease mortality than combat mortality.

Brad: 00:23:23

Elizabeth, I.

Elizabeth: 00:23:27

Entirely agree with that. Read on War and disease.

I think if you are bringing folks from all over the world to meet in configuration, they don't usually meet, especially at a point in time when people are. It is less common that people are traveling across the world, then you're creating kind of a perfect storm of conditions for infectious diseases.

John: 00:23:56

Yeah. And then you subject them to high levels of stress and often to malnutrition. That's a perfect storm, as Lizzie says, I think.

Brad: 00:24:06

Yep. You add to that, you know, injury cuts bacteria, poor living hygiene, you know, we hear a lot about.

And I know you just mentioned that the First World War was the first where, you know, Combat deaths outweighed disease deaths. But the conditions in the trenches is something that we've all read about, right, that breeds disease. So, yeah, war is a big one. And Brad, let me.

John: 00:24:30

I can't resist. I want to say two quick things about that. One is what I just said about World War I would not be true.

If you count the: 1918

nd, and that is that prior to: 1914

y medicine got good enough by: 1914

Brad: 00:26:05

Yeah, yeah, it is. And I mean, there's probably a whole history of military medicine, you know, that would be fascinating to dig into this, but great points.

Elizabeth, I wanted to jump over to you because the first time that I read or came across your work was this paper that was looking back at the maybe myth is the wrong word about the spread of disease in the Americas during colonization. And I think that this is, I don't know, colonization war. They kind of tend to go hand in hand.

But this idea that we've now solidified here with bringing large groups of people together or the movement of peoples, whether it's war, colonization, these kind of discovery, whatever we want to call it, is a huge factor. And then disease playing a role in the outcomes of those human efforts.

Your take on the movement of disease into the Americas from the Old World, let's say, went against everything that I had learned in school books in Canada.

What we learned about the first Europeans that came to the New World, the story that we were taught is they show up with all these diseases and those diseases spread like wildfire through the Americas. And that was largely what won the day for the colonists was this disease.

Now you have a different perspective on that and you can please give us, sort of walk us through your data, your thinking on that. And then also maybe we can explore then what the impact in this new scenario that you propose. How Might that have still aided the colonists?

Not aided the colonists, or. I don't want to put it in such a colonist versus indigenous framework. But I think you understand, again, where I'm going with this.

Elizabeth: 00:28:09

Yeah, it's a great question. It's a big question.

So I think my theory with the, like wildfire and why it's so persuasive to people and why it has dominated the way that we talk about the history of infectious disease is that infectious diseases today kind of spread like wildfire. And they're able to do so because we have vast air transport networks, because we are.

We have cars and trains and cities, very large cities, and something like COVID 19 did not take very long to reach the vast majority of the world. And we're working on that kind of intuition that that is how infectious diseases spread through populations.

And that in general works fairly well for the 20th and 21st centuries. But it's not an appropriate assumption for earlier periods in time.

ved, let's say that it is the: 1600

That journey is going to take order weeks, maybe four to eight weeks, depending on how lucky you are with the winds. Let's say that there's 20 of you. Let's say you're kind of traveling across to bring across some mail and do some trade.

You know, first you need to have one person who has a case of infectious disease when they board. Presumably that case isn't going to be too visible. Because presumably.

I mean, I don't know how good of an assumption this is, but I would want to hope that they wouldn't let somebody board a ship if they were really sick.

John: 00:30:17

That's a very good assumption.

Elizabeth: 00:30:20

I'm glad. Yeah. So then that person has to be at a very particular point in the infection where they are infected but not yet displaying symptoms.

And then once they do display symptoms and once they become infectious on board the ship, you need to have sufficient people on board the ship who are susceptible to the infection.

out smallpox In London in the: 1600

And then once they'd seen it, they would, we think, no longer be especially susceptible to it.

it across the Atlantic in the: 1600

You need to have maybe, maybe two or three people who are susceptible. So, yeah, so I think that it's.

It's something that we can and should reason about, qualitatively, reason about just by talking about it, like we're doing right now.

But also, you know, sciences like epidemiology and ecology have built a bunch of quantitative tools, a bunch of kind of mathematical and theoretical ways for thinking about how easily diseases tend to spread in a given set of conditions. And so the work that.

That I'm doing and that I'm interested in continuing is using some of these tools, kind of power tools, to think in a different way about how easily diseases spread.

Brad: 00:32:32

Right.

And so we have this set of circumstances that you need for a pathogen to get from, let's say, London to Boston or New York or one of these early landing spots in the Americas. So you need an unbroken chain of hosts.

And the timeline for a ship making it across it isn't very conducive for that for some of these pathogens, yet they did make it to the Americas. But I guess your contention is that it was a slower process than this. First settlers arrive, spread like wildfire. But so then how does that.

And I think your evidence is very compelling.

The models that you show and then some of the historical data about the frequency of outbreaks that were recorded in places like Boston and, you know, all the way to the west coast is great, and we can dig into some of that as well.

But I think the idea I have then is because when I first encountered it, I wonder how many people saw that and their instant reaction was, well, we can't think that, because that sort of lets the bad settlers off the hook. Right? It wasn't disease. But that's not to say that disease didn't still profoundly impact the process of colonization.

So maybe this is beyond the scope of that one paper that you wrote.

But what do we think about how, in this new view of it, how does disease still play a role in the dynamics that unfolded in the colonization of the New World?

Elizabeth: 00:34:09

I think what you've outlined there is a set of questions that I want to spend the next 20 years thinking about. I am fascinated to know kind of how aware people were of factors like the frequency with which diseases were introduced and the significance of that.

I think they probably had a better intuition for it than we do now in the 20th and the 21st century.

Brad: 00:34:41

John, do you have any thoughts on this one?

John: 00:34:44

Sure, lots of them. But I want to go back to Lizzie's paper, if I may, please. So it's a really interesting piece of work because.

And partly that's because Lizzie brings to it a set of skills that are rarely combined. The ability to do genuine historical research and the ability to do sophisticated epidemiological modeling.

You rarely find one person who can do these things. You rarely find a team that does these things together. So that's part of the charm of that article.

arrived for the first time in: 1492

ade it across the ocean until: 1518

But it's precisely the reasons that we've been talking about. You need a chain of susceptibles on a ship that's going to take six weeks to cross the ocean. And that just didn't happen. And didn't happen.

ppen. And didn't happen until: 1532

So just looking at that sample, the odds of this actually happening are on the order of 1 in 500. And that helps you think about the automaticness of the transmission of disease across the Atlantic. And it falls well short of being automatic.

So that's one of the really interesting things that you can see in Lizzie's paper to the larger question of the role of disease in the colonization of the Americas. This is enormously controversial and it has political overtones.

The political overtones result from the fact that, as you were intimating, Brad, the larger the role of disease in the colonization of the Americas, the smaller the role of violence, dispossession, enslavement and other forms of human brutality. So Scholars today are arguing about the relative roles of infectious disease.

And when they make these arguments, they normally maybe not always have in the back of their minds what the political resonance of the argument that they're making has is particularly alive, I imagine, in Canada, where First nations history is full of political resonance. But it's also true in the United States. The way I see it is that a lot depends on where you're talking about.

And parts of the Americas that had dense and concentrated populations were more susceptible to infectious disease than parts of the Americas that had scattered and less dense populations. So that's an important variable.

Secondly, elevation and latitude, because some diseases, mosquito borne diseases in particular, are temperature dependent and are much harder to communicate at high elevations, let's say Mexico City or high latitudes, let's say Canada or Patagonia, than in the Caribbean. The way I see it, the Caribbean was the place where the disease component was the largest.

And that's because partly climate and the propitiousness of the Caribbean for mosquito borne disease, but also because the Caribbean was the first port of call for a lot of shipping to the Americas just for reasons of prevailing winds. So Caribbean ports were the likeliest to receive maximal doses of pathogens crossing the ocean just because they were the first ports of call.

That would also be true for northeast Brazil when it comes to shipping from Angola. But for shipping from Europe and from West Africa, it would be the Caribbean, typically.

But other parts of the Americas, I think, had a different experience.

And disease probably played a sizable but smaller role in tipping the balance of power and the balance of demography in favor of settler populations and against indigenous populations.

Brad: 00:40:27

Mm. Yeah. So it's.

And I guess, wow, you know, like this just shows how gray this whole situation is, you know, And I think a lot of people, and maybe this goes back to Elizabeth, what you were talking about at the beginning, this, our instant reactions to these diseases, these situations, is to have this sort of black and white, you know, do this, don't do that. It's, it's those people, not that.

But we see how, you know, prevailing winds, you know, for shipping would bring you would change the course of what ships are going where and how many with the frequency of that. And that's going to, you know, tip the history of, you know, who knows what in all of these different directions.

So this is why I think it's so interesting. So I think we've got this situation where we can see that there's these broad human activities that set some of these things in motion.

And I'm talking really just about movement of people across the world or even within countries. Right.

But just movements of different people and their pathogens, their animals, you know, all of the things that were associated that can bring these, you know, pathogens and diseases. Right. And those factors remain. Right. Like that's we haven't stopped doing that.

We've kind of got this very connected world now, like you said, Elizabeth. But then you have local conditions on the ground that change things.

You have the relationships between those populations that are running into each other. Why are they there? Are they adversarial? Are they cooperating?

All of these things can sort of play out in ways that we just it'd be impossible, really, to predict. And I think that this is just so fascinating.

And maybe people have a sense of, again, disease playing a role in our history, but how much do you think is still left to be uncovered?

Let's say we're talking about you were going to spend 20 years on this question of how it impacted the Americas, but maybe just again, why looking at the past, what is this going to help us learn about our times or our present day?

What are we trying to what, what questions do you think are still left to be uncovered in terms of understanding these historical events that happened and what we can learn from them? Maybe, Elizabeth, if you want to jump on that one first, sure.

Elizabeth: 00:42:55

It's a huge question.

Brad: 00:42:57

I tend to do that. I tend to have these very broad, big ideas. And then I.

Elizabeth: 00:43:04

Something that I'm interested in that I imagine I'm going to spend a lot of time thinking about is not just the question of when a disease was first introduced to a particular region, but when.

d to learn that well into the: 1700

And this is because when you have a small population, measles might get introduced, but then it's just going to burn through the population and it's going to go extinct. It's a similar question to what's happening on these ships.

And unless and until you have a large population or a highly connected population, you're not going to see continued circulation of infectious pathogens. So I think that there's a lot of work to be done in cataloguing not just when diseases first showed up, but when they became frequent visitors.

In some ways, that's a little more challenging because I think the first arrival of an infectious disease is typically a very dramatic event, and people become less interested in the fourth and the fifth arrivals. But I think that there's a lot of interesting work to be done there in thinking about.

It's not a binary between a pathogen being present all the time and a pathogen never being present. Right. There's a lot of gray. There's a world in which you've never had a measles outbreak.

There's a world where you have a measles outbreak every 50 years. There's a world where you have a measles outbreak every 10 years. What difference does that make in terms of the health of your population?

What difference does that make in terms of the evolutionary pressures that different viruses experience?

For something like influenza, which evolves very, very fast, it is plausible to me that different levels of global connectivity could have had very important evolutionary effects on the evolutionary trajectory that the virus took.

But this is something that we don't really know anything about and that I would be deeply interested in thinking about, both in terms of the impact that it had on human populations and the significance it might have for the history of human health and just the kind of the basic knowledge that it can give us about how diseases occur more generally in conditions that we study less often from those that we study in the 21st century.

Brad: 00:46:18

John, I'll throw it to you if you have anything that you want to add to that or take it in a different way. What do we learn from the experience of the Spanish and the others battling over the Caribbean with diseases?

What can this teach us about our current time?

John: 00:46:39

Well, I'll answer that question in a moment, but I want to say that people with Lizzie's skills could really illuminate the history of the Americas by helping to figure out the process of endemization of these infections.

Because from the point of view of ordinary human experience, it's a gigantic difference between a world in which epidemics and outbreaks come, as she said, every few decades, and one in which they are essentially domesticated and childhood diseases and are of minimal consequence to adults. That's a vastly different circumstance. When, where, and how did that happen?

This is poorly recorded in documents because people at the time had no concept of endemization of an infection. They understood these things as typically as acts of God.

So the skills of the historian aren't all that helpful in figuring out this important historical question, and the disease modeler can probably do a better job. So I'm really interested to See what Lizzie and her ilk come up with in the next few years.

And if they ever fall short of questions to answer, I hope Lizzie will contact me and I'll suggest a handful. So, to your question, Brad.

One thing that I think this whole story of disease transmission and politically important epidemics should help us to think about in the very broadest of terms is the fragility of what we might call, with some exaggeration, perhaps, the golden age of health.

cteriological revolution, the: 1870

The period that Lizzie and I study contrastingly might be understood as the golden age of pathogens, not the golden age of health, because the field of operation open to pathogens was enlarged through transoceanic shipping. And while Lizzie's work shows that it wasn't automatic, nonetheless, as we have said, it eventually happened.

Pathogens got from one continent to another, from one population to another, and thereby expanded their scope of opportunities.

So in a sense, the 16th, 17th, 18th centuries, while the world was being linked up through transoceanic shipping, was, if not the golden age of pathogens, it was at least a golden age of pathogens. But that's outside of the frame of reference of everybody who's not historically educated.

Everybody who's grown up in 20th and 21st century North America, Europe, Japan, and a few other parts of the world too, has lived only in the golden age of health. And that makes it difficult to appreciate the fragility of the golden age of health and the normality of golden age of pathogens.

So it's a little bit worrisome. And the COVID 19 epidemic is a good reminder of the fragility of the golden age of health.

So that's the way I look at the past, as reflecting upon the present and possible futures.

Brad: 00:51:39

Yeah, I love the opposing of the golden age of health and the golden age of pathogens.

Once we started moving around at that broad scale, it at least open the door to, I think maybe the golden age of health and pathogens is still kind of. Maybe they're coexisting, but there's just one is kind of hidden under the other.

And this is where I wanted to go is because we think of our age right now as like, you Said the golden age of health.

We don't have to worry largely for, you know, I'm speaking of the Americas, Europe, you know, these places where we can benefit from these technologies. Right. We have the technology to sort of beat disease.

But like I was saying at the beginning, there's always this double edged sword or this circular thing.

Our technology is also exacerbating the thing that we've hit on that is the big, one of the big drivers of human disease, which is movement, movement of people, connectivities of population. So what do we think of the state of disease right now in the world?

Are we operating in one single disease ecosystem because of the connectivity that we have right now?

And maybe the next golden age of pathogens is just below the surface and we're kind of keeping it at bay with all of our different tools and stuff, or is there still a patchwork?

And I know again, this is a broad question because we could immediately just start with, well, it depends on what pathogen, virus versus bacteria versus animal borne versus mosquito, you know, insect, all of these things.

But in general, maybe this is something that I think about and you know, kind of keeps me up at night is how much of our technology, you know, we have the technology to combat the things, but we also are, you know, giving them the opportunity by again, our technology, in this case our communication, our travel and shipping and trade and economic networks that we've created. I'm going to throw that one out to the both of you. And who would like to jump in there? Elizabeth, please.

Elizabeth: 00:53:53

I'll start by giving you the answer that you don't want, which is that it does depend on the pathogen.

But I think something that I've been thinking about is that we actually, we know less than you would think about the extent of pathogen globalization in the 21st century.

And the reason that we know less than you would think is that to really get a census of how global a pathogen is, you need to be practicing global surveillance. And there are a lot of roadblocks and barriers to effective global surveillance of infectious diseases, unfortunately.

And unfortunately, as you would expect, our surveillance efforts are very concentrated in highly resourced parts of the world.

And so, for example, in, you know, large areas of Africa, of South America, we have much less by way of ongoing surveillance than we have in places like Europe and North America. And that makes it difficult to get a full picture of what's going at a global scale.

And there are organizations like in particular the World Health Organization that are leading efforts.

But it requires a lot of pretty challenging on the ground mobilization of resources for pathogens, where there have been kind of large global initiatives. One of the best studied is influenza. And fascinatingly, the degree to which influenza is global kind of varies on the strain of influenza.

For seasonal influenza, H3N2, we see these kind of big waves that sweep across the world pretty much every year. But then for other strains, for H1N1 influenzas, it can circulate for a longer period of time at a more regional level.

And then at the other end of the spectrum, we have things like dengue, where you have different strains are associated with different regions. So it's a fascinating question. It's a question that I would love to see more work on.

It is something that I think is going to be challenging to understand, but I certainly think it's important not to prepare, proceed from the assumption that in the 21st century, all diseases are global. To me, that sounds a little bit like the wildfire assumption. Even with planes and even with the level of human connectivity that we have today.

I think my starting intuition would be that there are important ecological roadblocks in terms of global pathogen landscapes. And, you know, I guess that also gives us something to be watching out for.

nfluence of people during the: 1600

John: 00:57:58

John, let me just emphasize, Lizzie has to be correct about the incomplete globalization of pathogens because many of them are vector borne and cannot be transmitted without competent vectors present. And the vectors are constrained by conditions of moisture, temperature, and so forth.

And so there is no yellow fever in the Arctic, and there will never be yellow fever transmission in the Arctic until the Arctic is warm enough to host certain kinds of mosquitoes, to use an extreme example. So it's going to be a patchwork.

It may be a landscape that is more globalized than it has been in the past, but it's still a patchwork and is going to remain a patchwork forever, which makes it complicated, harder to understand, and more important to understand.

Brad: 00:59:07

Let me, then, as we kind of start winding this down, then maybe it's the same question and put in a different way, but I don't think so.

But what are some of the, let's say, conditions, human conditions that you see in the world today that are maybe tipping the balance in favor of pathogens or not. So I'm thinking of just the trend of globalization.

Again, maybe it's commerce, maybe it's just connectivity via air travel, maybe it's political instability or unequal distribution of resources or something like this.

Is there something that you could look at today that would maybe mirror a historical setting where disease was tipped, the balance was tipped, and a disease situation happened, or an outbreak happened? Maybe there's a warning sign in the past that we can look to and say we're in a similar place right now.

Is there anything like that that you see or is that just. Am I just kind of going off in a different place here?

Elizabeth: 01:00:22

Well, I would say that the big one that folks in my field are concerned about right now is that changing land use and changing relationships between humans, the natural environment, and non human species are going to open the door for new, what we call spillovers of infectious diseases from non human species into human species.

There's good data that when, for example, Batman populations experience stress and experience habitat disturbance, that this can cause them to become more susceptible to infectious diseases and in turn can cause them to spread diseases in a way where there's an increased risk that those pathogens may find themselves coming into contact with humans. So that, to me is the one that I'm concerned about.

John: 01:01:32

And the recent history of SARS and Covid is a good reason why people are concerned about this. The other one that I would point to is the potential for breakdown in public health systems.

Our comparative and incomplete but still substantial success in checking infectious disease depends very powerfully on political stability and a certain historical calm that allows public health services to do their work.

And a breakdown of that necessary condition, whether it's through warfare or some other sort of black swan event, would disrupt the surveillance and the ability to treat and control pathogens. So that's also a possibility. Most of us have again in North America, Europe, Japan in particular.

This would not be true for people who grew up in Central Africa or Afghanistan.

But most of us have lived in conditions of comparative peace and stability and prosperity where public health services have been able to do their work with comparatively few obstacles. But that is not a given. And much of the human past has not been lived in that happy condition.

So that's another respect in which the human, the socio political circumstances are supremely relevant to the fate, the trajectory of infectious disease. It's that circle with which you began the podcast, Although it may be a little more chaotic than the average circle.

Brad: 01:04:13

Yeah, well, and that has me thinking and obviously I work in the science communication field and it's something that we talk about a lot is trust. So it doesn't even necessarily need a big event like a war or something like this.

But, but you see locally in a lot of places, whether it's people that take for granted public health initiatives, like you said, we don't know the condition of what it was like when people were suffering from polio and childhood diseases and stuff. But now there is this skepticism and not to go into the causes of where this is coming from, but this is something.

So I guess my point is human psychology, psychology also plays a role in this thing, whether we're going to go fight each other.

But also am I dealing with my, do I have the appropriate level of fear for a disease or maybe I have too much fear of a disease, these kind of things. And that's where it kind of hits people in the personal level. So I wonder what you think of this.

And I said as we're winding down, so this will be the last one. But, and again we can make it really broad so you can kind of take it wherever you want.

But human psychology in terms of this question, and I'm thinking again, like I said, in my career in my field, we talk a lot about trust and then trust in public health. So how does you know to bring it to the really local or the really individual level?

Human psychology play might play a role in these situations, either tipping it for good or for bad. Maybe. John, you want to start first on this one, then we'll give the last word to Elizabeth.

John: 01:05:54

Very good. So yeah, one of the interesting things in recent years is the rise of skepticism in public health systems and vaccination programs in particular.

This is an example of this question of trust as you put it. The way I see it, while this is tragic in many respects, it's also got built into it, I think a self correcting mechanism.

So if we see sufficient breakdown in vaccination programs so that disease X is allowed a larger scope of transmission, the results will sooner or later become conspicuous and the folly of, let's say, not getting measles vaccinations will become evident.

So I think that the scope for large scale breakdown as a result of lack of trust is self likely to be self limiting and therefore while tragic on individual levels.

And little kids will die unnecessarily because their parents don't believe in measles vaccines on a population level, I think it's likely to be self correcting.

And limited in its impact compared to what could happen if the mechanisms of the delivery of public health breakdown due to large scale social disruptions.

Brad: 01:08:04

Yeah, that makes sense to me.

Elizabeth: 01:08:07

Yeah.

John: 01:08:08

But hey, hey, we got to see what happens with RFK Jr in positions of power.

Brad: 01:08:18

I wasn't going to specifically bring it up, but yeah, I mean, that's. That it's something. Right.

And it's that chipping away at the sort of the wall or the infrastructure of that, the barrier that we have against our protections for these things. At what point does the dam break and then what does that unleash in terms of fear and mistrust or blame or everything else that goes along with it?

I'll give you the last word here, Elizabeth, on that topic, but if you wanted to put it in a more positive spin, I would allow it as an ending for the podcast.

Elizabeth: 01:08:58

I'll do my best.

I think that management of infectious disease is fundamentally always going to be challenging because we are asking people to believe in things that they can't see with their own eyes. Right.

We're asking people to believe that if you go into a crowded room during a COVID pandemic, then any one of these people who don't look visibly sick might be able to transmit this infection to you.

And when you're asking people to believe things, I think that that is, it comes back to history and it comes back to storytelling, and it comes back to the importance of telling good stories about what infectious diseases are and the effects that they can have on us.

We're living in a time where we don't necessarily have good intuition for how dangerous a truly novel infectious disease can be in populations that don't have previous immunity. This was a big challenge with COVID 19 was getting people to. It was kind of, you know, persuading people that it wasn't just the flu.

And I think in order to help people have the intuition that infectious diseases can be dangerous, we need to be tested. Telling good stories about the dangers of infectious diseases in the past. By the same token, you know, we.

It's very easy to take for granted with globalization that infectious diseases will spread like wildfire.

And if the only stories that we're telling about infectious diseases are that they spread like wildfire, then of course it's going to be challenging to convince people that social distancing can work and that non pharmaceutical interventions can be an appropriate and effective way of slowing the spread of COVID 19 through a population.

So I think for me, as a, as a scientist, this is one of My real motivations in doing the work that I do is in finding ways both in really understanding what's going on in the past and in finding ways to communicate that in a way that it helps us understand what infectious diseases are in the present and that it gives us the tools and the intuition that we need to help people believe in help people believe that infectious diseases are a threat, but also that they're manageable.

Brad: 01:11:50

Great. I gave you the challenge to put a positive spin on it.

And to me, you speak to me a lot as a journalist, as a communicator, when you speak of storytelling because that's such a powerful way in which we learn.

And so having accurate, appropriate stories about the histories of these things, how they unfold, what they do, what they can't do, what we can do, what we can't do, these kind of things I think is a great, is a perfect message to end it on. And I appreciate you both coming on here and sharing your expertise, sharing your opinions and your stories about these things.

I follow both of your work and I think you're doing a great job at storytelling and I appreciate you coming on doing that here with me and my audience. So thank you very much for taking the time.

John: 01:12:40

Thanks for inviting me on, Brad. I appreciate it and I'm really glad to see you bringing Lizzie's work to a broader audience.

It's really important and people like you, science journalists have a huge role to play, I think in helping the general population understand the reality of the potential of infectious disease. And at the same time the non inevitability fatalism is not an appropriate response to this knowledge.

And that's where Lizzie's work is really important. Showing the non automatic quality of infectious disease transmission. So the two of you have a role to play. Big role.

Brad: 01:13:33

He's put it all on our shoulders now. Well, well thank you both again. I appreciate the kind words and the closing sentiment there. So I would love to do it again.

Hopefully we'll have a chance, an occasion in the future to meet again and speak. So thank you very much.

Elizabeth: 01:13:50

Thank you so much Brad. And thank you John. It's been a privilege talking about this with you today.

Brad: 01:13:59

Once again, big, big thank you to both John and Elizabeth for taking the time to share their experience, their work, their stories. I really, really enjoyed this conversation. I hope you did too. Check the show notes for links to.

Brad: 01:14:11

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