Speaker 1: If you're a virus, you have this constant problem. There.
Speaker 1: You are successfully reproducing in some rabbit or some chicken,
Speaker 1: or let's say some person, and then one day the
Speaker 1: person's immune system gets wise starts attacking you, destroying you.
Speaker 1: You need to find a new host, and you need
Speaker 1: to do it fast. Viruses have evolved lots of strategies
Speaker 1: for solving this problem. Some of them fly out of
Speaker 1: people's mouths and noses and sneezes and coughs. Others ooze
Speaker 1: out in bodily fluids like blood and saliva, and some viruses,
Speaker 1: in a truly amazing twist of evolution, have enlisted mosquitoes.
Speaker 1: They're like these missiles that fly through the air, sucking
Speaker 1: virus out of one host and injecting it into another.
Speaker 1: Diseases like Zeka, West Nile, Japanese encephalitis, and yellow fever
Speaker 1: have killed millions of people over the course of human history,
Speaker 1: and they couldn't have done it without mosquitos. I'm Jacob Goldstein,
Speaker 1: and this is Incubation, a show about viruses. Today on
Speaker 1: the show, how mosquitoes learned to love people and how
Speaker 1: those mosquitoes and the viruses they carried changed human history.
Speaker 1: In the second half of today's show, we'll hear the
Speaker 1: story of how mosquitoes carrying yellow fever were enlisted as
Speaker 1: a kind of biological weapon and how they played a
Speaker 1: key role in shaping the history of the Western hemisphere. First, though,
Speaker 1: we're going to talk about how those particular mosquitoes, a
Speaker 1: species called eighties a gypty, came to love humans in
Speaker 1: the first place, and we'll also get a sense of
Speaker 1: what climate change and urbanization mean for the future of humans, mosquitoes,
Speaker 1: and mosquito born viruses. My guest for this part of
Speaker 1: the show is Noah Rose. He's an assistant professor in
Speaker 1: the Department of Ecology, Behavior and Evolution at the University
Speaker 1: of California, San Diego, and he is really really into mosquitoes.
Speaker 1: What's the most mosquito bites you ever had at one time?
Speaker 2: You Know what's kind of funny is in my old job,
Speaker 2: I would feed my own mosquitoes.
Speaker 1: When you say I would feed my own mosquitoes, what
Speaker 1: does that mean?
Speaker 2: Like I would stick my arm in a cage and
Speaker 2: they would bite me, and I always dress.
Speaker 1: You would fed them just like giving food to a dog,
Speaker 1: but instead of putting kimble on a plate. You'd put
Speaker 1: your arm in a box and your arm was not protected,
Speaker 1: they would just come and bite you so that they
Speaker 1: could live.
Speaker 2: That's exactly right. I was like, I'm gonna feed all
Speaker 2: my mosquitoes, and I'm just gonna like, I'm gonna like
Speaker 2: bite the bullet, and I'm gonna like know that I
Speaker 2: can just do this. The buck stops here. I can
Speaker 2: keep my mosquitos alive. And so I like went all in.
Speaker 2: I got I don't know, like tens of thousands of
Speaker 2: bites over a short period of time. And then I
Speaker 2: got to I got to my new job, and they're like, yeah,
Speaker 2: we don't really like let people do that here. We
Speaker 2: think it's gross and maybe bad.
Speaker 1: Fair enough, I guess fair enough. So, okay, if we
Speaker 1: go to the time when you're starting out studying mosquitoes
Speaker 1: as a postdoc, like, what are the big questions you're
Speaker 1: trying to figure out?
Speaker 2: Yeah, so, really, what we were trying to understand is
Speaker 2: what makes mosquitoes particularly good at spreading disease? Because there's
Speaker 2: lots of mosquitoes in the world, and not all of
Speaker 2: them are equally good at spreading disease. Actually, you know,
Speaker 2: of the over three thousand species that are out there,
Speaker 2: the vast majority are not really causing so many problems
Speaker 2: for people, but a few of them are really really
Speaker 2: good at spreading disease. Maybe the best example of that
Speaker 2: is eighties a gypty. Eighties agypty is like an amazing
Speaker 2: vector of viral diseases, in particular diseases like yellow fever,
Speaker 2: dangay zeka, chicken gunya. It's really good at spreading those
Speaker 2: diseases for a lot of reasons. But kind of high
Speaker 2: up on that list of reasons is it loves to
Speaker 2: live around and bite people. And if you want to
Speaker 2: spread disease, you know, from person to person, living around
Speaker 2: people biting people super super helpful.
Speaker 1: So just a sort of threshold question if you're looking
Speaker 1: at any of the thousands of species of mosquitoes, so
Speaker 1: obvious I wouldn't even think of it. Does it bite
Speaker 1: people a lot? Because if it doesn't, then for the
Speaker 1: most part, we're not going to be so worried about it.
Speaker 2: That is exactly right. Most of the species of mosquitoes,
Speaker 2: their life cycle, it just doesn't really involve people. It's
Speaker 2: not about us. It's you know, they're living in the forest,
Speaker 2: they're biting animals. They're breeding in some sort of natural
Speaker 2: standing water. They're just not spreading a ton of disease
Speaker 2: from person to person because they don't survive that well
Speaker 2: in human habitats. But a few mosquitoes are really, really
Speaker 2: good at that, and eighties Egypty is one of the best.
Speaker 2: And so the next question is how did it come
Speaker 2: to be that way? Because this mosquito wasn't always that way.
Speaker 2: It evolved from something, right, It evolved from an ancestral population,
Speaker 2: probably with a life cycle that did not involve living
Speaker 2: in a plastic bucket in near backyard and biting a human.
Speaker 1: And so to answer this question, you traveled to sub
Speaker 1: Saharan Africa right to study eighties agypty. What did you find?
Speaker 2: Yeah, so, basically, most populations of eighties of Gypty in
Speaker 2: its native range of sub Saharan Africa, they don't particularly
Speaker 2: love human hosts. They're willing to bite humans, but they
Speaker 2: actually they would like to bite a wide variety of
Speaker 2: vertebrate hosts, and humans are not their favorite of those.
Speaker 2: Humans are like, yeah, I'll take it if I have to,
Speaker 2: But they don't love how we smell.
Speaker 1: We're an acquired taste.
Speaker 2: We are a very acquired taste exactly. But a few
Speaker 2: populations are really really strongly specialized on human hosts and
Speaker 2: human habitats. They love how we smell. And those are
Speaker 2: populations living in this region called the Sahel. It's just
Speaker 2: south of the Sahara Desert, where for most of the
Speaker 2: year it's really hot, really dry, a terrible place to
Speaker 2: be a mosquito. You know, mosquitoes thrive on standing water,
Speaker 2: but for a couple months it's mosquito paradise. They have heavy,
Speaker 2: heavy rains, pools of water kind of everywhere, but that
Speaker 2: dry season is so hot and so long that it
Speaker 2: seems like the ancestral generalist form of the mosquito it
Speaker 2: just doesn't survive that well. There. Instead, we find these
Speaker 2: populations of eighties of gipty that are really tightly interconnected
Speaker 2: with settled human populations, right, So they're not breeding in
Speaker 2: their normal treeholes or rock pools. They're breeding in things
Speaker 2: like heavy clay vessels used to store water. It's an
Speaker 2: amazing habitat for a human specialist mosquito. And so we
Speaker 2: think that this is actually the original context that sort
Speaker 2: of drove eighties Egypty to specialize on humans.
Speaker 1: You observe this, and you're also doing essentially genomic analysis, right,
Speaker 1: You're trying to figure out kind of the history of
Speaker 1: how this came to be by studying the genetics of
Speaker 1: these different populations, and in particular the subpopulation that is
Speaker 1: like kind of a weird o mosquito, right, this weird
Speaker 1: oh mosquito that happens to love human dwellings, that happens
Speaker 1: to love these clay vessels where people store their water.
Speaker 2: That's exactly right. And so with the genetics, basically the
Speaker 2: question we're asking is like what is the genetic signature
Speaker 2: of this human specialist mosquito? And in particular, what we
Speaker 2: find is that there's a shared genetic basis in the
Speaker 2: Sahelian populations and the invasive populations that came to spread
Speaker 2: all over the whole world. Right, So we think that
Speaker 2: these populations in the Sahel are likely the origin of
Speaker 2: this human specialist form. But they didn't stay there. They
Speaker 2: spread everywhere across the global tropics, at least in urban areas,
Speaker 2: and they became this like total menace.
Speaker 1: Okay, so you are going off to sub Saharan Africa,
Speaker 1: so I get that you want to understand how eighties
Speaker 1: of gypsy evolved to love people and therefore spread disease.
Speaker 1: But what's the sort of smaller set of things you
Speaker 1: have to do to actually figure that out.
Speaker 2: Yeah, so there's a bunch of things, but the two
Speaker 2: main things are studying and quantifying their behavioral preference for humans.
Speaker 2: How much do the mosquitoes want to bite humans? And
Speaker 2: sequencing their genomes. That's the big thing. And the way
Speaker 2: we do that is using a device called a live
Speaker 2: host two port old factometer, which is a lot of
Speaker 2: very fancy words to say, a big plastic box with
Speaker 2: a lot of mosquitos on the inside and has two
Speaker 2: holes in the side.
Speaker 1: Old factometer, like measuring their smell or something. Is that
Speaker 1: what that is?
Speaker 2: Yeah, exactly, it's like measuring their smell. And basically they
Speaker 2: can choose to go in one of two traps. One
Speaker 2: leads to a human arm. One leads to non human animal,
Speaker 2: in many cases a literal guinea pig, because they have
Speaker 2: a nice temperament and they smell good to mosquitos.
Speaker 1: And what's the human arm? You got some undergrad sitting
Speaker 1: there all day for minimum wage or what.
Speaker 2: Usually it's me.
Speaker 1: It's your own arm sitting there to see what the mosquitoes.
Speaker 2: Like, yeah, it doesn't have to be me. And in fact,
Speaker 2: you know, we made sure that we got similar results
Speaker 2: with different people, because it would be awfully embarrassing to
Speaker 2: do a whole study of like what a mosquito's like
Speaker 2: and then have it be like, oh, no, it's just
Speaker 2: like it's just that they like just you.
Speaker 1: Yeah, So, how much time did you spend with your
Speaker 1: arm in the mosquito box?
Speaker 2: I mean, cumulative months of my life? It was it
Speaker 2: was a lot of sitting with my arm in the box. Yeah,
Speaker 2: it was you learn to type with.
Speaker 1: One hand or something. So would you listen to podcast?
Speaker 1: That's what you do?
Speaker 2: I mostly did audiobooks and just kind of zoning out.
Speaker 2: You know, it's it's I'm not gonna say it's meditative,
Speaker 2: but you know, it's it's there's something not so terrible
Speaker 2: about being like, I'm working while you're clearly just sitting
Speaker 2: in a chair. There's worse things in life.
Speaker 1: And are you getting bitten by the mosquitoes?
Speaker 2: Now there's like a piece of screen in the way,
Speaker 2: so they fly towards the arm or the guinea pig
Speaker 2: and they sort of accumulate up against the screen where
Speaker 2: they're like furiously you can see them. It's kind of
Speaker 2: it's kind of horrifying to see. They're like straining against
Speaker 2: the screen, pushing their body up against it and pushing
Speaker 2: their little prebosses through it.
Speaker 1: They want so badly to suck your blood.
Speaker 2: They really really, they're quite motivated, but they can't get
Speaker 2: to it.
Speaker 1: So so you've done this work this, you know, collecting
Speaker 1: the data, studying the sense of smell with your arm
Speaker 1: in the box, doing the genetic analysis, and in the
Speaker 1: end you publish a couple of papers that really kind
Speaker 1: of tell this thousands of years long story of how
Speaker 1: mosquitoes came to you know, bite people and more importantly,
Speaker 1: came to be this really important disease vector. So like,
Speaker 1: tell me that story. Start a long time ago.
Speaker 2: Go back thousands of years ago. There's eighties agypty mosquitos
Speaker 2: living in the forest, breeding in tree holes and rock
Speaker 2: pools and sort of opportunistically biting the first vertebrate hosts
Speaker 2: that they come across. So like, yep, over there, I
Speaker 2: see that little animal, I'm going to bite it great,
Speaker 2: and then they lay their eggs and you know, life
Speaker 2: cycle complete. It's like any one of those other three
Speaker 2: thousand mosquitos that were not that worried about. The Sahara
Speaker 2: Desert between about fifteen thousand to five thousand years ago,
Speaker 2: more or less, was not the desert we know it
Speaker 2: as today. It was sort of a grassland, the green
Speaker 2: Sahara people call it. And during that time, there were
Speaker 2: lots of sort of distributed human societies, like living as
Speaker 2: hunter gatherers. You can find rock carvings in the middle
Speaker 2: of the Sahara Desert in places where you know it's
Speaker 2: totally inhospitable, and they like depict these sort of idyllic
Speaker 2: scenes of like hunting big game on a rolling grassland.
Speaker 2: It's totally and a little bit strange. But what happened
Speaker 2: is that about five thousand years ago the Sahara Desert
Speaker 2: just dried up. That whole area dried up, and that
Speaker 2: changed a lot of things. But one of the most
Speaker 2: important things it did for humans was it drove people
Speaker 2: to kind of settle down and shift to these different
Speaker 2: ways of living. And in this hell you have the
Speaker 2: emergence of settled human societies on the edge of the
Speaker 2: Sahara Desert, storing water, farming things like millet. And when
Speaker 2: all that happens, that modern niche for human specialist mosquitos
Speaker 2: kind of emerged where you have this place that's otherwise
Speaker 2: inhospitable to mosquitoes, but there's an amazing ecological niche living
Speaker 2: with humans. And so it's the drying of the Sahara
Speaker 2: desert and the emergence of that human specialist niche that
Speaker 2: seems to have driven the evolution of the mosquito.
Speaker 1: So you have the humans presumably who were living their
Speaker 1: best life when it was a grassland hunting big game,
Speaker 1: and then it dries up, and the humans are adapting
Speaker 1: to this new environment conditions, you know, storing water, maybe
Speaker 1: farming in a way they didn't before, and kind of
Speaker 1: alongside them, you have the mosquito also adapting to survive.
Speaker 2: Yeah, yeah, exactly. It's a really interesting thing right where
Speaker 2: it's like the way that time works for humans and
Speaker 2: for mosquitoes is very different, right, Like mosquitos get like
Speaker 2: ten to fifteen generations a year a.
Speaker 1: Year, so like a month a mosquito, mosquito lives for
Speaker 1: like a month.
Speaker 2: They live for like a month exactly. And you know,
Speaker 2: the average generation time of a human is like twenty
Speaker 2: nine thirty years roughly, and so you know, for every
Speaker 2: human generation, you get about four hundred mosquito generations.
Speaker 1: H huh. So that's just that much more evolution, that
Speaker 1: much more genetic iteration exactly.
Speaker 2: So it's like the last ten thousand years of human
Speaker 2: history and cultural change is like, you know, equivalent for
Speaker 2: the mosquitoes to like the last four million years of
Speaker 2: human evolution. And when you think about like four million
Speaker 2: years of human evolution, it's like all the fun stuff, right,
Speaker 2: it's like everything that we care about. And so for
Speaker 2: these mosquitoes, all of their most interesting, like really interesting
Speaker 2: evolutionary changes they're taking place like over the time scale
Speaker 2: of human history, right, And so it's this really cool
Speaker 2: thing where we can simultaneously study how humans are sort
Speaker 2: of shaping the planet, how humans are changing the planet,
Speaker 2: and how that's changing mosquitoes.
Speaker 1: So we've been talking about the past, right, and your
Speaker 1: insights into how eighties egypty came to be this very
Speaker 1: important disease vector in the world. What does your work
Speaker 1: tell us about the future.
Speaker 2: Yeah, well, I mean this is a topic I'm really
Speaker 2: interested in, in particular because the story of eighties egypty
Speaker 2: it's not over. It's still playing out, right, we still
Speaker 2: have populations of eighties agypty that are not the amazing vector.
Speaker 2: In most of the native range, eighties e gypty is
Speaker 2: the generalist form, but that seems to be changing a
Speaker 2: lot of the fastest growing cities in the world. They're
Speaker 2: in sub Saharan Africa. There's places like Waga Doogu and Brikina, Faso,
Speaker 2: Kumasi and Ghana. And in those cities the mosquitos seem
Speaker 2: to be evolving a greater specialization on human hosts and habitats.
Speaker 1: Is this a future where disease transmission mosquito by mosquitos
Speaker 1: is going to get worse just because there's more density,
Speaker 1: more urbanization. Is that the story you're telling.
Speaker 2: I think there's good reasonably that that might be playing out,
Speaker 2: not just in the future, but even in the present day.
Speaker 2: For example, Wagga Doogo, Historically speaking, it was not thought
Speaker 2: to be a majorly problematic area for things like dangay fever,
Speaker 2: and in the last couple of years there have been
Speaker 2: these massive outbreaks of dang gay fever and waggadogo. And
Speaker 2: at the same time we can see in the genomes
Speaker 2: of the mosquitoes there that they're becoming more specialized on humans,
Speaker 2: they have more ancestry from that human specialist kind of
Speaker 2: gene pool. Right, the mosquitoes are changing like on contemporary
Speaker 2: time scales, Like the mosquitoes twenty years ago are different
Speaker 2: from the mosquitoes of today are different from the mosquitoes
Speaker 2: of twenty years from now. So it's not just like
Speaker 2: a hypothetical future thing. I think it's like a present
Speaker 2: day dynamic.
Speaker 1: So the initial wave of specialization thousands of years ago
Speaker 1: was triggered by environmental change, right by the drying out
Speaker 1: of the Sahara. In the modern context, is climate change
Speaker 1: relevant to this discussion.
Speaker 2: Yeah, that's a great question. It's one that I get
Speaker 2: all the time, and it's one that I'm very interested
Speaker 2: in understanding. It's hard to say for sure, because climate
Speaker 2: has really complex effects on mosquito born disease transmission. When
Speaker 2: it comes to some of the topics I've studied, Like
Speaker 2: so much of what we know about what seems to
Speaker 2: drive mosquitoes to specialize on humans, it's things like either
Speaker 2: urbanization or precipitation variation, but maybe not mean temperature per se.
Speaker 2: But there's indirect ways that I still think climate change
Speaker 2: might contribute to this. For example, climate change can very
Speaker 2: directly contribute to things like people moving very quickly into
Speaker 2: sort of informal settlements in rapidly growing urban areas, because
Speaker 2: it's just like the old way that people were living
Speaker 2: isn't working anymore.
Speaker 1: Right, So it seems like from what you're saying, urbanization
Speaker 1: is a much clearer driver than climate change of basically
Speaker 1: more mosquitoes and more mosquito spread disease.
Speaker 2: That's exactly right. Urbanization is so fast and so extreme
Speaker 2: and represents such a major change to the sort of
Speaker 2: ecosystem that these mosquitoes are living in.
Speaker 1: From like the mosquito pov urbanization domini, Yeah, exact.
Speaker 2: Yeah, if you're a mosquito sitting in a forest and
Speaker 2: the forest gets chopped down and replaced with a giant metropolis,
Speaker 2: that's a bigger change than an environmental change playing out
Speaker 2: more subtly over longer time scales.
Speaker 3: Yeah.
Speaker 4: So if you zoom out and think about what you knew,
Speaker 4: what your worldview was when you started studying mosquitoes, and
Speaker 4: what you know, and kind of the way you think
Speaker 4: about the world.
Speaker 1: Now, how do you think about the world differently.
Speaker 2: I mean, it's an interesting question because you know, the
Speaker 2: thing that got me interested in mosquitos was trying to
Speaker 2: understand how human are affecting our planet, right, like trying
Speaker 2: to understand how we're affecting the environment, how we're reshaping ecosystems.
Speaker 2: And you know, in those days, my main motivation was
Speaker 2: wanting to protect the biodiversity, wanting to protect ecosystems, which
Speaker 2: I still care a lot about. One thing that changes
Speaker 2: just you know, like I sort of realized not everything
Speaker 2: is like about us either like helping or heard things like,
Speaker 2: you know, mosquitos are evolving really quickly to exploit us,
Speaker 2: to make us sick. It's kind of amazing to me
Speaker 2: that mosquitos could do something like evolved to be better
Speaker 2: at taking advantage of us on the same kind of
Speaker 2: timescale that we're talking about, like oh, we're degrading ecosystems,
Speaker 2: or we're removing habitat for charismatic megafauna that we care
Speaker 2: about or things like that, like nature. Also nature is responding.
Speaker 1: So it's like it's like before it was like, oh,
Speaker 1: nature is a victim, and now it's like, yo, mosquitoes
Speaker 1: are kind of kicking ass.
Speaker 2: Yeah, they're really really good at what they do, and like,
Speaker 2: you know, we change the whole way that the place
Speaker 2: they live looks, and they're like, I can do this too.
Speaker 2: I can totally live here, and I can totally bite
Speaker 2: the organisms that live here. They make it work.
Speaker 1: Thanks to my guest Noah Rose, now as an assistant
Speaker 1: professor in the Department of Ecology, Behavior and Evolution at
Speaker 1: the University of California at San Diego. After the break,
Speaker 1: mosquitoes become a biological weapon. Eighties of gypty first came
Speaker 1: to the New World on European slave ships, and along
Speaker 1: with the mosquito came a new disease, a disease that
Speaker 1: until that point had not existed in the Americas, yellow fever.
Speaker 1: John McNeil is a professor of history at Georgetown and
Speaker 1: the author of a book called Mosquito Empires. In the book,
Speaker 1: John makes the case that yellow fever and the mosquitoes
Speaker 1: that transmitted it had a profound effect on the fight
Speaker 1: among European powers to control the Western Hemisphere. Tell me
Speaker 1: about yellow fever historically, going back a couple hundred years,
Speaker 1: so in the seventeen hundreds. What happens in the absence
Speaker 1: of modern medicine if you get yellow fever.
Speaker 5: That all depends on where you were born and raised,
Speaker 5: and what age you are. Children often show no symptoms,
Speaker 5: don't know that they're sick, survive it, and in the
Speaker 5: process acquire lifelong immunity. The worst thing to be is
Speaker 5: in the prime of your life and encountering yellow fever
Speaker 5: for the first time.
Speaker 1: This is going to be very important for our story today.
Speaker 1: What happens if you were in the prime of your
Speaker 1: life and you get yellow fever and you have never
Speaker 1: had it before.
Speaker 5: Odds are you get a high fever and jaundice, that
Speaker 5: is a sure white person in your skin begins to
Speaker 5: turn yellow, and after several days, either you get better
Speaker 5: you're among the lucky ones and immune for life, or
Speaker 5: after a brief respite, you get sicker and you begin
Speaker 5: to vomit up partially coagulated blood with the consistency and
Speaker 5: coloring of coffee grounds. And when that happens, not only
Speaker 5: are your day's numbered, your hours are numbered.
Speaker 1: So there's this one particular moment that you talk about
Speaker 1: in the book where yellow fever plays a central role
Speaker 1: in world history, and that moment is the Battle of Cartagena,
Speaker 1: which took place in modern day Columbia. It happened in
Speaker 1: seventeen forty one. And at this point, right, the Spanish
Speaker 1: control a lot of South America, the British control a
Speaker 1: lot of North America. And then this battle happens when
Speaker 1: the British launched this huge attack against the Spanish in Cartagena.
Speaker 1: So tell me about the battle. Why was this battle
Speaker 1: so important?
Speaker 5: Cartagena was one of the two or three lynchpins of
Speaker 5: Spanish colonial defense. It was also central to the trading
Speaker 5: system of Spanish America, and that included the annual exports
Speaker 5: of silver from mines in the Andes. Everybody who wanted
Speaker 5: to take Spanish America away from the Spanish, what they
Speaker 5: most wanted was silver.
Speaker 1: So was the notion that if a Britain conquered Cartagena,
Speaker 1: they could, like you know, to some degree, conquer the
Speaker 1: Spanish in South America, make Spanish colonies British colonies.
Speaker 5: Yes, that would be the first step. So back in
Speaker 5: London they sent huge reinforcements. They had a twenty nine
Speaker 5: thousand men between soldiers and sailors, and that was probably
Speaker 5: the largest amphibious military expedition in world history up to
Speaker 5: that time.
Speaker 1: So the British are bringing twenty nine thousand men How
Speaker 1: many men do the Spanish have to defend Cartagena?
Speaker 5: Approximately four thousand, seven hundred, so they're out manned what
Speaker 5: six six to one approximately?
Speaker 1: Yes? What are Spain's defenses like in Cartagena?
Speaker 5: The most important thing they had was massive stone fortifications, okay,
Speaker 5: and the significance of that, which the Spaniards well understood
Speaker 5: by seventeen forty, was that the massive fortifications would require
Speaker 5: any attacking force to lay siege to the city, to
Speaker 5: try to bring artillery within range, bash down the walls,
Speaker 5: permit an assault, and that would take weeks.
Speaker 1: So the fortifications wouldn't necessarily prevent an attack, but they
Speaker 1: would slow it down. Why is that important? Why is
Speaker 1: it important that it would take weeks for the British
Speaker 1: to get through the fortifications.
Speaker 5: It's of central importance. The reason is because in the
Speaker 5: course of those weeks, the attacking force would be bitten
Speaker 5: by the local mosquitoes, would acquire the yellow fever virus,
Speaker 5: and the men in question young men in the prime
Speaker 5: of their lives. Born and raised in places such as
Speaker 5: the British Isles. These were people who had no prior
Speaker 5: experience of yellow fever, so they are maximally susceptible and
Speaker 5: within six weeks. The Spanish tended to think the climate,
Speaker 5: which really means yellow fever, would wreak havoc upon the
Speaker 5: attackers and force them to call off their siege.
Speaker 1: So the Spanish are using this, this virus yellow fever
Speaker 1: as like a core part of their military strategy, because
Speaker 1: they know that their own forces are made up of
Speaker 1: people who have immunity. Right, they've grown up locally, they've
Speaker 1: had the disease, whereas that is not true for the attackers.
Speaker 1: For the British.
Speaker 5: Correct they didn't understand yellow fever's mode of transmission, but
Speaker 5: they knew it was extremely deadly to people are fresh
Speaker 5: off the boat from Europe.
Speaker 1: It's almost like a kind of early form of biological warfare.
Speaker 5: Yes, in effect, it was biological warfare.
Speaker 1: Okay, so this is the Spaniard's idea. The British arrive
Speaker 1: with their dozens of ships and their tens of thousands
Speaker 1: of men. What happens?
Speaker 5: So the British prosecuted a siege, tried to move man
Speaker 5: and artillery across the difficult and damp terrain close by
Speaker 5: to Cartagena. Progress was slow. People started to get sick
Speaker 5: within days of disembarking from their ships.
Speaker 1: You mentioned that the British soldiers who had landed at
Speaker 1: Cartagena and were laying siege to the city didn't have tents,
Speaker 1: so they were just lying on the ground, getting bit
Speaker 1: by mosquitoes and getting yellow fever. Yes, why what happened?
Speaker 1: Why didn't they have tents? Like tents had been invented?
Speaker 5: Tents had been invented. There are two things to bear
Speaker 5: in mind here. One is the difficulty of outfitting a gigantic,
Speaker 5: amphibious military expedition on schedule in the eighteenth century is
Speaker 5: not all that easy in the twenty first century. Second
Speaker 5: one is that nobody knew how yellow fever was transmitted.
Speaker 5: Being bitten by mosquitoes did not automatically seem to anyone
Speaker 5: at the time to carry any particular risk.
Speaker 1: A right, like they just thought it was like my
Speaker 1: asthma or something. So what ends up happening in the battle?
Speaker 1: How does it end?
Speaker 5: The admiral got frustrated with the army commander with slow progress,
Speaker 5: and before long they were losing hundreds of men daily
Speaker 5: to yellow fever, and after thirty three days and a
Speaker 5: premature attempt to storm the fortifications, the British withdrew and
Speaker 5: the Spanish defenders were triumphant. They became great heroes in
Speaker 5: Spanish military history. But what they did was not lose
Speaker 5: before yellow fever forced their enemies to withdraw.
Speaker 1: Yeah, it's like the virus with the real conqueror. For Spain, the.
Speaker 5: Virus killed probably twenty men for every one killed in
Speaker 5: combat in this particular encounter.
Speaker 1: Wow. And then you say that the same dynamic plays
Speaker 1: out once the fighting in the Caribbean and South America
Speaker 1: shifts from being one colonial power against another two being
Speaker 1: wars of independence.
Speaker 5: Yes, and the large scale wars for independence in the
Speaker 5: Caribbean really begin with the Haitian Revolution in seventeen ninety one,
Speaker 5: and there British forces and then French forces tried to
Speaker 5: prevent a slave uprising, and those British and French forces
Speaker 5: suffered extreme disease mortality, and they both went after the
Speaker 5: other gave up and Haiti won its independence. I think
Speaker 5: it is in some ways analogous to the way that
Speaker 5: Spanish colonial authorities used their understanding of the disease climate
Speaker 5: to military advantage in places like Cartagena. And the reason
Speaker 5: for that is their own armies were composed of men
Speaker 5: who had either grown up in the Caribbean amid yellow fear, malaria, denge,
Speaker 5: and other infections, or had grown up in Africa and
Speaker 5: similarly had encountered these diseases and were either immune or resistant,
Speaker 5: Whereas the forces sent out to quell the Haitian Revolution
Speaker 5: were recruited from the British Isles, North America, France, in short,
Speaker 5: people who had virtually no immunity or resistance against yellow
Speaker 5: fever and malaria.
Speaker 1: How should this story about yellow fever and colonial warfare
Speaker 1: in the Caribbean, How should that change the way I
Speaker 1: think about history?
Speaker 5: We should understand that until the twentieth century, the great
Speaker 5: majority of death and dying in military campaigns was not
Speaker 5: a result of combat. It was a result of various diseases.
Speaker 5: And there were certain times in places, including the Caribbean
Speaker 5: and the seventeenth, eighteenth, and nineteenth century, in which those
Speaker 5: diseases were you could say partisan, that is, they systematically
Speaker 5: favored one side over another and powerfully influenced the results.
Speaker 1: So it wasn't until the twentieth century, after thousands of
Speaker 1: years of war, that most people who died in war
Speaker 1: died from injuries inflicted by the enemy rather than died
Speaker 1: from infectious disease.
Speaker 5: Yes, and that entails a gigantic and brutal irony. The
Speaker 5: mass slaughter for which the First World War is justifiably
Speaker 5: famous was possible only because military medicine had become sufficiently
Speaker 5: effective that large armies of millions of men could be
Speaker 5: kept alive long enough to butcher one another. Prior to that,
Speaker 5: it was impossible to maintain gigantic armies for any length
Speaker 5: of time because they would get too sick.
Speaker 2: But by the.
Speaker 5: Twentieth century that constraint was relaxed, and mass armies could
Speaker 5: last long enough to kill one another. That's a horrible irony.
Speaker 3: So if we think about this history we've been talking about,
Speaker 3: and then we think about the modern world, where obviously
Speaker 3: we have lots more treatments, medicine is just better now
Speaker 3: than it was then, what lessons does this story hold
Speaker 3: for the dynamics of the modern nace?
Speaker 1: What does it teach us about the way the world
Speaker 1: works today?
Speaker 5: It should help us recognize the fragility of what we
Speaker 5: might consider the Golden Age of health, an era ushered
Speaker 5: in by public health systems, by urban sanitation, by vaccination
Speaker 5: regimes which protect a significant proportion of the entire human
Speaker 5: population from the ravages of infectious disease, and that is
Speaker 5: a comparatively new phenomenon and it is not to be
Speaker 5: taken for granted.
Speaker 1: Thank you so much for your time. It was great
Speaker 1: to talk with you, Jacob.
Speaker 5: Thank you very much. Thanks for inviting me on the show.
Speaker 1: John McNeil's a professor of history at Georgetown and author
Speaker 1: of the book Mosquito Empires. Thanks to both my guests today,
Speaker 1: Noah Rose and John McNeil. Next week on the show,
Speaker 1: Ken Measle's Cure Cancer, A very weird good thing was
Speaker 1: going on. Incubation is a co production of Pushkin Industries
Speaker 1: and Ruby Studio at iHeartMedia. It's produced by Kate Ferby
Speaker 1: and Brittany Cronin. The show is edited by Lacey Roberts.
Speaker 1: It's mastered by Sarah Bruguire, fact checking by Joseph friedman Or.
Speaker 1: Executive producers are Lacy Roberts and Matt Romono. I'm Jacob Goldstein.
Speaker 1: Thanks for listening.