Six years ago, science writer Sonia Shah began work on a book that would explain how the next pandemic might originate: It would start as a pathogen found only in animals, adapt to humans through close contact, and spread rapidly thanks to urbanization and modern travel. Since then, the Ebola virus has ravaged the West African nations of Guinea, Liberia, and Sierra Leone. The chikungunya virus established itself in the Americas for the first time. And on February 1, 2016, within weeks of Shah publishing her book, the World Health Organization (WHO) declared the Zika virus a global health emergency. All three followed the same animal-to-human pattern, aided by fast and easy transportation.

If Shah sounds prescient, it’s at least in part because she’s a student of history. Her new book, Pandemic: tracking contagions, from cholera to Ebola and beyond, takes cholera as its central simile. The microscopic bacteria that causes that disease floated benignly in the coastal waters of the Bay of Bengal, attached to tiny crustaceans, until British-driven settlement of wetlands allowed it to adapt to humans. Cholera caused its first pandemic in Bengal in 1817, killing 10,000 people. Ocean travel got it to Paris by 1832. The world’s seventh cholera pandemic, ongoing right now in Haiti, got an assist from airplanes. Some 770,000 Haitians have been stricken and more than 9,200 killed by the disease since 2010. (“Pandemic” is usually defined as a disease outbreak afflicting a whole country, region, or the world—or, in Shah’s words, “an epidemic gone global.”)

The Zika virus, meanwhile, rarely kills its victims, but is strongly linked to birth defects and an increase in the rare Guillain-Barré syndrome, which can cause paralysis. In March, the World Health Organization forecast that as a result of Zika, Brazil would see about 2,500 babies born with microcephaly, which is characterized by brain damage and abnormally small heads. Zika wasn’t seen in the Americas until 2015, when Brazil confirmed its first transmission. Now it has appeared in many parts of Central and South America, and Puerto Rico is bracing for an epidemic.

Shah is the author of three previous books, including The Fever, an acclaimed history of malaria, and The Body Hunters, about pharmaceutical testing on poor patients. In this wide-ranging interview, Shah talked to Bulletin columns editor Elisabeth Eaves about Zika, the role of human behavior in spreading novel pathogens, and how to prevent the next pandemic—which, she suggests, will require a very different approach than the one we rely on now. Today, she says, we need a new sanitary movement, like the campaign for public health that arose to combat disease in the 19th century. Shah also shares her views on two of the world’s most powerful health institutions, the World Health Organization and the Gates Foundation.

BAS: Your new book, which warns that we’re going to see novel pathogens cause pandemics, came out within weeks of the World Health Organization declaring Zika an international public health emergency.

SHAH: Zika virus is a great example of what’s been going on since I started writing the book six years ago, and why I wrote it to begin with. We’ve had over 300 of these infectious pathogens either newly emerge or re-emerge into new places. Zika is really just the latest in a long string—Ebola in West Africa, novel types of avian influenza, tick-borne diseases, mosquito-borne diseases. All of this stuff has been happening because of changes in the way we live. And Zika is taking advantage of the changes, just as the other ones have.

BAS: You use cholera as your central point of comparison. How does that disease help us understand today’s emerging pathogens? Why did you choose it?

SHAH: To try to understand how a microbe turns into this very deadly, destructive social phenomenon—pandemic—I wanted to look at the history of pandemics and see how it could shed light on new pathogens that are emerging. Not that many microbes have actually been able to cause pandemics in modern history. There have probably been about five. Among those, cholera really stood alone for me because it’s one of the most successful in terms of causing pandemics. It hasn’t just caused one or two. It’s actually caused seven pandemics, and the seventh is going on right now just a few hundred miles off the coast of Florida, in Haiti. Cholera is also extremely deadly. It kills half the people who get it unless they’re rapidly treated. And it’s been well-documented from the beginning, because cholera first emerged in 1817. So we have a really good history of how this thing came out and plagued the world over and over.

BAS: Many of these novel pathogens first emerge in animals and then jump to humans through human-animal contact. Can you explain why and when that jump occurs? Why is it that a pathogen might not adapt to humans for a long time, and then suddenly does?

SHAH: It’s just like any living organism in a new environment: There are going to be new challenges, and most of the time it’s not going to survive. And of course our bodies are designed to repel such intrusions with our immune system, so most new microbes that invade our bodies are going to be neutralized. But that means there’s a lot of pressure on those microbes to change. If they can change in ways that allow them to get around the immune system, they get this huge prize, which is all of the cells and tissues in our bodies.

We see a lot of these pathogens come from species that are closely related to us because the pathogens don’t have as far to go to adapt to our bodies. A lot of our major pathogens—malaria, HIV, probably Zika virus—come from other primates. We also see a lot of pathogens come from livestock that we domesticated a long time ago, like cows and sheep. What’s happening now, though, is a little bit different, because we are invading wildlife habitat, disrupting it, and shrinking it all over the world. We’re living in an age of extinction because human activity is impinging on so many wildlife habitats, but the animals that are able to survive come into close contact with humans. Bats are a great example—we’re getting a lot of these diseases from bats right now. Ebola is from bats. Nipah virus is from bats. Marburg virus is from bats. SARS is probably from bats. And it’s partly because they’re mammals like us. On top of that, they can fly, so they can spread things around. And on top of that, we’re destroying so much bat habitat because of deforestation.

Bats are highly adaptable, so they’re able to survive even in close contact with humans. They come and live in your suburban backyard, your garden, your farm. All it takes is being exposed to, say, the saliva of a bat or excretion from a bat. That happens pretty easily because fruit bats, in particular, spit all over their fruit before they eat it. They pierce a fruit, cover it with saliva, and drop it down after sucking out all the juice. The ground below fruit trees where bats live are littered with these saliva-covered half-eaten fruits. Having lived with a mango tree in Australia, I can attest to this. The entire garden was full of bat-saliva-covered fruit. If you have little kids, they’ll go pick it up, touch it, then put their hands in their mouths. And that’s it—you’ve created a bridge for these microbes to pass into the human body.

These microbes can replicate really fast, and they’re messy in their replication. So just by chance, one will arise that will survive in this new environment, the human body. And that’s how it happens. That’s also why it doesn’t happen all the time. There’s a series of unlikely events that all have to line up perfectly for this to happen. So pandemics are actually really unlikely events, because if you think about all the microbes out there with the biological capacity to potentially cause a pandemic or an epidemic, that’s a huge number, but in fact, pandemics have only happened a handful of times in the past few centuries.

BAS: So repeated human-animal contact increases the odds.

SHAH: That’s right. With more and more contact, the probability rises. That’s not to say it always takes a long time, because it’s probability, right? It could happen right away, but chances are it’s going to take a lot of exposures for these microbes to adapt to the human body.

BAS: Pandemics have both biological causes and human-behavior causes. What are the current most potent human behavioral causes?

SHAH: There are a bunch of them that have to line up. The way we invade and disrupt wildlife habitat allowed Zika to cross over into our body, but then we also have to provide a virus with amplification opportunities so that it can get good at transmitting between people and fuel a global epidemic. That is happening mostly in crowded places around the world—slums and cities with a lot of ad hoc development, and factory farms where lots of animals are crowded together closely, which is kind of the animal equivalent of slums. These are places where human pathogens can gather steam to cause pandemics.

We saw this with Ebola, for example. We’ve had Ebola outbreaks since the 1970s, but for a long time, they never infected any place that had more than a few hundred thousand inhabitants. Now, we’ve had massive urban expansion, especially in tropical areas. So in 2013, when Ebola emerged in West Africa, within a few weeks of emerging in a pretty remote part of Guinea, it had reached three cities with a combined population of about three million. And that’s very important to why it was such a huge conflagration and spread to other countries.

The same thing with Zika. We’ve had Zika virus since at least the 1940s, possibly before that, but it never caused a major epidemic. It was carried by a forest mosquito that mostly bit animals, not people. Then it hitched a ride on an airplane, probably from French Polynesia into Brazil. And there it found these huge susceptible populations in these massively expanding cities. And it’s being carried by a mosquito that thrives in exactly those conditions, a mosquito that thrives in human settlements and only bites people and has dramatically expanded its range because of urban expansion in the tropics.

So it comes down to urbanization, invasion of wildlife habitat, and that great ability to carry these things around really rapidly. In the past, a highly virulent pathogen couldn’t travel that far because its carriers would get sick or die. What we’re seeing now is that the people, animals, or insects carrying these things can travel really far, really fast. Even if they are highly virulent, they can actually get around the world because we have airplanes. If something occurs in one part of the world, it’s going to very rapidly be carried around the globe.

BAS: Now that Zika is upon us, how should the world be responding?

SHAH: There were so many missed opportunities to prevent the Zika pandemic from happening. Now that we’ve already missed them, what do we do?

Our typical response to epidemics is to wait until they happen, wait until a bunch of people get sick, then say, oh my gosh, we need drugs and vaccines right away. This is part of our reliance on the biomedical establishment. For many decades, we decided that infectious diseases were not a threat anymore. We conquered them with antibiotics, and we had this evidence-based medicine that could very rapidly come up with drugs and vaccines, so we didn’t really have to worry about it. The thinking was that it was okay if some new infections emerged, because we would just stamp them out.

That is still our attitude today. And we have the Zika virus now, affecting a lot of people, endangering babies, and we’re waiting for the biomedical establishment to hurry up and create tools that are going to kill it. But the best-case scenario is we’ll have a vaccine in maybe three to 10 years. By then, millions of people are going to be infected. So right now, our best defense is our own immunity. The vast majority of people who get Zika virus are going to survive. The people who are really most at risk are women of childbearing age and pregnant women. So how do you protect them?

You give them access to contraception. Half of all pregnancies in the United States are unplanned, and it’s even worse in Latin America where the Catholic Church has been so prohibitive towards contraception. If we give women good access to contraception and access to abortion if they need it, we can minimize the damage that this virus can cause in the next generation. But we can’t wait for a vaccine. That’s going to take too long. The Zika virus is going to wash over all of the susceptible populations well before we get a vaccine. The vaccine is for the next Zika pandemic, not this one.

BAS: Does controlling mosquitoes help, or is that too little, too late?

SHAH: Mosquito control is a very blunt instrument. It kills all mosquitos, but Zika is only carried by one genus of mosquito, and only by females because those are the only ones who bite people. On top of that, in order for a mosquito to infect a person, it has to first take a blood meal from an infected person, then survive another week, because that’s how long it takes for the virus to get back up into its salivary glands. So the only mosquitoes you really have to kill are old females.

You could kill all the mosquitoes in a whole population in order to target a very, very small subset of disease-carrying individual insects. But there’s no real evidence that simply depressing the overall population will work. How much do you have to depress a whole population to get to those particular mosquitoes? It could be 80 percent. It could be 99 percent. And our best control methods never get to 100 percent, ever. And if you reduce the mosquito population by 60, 70, 80 percent for a week, is that going to be long enough?

I don’t know, but the evidence from all the mosquito spraying they’ve done to try to stop dengue fever is that it hasn’t actually worked to diminish transmission. I really question the whole idea of trying to attack the mosquito population. You do have to protect people from getting bitten, but that’s different.

BAS: What policies—local, national, global—do we need to prevent a pandemic from wreaking havoc?

SHAH: We need a new sanitary movement. In the 19th century we had repeated epidemics of cholera, yellow fever, tuberculosis, and all kinds of things. There were entrenched private interests that didn’t want to do anything about it. But people said we need to clean up the water, manage our waste better, have housing with screens, and all these things to protect our health, and a social movement grew out of that—the sanitary movement. That’s what ushered in all of those changes that prevent epidemics to this day. Except in Flint, we have clean water. We have good sanitation, we have electricity, we have decent housing that keeps mosquitoes from coming inside. Not to say that everyone does, but most of us do.

Those are all the result of government policies that were put into place to protect public health, and they still work to this day. So how do we build on that to protect us from this new threat? There are many ways, but it’s going to take political will. It’s going to take our government and public health leaders standing up to entrenched special interests. And they’re not going to want to do it. It’s going to take controlling trade, to some extent, controlling shipping, addressing poverty, addressing slums, addressing all of these things that make us vulnerable to epidemics. That’s major social action, and the big missing piece is public pressure. There’s no public pressure to do any of these things because the public just thinks, let the doctors deal with it, they’ll come up with a drug, they’ll come up with a vaccine. But that’s not going to be good enough anymore. We can’t do that fast enough.

BAS: How confident are you that we will be able to do those things given how contentious science, health care, and the role of the federal government are in American politics?

SHAH: If people understood how these diseases have been emerging—if people understood the risk better—I think things would change. Look at the dengue outbreak in Florida in 2009, which was precipitated in part by the foreclosure crisis in 2008 which allowed all these homes to be abandoned and so many swimming pools to be ignored while they filled up with water and became giant mosquito hatcheries.

If the people in that community had known that it was a public health risk to have these empty swimming pools, they might have said, “we need to protect our community.” We do that with other things. There are communities that stand up to toxic waste dumps being sited near them because they know it’s a public health risk, but we don’t have that understanding about the risk of a mosquito habitat being formed.

You have neglected neighborhoods in the middle of cities—in, say, Houston and parts of Florida—where there is sporadic garbage collection, and when it rains, bins fill up with standing water and mosquitoes hatch out. Then you’re going to have outbreaks of West Nile virus and dengue and probably Zika when it comes. These are all things that we could become more aware of and think of as public health risks and be involved in. I just don’t think we’ve gotten that public awareness yet. We’ve been so passive because we have this great faith in our biomedical establishment to come up with drugs and pills.

BAS: You talk in your book about the possibility of a global disease surveillance system. Supposing we had a good one to catch emerging diseases, what should that system be looking for and where?

SHAH: Since we know the main drivers for new pathogens, we can predict where they’re most likely to occur. So we need experts to come up with hot spot maps, showing places where there’s a lot of invasion of wildlife habitat, a lot of slums, a lot of intensive livestock agriculture, or some combination of all those things. In those places, you could do active surveillance for microbes. We have the technology to do that now. It’s only just recently that we can even detect microbes in their natural environment. Before, we were only seeing a tiny fraction of the ones that are actually out there. Now we see that they’re everywhere, and we can pick up their genetic fingerprints from a desk, a toilet seat, or soil in the garden. We weren’t able to do that until quite recently.

It’s like our eyes are finally being opened to see the microbial world for what it is. And that means we can track it, too. We can actively surveil places where microbes are exploiting the habitat. You can also track how they might be changing in ways that might allow them to infect people or spread rapidly among them. If we had a system to do that in a coherent way, looking at international hotspots, you could even develop a forecasting system.

Timing is everything with these things, because they erupt and spread exponentially. So even if it’s just a matter of months or weeks or days, advance notice can make a huge difference in the toll these outbreaks take.

BAS: So we have the technology for such a surveillance system, but we don’t have a system at the moment?

SHAH: There are certain initiatives to try to encourage groups to do surveillance, and some NGOs doing that kind of work, but we don’t have a coherent international system. We don’t really have a coherent international system for anything.

BAS: That’s for sure. Moving on, how is climate change linked to the spread of the kind of novel pathogens that lead to pandemics?

SHAH: In a lot of epidemics there’s a climate change aspect, because a lot of pathogens are dependent on climatic conditions. The other part of it is, you can’t really predict how climate change will affect human pathogens. For example, a lot of precipitation could create a lot of standing water and puddles where mosquitoes can breed, and lead to more mosquito-borne disease. But a lot of precipitation also could wash away mosquito eggs and lead to a decline in mosquito-borne disease. There’s no easy correlation between climatic changes and whether a disease is going to get worse or decline.

But the main thing is that climate change creates new opportunities. Diseases can spread into new landscapes and populations because climatic conditions make it possible. That means you’re going to have more disease because people will have less immunity. When diseases stay in one place, people gain some immunity to it and the overall level of disease goes down. When diseases are able to spread into new places, that’s when you see people getting sick and dying in greater numbers. Just by changing the landscape of where new diseases go, climate change is likely to cause more disease overall.

BAS: Your book talks about the cholera riots of the nineteenth century and how even in contemporary times communities turn on scapegoats in times of disease. How can our behavioral reactions to disease in and of themselves be dangerous?

SHAH: We’ve seen that again and again: When new pathogens emerge and people don’t know where they came from, people tend to blame their favorite scapegoats. In the 1830s, Irish immigrants were blamed for cholera, in 1840, Muslims were blamed for cholera, and in the 1890s, Eastern Europeans were blamed for cholera. We see this today as well. During the Ebola outbreak, healthcare workers were actually blamed for bringing Ebola, and in some case were violently assaulted and even murdered. In Haiti, UN troops, government actors, and even the Red Cross and Doctors Without Borders were blamed for bringing cholera. [A UN soldier may, in fact, have brought the first cholera case to Haiti.]

The new pathogens, even if they don’t cause a lot of death and sickness, exert a destabilizing force throughout society, especially when there’s already mistrust between different parties.

BAS: What role do antibiotics have to play in combating emerging pathogens? Are they up to the job?

SHAH: We’ve known since the 1920s that if you use antibiotics in ways that are not medically necessary, you will encourage the emergence of bacteria that can resist antibiotics. But in the United States, 80 percent of antibiotics are used for non-medical purposes. They’re used for commercial purposes in livestock agriculture. So we’ve had a steady increase in antibiotic-resistant bacteria. Just recently we’ve seen the evolution of the MCR-1 gene plasmid, which is like a piece of genetic material that can move between different bacterial species. This was found in pigs in China, and it allows bacteria to resist our very last-resort antibiotic—a drug called colistin—that is reserved for use in the most drug-resistant bacterial infections. We don’t use colistin much in human medicine.

But in China, tens of thousands of pounds of colistin are used every year in livestock agriculture, and so now we have this new plasmid that can move into new species where it could cause absolutely untreatable bacterial infections. That means that simple things—a minor injury or common infection—could become deadly events. That also would change the face of modern medicine. You wouldn’t do routine things like knee replacement surgery, for example. Unless it were a question of life or death, having a routine procedure wouldn’t be worth the risk of getting an untreatable deadly infection. Many medical procedures would just become obsolete.

That said, there’s a way out of this problem. We know that if you use antibiotics rationally—only for medical purposes—you can steward them for a lot longer, and you don’t have as much of a problem with resistant bacteria. It’s really about the timeline, because it takes time to develop new antibiotics. Right now there’s not enough market incentive, so 15 of the 18 biggest drug companies in the world have dropped out of the business of developing antibiotics altogether because it’s not lucrative. These are drugs that people don’t want to spend more than $200 for, even though they save your life. We only take them for a week. Compare that to an arthritis drug that you have to take every day for decades. Companies can make maybe $50 million a year from an antibiotic, compared to $1 billion a year for a drug that treats erectile dysfunction, arthritis, hypertension, or high cholesterol—any of those conditions that are chronic. So you have massive market failure.

And, even if we create new antibiotics faster—which we do need to do—we also have to steward each of those new drugs for longer, which will take changing the way we use them.

BAS: Like stop giving them to animals?

SHAH: Stop giving them to animals. Antibiotics are given to animals to get them to grow faster, and they are designed not to easily biodegrade. That’s the whole point of a drug—it’s not supposed to be metabolized and disappear. Then, we have no system for managing livestock waste. We have unlined open cesspools that have spilled out into the greater environment, into the water, into the soil. That’s where all of our microbes are, too. We’re just constantly exposing the whole microbial world into a wash of antibiotics because of this.

BAS: In your book you observe that the World Health Organization has become weaker in recent years. Why has that happened? Why is it a problem?

SHAH: The WHO used to take on pretty powerful private interests. It took on a big campaign against smoking, which was in direct conflict with the tobacco industry, and it took on infant formula marketing. It went up against Nestle and other major companies marketing infant formula, which is very dangerous in places where the drinking water is unsafe. This was back in the 1970s and early 1980s. And then the WHO became perceived by major donors to the UN system as too political, and so it has been slowly defunded. To make up the shortfall, the WHO started accepting private contributions, and those now make up a majority of its budget. But the contributions don’t just replace the old money, they come with strings attached, so private donors are able to buy control of what the WHO does.

So the majority of the WHO budget is under the control of the donors who earmark the money for certain kinds of campaigns and projects. They’re not going to earmark it for projects that undermine their interest, right? We already see a distortion in the WHO budget. The money that the WHO controls goes to the diseases that cause the most burden in the world, but the money they get from these private donations are allocated in a much more uneven fashion. Ninety-one percent of those [private-donation] funds are dedicated to diseases that cause about eight percent of the global burden of disease. It’s really not targeting the major public health problems.

And the WHO is now doing a lot of these “public-private alliances,” which are basically what we used to call industry influence on the public sector. We have Coca-Cola and fast-food companies helping the WHO pass recommendations on how to diminish obesity and heart disease and all these things that their products directly contribute to. The WHO’s guidance becomes very much contaminated by these industry interests, so instead of saying eat fewer packaged foods, they’re saying exercise more. And that’s happening across the board. Some of the most effective public health interventions are falling by the wayside because they don’t intersect with industry interests.

BAS: You observed that the Gates Foundation has become the world’s third biggest financier of global health research after the US and UK governments, but you’re uncomfortable with that picture.

SHAH: I think the Gates Foundation is doing great work—they’re doing important work that nobody else is doing. It’s good that they’re doing it, but the fact is, the Foundation is now really calling the shots. It is in charge of the public health agenda, and yet there’s no accountability. Right now we like what the Gates Foundation is doing, but what if in five years, things change there? There are, like, five people in charge of it, so it could change. And if it does change, we have no mechanism for demanding accountability. The Gates Foundation is a private entity. It can do whatever it wants, so we just have to hope that what it wants is good for all of us. We’re really just relying on its good intentions. Maybe that will work, but maybe it won’t.

We know, in larger society, that the whole reason we have political accountability is because even though we might trust our politicians today, we want assurances that we can always trust them. And that if we don’t trust them, we can switch them out for new ones. But we don’t have any of those accountability mechanisms with private entities. That’s why, in my opinion, they shouldn’t be in charge of large public projects that we all have a stake in, like our health.