Now just two years later experts are scrambling to control another devastating virus, the mosquito-borne Zika, which threatens to spread from South America further across the continent and to Europe this summer.

We talk to investigative journalist and author Sonia Shah to find out why viruses including Ebola and Zika thrive and how modern lifestyles have incited their rise.

Sonia Shah has spent her career exploring some of the most significant issues in science, politics and human rights. Her 2006 book The Body Hunters is a bold exposé of the exporting of clinical trials by the pharmaceutical industry to the developing world, and Bill Gates has cited her examination of Malaria The Fever as one of his top four books on diseases.

Now Shah is once again turning her attention towards the fascinating and frightening world of infectious diseases in her new book Pandemic: Tracking Contagion, from Cholera to Ebola and Beyond.

Sonia, what is it about deadly pathogens that are such a fascination for you?

I’m interested in how these microscopic creatures with no independent locomotion can cause history-changing events, epidemics and pandemics. They can exert such a significant influence on culture and history, and yet we don’t really think of them in that way.

Your book, Pandemic centres around cholera in particular. What is it about this particular disease that is so interesting and tells us so much?

Well, it’s our most successful pandemic causing pathogen. Cholera has caused seven pandemics, not just one or two like most pandemic causing pathogens, and we have a really good recorded history of cholera. Also, it kills people fast. It kills about half the people that get it, and it can kill you in a matter of hours. So when it has struck, it has been very dramatic, even though the cure for cholera is straightforward – clean water. It took nearly a century to figure that out.

In a recent article, you wrote that there were 150 per cent more outbreaks of avian influenza in 2015 than in 2014. That’s a staggering statistic. What is the reason for this?

The reasons aren’t known for sure, but there are a lot of theories. One has to do with the growth of factory farming in parts of Asia, especially along migratory waterfowl routes. Most migratory waterfowl live in Asia. That’s where the most significant populations are, and we have hugely expanded factory farms of poultry in those areas. So the viruses from these wild ducks are falling into factory farms, and that allows them to replicate more quickly and mutate and become more virulent. Climate change is also affecting the migratory routes of these wild waterfowl, and that changes the ecology and the frequency of outbreaks.

It’s fascinating to hear that climate change is affecting this issue. Could you explain a bit more about that?

Well, birds are the primary carriers of influenza viruses, and migratory birds are very sensitive to climate change. Some years ago there was a cold snap in parts of Europe, and that changed the migratory routes of some waterfowl which ended up allowing avian influenza to break out into new places. The outbreaks were directly linked to these wild birds migrating in different ways. It’s all about where they stop over in ponds and lakes and other bodies of water. So in that way, climate change affects where they go. Let’s say a bunch of ducks end up in a pond in your back yard, well they’re going to mix and mingle with the other birds that come there. These viruses are carried in faecal matter, and it can stay stable in the water. So when these birds land, they contaminate the water and get the other birds sick. It can spread into domesticated birds or even people, depending on the strain.

What kind of discussion is happening with governmental bodies, NGOs, think tanks etc. around the impact of global warming on the spreading of pathogens?

A conversation about this is definitely happening. The trouble is that while climate change will clearly have an impact on where pathogens can spread and how it is challenging to predict exactly how.

The other thing you talk about at the beginning of your book is air travel and its effect on the spreading of pandemics. Is it the culmination of these things like climate change and air travel, all products of modern life, that are resulting in a very rapid increase of pandemics? 

Absolutely. Pathogens that appear in one part of the world can now extend across the planet thanks to air travel. We’ve been carrying microbes across the globe from the very beginning of human mobility. In the 19th century, we were carrying them around on ships and canals, and now we take them when we fly in the air. The thing about flight is that it’s so much faster and it’s penetrating remote areas. We don’t have just two airports in capital cities; we have hundreds of airports and tens of thousands of connections between all of them.

If you plot a flu pandemic on a geographic map, you’ll see an outbreak in one part of the world, and it spreads throughout the globe in an unpredictable, messy fashion. But if you plot that same pandemic on a map that shows all of the cities as direct fights connect them, then that pandemic resolves into a perfect series of waves. The way we travel through the air shapes our pandemics.

You make the case that the best way to fight malaria is to fight poverty rather than the virus directly. In a couple of years since that talk, we’ve seen the outbreak of two significant viruses, Ebola and now Zika. Should these be tackled in the same way?

Both Ebola and Zika are fueled by poverty. That is obvious. Ebola is a horrible virus, and we don’t have any excellent treatments for it either. But it’s straightforward to contain. You don’t need high-tech measures, and you don’t need experts with PhD’s to do it. You have to isolate each person who gets infected and make sure they don’t spread it to anyone else if you do that you’ve broken the chain of transmission.

So what do you need to do that? You need a few basic primary health centres, and you need running water and soap so that health officials can wash their hands and stay hygienic when handling patients. That doesn’t require a fancy vaccine that costs thousands of dollars. The reason we had such a significant outbreak in West Africa recently is that we didn’t have any of that. Ebola emerged in a very remote part of Guinea, and it spread rapidly. Within a few weeks, it reached three capital cities, but it was still under the radar because there weren’t enough primary health services for all the people that were getting infected.

Zika is similarly exploiting the expansion of urban centres in the tropical Americas. We’ve had Zika since at least the 1940s, maybe before that, but it was in the equatorial forests of Asia and Africa, and it was carried by mosquitoes that mostly bit animals. Then suddenly Zika expanded dramatically out of Asia into the Americas via an aeroplane flight. It drops into Brazil where there are these huge slums and the perfect climate for the mosquitoes which carry the Zika virus.

People can live in these places if they have a ceiling fan, air conditioning, screened windows, well-maintained roads and running water – this was a huge factor in slums in Brazil. People did not have regular access to running water so they would collect water in containers and leave that outside. They became perfect breeding spots for these Aedes mosquitoes, and they were right next to people’s houses. So if you get a virus like Zika introduced into conditions like that it just explodes.

Do you think that enough is being done to fight Zika at the moment? Are the right choices being made?

Well, we’re playing catch up. In a lot of the places that are most vulnerable to this disease, we’ve suffered multiple outbreaks of mosquito-borne viruses. This has happened again and again. If you look at places like the poor neighbourhoods around Houston in Texas, they’ve had St Louis encephalitis, they’ve had dengue, West Nile virus, chikungunya. This has been happening for decades because there are a lot of slums, a lot of standing water, people don’t have good access to window screens or air conditioning, there’s a lot of homelessness, a lot of abandoned homes – these are all things that allow Aedes mosquitoes to breed and make people exposed to them.

Suddenly we have Zika, and it’s looming over the United States. It’s going to move in here as our mosquito season starts, and now suddenly we’re saying – “oh my god, we need to do something, let’s throw two billion dollars at it with chemicals to try to suppress the population of mosquitoes”. But we’ve known since we started fighting mosquitoes that it’s impossible to control their populations completely.

Do you think that all the hysteria in the U.S about Zika is warranted?

I think what we need to be doing is protecting the most vulnerable people and that’s women of childbearing years living in poverty. About half of all pregnancies in the U.S are unplanned, so that means there are a lot of people getting pregnant because they don’t have access to contraception, or they’re victims of assault, or they lack education. Whatever it is, this is a pretty widespread problem.

Yet what we know is that if we have Zika outbreaks in the United States or Europe, it’s only going to be seasonal. It won’t be all year round because mosquitoes don’t bite us all year round. So women need to be able to control their reproduction. That’s true all the time but especially when there’s a risk of congenital defects from mosquito viruses. If you can put off your pregnancy for the two months that mosquitoes are biting, then you have adequately protected yourself from 99.5 per cent of the risk that Zika poses.

We interviewed an epidemiologist named Prabhat Jha, who has been undertaking this incredible ‘Million Deaths Study’ in India. He found that there were considerable inaccuracies in the numbers of deaths thought to be caused by things like HIV, malaria and even snake bites. A lot of people believe that the World Health Organisation acted too late in West Africa when Ebola broke out because they weren’t aware of the sheer scale of the problem. Would you agree that we need better data before we can know how best to tackle and prevent pathogens from killing people?

We absolutely need better data, but even before we do that we need independence in our health agencies — the WHO delayed announcing an emergency with Ebola because they were afraid of disrupting commercial interests. The Associated Press has found documents that prove that.

By commercial interests do you mean trade?

Yes, and mining interests and tourism, all of these things. This goes back hundreds of years too. When there were cholera outbreaks, government officials would purposely suppress the news because it was disruptive to commerce. You don’t tell anyone you have a cholera outbreak because then no ships will want to come into your ports. Places like New York, London and Hamburg repeatedly suppressed news about cholera outbreaks for that reason.

So we saw a similar thing happen with Ebola where the WHO officials in infected countries didn’t want to call an emergency because they were afraid it would be hostile to commercial interests. They didn’t want all the mining companies to pull out because it would damage the economy. So yes, we need useful data, but we’ll never get good data if our health organisations aren’t more independent.

So what’s being done now by governments and the WHO? Have they learned from what happened with Ebola? 

I think how the WHO has responded to the Zika outbreak shows that they have learned from the Ebola fiasco and all the criticism they got. But the fact is that the WHO only controls about 20 per cent of its budget. Eighty per cent of the money it gets is all voluntary contributions and whoever gives the money can say – okay we’re going to spend it on this. It’s not being done with the best interest of global health. So that’s a structural problem, and it’s not going to change until we start financing the UN system again.

One concerning thing we saw with Ebola was this fear that manifested itself in a very cruel attitude, particularly in the U.S but also here in Britain, of people wanting to ban all flights from Ebola-infected countries. Do you think that pandemics fuel racism?

Yes, there’s a long and deep connection between xenophobia and infectious disease. Xenophobia is so maladapted today. Usually, when immigrants come into a society, they make society stronger and more prosperous and productive. Having strangers around is good for us, and yet we still have this huge problem of xenophobia across the globe. Look at what’s happening in Europe right now. The countries that have the most virulent xenophobic attitude towards Syrian refugees are the ones where there are not enough workers to fill jobs. So where did this attitude come from? I think in our deep past we knew that having strangers around would potentially introduce new pathogens. We know what happened in the 16th century when Europeans came into North America and spread all kind of Old-World diseases that had never been seen before. Lots and lots of people died, and that has happened repeatedly in history.

I can understand the psychology of it but in fact, if you look at what is really the big risk, it’s travellers. It’s the businessmen jetting around the world all the time. We have a billion people in the air every year, and no one is scared of that, but they should be. That is what is spreading all these pathogens, much more effectively than people travelling on foot from Syria.

Do you think that specific demographics also become stigmatised with their diseases in some way in the eyes of other cultures, almost like ‘poster boys’ for a particular condition?

Yes, sometimes particularly marginalized groups do get associated with certain diseases, like African Americans with syphilis before the Tuskegee Syphilis Study, or Central American immigrants with Zika – as when Trump recently said something like, “these Mexicans” are bringing “all kinds of diseases.” What is clear is that the most critical factor in outbreaks is generally not particular populations that “bring diseases,” but social conditions that allow pathogens to spread, for which we all share a responsibility.

Do you think Western society responds to pandemics appropriately?

I think it varies. With Ebola, everybody freaked out, but then you have the dengue virus that arrived in Florida in 2009 and people there didn’t take it seriously at all, they laughed. There were parades where people would dress up as mosquitoes, and there was a band called dengue fever. It reminded me of cholera balls in 19th century Paris where thousands of people were dying of cholera, and the rich were having masquerade balls and dressing up like cholera, laughing in the face of this deadly disease.

We’ve conceded a lot of control of infectious diseases to our experts. We don’t think of them anymore as things that we can prevent through our behaviours, we think of them as a problem that doctors have to solve. They give us the vaccine so that we don’t have to think about it or change our behaviour at all. We wait for the magic cure to come. But what that means is that when we have these new pathogens against which there are no magic vaccines, we feel very powerless.

How big of a threat do you think a man-made pathogen is? Bio-terrorism is a very hot topic at the moment so I’m keen to hear your thoughts on this.

I think it’s overblown actually. If you look at the history of attempts to come up with these bio-terror weapons it’s been pretty paltry. No one has ever been able to do it that well, with the exception perhaps of the anthrax attacks in the United States after 9/11, which still had a relatively small effect. So I think it is a bit exaggerated. But because we threw so much money at potential biothreats we actually started doing research on things like Ebola and other diseases. The whole reason that we might soon have an Ebola vaccine is that we did all this research because we were afraid that Ebola would be used as a weapon. So nature has been better at it than we have, but it’s good that we did the research.

How will technology and the proliferation of big data shape our relationship with diseases?

We’re already seeing big data being used to predict where outbreaks will occur. Satellite data, for example, is being used to detect chlorophyll signatures that precede cholera outbreaks. Social media chatter is also being used to detect outbreaks of unusual diseases. I think there are a lot more opportunities in this area. And early detection makes a huge difference in our ability to contain epidemics since they grow exponentially. Even a few days’ notices can potentially save a lot of lives.

You’ve talked about this fascinating functional aspect that pathogens have. Could you explain?

It has been said that by causing disease pathogens could perform a useful function for the ecosystem. One example might be diseases common in tropical jungles, which made the human invasion of those environments difficult. Probably a lot of rainforests has stuck around for a lot longer because of that.

How close are we to understanding the world of pathogens? 

There are three existential threats to every species; predators, the hostility of the climate, and microbes. If you think about our history, we killed off all of our main predators not very long after we evolved. We drove the giant mammals into extinction. We developed fire pretty early on as well, and since then, we’ve been able to shape the environment in ways that protect us from the most hostile parts of the climate. So we’ve dealt with both of those existential threats, but when it comes to the threat from microbes, we’ve only just been able even to detect their presence. In a way, I think our fight with microbes, and coming to terms with the threat that microbes pose to us, has only just begun. When we got to the 1940’s and developed antibiotics, we thought, “Oh wow, we figured it out! We’re on top of this threat.” But that is like a mountaineer who climbs a foothill, looks out and thinks he’s on top of the mountain.

If you look at the last five years, with new genetic techniques, we’ve been able to detect microbes in all of these places where we never even knew they existed. Now we know there are hundreds of thousands of microbes on your hands and in your body and on your desk. We’re completely immersed in this microbial world that we’ve only just begun to see. I’m hopeful that there’s a lot more we can do to resolve our dilemma with microbes, but at the same time, this is their planet, not ours.