31 Mar Environmental Practices and Pandemics
The story we tell about pandemics casts us as victims of nature. It’s the other way around.
Although we are (hopefully) not using a racist term to refer to this virus, many of us have unwittingly bought into a particular paradigm for understanding pandemics. Call it the paradigm of invasion: the idea that we’re being attacked by an onslaught of foreign pathogens that come from animals, and we’re just passive victims.
But what if we, the humans, are the ones staging the onslaught? What if the real story of modern pandemics is not about how animals and their germs are invading our human realm but about how we’re invading theirs?
That’s the argument of Sonia Shah, author of the 2017 book Pandemic. She says the paradigm of invasion — or “microbial xenophobia,” as she calls it — often fails to explain why a microbe that’s existed for ages suddenly turns into a pandemic-causing pathogen. After studying outbreaks ranging from cholera to West Nile virus to Ebola, she’s found that human activities play a huge, and hugely underrecognized, role.
Our environmental and social policies — like cutting down forests or failing to address a housing crisis — make it much likelier that a previously harmless microbe will cause a devastating outbreak.
Shah is not alone in advocating for a paradigm shift in how we understand pandemics. The One Health movement, an interdisciplinary way of thinking espoused by some global public health authorities, emphasizes the connections between people, animals, plants, and their shared environment. It’s pushing for this change, too.
I talked to Shah about how this approach can help us better understand the true origins of pandemics. A transcript of our conversation, edited for length and clarity, follows.
The reigning narrative in a lot of people’s minds is that “exotic” animals are to blame for the coronavirus crisis — that they’re dirty and infested with tons of pathogens that just can’t wait to kill us. What’s wrong with this narrative?
First of all, we all have lots of microbes inside of us. Humans give animals microbes that turn into pathogens all the time, so we are also the source of disease for other species. But we don’t talk about that.
Species everywhere are full of microbes, but if they stay in the bodies in which they’ve evolved, they don’t cause disease. Ebola doesn’t cause disease in bats. Neither does coronavirus. They cause disease in our bodies because they’re new to us — they’re exploiting a new habitat.
So why are they exploiting that new habitat, namely us humans?
It’s because we are building roads between wild animals and human bodies. We’re using up a lot of land — for our cities, our mines, our farms — and while doing that, we’re destroying wildlife habitat. That’s why 150 species are going extinct every day. And the species that are remaining have to squeeze into these tiny fragments of wildlife habitat that we leave for them.
When you cut down the forest where bats live, they don’t just go away; they come roost in the trees in your backyard or farm. That means it’s easier to have casual contact with their excretions.
If a little kid goes outside and plays near a tree where bats roost, they might pick up a piece of fruit that has some bat poop or bat saliva on it and put that in their mouth, and then you’ve created an opportunity for the microbes that live in the bat’s body to enter into a human body. We know that with Ebola, there was a single spillover event — the first case was a 2-year-old child in West Africa who was playing near a tree where bats live.
These are accidents waiting to happen. Now we have this amazing flight network, so even if pathogens emerge in a place where there aren’t a lot of transmission opportunities, they can easily get to somewhere where there are. We’re also urbanizing in an ad hoc fashion, so we have a lot of places where people are being exposed to each other’s waste. There’s not a lot of infrastructure in many of the places that are rapidly urbanizing. All these factors combine to increase the risk that a microbe will spill over into human bodies and then start to spread.
What strikes me is that when you talk about the origins of pandemics, you talk on this macro level — like our environmental and social policies — rather than on the micro level. What kind of explanatory power does this approach give you, in terms of explaining the origins of previous outbreaks?
We often look at an outbreak as a foreign problem — like Ebola and SARS and Zika are coming from outside and encroaching upon us. That’s the traditional narrative: the germ invading from outside. I call it microbial xenophobia.
But these are things that are happening right here in the United States. So for example, West Nile virus is a virus of migratory birds from Africa. They’ve been landing in North America for hundreds of years, but we never had West Nile virus here until 1999. Well, why is that?
It turns out that when you have a diversity of bird species in your domestic flock, you don’t get a lot of West Nile virus because birds like woodpeckers and rails are really bad carriers. So as long as you have a lot of those diverse bird species around, even if you have an introduction of West Nile virus from a migratory bird, you’re not going to get a lot of virus overall.
But what happened over the last 20 years or so is that we lost a lot of that avian biodiversity. Woodpeckers and rails became rare in a lot of environments. Instead, we have a lot of birds like crows and robins, which are generalist species that can live in any kind of degraded environment, and they’re really good carriers of West Nile virus.
So the fewer woodpeckers and rails you have around, and the more robins and crows you have around, the more West Nile virus you have around. And the more likely it becomes that a mosquito is going to bite an infected bird and then bite a human.
Since tick-borne diseases are a huge problem in the US, I’m curious: Is there a similar story to be told about Lyme disease?
Yes, it’s a very similar story with Lyme. When we had intact forests over the northeast, we had a diversity of woodland species that lived in those intact forests — like opossums and chipmunks — that helped control the tick population. But over the past 50 years or so, suburbs have expanded into the forest and broken it up into little patchwork quilts, so opossums and chipmunks have become [relatively] rare.
Instead, we have a lot of white-footed mice and deer, and it turns out that white-footed mice don’t control tick populations well. A typical mouse destroys about 50 ticks a week, compared to a typical opossum that will destroy hundreds and hundreds of ticks a week just by grooming.
So the fewer opossums you have around and the more white-footed mice you have around, the more ticks you have around. And the more likely it becomes that you’re going to have outbreaks of tick-borne disease like Lyme.
I think that really helps make the case that our interaction with the environment — for example, deforestation — has major impacts on human health. Social policies can also affect the risk of an outbreak, right?
Right, so, when dengue broke out in South Florida in 2009, it was immediately considered an invasion from some foreign place. We coated the environment with insecticide and staged a military-style assault on these mosquitoes. But it turns out the mosquitoes that carry dengue have been in South Florida for a long time. That wasn’t new.
What was new was the foreclosure crisis. It had shuttered all these houses. The epicenter of the dengue crisis was also the epicenter of the mortgage crisis.
And of course in South Florida people have a lot of swimming pools. So with all these homes closed, these swimming pools were vacant. Lo and behold, it starts to rain and these empty pools fill up with water and it creates these little pockets around the garden that mosquitoes can breed in. And then we have this “unprecedented” outbreak of dengue.
Nobody thought to address the housing crisis as a possible driver of the outbreak.
It sounds like what you’re advocating for is a more holistic approach, a systems-thinking approach. How much of an outlier are you in that?
There’s a whole movement in global health called One Health. It’s the idea that human health is connected to the health of our animals — pets, livestock, wildlife — and our ecosystems and other societies. All these things are connected and we have to look at these broader drivers because that’s going to get to the root of the issue. Otherwise, we’re constantly just mopping up problems that are going to keep erupting again and again.