The coronavirus is just a small part of a bigger story. Animals’ viruses keep causing outbreaks.
The novel coronavirus outbreak presents an immense challenge for global health. But it’s also part of a larger pattern: Viruses that circulate in animals keep jumping over to infect humans. The story of the novel coronavirus is the story of HIV, of SARS, of Ebola, and even the measles. These are all diseases that have been introduced to humans — with deadly effects — via animals. And as humans encroach more and more into animal habitats, it’s believed these spillover events may only grow more common.
The current outbreak — which has grown to infect 45,000 people and kill 1,117 — is thought to have started in a food market in Wuhan, China. But uncertainties remain: Researchers are still not sure which animal started the outbreak. DNA evidence suggests it’s likely related to bats (which also were the origin of the SARS coronavirus outbreak in 2003). But there’s also new, unconfirmed evidence, that the illegal pangolin trade may be implicated.
To better understand why health officials want to know which animals were involved in the new outbreak, I called up Jonathan Epstein. He’s a veterinarian and an epidemiologist with the EcoHealth Alliance who was involved in tracking down the animal source for the SARS outbreak.
He outlines what’s known about the source of the new outbreak, the challenge of preventing outbreaks, and why zoonotic disease (i.e. disease that passes between animals and humans) is a two-way street. Animals can infect humans. And humans can infect animals right back.
This interview has been edited for length and clarity.
Why it’s important to track down the animal reservoirs of disease
Scientists are trying to find the animal host of this novel coronavirus. And I have a big, dumb question: Why do we need to know this?
There’s a very simple answer: so this doesn’t happen again.
Right now, we have a lot of attention focused on containing this outbreak, which is spreading from person to person, but a critical question we still need to understand is, “How did the first person get infected with this?” Because that’s where we need to focus efforts to make sure that that doesn’t happen again.
What do we know right now about where this novel coronavirus came from?
I think that we have very strong evidence that supports the idea that this virus ultimately comes from bats. But we don’t know what other animals may have been involved.
What do you mean by “what other animals may have been involved?” Is it possible this didn’t come directly from bats?
A good example here is the story of SARS. When SARS emerged in 2003, it was also in a live market in Southern China, in Guangdong. It turned out people that were handling and trading civet [cats] had a higher instance of exposure and infection to this virus. Then they tested animals within the markets, and civets were found to be infected with the same virus that was infecting people.
So the assumption was made that people were getting it from civets, and civets were very promptly and publicly removed from markets and stamped out.
But a very important study came out a few months after the epidemic looking at civets on farms that supplied the live animal markets, and it turned out that none of the civets that were being farmed had any evidence of exposure or infection to SARS coronavirus.
That was important because this was not in fact a civet virus that was getting into the markets. Civets were getting infected in the markets themselves, just like people.
So what was giving civets SARS? Was it bats?
So this is where I come in, and my colleagues. We started working on SARS back in 2003 trying to understand what the wildlife reservoir was.
And we found it to be bats, horseshoe bats specifically. We now know that there’s a whole group — a whole diversity — of viruses related to SARS that are circulating in horseshoe bats.
One of the viruses we identified with our partners at the Wuhan Institute of Virology back in 2013 is 96 percent similar to this novel coronavirus. That gives us confidence that this new coronavirus also is a bat virus originally.
These bats are hunted and eaten in China, and in fact were brought into the markets in the case of SARS, and that is how other animals including people were infected.
The new coronavirus likely originated in bats. But experts still aren’t precisely sure.
Do you feel strongly that this new coronavirus outbreak started in a market?
The epidemiology, the investigation of the earliest cases, the first 41 cases of pneumonia, found that just over half of them had contact or exposure to the market. Some of them worked in that market. Others had visited the market. There were other cases that had no contact with the market, and that simply suggests that they may have been exposed either to other people that were sick or to animals that were sick perhaps somewhere else besides that market.
It’s clear there was some environmental contamination in the market that includes this virus. And that’s what we know so far. So it’s likely that people were infected in that market. But I think there is still some question about how the earlier cases may have been exposed.
So just to be clear, it’s not known for certain that this outbreak started with bats in an animal market.
Right, it’s not known. It’s still not known.
So what’s this I’m reading about pangolins?
Pangolins have been found to carry a coronavirus, and a short piece of that virus’s genome seems to match a short segment within the novel coronavirus sequence. So there’s been this suggestion that perhaps at some point this virus mixed with a pangolin virus, maybe in a pangolin, meaning the bat virus and the pangolin virus may have coexisted in a pangolin and traded genetics. [In other words, they] traded genes a little bit to the point where it’s got a piece of pangolin.
Now just to say, I haven’t seen data on this yet. There’s been talk about it in the media. There’s been discussion of it, but until we see the studies and the data, I can’t comment on whether this is likely or not.
So that pangolin connection, what are they suggesting? Like this was actually a bat virus that got into a pangolin, and that infected people, or it was pangolin virus that got into a bat, and then that infected people?
What they’re suggesting is that it mostly looks like a bat virus, but there’s a little, tiny piece that looks like a pangolin virus. And so they’re suggesting that perhaps the bat virus may have gotten into pangolins and then evolved.
Zoonotic diseases are on the rise
Backing up a bit: Have these zoonotic diseases been with us since the dawn of humanity? Or are they kind of a product of our modern world?
It’s always [happened], but it has certainly accelerated historically as people and animals have learned to live together.
What we’re seeing now in a historical context is an unprecedented acceleration of spillover or jumping of animal pathogens — it could be viruses or bacteria. Frequently they are viruses. We’re seeing a great instance of this happening, and that is largely because of human population growth and the fact that we — people — are changing the environment around us in ways that influence how we interact with animals.
Now, about half of all known human pathogens are zoonotic, which means they originated in animals. When we talk about emerging diseases, things that are new to us historically or things that we’re seeing in the new context, three-quarters of those are zoonotic, and most of them come from wildlife.
There is a pool of viruses out there in nature, and we’re just scratching the surface in terms of our understanding of how many are out there.
Are there some common diseases that we don’t think of as being zoonotic but they are?
People might be surprised that measles originally — although it is now wholly a human virus — is a virus that adapted from something called rinderpest which was a cattle disease. Also, HIV is an example, probably the most important zoonotic virus in terms of global burden of disease and public health where this was originally a chimpanzee virus called SIV, simian immunodeficiency virus.
Does this go the other way? Do we get animals sick sometimes with our human infections?
Absolutely, yes. Zoonotic disease is a two-way street. An example is measles. That can be fatal when it gets into chimpanzees or gorillas and to great apes.
The respiratory syncytial virus, which is common in children, can also be fatal in great apes.
It’s in fact a serious conservation issue, and it’s why if you go to visit chimpanzees or gorillas in the wild through a responsible ecotourism operation, they will not allow you to visit those animals if you’re sick, in many cases if you’re unvaccinated against measles. Because there’s too great a risk to the animals.
The current Ebola outbreak in Congo has brought up a lot of discussions because there have been people infected around mountain gorilla wildlife preserves, and gorillas are also susceptible to Ebola virus just like people are. They die from it.
How are these viruses passed from animals to humans? In my mind, I have this cartoon image of an animal sneezing, and I’m getting, I don’t know, flu from that.
There are a number of different ways it can happen. Many of them are just like how people give viruses to each other. It could be airborne, or respiratory, where an animal can develop a respiratory disease and by coughing or sneezing create droplets that travel through the air and infect a person that’s nearby.
Sometimes it’s the contamination of food or water. So animals can carry a virus and shed it in their feces or saliva, just like people can, and if they contaminate food supplies or water supplies and people eat that contaminated food, they can get infected that way.
Then one other thing is butchering animals. So the process of handling and butchering live animals can expose people to viruses or bacteria. That’s a great way for an animal virus to get into a person. And that’s likely how it happens in live animal markets.
These diseases are on the rise because of human behavior
Is there anything here that you are seeing routinely misreported or misconstrued in the press on animal-to-human diseases?
The majority of these epidemics happen because of humans and human activity. So it’s really important to say this is not the bat’s fault. People get fixated on the animal sources of these viruses. I think we don’t want to create panic or anger toward these animals because they’re very important to us ecologically.
We need to understand why these viruses get into people, how they get into people. Then we need to change the way we do things so they can’t.
I imagine there’s like a kind of thorny cultural issue here. People are trading wildlife in China because they want to buy and eat it. How do we put an end to that without being patronizing or stigmatizing?
You have to approach issues like this with a cultural sensitivity and awareness. A lot of these behaviors are deeply ingrained in a culture.
But let’s turn the lens on ourselves. Let’s talk about, for example, the fact that Americans, we love to eat beef. We love our cattle, and now there’s … you know, arising awareness of the environmental impact of raising cattle in intensive situations. And we also know about potential health risks associated with red meat consumption. So how quickly are Americans changing and adapting to new information about the personal harms that could be associated with that and perhaps the global environmental harms? We’re not so quick to change behavior either when it’s something we enjoy.