The COVID-19 pandemic that’s currently ravaging the world started with a simple virus in an animal. Viruses like this, which can jump from animal to human, are called zoonotic viruses. They account for 75 percent of all the emerging diseases people grapple with today and are one of the most critical areas of study when it comes to protecting public health.
Epidemiologist Christine Kreuder Johnson knows that a virus carried by wildlife in any seemingly far-flung corner of the world can potentially threaten the health of humans globally. She studies how viruses in animals “spill over” into human populations as associate director of the One Health Institute at the University of California, Davis. “One Health” is a framework for thinking about how the health of people, animals, and our shared environment are all connected.
Johnson is the lead author of a new study that found that domesticated animals, along with wildlife that have adapted to humans encroaching on their habitats, like bats and rodents, are responsible for a majority of viruses studied to date that have afflicted human beings after originating in animals. Those results are evidence that the effects humans have on animals can have grave consequences on our own well-being.
The study was funded through the USAID Emerging Pandemic Threat Predict program. Since 2009, that program has collected over 140,000 biological samples from animals to identify 1,200 viruses — including more than 140 new coronaviruses — that could one day pose another global threat. Over the next several months, they’ll comb through their samples to see if the novel coronavirus might have jumped from animal to human even earlier than suspected since it can often go unnoticed before an outbreak erupts.
The Verge talked with Johnson about the COVID-19 crisis we’re in today and what might be done to prevent another pandemic like it in the future.
This interview has been lightly edited for length and clarity.
What are zoonotic viruses, and what makes them particularly dangerous?
Some are not dangerous. Many circulate, and they’re endemic globally. They place a burden on people who have contact with animals — especially livestock keepers.
But the novel coronavirus made the leap from animals into humans and was able to be human-to-human transmitted. Because it came from animals, all humans are susceptible.
The entire world population, for the most part, is naive to this new virus because none of us have been exposed to it before. And that’s what makes it especially dangerous. When they are transmitted human to human and everybody’s naive, we all get sick around the same time. And that, as you’ve seen, places a huge burden on public health resources and health care facilities that now have a large number of sick people to deal with all at once. It can be quite tragic in that way.
How do scientists study or surveil those viruses in wildlife?
Very, very carefully. And I can speak from the heart here because I have the great honor to work as part of the Predict project with colleagues in countries in Africa, Asia, and Latin America. For the most part, they are wildlife veterinarians, and they are some of the best ambassadors for ways to work safely, effectively, and especially ethically with wild animals. We have to be careful to not increase disease risk.
As part of the Predict project, we all agreed that we would have basically no ecological footprint. We would capture animals, sample animals, and put them right back. We take swabs. We also do take blood samples so we can look for other viruses. But swabs are the best way to do it for coronaviruses. And we would do so in a way that was absolutely biosecure. These are the pictures of us in the PPE with masks, and the shields and the white Tyvek suits. That is how we did our sampling to make sure that we were not putting health workers at risk themselves. And also, there’s a chance we could give things to animals. So we have to make sure we’re not upsetting the balance that way either.
How might zoonotic diseases like this one spill over into people?
We’re sharing habitats that we hadn’t shared previously. In doing so, we have the opportunity to interact with animals through basically them taking up residence closer to human communities. A lot of these viruses are potentially shared through contact with feces or urine or other ways when these animals share the landscape.
It’s very important that we consider how our actions are changing their numbers. We do have good evidence in disease ecology that when these animals have disruptions to their habitat, their need to move around more actually increased epidemics in their own population. We have a situation now where, as this pandemic progresses, we’re being asked to shelter in place and stay put because it’s obvious to everyone that when we move around, we increase the likelihood of these epidemics to get started. The same disease dynamics take place in wildlife. As wildlife are hunted or as their habitats are destroyed and they have to move, it’s that movement that actually increases disease dynamics and increases the likelihood of epidemics in both populations of animals and humans.
In market settings, you have very different wildlife species, bats and carnivores and ungulates [hoofed mammals]. Those different types of animals are all together, and they’re alive, so they’re able to share viruses. This tendency for viruses to jump species should be a very rare and difficult capability, but we’re providing opportunities for viruses that naturally mutate to have these other species nearby. They’re sharing respiratory droplets or there’s contamination by urine and feces. In those close settings with dense numbers of animals, we’re increasing the opportunity that one of those mutations will take off. And then we’ve, of course, got humans in that same situation, often in dense numbers as well, so it’s kind of this perfect epidemiological situation for viruses to jump hosts and find a way out.
What can we do to minimize the risk of another pandemic like the one we’re seeing now?
There’s a lot that should be done to regulate wildlife trade and wildlife trafficking. But I also think there’s a lot we can inform on how to live more safely with wildlife.
We really need to think about wildlife health as sort of this last frontier. We’ve had big investments in human health, which is needed, of course. And then we had big investments in domesticated species or a domesticated animal health because of food safety, and they’re our pets. But wildlife health has kind of been the last one to come along with relatively fewer people working in that sphere, and with less investment oftentimes, certainly from governments. We’ve learned a lot, but there’s so much more to learn.
What do the health of animals and their environments have to do with human health?
There was a bit of a paradigm shift in the health profession where we started to realize animal health and human health are quite connected, that there are zoonotic diseases that we get from animals. We started to do a lot of good policy around making sure that animal and human disease surveillance was more connected, that we were reporting our findings to each other, and that we were all more informed. But what has lagged a little bit is the idea that our health — and certainly the health of animals, especially wildlife — is also very dependent on environmental health and ecosystem integrity.
We’ve got public health and conservation, and we’ve got a lot of fields that we’re merging in one conversation now to try to understand disease risk. This is where the One Health approach really makes sense, where we see that animal health and human health are tightly, tightly interconnected. And then we also need to think about how environmental health is really at the core of both of those. Public health is really an environmental health issue.