Watch the replay of this event held December 16, 2020. Transcript below.
On December 31, 2019, the World Health Organization was notified about a cluster of pneumonia cases with unknown cause in the city of Wuhan, China. As the weeks and months unfolded, new and existing research on the origins of infectious diseases and their mechanisms of spread took on critical importance. For decades, scientists across the globe have been studying the events that must converge for a pandemic to happen, but in 2020, much of the world was blindsided by SARS-CoV-2.
During this discussion, two leading wildlife epidemiologists described how new infectious pathogens are transmitted from one species to another, a process called “spillover,” and what can be done to prevent future pandemics. Are human activities accelerating the emergence of infectious diseases? What can we learn from parts of the world where spillover is common? In densely populated areas of the species-rich tropics, for example, how are land-use changes driving transmission of pathogens from wildlife to people? What other factors influence spillover?
One key to understanding a disease’s origin, researchers say, is to examine the contact between people and animals known to host certain pathogens. And once an outbreak has occurred, controlling the disease’s spread requires a swath of activity across multiple institutions, to quickly prepare diagnostic labs and craft public health outreach, guidance and regulations.
Speakers
Jonna Mazet, DVM, MPVM, PhD
Professor of Epidemiology and Disease Ecology, UC Davis and Founding Executive Director of the One Health Institute
Dr. Mazet’s work focuses on global health problem solving for emerging infectious diseases and conservation challenges, and preparing for unknown viral threats to human health and food security. She is active in international One Health education, service and research programs, most notably in relation to pathogen emergence; disease transmission among wildlife, domestic animals and people; and the ecological drivers of novel disease dynamics.
Raina Plowright, B.V.Sc., MSc, PhD
Associate Professor of Epidemiology, Montana State University and Principal Investigator, Bat OneHealth
Dr. Plowright is an infectious disease ecologist, epidemiologist and wildlife veterinarian. Her lab focuses on the dynamics of infectious diseases in reservoir hosts, the process of pathogen spillover and the links between environmental change and disease emergence. She is leading a team of scientists investigating the complex causes of bat-borne viruses that have recently made the jump to humans. Dr. Plowright has also worked as a domestic animal and wildlife veterinarian in Europe, Asia, Australia, Africa and Antarctica.
Moderator
Rachel Ehrenberg, Associate Editor, Knowable Magazine
Rachel Ehrenberg is an editor and writer at Knowable Magazine. A science journalist for more than 15 years, she’s covered a range of research, including a recent look at how bats cope with various viruses. Rachel has a master's degree in evolutionary biology from the University of Michigan and a graduate certification in science communication from the University of California, Santa Cruz. In 2013-2014, she was a Knight Science Journalism Fellow at MIT.
About
This event is part of Reset: The Science of Crisis & Recovery, an ongoing series of live events and science journalism exploring how the world is navigating the coronavirus pandemic, its consequences and the way forward.
Reset is supported by a grant from the Alfred P. Sloan Foundation. Knowable Magazine is a product of Annual Reviews, a nonprofit publisher dedicated to synthesizing and integrating knowledge for the progress of science and the benefit of society. Major funding for Knowable comes from the Gordon and Betty Moore Foundation.
Resources
Related Annual Review articles
- Bats as Viral Reservoirs
- The Potential Role of Endogenous Viral Elements in the Evolution of Bats as Reservoirs for Zoonotic Viruses
- Detection of Emerging Zoonotic Pathogens: An Integrated One Health Approach
- Disease and Human/Animal Interactions
- Coronavirus Article Collection
Other online resources
- Global Virus Tracking by Science Consortium: One Health Institute’s Jonna Mazet Discusses their Work
- PREDICT
- Global Virome Project
- Bat OneHealth
- Bozeman Disease Ecology Lab
Transcript
Rachel Ehrenberg: Hello and welcome to “Preventing the next the next pandemic: Exploring the origins and spread of animal viruses.” I’m Rachel Ehrenberg, I’m an editor at Knowable Magazine from Annual Reviews. This is the fourth in a series of conversations about the pandemic, its consequences and the way forward.
As many of you know, the current pandemic originated when a coronavirus made the jump to humans — it very likely came from a bat with perhaps some other animals in between. While there’s now a light at the end of the tunnel for this pandemic, we very well may encounter another in our lifetime. A policy paper published earlier this year in the journal Science suggested that there may be upwards of 800,000 unknown viruses in animals that could make the jump to humans.
When we’re talking about dealing with new viral threats, the conversation often focuses on treatments, like vaccines. These are certainly important, but they aren’t about prevention. Today we are very lucky to have with us two wildlife epidemiologists who have done extensive research that’s helping on the prevention end of things. This includes things like surveying wild and livestock animals for viruses, research on the circumstances that need to line up for a virus to move from one species to another — a process called spillover — investigating how human activities may be increasing the likelihood of such spillover events.
We’ll also talk about what can be done once a new viral threat emerges, how public health agencies, academic institutions, environment and tourism agencies and more are and can take steps to quash an outbreak before it becomes a full-blown pandemic. I’m thrilled to be talking about all of this with Jonna Mazet, a professor at UC Davis and a founding director of the One Health Institute, which we will hear more about. Jonna is also on the board of directors of the Global Virome Project, an organization whose work led to that scary virus number I mentioned previously.
We also have Raina Plowright, a professor at Montana State University who’s done extensive research on bats and the viruses that they carry. This work includes investigating the process and events that lead to spillover. Raina is a lead investigator for Bat One Health, which focuses on bat-borne pathogens and develops recommendations to stop spillover.
Before we begin, I want to remind everyone to add their questions to the question box. If they’re not addressed during the to-and-fro of the discussion, I’ll ask them in the last part of the event. Jonna and Raina, thank you again for joining me to talk about spillover and preventing pandemics. In addition to your PhDs, you both have veterinary degrees. Let’s start with how each of you got involved with this field of work. Jonna, do you want to go first? I know that some of your early work focused on sea otters. Tell us about that.
Jonna Mazet: Yeah, so I’m really thrilled to be with you today. Thank you, Rachel, for having me. When we think about the interconnectedness of people’s health, animals, the environment, even plants and our foods, it’s important to really be thinking broadly about what’s happening in the world. I got that introduction really early in my career, as you mentioned, when I first was working on my PhD and even before that, while I was finishing up veterinary school, I was lucky enough to be working with sea otters and helping to try to save the species that was threatened here in California.
And very quickly, what we found was that the diseases that were killing sea otters were coming from human habitation in the coastal climate. Unfortunately what was killing sea otters was also killing a lot of friends in my San Francisco Bay Area home due to HIV AIDS. As you know, people die of secondary infections diseases often because of the altered immune system with HIV AIDS. So it very quickly brought everything together for me about the connection of our environment and what we need to do to stop impacting our earth so much because it is in fact ourselves that put us at risk from these infections. It’s not the environment or some crazy viruses that are out there lurking to jump into us or even the animal host. So in trying to save sea otters, I realized there was a lot we need to do to the planet, to be better to the planet to save ourselves.
Rachel Ehrenberg: Great. And Raina, you were a veterinarian for both wild and domestic animals on several continents, including Antarctica. What was that like and how did you end up focusing on bats?
Raina Plowright: It was a long ride to bats but I started off wanting to work on wild animals and particularly I was interested in endangered species when I was a veterinary student. And then I had these opportunities to be involved in wildlife projects like in Antarctica. So Australia, which is my home country, has a very large Antarctic program and I was able to go down and work on penguins and seals while I was a veterinary student and then when I was a veterinarian. But the real change for me was when I went to UC Davis to do my PhD and master’s. I was lucky to be at a school that had very strong ecology program, veterinary program and epidemiology program.
And so I decided to take a course in ecology there and that just blew my mind because ecology, it’s really about the interconnectedness and interdependence of our natural world and I realized that was how my mind worked. I loved complex, dynamic systems. So then I was lucky to be able to do my PhD on bats right at the time when we were discovering that they were important hosts of emerging diseases. So bats had just been linked to Ebola, to SARS, to Marburg, Hendra virus had just emerged in Australia, and then Nipah virus in Malaysia followed soon after. I did my PhD on Hendra virus soon after its emergence, looking at the connection between landscape change and viral disease in bats.
Rachel Ehrenberg: OK. So that brings me to something I want to talk about right at the outset. We’re going to be talking about a lot of viruses today and many animals that people may know or encounter. And I think it’s important to say that while some of the conversation may get a little scary, trying to rid the world of animals that carry viruses is not a solution. Raina, you said that bats are not the enemy, they are the canary. What does that mean?
Raina Plowright: Bats really are a signal of our changing relationship with the environment. So first, bats are so poorly understood by society and I think that is because they’re nocturnal; we’re diurnal. They look different from most other species, and humans tend to have a fear of things that are different. But bats are just fascinating. I mean, we have five-gram bats that can live 40 years. And the fact that they’re the only mammal that can fly; they have these huge metabolic rates. Every time they fly they increase their metabolic rate sixteen-fold, yet they don’t experience metabolic stress, oxidative damage to cells, which is probably related to their ability to live a long life and not go into senescence. So they’re fascinating animals. They also do harbor many of these infections that are very dangerous to humans and domestic animals, but they don’t make bats sick. Why is that? So we have a lot to learn from bats.
We think there’s something special about their immune system, perhaps tied up to their ability to fly. That helps them to dampen the replication of the viruses and not have the ill effects of, say, inflammation caused by viral infections. So it’s really important to be able to not take this out on the bats. We need bats. They’re critical pollinators. In fact, in Australia, they’re the bees of Australia. One of the most critical pollinators of native forests. They disperse seeds long distances, certainly helping fragmented landscapes become more resilient in the face of climate change by dispersing genetic material long distances. And they consume huge quantities of insects — it’s really important for agriculture.
Also, there are studies showing that if you do take this out on bats, for example culling bats, it backfires, because the populations respond by producing more offspring that are susceptible to disease and that can actually fire up infections. It’s like adding fuel to a fire. It can make the outbreaks of pathogens within bat colonies worse. Plus, we need ecosystem services that bats provide. So what we need to do is look at why are we suddenly seeing all these emerging diseases from bats? What can we learn from those processes? And then try to get to the root cause of those diseases, to those emergence problems rather than just blaming the bats.
Rachel Ehrenberg: OK. So we’ve talked a little already about some of the viruses bats carry. I mentioned that scary number earlier: hundreds of thousands of viruses that could potentially infect people. That’s a lot of virus. Jonna, you’ve been very involved with both the Global Virome Project and PREDICT, which has identified more than 150 coronaviruses alone that could potentially infect people and cause epidemics. But many animals — humans included — carry viruses that never cause any harm. How frightened should we be? Can you put some of these numbers in context?
Jonna Mazet: Well, I don’t want us to be frightened and you said it very nicely, Rachel: We’re bringing up some scary topics, but I think this group, the audience here, is among the individuals who really helped generate the knowledge that can reduce fear, and that has been a big driver for me. The idea that there are many viruses out there that we don’t know about is what’s behind the Global Virome Project and that it is completely within our capabilities now to find those viruses and characterize them and understand the risks that we put ourselves in by the way we interact with their hosts or the environments in which those viruses exist. So I think it’s important to understand that there are definitely underlying drivers that are increasing our risk for being exposed and infected with these viruses.
So with our PREDICT project that you mentioned, we worked in more than 30 countries around the world, with the communities and the governments of those countries, to identify hotspots. We use much previous work by Jones et al to start out looking at the globe and finding hotspots. And those early models were driven by a human population growth and biodiversity. And over time, we were able to improve those models by getting more data that fed them, that showed that land use change is really an important, predictor, driver of this connection. And that makes sense, because when we disrupt a system — so your own system, when you’re disrupted, you’re stressed, you’re out of sorts, you’re hungry, your body gets out of equilibrium. Often you might get a cold sore or you might get sick.
It is the same for ecosystems. So if we disrupt an ecosystem, we change the way that the land is being used in that ecosystem, it disrupts every part of that ecosystem, including the organisms and microorganisms that are in that ecosystem. So for the host humans may become more susceptible when they’re stressed and working in a changing environment, cutting down forests to make room for agriculture. The animals, the native animals, the evolutionary host of many viruses, also become out of balance and what we know from that is that they tend to shed more virus.
So while we evolve with our own viruses and we’re less likely to be sick from them, especially when we’re imbalanced, the same happens with all the other animal hosts. It’s very unusual for an evolutionary host, a reservoir, if you will, like a bat, and when we’re talking about coronaviruses to really be able to be sick from that virus, but that doesn’t mean that they don’t harbor that virus, that it doesn’t replicate in them and spillover and be available when they are stressed or when their life history events push that virus that’s evolved with them to be shed.
So with PREDICT, we were able to look at those hotspots, both from a global perspective and a very local perspective, where we add transmission interfaces that were at high risk for viral sharing amongst the animals and including humans in those ecosystems. And we were able to intensively sample certain species in those locations and really look at the viral discovery. So the more individuals we sampled, the more virus we found, but as we pushed that out into time, we saw that we were saturating that viral discovery curve. And what that showed us was that there was a discoverable, non-infinite number of viruses in each of the host species and that we could predict how many samples we needed to take to get all of the viruses, or nearly all of the viruses, in those species, and then we would also understand how much it costs to sample them.
So that viral discovery curve helped us to understand that we can find all the virus that’s out there, and it’s knowable and we could do it in a 10-year period and it would cost less than 10 percent of a single response to a large epidemic and less than 0.01 percent of what this pandemic is going to cost us. So I think we can reduce that fear by really being more knowledgeable.
Rachel Ehrenberg: Great. We’ll come back to some of the things you’ve touched on again. For now, Raina, you’ve done a lot of work investigating the circumstances and mechanisms that lead to spillover and how this can lead to a pandemic. A simplified version of what happens is captured in four words: infect, shed, spill, spread. Please explain.
Raina Plowright: Sure. And I will keep talking about bats here — bats and viruses — to keep it simple. So we have been working on what are the processes that have to come together to allow the passage of a pathogen from an animal from one species to another and that’s called spillover. When it’s from an animal to a human that’s called zoonoses — zoonotic spillover. And we’ve been able to simplify to those infect, shed, spill, spread stages. And so if you think about it, you’ve got to have an infected reservoir host. So we have to have say a bat that’s infected on the landscape. That infected host has to be able to release that pathogen somehow, so it’s available for the next host. And that happens in many different ways.
So for coronaviruses, we know that they’re shed by bats in feces, for the Henipaviruses, the Hendra and Nipah viruses that I work on, they’re shed in urine. But for something like Ebola the release may actually be during the butchering and preparation of the carcass of a bat for bushmeat hunting, as an example. Then the virus has to be able to make that jump into the next species, that’s spillover. It sounds simple, right? That pathogen just jumps from one individual to another, but it’s actually very complicated and it’s probably very hard.
So if we think about every time we leave our house and breathe the air, we are bombarded with pathogens or microbes from other species. It might be fungi, it might be bacteria or viruses from plants, from soil, from cats, dogs, birds — but we rarely get sick. And that’s because we have a lot of barriers from our immune system, all sorts of barriers that stop that from happening. So if we think about what has to happen for that bat virus to actually get into a person and cause an infection, well, it’s got to be able to get into a human cell. And so the cells will have receptors. You can think of it like as a lock: the virus has got to have the right key to get into that receptor.
So for SARS-CoV-2, the spike protein binds to the ACE2 receptor in humans. But actually many of the coronaviruses in bats don’t have the right protein to be able to gain entrance to human cells. Once the virus is in the cell, it’s then going to be able to take over the machinery within the cell to replicate itself. It then has to be able to get outside the cell. And that’s no mean feat. That’s actually one of the big barriers for influenza viruses from birds infecting us. Then it has to be able to get to more cells, spread through the body, overcome the innate immune system, get to the right tissues for spread. So there’s a lot of processes involved. Then it has to be spread amongst humans and of course that’s facilitated by our large communities, road building and so in all the various ways that we increase connectivity of human communities.
Rachel Ehrenberg: OK. So that leads nicely into where we are today, the current pandemic, everything lined up just so. Jonna, can you break down for us what happened and could things have been done differently to change how things unfolded?
Jonna Mazet: Yeah. First, there was information within our reach. I don’t want to sound like a broken record, but there was information that was within our reach that we didn’t have and we still don’t have and that is, we need to understand the viruses and their transmission circumstances. We know, for example, that many, many more spillover events are happening than we had ever thought of before. And so Raina mentioned Ebola. Well, we can do a specific serology for different filoviruses now and understand in different regions, there is much, much more frequent spillover of Ebola into humans that doesn’t result in either severe illness to be detected or to be diagnosed even in endemic areas, or just one person gets sick and dies.
Because frankly, around the world, people get fevers and die and go undiagnosed. Most frequently, frankly, they either get better or they go undiagnosed. So “fevers of unknown origin” is a big issue that we need to address. We also know from coronaviruses in China, specifically, we’ve done work, our team’s done work and shown that people that interact with and work with animals have a much higher seroprevalence to SARS-related coronaviruses specifically than others. So we didn’t take advantage of these risks that we were knowledgeable about and we didn’t do broad-scale viral discovery and circumstantial analysis to be able to characterize risk.
Second, unfortunately many countries missed the boat. So I’m really proud of our PREDICT teams. Our PREDICT teams around the world actually jumped in and even before there was a specific diagnostic test for SARS-CoV-2 they were able to use more broad coronavirus protocols that we use in PREDICT for a virus discovery, and they were able to diagnose the very first cases being introduced from China into their countries. This happened in Nepal, this happened in Thailand, this happened in Cambodia.
And what that meant was before the second or third week in January, these countries were already identifying introduced cases and throwing their public health systems at it, full steam ahead. So some of these countries have much more active and, frankly, compliant populations that when the government says there’s a risk, put on your masks, stay home, they are more likely to do it than some other countries. So that was another miss in countries that we see still are really challenged and in the US right now we’re so horribly challenged and back on lockdown and our ICUs are almost out or out of capacity in many areas. So that’s the second problem.
And then I think the third and bigger problem, and another one that we can completely fix, is that the academic sector was not fully integrated with the government sector and the private sector. There had been good work done. We actually knew that coronaviruses were a big risk, we knew scientifically, and academically we were waving the flag that we should be ready for this, and “Disease X” was beginning to show up on things like the WHO blueprint and even in drills, but we didn’t provide a plan that was integrated across all the surge capacity needed, especially I think bringing academia and academic labs that can do testing. We didn’t bring those resources to bear for months and months. And that just delayed our response and let the virus unfortunately spread — or we spread it — throughout our nation and it similarly happened in many other countries where people were just a little too comfortable.
So making sure we integrate and making sure that we inspire confidence in science is really, really important. So thank you for this forum and thank you for Raina and other scientists who are stepping up and really taking on the burden of — it shouldn’t be a burden — but it’s a lot of work. We all like to go and just do our research, right, and taking on this new area that we’re maybe less comfortable with, of really speaking out and speaking to the public and making science accessible is critical, but it’s an added task to busy people’s lives. So thank you, Raina, for that.
Rachel Ehrenberg: Thanks, both of you. So early on in that scenario, there’s the tracking of viruses, monitoring wildlife. Raina, you’ve done a lot on how human activities play a role in the emergence of infectious diseases in terms of how we use and interact with the environment, whether agriculture or palm plantations or just the expanding human population. Can you talk about that relationship between ordinary human activity that’s going on and how that relates to the emergence of new infectious diseases?
Raina Plowright: Sure. And I could go back to just that infect, shed, spill, spread cascade and think about all of those processes that are happening on a landscape. And so they’re all affected by how we are treating the landscape and how we’re affecting the animals that live and interact on those landscapes. So just if we start on infection, we talked about having an infected reservoir host. Well, you know, if you go to a crowded bar you’re more likely to get infected with SARS-CoV-2 and that’s the same for animals. I mean, animals, they don’t go to bars, but they are also forced into situations of crowding.
So, for example, during a drought at a watering hole, we’ll see ungulates crowd around that resource. When food is limited animals crowd around the resource, for example, elk on haystacks in agricultural areas, or we see actually the exact opposite. And that’s what we see in Australia, where we’ve been able to track the bat populations over 24 years. We’ve seen that when food is not available, the bats actually disperse into many small populations. They fragment across the landscape because there’s little energy for bats, so they roost really close to reliable sources of food, which are usually very crappy in quality. It’s kind of like camping next door to McDonald’s because you don’t have the energy to go to that nice restaurant you’d prefer.
So we’ve got infected animals on landscapes, but we have to get those pathogens into humans through spillover and that’s all about our behavior and wildlife behaviors, so human-wildlife proximity. And as we fragment landscapes, we create edges, and those edges are places where animals and people can interact. As we create roads, we create access for humans into these high-risk situations, whether it’s bushmeat hunting or guano gathering.
If we think about this, in the next 25 years, we are going to double the mileage of paved roads on the planet and that is going to be happening in high diverse areas that are more likely pristine at this point in time. So, we have a crisis on our hands in terms of human-wildlife proximity. And then there’s the spread issue amongst humans. Ebola was understood as a pathogen that was emerging in Central Africa with limited outbreaks in isolated villages; when Ebola emerged in West Africa in highly dense urban populations that were well-connected, it exploded. And so that’s where our human settlement and density is really important in how these pathogens can spread once they emerge out of wildlife into humans.
Rachel Ehrenberg: So that ties nicely in with the One Health approach. Jonna, let’s talk about this, it works from a premise that human health is very intertwined with the health of animals, plants and the environment. Tell us about the idea behind the organization and the organization, what it’s doing.
Jonna Mazet: Yeah. So, organizationally, thank you for mentioning the One Health Institute. We’re really proud to have been working at the interface that we mentioned — the interface of human, animal, environmental health, including our food, for decades now. But I think a good example of how One Health all comes together is thinking about the food chain. And if we add into the mix of what we might — those of us listening to this webinar might think of as a traditional food chain — if we add wildlife into that human food value chain, I think it helps to bring this One Health concept really home. And that is that we are all connected and what we do and what we desire and what we buy is connected way upstream to other effects that affect our health like where we get the food.
So, for example, in Vietnam, rodents are a regular food item. And rodents in Vietnam, when they are out in the field and are being captured frankly, by hunters to put them into the food value chain we know that we can detect prevalences around 20 percent for coronaviruses. And then as they get into the large market setting and, just as Raina said, you get them concentrated into mixed species and small spaces in a market then we see that prevalence of coronaviruses jump up above 30 percent. And sadly when it gets into the food-delivery portion — so in the restaurant — we see the prevalence getting above 50 percent. So 50 percent of the people in the restaurant are potentially exposed to coronaviruses.
So those rodents that are running around in the field and every person that handles them through that food value chain, and this works for poultry and others, are amplifying that effect again, along that pathway that Raina so eloquently described. So when we think about One Health, what we really want to do is we want to take two central tenets, that is, one, that it can’t just be someone like me, an epidemiologist studying data that’s been collected somewhere else. We need to bring all the disciplines together collaboratively, have mutual respect and really be working to solve these big problems.
So it’s an integrated approach. You need the hunters, you need the farmers, you need all the different disciplines in human public health, in ecology, in environmental engineering. You need to bring those minds together to really think about every step along each pathway of a problem to solve it. And then, you need to put your energy at those interface and connections among people, animals and the environment and the food, including plants, to be able to really solve these problems.
Rachel Ehrenberg: I’m glad you mentioned farmers, and I don’t want people to think that this is just exotic species in strange lands. How does the agricultural sector — we know pigs, swine, there’s swine flu, there’s bird flu — is part of the way forward about integrating the agricultural sector more into some of these efforts? Where does that fit in, Jonna?
Jonna Mazet: Yeah, I truly believe that, that’s another piece. Just as I mentioned, that where we went wrong with this one was not having the different parts integrated and talking to each other. I think moving forward — and we’ve seen that even with influenza especially in the past — if we don’t actually engage small and large agriculture and think about the agricultural systems we’re really not going to be able to address these problems.
There are some real barriers to bringing those sectors together. It’s not just like, “Hey, let’s talk.” There are proprietary issues, there are biosecurity issues, but the concepts that underpin them are exactly the same and the ones that we’ve been discussing today. And that is, the more intensively we push animals, like people in cities or animals on intensive farms together and stress them and mix them, the more likely we’re going to share pathogens. So it behooves us to work together, but there are some obstacles around profit and lots of other issues for doing it.
Rachel Ehrenberg: OK. Raina, I know some of your work has focused on the spread of viruses from bats to horses, you’ve worked with veterinarians in Australia who have to don hazmat gear when they’re going to treat horses and then palm plantations for palm oil. Bats drink that up like soda pop. Can you tell us a little bit about places where spillover is perhaps becoming common or is somewhat predictable, and what we’re learning from studying those areas?
Raina Plowright: Sure. Many people say spillover is unpredictable, that it’s this rare stochastic event that we’ll never be able to predict and I just don’t think that is true. I think it is true for some systems, but I think the key is when you have data and you start to pull together an understanding of the mechanisms on every part of that spillover process, you actually can get to a point of prediction. But SARS-CoV-2 is the third bat-borne coronavirus emerging into human populations causing large outbreaks in 20 years, with SARS in 2002, MERS in 2012 and now this virus.
And each of those events has probably originated from a single spillover event from a bat to another species and then eventually made its way into humans. But if we’re thinking of spillovers, that’s n=3 and that’s just not enough data to be able to understand that spillover process or get to any point in prediction. So what we do is we look to places where spillover is common and then try to disentangle all of the mechanisms, build data, build models, to understand the process. So that’s why we work in Bangladesh on Nipah and Hendra in Australia, where we see spillover every year.
Australia in particularly is becoming a model system because we have spillovers, but we also have long-term data on the bats — 24 years of ecological data. We don’t see spillover just evenly every year. We’ll see one, two, three years with one or two spillover events or none and then we’ll have a burst and that may be five, six, seven spillover events where we see sick horses that have been infected with Hendra virus from a bat. That then allows us to try to find patterns: what’s different about those years when we have a big cluster of spillover events or in years when we have none.
We’ve been able to delineate some factors -- we’ve got a massive loss of winter habitat for bats. So winter is always a tough period because there’s little nectar. We also have natural climatic cycles of El Niño, La Niña. When we have this interaction or intersection of climatic cycles with this habitat loss, we get periods when the bats don’t have enough food. And that’s what I described before when they split up into small groups and go and feed on poor-quality foods and that tends to be in agricultural areas and urban areas.
So that creates an interface with horses. My PhD student has put GPS trackers on bats and we’ve looked at where they go, what they do during these periods. What we find is that when there’s no native food, no native nectar, the bats are feeding on fruit in horse paddocks, but when there’s nectar their behavior is totally different. I mean, it’s like kind of watching, I don’t know if you have ever given your kids soda and then just watching them bounce off the ceiling. It’s literally what the bats do when they have nectar, they fly 50, 80, hundreds of kilometers for the nectar and then they bounce across the landscape, moving huge distances.
And when there’s no nectar, it’s like they’re in one place right next to this poor-quality food. They just move to the same tree night after night. It’s very different behavior. And that’s also when we see the bat shedding the virus, when they don’t have that natural food, when they’re just really low in energy. So we think that there’s perhaps not enough energy for their immune response and therefore these viruses are suddenly shed in large quantities and that’s when we see spillover.
Rachel Ehrenberg: I want to just remind people to submit questions, which we’ll turn to in just a moment. I just want to ask Jonna one more thing relating to what Raina just talked about. So we have some systems that are very well-studied and, or relatively anyway, and we may know where to look. In terms of the work of One Health and PREDICT, Jonna, and a lot of, it seems, involves training local people on the ground to maybe start to gather data that can inform measures, preventive measures we could take in years to come. What are some of the challenges to getting local people involved and trained? Are there places where this has worked especially well? Are there things that make it more challenging than others?
Jonna Mazet: Well, this works begins and ends in communities, and communities need educational leaders and educational systems that can help to inform. I think, as I’ve been saying, getting the knowledge requires the global community to participate. So certainly we’re very proud to have support from the US Agency for International Development to build a One Health Workforce and we’re working with more than a hundred faculties throughout Southeast Asia and Africa to really bring these concepts into primarily graduate education and undergraduate education, but even dipping down into K-12 level, primary school education.
It is challenging in that primarily the experts are in the global north if you will, or the more developed countries and that’s not right. The more developed countries don’t usually bear the burden of at least the beginnings of these events or the day-to-day events. Certainly we are now, because of our maybe arrogance of being able to think that we’ve got everything handled. I think some of the low- and middle-income countries have done better. So we need to learn from each other and share information and do twinning and really improve how people are thinking about these problems so that we can have a next generation of global thought leaders and educators to do this work. I think, it’s very inspiring that the scientific community has come together so nicely in response to this terrible tragedy and we have really seen a level of collaboration in the scientific community like never before.
And then not to let a good tragedy go to waste, just like we’re doing now, the Zoom platform, the Crowdcast platform, all the different electronic platforms are letting us work in ways that we never did before or maybe make people more comfortable with working remotely with each other and that is really, really changing I think the future of the planet, because we also need to commute less, fly around the world less and allow us to walk more gently and reduce those drivers that we mentioned like travel, trade, climate from fossil-fuel use. So I think there are some real benefits that we will recognize later, but it’s hard while everyone’s dealing with tragedy.
Rachel Ehrenberg: So that brings me to a question we have from Annalise and something I wanted to ask anyway, which is, what can we do? What can regular people do to aid in this preventing-pandemic effort and what should we be asking of our institutions and policymakers or our elected officials? Jonna, why don’t you take this one?
Jonna Mazet: OK, well, maybe Raina can top up. I think we all have ideas about this, but I do believe that we can benefit from what we’re learning on drivers and think more upstream about these issues and think about what our behavior is doing that causes us to become exposed and, more broadly, what our behavior is doing to upset ecosystems and change the activities. So really that pushes me to recommend that we think about our behaviors, our consumption, our day-to-day activities that each one of us as an individual — not even as a scientist — as an individual can do to reduce our impact and walk more gently on the planet.
On top of that, I do think that we need to completely change our thinking around diversity, equity and inclusion, in our country for sure. The Black Lives Matter movement has helped to accelerate this thinking, and we can’t go backwards from that. We need to continue to move forward. And many, many of the impacts that we’re seeing — both the exposures and the outcomes of that exposure — are amplified in communities that had less access to things like education, nutrition, health care. And those things cause predisposing factors for severity of illness, as well as exposure. So I think there are things we can do to just be present in conversations and speak up for diversity and equity. Raina.
Raina Plowright: I couldn’t agree more. And that was so eloquently said, thank you. I would add that we need to embrace science, become eloquent, as everyday citizens be eloquent in the science and be advocates for science. Yesterday I had to walk through a picket line of people with banners saying things ironically like, “I want to be able to breathe” — an anti-mask demonstration. So we have a crisis in terms of our literacy and acceptance of science and our understanding of the scientific method. To understand how science progresses through these increments of understanding, always trying to discredit hypotheses and find better information, as opposed to we have to be perfect at the beginning — it’s not how it works.
I think then in terms of our advocacy for our place in the natural world, we need to understand that human health is an ecological service. So it’s a service that nature is providing us, so we need to protect nature to protect ourselves. It’s also a biosecurity imperative. And so programs like the one where in Australia, where we’re trying to now replant that winter habitat that bats lost because it is the root cause of this whole spillover dynamic are critical. Replanting that winter habitat, that should be a biosecurity imperative.
Then there’s the investment in the transdisciplinary research. And Jonna just said it so nicely when she described the One Health approach. It’s that massive research effort of all the different disciplines, trying to understand, how is this happening? How are these spillover events on these landscapes happening? Because once we understand why and how they’re happening, then maybe we can figure out what’s generating this whole cascade of processes and then address that, rather than be in the situation now where we’re just playing catch-up on this pandemic, where the cat left the bag a long time ago and it’s really, really hard to contain. Let’s stop it before it even happens.
Rachel Ehrenberg: Related to that, we have a question about climate change and whether melting glaciers or climate change in general and how that relates to emerging infectious diseases. I think climate change is a problem that can feel far away and like an individual may not be able to do much to tip the scales in any way, and it can also feel an optional concern like mask-wearing, perhaps. How is climate change also a biosecurity issue? Raina, maybe you can talk about some of the work you’ve discovered in terms of bats, and Jonna, please add.
Raina Plowright: Well, climate change is disrupting all of our systems. So everything that we talked about it’s just exacerbated by climate change. If we go back to that infect, shed, spill, spread cascade -- climate is really determining where our natural resources are that the animals depend on, where’s the food, the flowering. For example, the bats’ preferred food is nectar from flowering native forests, but that’s completely climate-dependent as to when that happens. So when it doesn’t happen or when it’s unpredictable or, even worse, when it happens all at once so we have the synchronization effect of extreme climatic events. If all of the forest flower at one point in time, then all of the forest will stop flowering then at another point in time and there’ll be no food available. So it has a huge effect on these natural systems.
I think we see it more in the vector-borne systems where temperature, all of the processes that determine how a pathogen gets from say a mosquito into a human — are temperature-dependent. And so for pathogens like Dengue that do well at warm temperatures, climate change is increasing the distribution of disease across the globe. So there are many, many ways in which climate change is a problem.
Jonna Mazet: Yeah, I can just add on. I completely agree, and there are things that we can do as individuals. I know people think about it as being a really long-term futuring kind of problem. But again, if you’re sheltering at home and working from home, you’re helping with climate variability and long-term climate change. So I commend you for that, even though I know it’s difficult and probably you don’t have much choice.
On top of that, I really want to just go back to your example, Rachel, about the polar ice cap. There are things that are within our knowable timeframe of people’s careers rather than thinking about it as 50 years forward. A lot of people are asking me recently about, well, what about those viruses as the ice melts and the viruses that are in there coming out that we’re not expecting? That’s an issue potentially, but I think it’s a fraction of the problem that we have — viruses that are already out that we’re not even knowing and studying, and that’s why we want to do that good work collaboratively across nations in the Global Virome Project.
But we have been able to document pathogen movement because of climate change. So real health impacts happening right now from climate change can be documented with this polar ice cap issue. And our team has shown that pathogens that previously circulated only in animals in the North Atlantic actually have moved into the Pacific now because of shrinking ice caps and the ability of animals to change their migratory pathways. So we’re seeing vectors, mosquitoes and others, changing their distribution because of warming climate, as well as large vertebrate seals moving with their pathogens into whole new ecosystems and exposing susceptibles. So it is very similar, frankly, to a sick person getting on a plane in one part of the world and moving to another part of world, that one causing climate problems while it happens.
Rachel Ehrenberg: Someone has written in about minks, which I did want to make sure we talk about. This goes back a little bit our bringing agriculture into the fold, in terms of factory farms, animals being raised on fur farms. Can one of you speak to transmission spillover, those situations and events?
Raina Plowright: Well, I think, and actually there’s a report of SARS-CoV-2 in a wild mink now in Utah, which is really, really concerning because one of our big worries with this pandemic is spillback, or reverse zoonosis — when the pathogen that spilled from bats into humans spills into other species like other bat species and so on, and then may potentially spill back to humans. And mink have been one of the most susceptible other species that we have known. Actually, their relatives are used in experiments for developing therapeutics vaccines for humans.
So whenever you aggregate a lot of individuals in a small space you’re creating the conditions that are very good for disease spread. I mean, it goes back to the bar example. We aggregate in the bar, we’re more likely to get SARS-CoV-2. We aggregate a lot of animals in an intensive situation like a mink farm, but also like in wildlife trade, as Jonna had said, that the increase in the prevalence of coronaviruses was seen through the wild trade. And again, that’s bringing a lot of animals together at a really intensive, aggregated experience.
Rachel Ehrenberg: We’re almost out of time. I want to ask each of you — let’s start with you, Jonna — just if there’s a moment that’s stayed with you since the pandemic, whether related to your work or personal moment or otherwise?
Jonna Mazet: Well, you might be able to imagine that having worked for a couple of decades on emerging infectious diseases and trying to raise the flag or help people understand that we need to change our behavior both in the global community, as I mentioned, for environmental impacts but also in the scientific and political climates to work better together, to be able to trust each other and inform each other and find solutions. Seeing that not happen, especially in my own country, where I work every day, has been completely devastating.
I’ve seen three of my friends lose parents already to Covid-19 and I really, I guess, have been trying to help for a long time, and it’s been pretty hard to be in the situation of now what? But you just get on with it, you contribute, you... I’ve been just trying to continue to advocate for science and continue to show that the risks are knowable, we can rank the risks from viruses that we find. Raina’s described some of that. We’ve done a bunch of work with many, many scientists around the world to come up with risk factors and ranking criteria for viruses that are newly discovered. All of that is possible, but we need to do the work. We need to do it collaboratively, and then we need to act on it.
Raina Plowright: So two moments in the pandemic… getting that first email about a new virus in Wuhan, undiagnosed pneumonia, finding out it was a SARS-like virus, a bat virus, and then watching this unfold day by day, really hour by hour at the beginning. The second moment was, I was boarding a plane in Bangladesh in January and I got a text with the New England Journal of Medicine article showing asymptomatic transmission. And I immediately donned my N95 mask and I remember my heart rate increasing and I thought this is going to be really bad, really, really bad. It was a moment of terror. And then just watching this unfold.
I’ve worked on the idea of pandemic potential pathogens my whole career, but the actual unfolding of the pandemic was just beyond anything I could imagine. So terribly awful. But there have been silver linings, and I’d say the silver lining for me has been watching my science colleagues rally around this and put enormous energy into doing everything they can to help when it’s of no benefit really personally or professionally, but just wanting to help, whether it’s setting up testing on campus, whether it’s communicating science, whether it’s helping our local public health officials. It’s really been inspiring just to see wonderful people doing what they can to help others.
Rachel Ehrenberg: Well, I want to thank both of you. It’s an enormous service and it’s been a pleasure as much as it’s also very concerning stuff we’re talking about. So Jonna, Raina, thank you so much for joining today. Everyone in the audience, thank you for joining the event. If it’s been a good experience, we just launched a donation drive at Knowable, which is free to all so please consider donating. You can do that at knowablemagazine.org. I’d also like to thank the Alfred P. Sloan Foundation, the Gordon and Betty Moore Foundation for their wonderful support of Knowable Magazine. And again, special, thanks to Jonna Mazet and Raina Plowright for the fascinating discussion.
This conversation will be posted on the Knowable website, where it will be free to view and share. Look for the “Reset” collection and additional resources including links to articles, Knowable articles that where Raina and Jonna have been interviewed, scientific papers, links to some of the projects that they’re involved in will also be on that event page.
Let me remind you that this is one in a series of discussions. The next one is “How to Change Behavior During a Pandemic: From Personal Habits to Public Health.” It’s going to take place on January 15th at noon Pacific. The registration for that will be opening soon, and the best way to keep up with these discussions and as much reporting as we get to do on the work of Raina, Jonna and other scientists is to sign up for our newsletter, which you can do on our website, knowablemagazine.org.
And that’s all from me. Thank you, everyone. Have a safe and happy as you can holiday season. Thanks again for joining us.
Jonna Mazet: Take care. Happy holidays.
Raina Plowright: Thank you. See you later.
