Inside a bright, bustling laboratory, virologist Ryan Troyer holds up a tray of tiny test tubes.
“Are these spleens?” he asks a nearby doctorate student. “Or are these kidneys?”
This round of samples is spleen tissue — from a Chinese species of bat, to be precise. And to Troyer, the little globs of goop are a treasure trove: potential reservoirs for undiscovered coronaviruses that could, one day, spark future pandemics.
Troyer knows much better than most how often animal-borne diseases leap into humans. Over the last two decades, the Western University researcher has studied species ranging from black bears to bobcats, and infections ranging from dengue virus to HIV.
Not every viral threat has the potential to wreak havoc at the level of COVID-19, an illness that’s now kept the world in its grip for nearly two years.
But the disruption to animal habitats caused by climate change and encroachment caused by booming population growth is hiking the chance of another pandemic — one likely to happen through the spillover of a pathogen from animals to humans, and almost surely within our lifetime.
With that possibility looming, scientists around the world are gathering animal samples, building viral surveillance networks and collaborating on potential vaccines.
For Troyer’s team, it’s a race against time to maintain momentum before another global health crisis hits. His latest research involves analyzing hundreds of samples of bat tissue, aiming to ward off a worst-case scenario by building a bank of coronavirus vaccines.
It’s a daunting task, but an urgent one. The opportunities for virus transmission from animals to humans are only increasing over time, Troyer warns.
“It’s likely that this is going to be something we need to keep dealing with in our world, and need to be prepared for in any way that we can.”
History is rich with examples of pathogens leaping from animal hosts into humans and producing new, unfamiliar threats — ones our immune systems aren’t yet prepared to fight.
In many cases, it’s a run-of-the-mill event. Perhaps an isolated illness, or an outbreak relatively small in scope. But in certain cases, disease-causing organisms have latched onto their new human hosts a little better, spread a little faster and managed to explode to the level of a pandemic.
In the 1300s, the Black Death tore through Europe, Africa and the Middle East, all thanks to a bacteria spread by fleas feasting on wild rodents. The 1918 flu pandemic, which infected an estimated 500 million people globally, came from an H1N1 virus that originated in birds. SARS, MERS and swine flu were all traced to non-human hosts.
And COVID-19 has long been suspected to have an original animal source, regardless of whether the spillover to humans happened in a market or a lab.
Climate change, many scientists speculate, is increasing the risk that animal-borne diseases will transfer to humans in the decades ahead. Shifting global temperatures are forcing some species to adopt new mating or migration patterns — from tiny ticks to Arctic caribou — all while humans encroach on existing animal habitats.
“We’re disrupting their habitat,” said Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan.
“Anytime you have that ecological disruption, you have unpredictable results. And maybe you’re getting exposed to a virus that you wouldn’t have been otherwise exposed to.”
There’s also a whole lot of us dotting the globe: Billions of mouths to feed, billions of animals needed for food, and billions of daily interactions with birds, pigs, bats and other wildlife.
“I think many more people now are aware of the fact that these viruses can come from animals, but I don’t think people are fully aware — or fully prepared to accept — that this is largely driven by human activity,” said Simon Anthony, a researcher and associate professor in the department of pathology, microbiology and immunology at the UC Davis School of Veterinary Medicine in Sacramento, Calif.
A review of 40,000 species around the world found that roughly half were already on the move as a result of changing climate, according to a recent report from a pandemic prevention task force convened by the Harvard Global Health Institute.
Report co-author Ari Bernstein is among the researchers ringing the alarm about the coming heightened risk of what scientists call “zoonotic spillover.”
Deforestation, wildlife handling and mass farming all present risks for spillover, he said.
When asked if humanity could experience another global threat like COVID-19 in our lifetime — perhaps within the next few decades — Bernstein is quick to answer: Yes.
His sense is that an influenza pandemic is most likely.
“It’s hard to give a really precise estimate, because, in part, it depends on how well we do surveillance in, particularly, pig and poultry farms,” said Bernstein, noting the 2009 H1N1 virus, or swine flu, has been traced back to pig farms in Mexico.
“There was a massive flu pandemic early in the 20th century, and then we had, in short order, sort of three in the latter half.”
It’s unrealistic to try to avoid future pandemics by telling people not to travel, or to stop living in cities, Bernstein said. “That leaves us with either focusing on trying to contain these things after they’ve already started to spread ... or working upstream.”
Preparing for future pandemics is both increasingly urgent and immensely complicated. Figuring out which of the world’s animals could carry the next major threat is no easy task — and preventing an explosion into human populations might be impossible.
Yet there’s extensive collaboration happening to ward off another global catastrophe, according to Anthony, from surveying wildlife and looking for viruses, to developing potential vaccines.
“There’s a lot of creativity and a lot of ideas about what we need to do,” he said.
Before there’s any hope of developing a vaccine to ward off potential pandemic-level threats, scientists need to do the dirty work to track the animals that might be carrying those pathogens.
In rural Belize, amid the remnants of the Mayan city of Lamanai near a remote jungle lake, a team of roughly 40 scientists spent several weeks this fall studying vampire bats.
It meant sleepless nights spent setting up large nets, at least six metres long, in strategic areas where the animals typically fly after sundown.
On trips like this, researchers live on the bats’ schedule, catching them in the nets in the evening, bringing them back alive to a classroom to study and adding tracking tags — before sending the creatures back into the night.
Speaking on a crackly Zoom call from the site, renowned Canadian bat biologist Brock Fenton said the scientists typically take biopsy punches of the bats’ wing membranes to provide genetic information, alongside samples of their digestive tracts and blood.
“We’re also screening for different pathogens,” said Dan Becker, an earlier trip attendee and an assistant professor of biology at the University of Oklahoma.
“We try and get as many samples as we can from each individual bat, so that we’re really maximizing the kind of data that we’re getting back in the lab.”
While a large part of the effort is to learn more about the bats themselves, the tissue can also fuel research like the project underway back at Western, where Fenton is a professor emeritus.
Some of his own collection of samples — bat droppings, specifically — are among those being analyzed by Troyer’s lab team.
Fenton also put the researchers in touch with an opportunity to access decades worth of samples, all housed in one place.
Deep in the underbelly of the Royal Ontario Museum in Toronto, freezers set at a temperature of –80 C store bat tissue from around the world, dating back to the late 1980s.
“These specimens might actually be even more valuable than what we originally thought they were going to be,” said Burton Lim, the museum’s assistant curator of mammalogy, during an interview inside the ROM’s bat cave exhibit.
Over the last three decades, Lim has taken one or two field trips each year to countries like Guyana, Ecuador, Peru, China, Vietnam, Malaysia, Indonesia and the Ivory Coast. He has amassed roughly 15,000 bat specimens from 400 different species.
He began collecting and freezing tissue samples in liquid nitrogen in order to study taxonomy and genetics, but the technique also preserves whatever viruses are hiding in the mammals, he explains. And bats carry a lot of viruses.
That’s in part because they’re diverse and plentiful across the planet — there are likely more than 1,000 different species, making up a fifth of all types of mammals. But it’s also a bit of a mystery, as these animals don’t actually get sick very often, says Lim, even though the viruses they carry can sometimes ravage humans.
While scientists like Lim, Becker and Brock are busy collecting field samples to understand more about these curious creatures, others are striving to build surveillance systems to track all that data — and potentially make important predictions: Which animals, regions and viruses could result in the next pandemic hotspots?
Here in Canada, interdisciplinary researchers from institutions across the country that have been tackling COVID-19 are also now laying the foundations for a pandemic preparedness network.
It’s currently known as CoVaRR-Net, short for the Coronavirus Variants Rapid Response Network.
That work includes a focus on surveillance of animals in the country, said Rasmussen, who leads CoVaRR-Net’s host-pathogen interaction team.
The goal is to identify which species are carrying the virus behind COVID-19, and if it’s acquiring mutations that might be capable of altering the trajectory of this pandemic, much like the world has experienced with the dominant delta variant or recently-discovered omicron.
Minks, for instance, are known carriers. White-tailed deer populations in North America are considered a major reservoir for the virus as well.
“New variants could emerge from these different animal species through their interactions with people,” warned Rasmussen.
So what if you could somehow spot an early warning sign — and then act on it?
That’s the hope among those working on the Global Virome Project, a collaboration among various organizations and research teams to detect the bulk of the world’s yet-unknown viral threats and stop them in their tracks.
The team shares their findings through an online tool that directly compares hundreds of viruses and corresponding risk factors — such as global distribution of a species and level of interaction between those hosts and humans — to identify those at the highest risk of spilling over from animals to humans.
(Coronaviruses infected bats and mice are among those currently deemed among the highest spillover risk, according to the tool.)
Dennis Carroll, the organization’s chair, spent more than a decade as director of the United States Agency for International Development’s Pandemic Influenza and other Emerging Threats Unit. During that time, he designed and led PREDICT, a project geared toward identifying high-risk viruses in animals.
A firm believer that pandemics are preventable, Carroll said there’s been a “really steady drumbeat” of emerging diseases coming out of Asia in recent decades, largely tied to population growth that has disrupted wildlife habitats.
And a similar pattern is being observed elsewhere, he said. “That epicenter for hotspots is going to gradually shift more and more, I believe, to Africa.”
Yet for every prediction in the pandemic preparedness space, there’s another voice warning that even the most diligent efforts can’t possibly zero in on which specific region or species could spark a catastrophic viral spillover event.
Becker, from the University of Oklahoma, said it’s a little like searching for the proverbial needle in a haystack.
“I think the hope with doing all this wildlife surveillance — studying the ecology of these animals — is that hopefully we could try and cut off transmission before it gets to that point,” he said. “And that’s easier said than done.”
First you need to have a virus that has the ability to infect people, and then it has to have the opportunity to do so, notes Anthony, from UC Davis.
“Predicting both of those things is almost certainly impossible,” he said. “Because there are just so many barriers along the way, so much randomness in that whole process.”
All the challenges that come alongside predicting, preparing for and potentially preventing another pandemic haven’t stopped researchers from trying.
Standing in the Western University lab near a fridge with a “Guano Happens” sticker slapped on the side — guano, for the uninitiated, means bat droppings — virologist Stephen Barr says he believes it’s just a matter of time before the world is hit again by a threat the likes of COVID-19.
“It may not be a coronavirus,” he said. “It may be something else that may be more dangerous.”
Barr is working alongside Troyer in the push to identify viruses in order to build a bank of future vaccines. They’ve analyzed dozens so far, but their work is just one small piece of the puzzle.
It’s also fragile, rooted right now in the momentum and funding tied to the current global crisis.
“At this moment in time, there is a lot of motivation — and there is certainly funding — that has gone in Canada and in the U.S. to address emerging viruses, potential pandemics,” said Rasmussen.
“My question is: Will that investment be sustained?”
Right now, the world has just a “brief window of opportunity before attention shifts to other issues,” warns a scathing recent report from the Global Preparedness Monitoring Board, an independent pandemic readiness panel formed by the World Health Organization (WHO) and World Bank.
In late November, WHO also pushed the need for a global action plan to tackle future pandemics.
“More than any humans in history, we have the ability to anticipate pandemics, to prepare for them, to unravel the genetics of pathogens, to detect them at their earliest stages, to prevent them spiralling into global disasters — and to respond when they do,” said Dr. Tedros Adhanom Ghebreyesus, the organization’s director general.
Here in Canada, the Public Health Agency of Canada says it has begun work to strengthen preparedness and response for future pandemics, based on March recommendations from Canada’s auditor general — including updating and testing emergency plans, improving health data collection, and improving surveillance and risk assessment tools.
Troyer says the COVID-19 crisis caught most public health authorities and governments off guard, himself included.
Yet against all odds, he’s optimistic the world has an opportunity to be ready for another threat to global human health — and he hopes his team’s work might play a role.
“It’s not going to really be possible in the future to prevent the transmission of viruses from animals to humans,” he said. “But if we’re ready to prevent a small outbreak from becoming a pandemic, that’s really, I think, the key.”
Editing and layout by Amy Husser | Top image credit: Pond 5