When piglets began dying on farms in southern China in late October 2016, their owners thought they knew what was going on. Baby pigs on farms are especially vulnerable to illness, and one particular disease, porcine epidemic diarrhea virus, causes exactly the symptoms the piglets were having—vomiting, severe diarrhea, death from dehydration, and stress. The farms had seen it before.
But when animal disease detectives swooped in, they found something puzzling. Early tests were positive for PEDV, but by January 2017, they began coming back negative—and piglets were still dying. The mystery epidemic had spread to four farms and was killing the piglets, almost 25,000 of them. By the time the outbreak burned out in May, it seemed to be something no one had seen before. They were right: The cause of the piglets’ illness, identified by the US-based EcoHealth Alliance and published in Nature last week, was a totally new virus.
Solving that microbial mystery is an accomplishment, but its origins should make us nervous. This pig virus, since dubbed swine acute diarrhea syndrome coronavirus, is just one example of the viral threats that develop where humans bump up against the fringes of the nonhuman world—along roads that have been paved into forest, or farms that have pushed out from existing cities. Understanding those intersections is a critical part of defending against new human viruses. We need more surveillance, and much more robust defenses, all along that border.
“Globally we let viruses emerge and trickle through our net quite often,” says Peter Daszak, parasitologist and the president of EcoHealth Alliance. “That needs to stop. We need to start taking these things seriously.”
Which isn’t to say we’re not trying. The pigs’ illness and the virus were associated thanks to a USAID-funded project called EPT/Predict, which tries to find viruses as quickly as possible. All around the world, scientists capture viral samples from wildlife in areas where spillover into new species is likely. One of those countries is China. Earlier in 2016, before the outbreak began, the program took samples from horseshoe bats in Guangdong, which fly over farms, roost in farm buildings, and generally spend their lives where humans, domesticated animals, and wildlife come together. Sequences of those samples went into a database, where researchers matched them with samples from the pigs.
Predict also uses molecular tools to understand whether those viruses are (or may become) a threat to human health. It studies the behavior of humans who live along the border with wildlife to understand what makes them vulnerable. And with all that data, it uses predictive modeling to locate where the next spillover might occur. Lab work on the new virus shows that it doesn’t bind to human cells—that is, the strain found in the Chinese pigs isn’t capable of causing the kind of infection that sparked the rapidly moving SARS epidemic. (The SARS virus, which turns out to be a relative of this one, also resides in horseshoe bats.)
But that shouldn’t be taken as any kind of guarantee. “New viruses are never one-off events,” Daszak says. “Look back at just about every big disease of people: HIV spilled over into humans seven, eight times before the last time created the modern pandemic. Hantavirus, which was transmitted by mice in the Four Corners area of the US, had spilled over before; there were Navajo legends about it.
“When viruses spill over into people from wildlife and start to go person to person, they don’t just remain static; they evolve and become better at infecting people.”
Predict was launched in 2009, and now it reaches 30 countries clustered in Asia and sub-Saharan Africa. But that’s only a small fraction of the network of detection that we ought to be deploying. “We need spillover surveillance anywhere where the barrier between humans and wildlife is porous,” Maimuna Shahnaz Majumder, a computational epidemiology research fellow at HealthMap, says by email. “This includes regions that are vulnerable to climate change and deforestation.”
To do that, some researchers have proposed a project that’s laser-focused on disease detection: the Global Virome Project. Predict detects new viruses, yes, but it spreads its resources to study human behavior and disease epidemiology too—not to mention training lab researchers and field epidemiologists, about 2,500 so far, in the countries where it is harvesting samples.
The Global Virome Project, described in Science in February, would focus on Predict’s viral surveillance and scale it way, way up. Daszak and a slate of other distinguished researchers, including virus-hunter Nathan Wolfe, have laid out this simple math: Science so far has identified 111 different families of viruses. Among them, 25 families contain viruses that either have been shown to infect people or seem likely to. But not all the viruses in those families have been identified yet. In fact, the total estimate of how many undiscovered viruses those families still contain hovers at about 1.67 million; the estimate of how many would be dangerous to people, if we came in contact with them, ranges from 631,000 to 827,000. The goal of the Global Virome Project would be to identify as many of that 1.67 million as possible, and do deep analysis on the ones most likely to be human threats.
No one pretends this would be cheap. Going for the entire “global virome” could cost more than $7 billion. Aiming for 71 percent of it—which would capture most of the presumably dangerous viruses, though not the ones that are hardest to find—brings the cost down to $1.2 billion.
Which is a lot of money. But given how much each new pandemic costs the world, the researchers argue that it’s more than worth the expense.
“There are two ways to discover new pandemics,” Daszak says. “We can get out there and look in wildlife, discover where the viruses are and block transmission. Or we can sit here and wait, and hope we have the right vaccines and drugs. The second approach is what we do now, and every time it happens, it overwhelms the healthcare system.”
Fifteen years ago this spring, SARS ripped across the world. Before it sickened more than 8,000 people in 27 countries and killed 774 of them, that virus was a mystery too. It first appeared in late 2002, in a town in Guangdong province in China just 60 miles from the pig farms where the new coronavirus was discovered. Later, a visitor from Guangdong with a strange flu-like illness carried it into a Hong Kong hotel and then into a hospital—and within a week, the virus had hopped on flights around the world.
“SARS cost the world at least $30 billion,” Daszak says. “Surely it makes more sense to spend less money up-front.” Then the next time a virus prepares to jump the fence, we’ll be ready.