Map: Where the next coronavirus could pass from bats to humans
This story is part of Down to earth, a Vox report initiative on the science, politics and economics of the biodiversity crisis.
For more than a year, we have been living with the devastating consequences of a highly transmissible coronavirus. While the pandemic it has caused is unprecedented by many measures, the new coronavirus that causes Covid-19 is just one of many SARS-linked coronaviruses lurking among wildlife in some parts of the world, many of which could theoretically pass to human populations under the right conditions.
Determining what these conditions are is an urgent priority, and scientists have made a lot of progress on this front. They learned, for example, that when forests are fragmented by deforestation or roads, it increases the likelihood of a virus ‘spreading’ from animals to humans. Moreover, a mystery is where, exactly, these conditions meet to create the highest risk of the next coronavirus emergence.
A new analysis, published Monday in the journal Nature food, begins to answer this important question – in particular, by identifying where another coronavirus could jump to humans from the horseshoe bats, which are known to carry SARS-linked coronaviruses. By combining data on horseshoe bat habitats, land-use change, Population density and other factors known to increase the risk of fallout, the researchers produced a map of “hot spots” in Asia and Europe where the risk is highest.
While the study does not offer new information on the origins of the new coronavirus, which researchers suspect to be from bats, it does indicate where similar coronaviruses could emerge in the future. Alarmingly, the study finds that in many regions, especially southern China, these fallout risks are high. And that provides even more evidence that preventing the next coronavirus pandemic will require reducing the root causes of fallout, such as deforestation – not just responding to outbreaks after they occur.
The perfect recipe for a spillover
Zoonotic disease outbreaks – i.e. those of animal origin – are on the rise. And, unfortunately, we are largely to blame. Among the main drivers of the pandemic are deforestation and destruction of wildlife habitat, according to a report by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES). In fact, almost a third of new diseases that have appeared since 1960, like Ebola, can be traced back to land-use change, the report says.
Basically, the problem with land use change is that it creates more opportunities for humans to come into contact with wildlife. Fragmentation of a forest, for example, increases the amount of edge – where forests meet human settlements – and pushes wild animals into urban areas. “The edges of tropical forests are a major springboard for new human viruses”, group of scientists written in Science last summer.
Studies have shown that humans and their farm animals are more likely to come into contact with wildlife when more than a quarter of the original forest has been lost, and that fruit bats are more likely to feed near humans when their habitat is affected. In addition, destroying habitats maybe doing wildlife that can harbor human pathogens – such as bats and rodents – is more abundant.
Land use change is just one factor that scientists believe could help a virus pass from animals to humans. Dense human populations also pose a risk, as do intensive agricultural practices. Cattle, for example, can harbor a number of pathogens and have been implicated in several major epidemics, such as the H1N1 flu and the Nipah virus. The risk is even higher on modern farms, which tend to pack large numbers of animals in small spaces, and often these animals have weak immune systems.
While these risk factors are pretty clear, what’s less obvious is where they converge and what it means to us.
Mapping the risk of viral epidemics
To date, most research on coronaviruses has focused on how they pass from one human to another, said Paolo D’Odorico, study co-author and professor of environmental science. at the University of California at Berkeley. While this serves an obvious benefit, it has left a gap in our understanding of how these viruses move from wildlife to humans, which D’Odorico and his co-authors sought to help fill.
When the lockdowns began last year, they began collecting data on land use change, livestock density, human density and a handful of other spillover factors. Then, they overlaid this data with the habitat of horseshoe bats in Asia and Europe. Horseshoe bats are known to harbor a large number of coronaviruses linked to SARS, including one closely linked to SARS-CoV-2, the virus that causes Covid-19.
With all this information, the researchers produced the hotspot map, which highlights areas where these risk factors overlap with bat habitats. Dark red dots indicate areas where there is a high risk of a coronavirus spreading to human populations, said David Hayman, another co-author and professor of veterinary science at Massey University in New Zealand. Blue dots, on the other hand, indicate where there are relatively few overflow factors.
The main takeaway, says Hayman, is that there are still large parts of southern China where there is a high risk of a new coronavirus emerging. “Conditions [for spillover] are still there, ”said Hayman. “This means that there may well be new emergence events.”
Importantly, scientists have also mapped areas that are not yet hotspots, but could soon become hot spots if forest fragmentation increases or other known fallout factors. They include an area south of Shanghai, China, in addition to Japan and the northern Philippines.
“These are the places where you need to do disease surveillance to watch for new emerging infections,” Hayman said.
Two researchers who were not affiliated with the study said the research was important and added a new dimension to the conversation about coronavirus outbreaks. Some previous efforts to identify the next emergence have relied on the location of past outbreaks, which is not so helpful, said Andrew Dobson, professor of ecology and evolutionary biology at Princeton University. This research goes further by focusing on the causes of the fallout in the first place, Dobson said.
“This study paints a very good picture of where in the world some of the most important factors driving zoonotic viruses like SARS-CoV-2 to emerge overlap,” said Jon Epstein, vice president of the science and awareness at EcoHealth Alliance, which is a non-profit organization focused on wildlife and public health. (Epstein was not involved in the study; however, his EcoHealth Alliance colleague Peter Daszak was involved in the World Health Organization’s effort to investigate the origins of the novel coronavirus earlier. this year, which triggered controversial.)
Just because a particular area has a higher risk of a contagion event does not mean that it is likely to occur or that it will become a pandemic. Various measures, such as disease protection protocols for livestock – which were not incorporated into the study – can reduce the risk.
Prevent another devastating coronavirus outbreak
When you are experiencing the devastation of a pandemic, it is difficult to look to the future, let alone prepare for another pandemic. But it’s essential that we do, scientists say. They believe that there is almost 1.7 million viruses not found in mammals and birds, and half of them could infect humans.
Covid-19 has been a wake-up call, Dobson said. “The most important thing is to determine what we need to do to reduce the frequency of these events,” he said. And we already have a pretty good idea of where to start: to stop deforestation and forest fragmentation.
People who live in hot spots, for example in southern China, “should put more pressure on politicians to address these mechanisms,” Dobson said. Policymakers can also use the analysis to determine how to prevent certain regions from becoming hot spots in the future, said Cristina Rulli, lead author of the study and professor of hydrology at Italian University Politecnico di Milano.
The cost of conserving forests and regulating wildlife trade would be far less than what we pay for pandemics, according to an IPBES study. Reducing deforestation has a host of other benefits as well: Healthy forests absorb carbon dioxide, clean the air and water, and harbor biodiversity.
Meanwhile, the rapidly growing agricultural industry should take action to prevent livestock from becoming infected, Epstein said. “As farms grow and scale up, they are vulnerable to outbreaks of wildlife viruses,” he said. “So more specifically, one thing we can focus on is farm biosecurity.” This includes measures like ensuring that bats do not roost around a farm.
We also have a lot more to learn, experts say, about how fallout works and what’s happening on the ground in those areas.
“The biggest scientific problem of this century is understanding how natural ecosystems work,” Dobson said. We’ve known how to send a rocket into space for decades now, he said. But understand how diseases spread from wildlife to humans? Well, that’s a “much more difficult set of math problems.”