Zoonotic Diseases

Introduction

A bamboo rat, still in its bamboo home, is offered for sale at an outdoor food market in Myanmar. Scientists say the sale of such animals in markets across Asia plays a major role in the spread of zoonotic diseases, which travel from animals to humans. (Getty Images/LightRocket/Jerry Redfern)

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Overview

In the second week of January, a 61-year-old man died from a mysterious pneumonia that was causing a spate of illnesses from an unknown virus in Wuhan, China. The man was a regular customer at Wuhan's giant seafood market, which also sold exotic animals, some live, for meat. Of the first 41 cases of pneumonia tied to the viral infection that first arose in December, two-thirds had either been workers or customers at the market.1

According to a widely circulated menu and to reports from vendors and observers, offerings at the market included snakes, dogs, baby crocodiles, arctic foxes, raccoon dogs, bamboo rats and civet cats, sometimes butchered on site.2

At such Asian markets, exotic animals are often stacked in cages on top of animals they would never encounter in nature. Exchanging excretion and saliva under stressful conditions makes animals prone to contagion and creates a petri dish for viruses to jump from one species to another, scientists say.

Speculation was rampant that the Wuhan market was the source of the virus that causes COVID-19, which erupted into a pandemic that has killed hundreds of thousands of people across the globe. But in recent months, scientists have cast doubt on the theory. They instead fear that the virus jumped earlier from an animal to a human, perhaps in the wild, and that the market's crowded conditions simply helped to spread the virus from one infected human to many others.3

A COVID-19 patient is transported by ambulance to Mt. Sinai Morningside hospital in New York City on May 18. The virus is only the most recent example of a disease that originated in animals and then spread widely and lethally among humans. (Getty Images/NurPhoto/John Lamparski)

Regardless of what exactly happened, COVID-19 is just the most recent example of a growing threat to human health — zoonotic diseases, which leap from animals to humans and which, if the virus mutates successfully in humans, can also be transmitted from human to human. Researchers believe COVID-19 spilled over from a horseshoe bat in China, possibly to another intermediate animal, such as an endangered pangolin, considered a culinary luxury in China, and then to humans.4

Scientists have long warned of a new epidemic of zoonotic diseases, but it is only recently that the environmental roots, such as human encroachment on wild habitats, are gaining the kind of public and media attention given to climate change.

Some of the most well-known epidemics originated with animals, including HIV (from chimpanzees), severe acute respiratory syndrome or SARS (from bats) and Middle East respiratory syndrome or MERS (from camels). An epidemic is a disease that affects a large number of people within a community or region, as opposed to a pandemic, which affects most of the globe.

Scientists say the frequency of such outbreaks has been increasing in recent years. According to estimates, 60 to 75 percent of newly emerging infectious diseases can be traced to animals and more than 70 percent of those come from wildlife.5

In fact, scientists have been predicting a zoonotic epidemic similar to COVID-19 for more than a decade, and some even targeted coronaviruses from bats, which likely produced both SARS and COVID-19. For example, in 2007, a Hong Kong scientists' study of SARS said the presence of SARS-like coronaviruses in horseshoe bats, “together with the culture of eating exotic mammals in southern China, is a time bomb.”6

Andrew Cunningham, a professor of wildlife epidemiology at the Institute of Zoology, London, said in March, “The emergence and spread of COVID-19 was not only predictable, it was predicted [in the sense that] there would be another viral emergence from wildlife that would be a public health threat.”7

Some scientists and advocacy groups say the spread of both new and existing zoonotic diseases can be attributed to declining biodiversity in natural animal habitats, as humans slash forests for agriculture, mining, roads or housing. Other studies pinpoint increasing human contact with wild animals as the root of growing risks.

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With the human population growing and global trade and travel expanding, the human activities that trigger outbreaks “are accelerating and magnifying globally, which is why we're seeing more and more outbreaks happening and will continue to,” says Jonathan Epstein, one of the researchers who discovered that horseshoe bats were the likely origin of the SARS virus, and who is vice president for science and outreach at EcoHealth Alliance, an environmental health research group in New York. “The single biggest cause of these epidemics is people…. We're encroaching on natural systems and disrupting them, and it's leading to epidemics and pandemics.”

Yet traditional public health approaches to disease outbreaks have ignored the role played by environmental destruction, says Samuel S. Myers, an environmental health scientist at Harvard University's School of Public Health, who is promoting a new discipline, planetary health, to unite environmental health and medicine.8

“The way we're transforming our natural systems is a dominant driver of the global burden of disease,” he says, but “we're completely unequipped to confront these [environmental] problems as a public health community.”

That problem extends to the approach to pandemics such as COVID-19 by the U.S. Centers for Disease Control and Prevention (CDC), says Howard Frumkin, a former director of the CDC's National Center for Environmental Health and professor emeritus at the University of Washington School of Public Health. “If you focus on vaccines and public health strategies like contact tracing and isolation, you may overlook some of the root causes of diseases that lie outside the biomedical world,” he says.

Along similar lines, several bills in Congress aim to promote greater collaboration among environmental experts, veterinarians and human health experts to anticipate and tackle future pandemic threats in an approach known as One Health.9

Some scientists are trying to raise money to create a comprehensive library of zoonotic viruses, saying such a repository could predict and prevent pandemics. But critics point out that similar efforts along those lines, including one funded by the U.S. Agency for International Development (USAID), failed to find COVID-19.10

“It's hard to claim success in searching the world over for the virus that will cause the next pandemic when this virus eluded all that tremendous effort,” says Richard S. Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies, a private research center in Millbrook, N.Y.

Many scientists agree that the dramatic changes humans have imposed on the planet as a result of world population growth is one major reason for the increase in new zoonotic diseases. “The 21st century is paying the price for what happened in the 20th century,” when the world population grew from 1.6 billion to more than 6 billion and humans pushed deeper into virgin forests, says Dennis Carroll a former USAID official who oversaw efforts to forecast zoonotic disease outbreaks.11 “As we're accommodating this increasing population, we're seeing the increasing frequency and intensity of these spillover events” when diseases leap from animals to humans, he says.

As the world's population heads toward a projected 11 billion people in 2100, developing countries are increasing their wealth and their appetite for meat, with an accompanying demand for more agricultural land in the vast tropical rain forests of the Amazon and Congo River basins.12

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The loss of biodiversity that results is a major cause of zoonotic disease, according to Ostfeld. As humans cut down and transform virgin forests, coming into extended contact with displaced wild animals and their viruses for the first time, “we've made [these regions] increasingly dangerous by disturbing them and fragmenting the natural habitats,” he says. But other scientists question Ostfeld's biodiversity theory, arguing that urbanization and growing wealth helped reduce infectious disease rates between 1990 and 2010.13

“Cities bring people into close contact with doctors, make it efficient for public health to do mosquito spraying, vaccinations, offer drugs to infected people. Cities are good for people's health,” says Chelsea L. Wood, assistant professor at the University of Washington School of Aquatic and Fishery Sciences. “When you stack up biodiversity against all these other drivers, biodiversity is totally inconsequential.”

Experts also disagree on whether governments should ban the trade in exotic animals for human consumption.

“We're creating the perfect storm. If you're a virus whose goal is to spread, you couldn't design a better system to aid and abet a pandemic than these wildlife markets” in Wuhan and across Asia, said Steven Osofsky, professor of wildlife health and health policy at the Cornell University College of Veterinary Medicine. “A lot of these pathogens are meeting species they've never met before, and that's when we have these viral jumps — and create the situation we're in now.”14

Some researchers and environmentalists argue that certain kinds of well-regulated legal wildlife trade pose little danger of transmitting disease, but other environmental groups dispute that.

As scientists, conservationists and members of government in the United States and around the world debate the threat of zoonotic disease, here are some of the issues they are considering:

Is loss of biodiversity increasing the spread of diseases from animals to humans?

Environmental advocacy groups and some scientists say human incursion into natural habitats is causing viruses that circulate harmlessly in animals to jump increasingly to humans, with sometimes fatal consequences. Other scientists, however, argue that the loss of biodiversity is not necessarily a bad thing because it can reduce the populations of disease-carrying animals.

A widely cited study by British and American ecologists estimated that outbreaks of newly emerging zoonotic diseases are occurring about two to three times more frequently per decade than in the 1940s.15

That increasing frequency is “pretty clearly linked to our human footprint and what we do on the planet — building roads, cutting down forests, global trade and travel — all increasing exponentially,” says Peter Daszak, president of EcoHealth Alliance, a nongovernmental research organization, and a co-author of the study.

A fire cleared out this swath of Amazonian rain forest near Porto Velho, Brazil, in 2019. Clearing forestland for human activities has contributed to the spread of zoonotic diseases, scientists say. (AFP/Getty Images/Carl De Souza)

“In some areas where there is a high risk of emerging zoonotic disease, maybe we shouldn't cut the forest down and have people move in and eat wildlife,” he says, pointing to his group's research finding that cutting down tropical forests in Asia for palm oil is leading to workers contracting malaria and occasionally a new zoonotic disease.

Two New York-based researchers argue that the reduced diversity of animals that results from such human activity is leading to an increase in zoonotic disease and that conserving biodiversity can protect against such new diseases emerging and spreading.

The researchers, Ostfeld of the Cary Institute and Felicia Keesing, professor of science, mathematics and computing at Bard College in Annandale-on-Hudson, N.Y., say they have demonstrated this theory in their study of Lyme disease in the U.S. Northeast. (See Short Feature.)

The number of ticks carrying the disease is lower in undisturbed forests — areas with more animal diversity — than in the fragmented forests typical of suburban sprawl, their research finds. They theorize that is because expansive forests can support more large predators of the mice that are the hosts of Lyme disease, and can also support opossums, which typically remove the ticks through grooming and also transmit Lyme to far fewer ticks than mice do.16

“The species we lose in the Northeast when we lose biodiversity are foxes and bobcats, and those species actually protect us because they keep mouse numbers low,” says Keesing. “We should be protecting biodiversity far more than we're doing now; because the best way to keep [the animals that host] these pathogens in check is to let biodiversity do it.”

Keesing and Ostfeld say this conclusion — that more diversity equals less disease, which they call the “dilution” theory — is applicable globally, and they argue for resisting land development that cuts up natural forests.

However, other scientists question whether biodiversity loss is always to blame for infectious disease or is even a bad thing — particularly if it reduces the presence of disease-carrying animals. They also argue that the “dilution effect” does not hold true in all settings.

In one study of 60 countries, researchers found that urbanization and growing wealth were the main drivers behind reducing infectious diseases between 1990 and 2010. Contrary to the dilution theory, biodiversity was not correlated with improvements in human health, the study found.17

Lead author Wood of the University of Washington says rainforests and other areas that are rich in biodiversity also tend to be rich in viruses and parasites that circulate in animals, so in some cases, when humans preserve those areas or reforest them, “we're also potentially facilitating other diseases.”

Both sides in the debate agree that the more contact people have with wild animals, the greater the possibility of animal diseases jumping to people, especially as humans enter natural habitats. But the solution proposed by some environmentalists — to turn those habitats into national parks — “doesn't necessarily recognize the reality of people's lives; lots of people who live near biodiverse forests depend on those forests for their livelihoods, so saying they can't live there is akin to taking away their livelihoods,” Wood says.

Some researchers have found that it is often degraded areas on the edge of pristine habitats, rather than the undisturbed core, where humans are most likely to come in contact with animals in ways that could lead to a spillover — when a virus or other disease pathogen jumps from an animal to a human.

In a recent study of farmers living next to Kibale National Park in Uganda, Stanford University researchers found that fragments of residual forest, not larger expanses of habitat, were most likely to be the site of human contacts with primates because they shared borders with farms. For example, a monkey bit a boy digging in his garden, according to lead author Laura Bloomfield.18

“We humans go to these animals,” said study co-author Eric Lambin, professor of earth system science at Stanford. “We are forcing the interaction through transformation of the land.”19

In such situations, where humans are chopping up a natural habitat into a mosaic of forest and human dwellings, the loss of diversity may be the “visible result,” but the real driver of zoonotic disease is the man-made environment, says Roger Frutos, an infectious disease specialist at CIRAD, a French government research center working in developing countries.

A study from the University of California, Davis, finds the more abundant a species, the more likely it is to carry a disease that jumps to humans. Domestic animals such as cattle have been the most frequent carriers of a zoonotic disease. But among wild mammals, most zoonotic diseases can be found in three groups — rodents, bats and primates.20

“They're super-adaptable” animals, explains Christine Johnson, lead author of the study, and professor of epidemiology and wildlife health at the University of California, Davis, School of Veterinary Medicine. She points to rats and mice that feed on human garbage and white-faced monkeys that steal tourists' food in Costa Rica. Once people clear land for farming and housing, she says, these animals “move right in, they shelter with us, they depend on our food.”

Ostfeld says Johnson's research is consistent with his findings about Lyme disease — that such diseases thrive best in ecosystems that have been highly disturbed by humans. “It's the little weedy species [like mice] that are often the best reservoirs for zoonotic pathogens; they're the ones that benefit when we muck things up,” he says.

Since 1940, agricultural drivers such as clearing land for farms have been linked to about half of emerging zoonotic diseases, according to a study co-authored by Jason R. Rohr, a professor of biological sciences at Notre Dame University.21

Growing demand for meat among developing nations means agricultural production will need to double or triple to feed the planet's population by 2100, Rohr projects, posing the threat of more land clearance and more zoonotic disease. At the same time, he says, more food and meat protein equate to better health. “We shouldn't be thinking of biodiversity and disease in a bubble. We have to think about the cost and benefits,” he says. “In some cases, the land may be better used for agriculture.”

Should selling wildlife for human consumption be banned?

Many critics point to markets in China and other parts of Asia where wild animals in cages are often stacked on top of chickens and in close proximity with humans, making it more likely that they will get sick and transmit viruses to other animals and people.

Species that are endangered because of hunting, wildlife trade and habitat loss have twice the number of zoonotic diseases as other threatened species, according to a recent study by University of California, Davis, researchers.22

The stress that wild animals experience in being transported to markets is akin to the “shipping fever” contracted by cows that get sick after being crowded into a trailer for the slaughterhouse, says Johnson, the study's lead author. “Basically, we've given these viruses a unique evolutionary pathway,” she says.

The Wildlife Conservation Society, together with other environmental groups, has formed an “End the Trade” coalition, urging governments around the world to enact legislation to “permanently end commercial trade and sale of terrestrial wild animals” for human consumption.23

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Susan Lieberman, vice president for international policy at the Wildlife Conservation Society, says there is clear evidence that wildlife markets have contributed to zoonotic disease epidemics such as SARS. “Do we spend years investigating which might be the next one? Or do we say we can't accept any risk of this happening again? … If we stop the commercial markets where people eat wildlife, the chances of this happening again are infinitesimal.”

But some experts say some kinds of legal wildlife trade pose little danger of transmitting disease. For example, kudu and springbok, two species of antelope, are raised in South Africa in settings “almost like farmed systems, controlled and traceable — that's a really important food source there,” says Catherine Machalaba, policy adviser at the EcoHealth Alliance. She argues that any ban should be limited to the species experts know are most likely to put humans at risk of disease, such as rodents, bats and primates.

EcoHealth is supporting a more restrictive proposal to ban high-risk wildlife, an approach taken in a bipartisan bill introduced by Sens. Lindsey Graham, R-S.C., and Chris Coons, D-Del., and supported by the World Wildlife Fund.24

In that proposed ban, “we're not including farmed wildlife, livestock that has appropriate veterinary management and that is well regulated,” says Jan Vertefeuille, senior adviser for wildlife conservation advocacy at the World Wildlife Fund.

In a recent opinion piece, economists at the University of Oxford in England wrote that “banning all wildlife trade is a knee-jerk and potentially self-defeating measure.” Bans, especially those that remove currently legal supplies of farmed wildlife, could “drive up black market prices and increase incentives for poaching,” they wrote.25

In China, the wildlife breeding farms and the associated trade are estimated to involve 14 million people and be worth $74 billion, so the impact of a ban on that economy would be “uncertain,” the economists said. In January, China imposed a temporary ban on the wildlife trade in the wake of the Wuhan outbreak, and in May, China's legislature began consideration of a permanent ban.26

A previous Chinese effort to ban wildlife trade in southern China in the wake of the SARS outbreak in 2002-03, which was traced to a market, was a failure, critics say. Wildlife markets in Guangdong closed down, but reopened a few months later. Black market activity ramped up, and after the outbreak ended the ban was abandoned under a combination of cultural and economic pressures.27

Nurse's aide Benetha Coleman, herself an Ebola survivor, comforts an infant girl with symptoms of the disease in Paynesville, Liberia, in 2015. Following the Ebola outbreak in West Africa in 2014-16, governments imposed a ban on hunting wild animals and eating their meat in an effort to halt the spread of zoonotic diseases. (Getty Images/John Moore)

Following the 2013-16 Ebola outbreak in West Africa, governments across the region imposed a ban on hunting and eating meat from wild animals.28

But those bans led to illegal markets and sometimes a boomerang effect, where consumption of bush meat actually increased, perhaps because the meat became more desirable after the ban took effect, says Diogo Verissimo, an economist and research fellow at Oxford. “We also saw unequal impacts,” he says, where communities dependent on bush meat suffered nutritionally.

Harvard's Myers points to research he has overseen in Madagascar villages where people eat wild lemurs and tenrecs (a mammal resembling a hedgehog). “If people in those villages stopped giving bush meat to their children, you would see a 30 percent increase in anemia rates in those kids,” he says. “It means a blanket policy [banning wildlife] could cause a lot of hardship and suffering.”

Verissimo says that although cattle have often been the source of outbreaks of illnesses such as mad cow disease, “our response to those pandemics was not to ban that industry, because we understand that millions of people rely on that for nutrition, and lots of livelihoods depend on it. What we did was to say, we need to improve regulation.”

Many experts say a ban alone will not change traditional food habits. Verissimo has been studying a different strategy — using advertisements with celebrities to shift consumer preferences away from eating pangolin, an anteater-like animal that is the most highly trafficked mammal in the world, prized for the supposed medicinal properties of its scales and its meat. Some scientists think the pangolin may have been the intermediate animal that passed the COVID-19 virus from bats to people.29

In one such ad, Miss Universe Vietnam looks horrified and stalks away when her host ceremoniously presents her with a pangolin dish at a restaurant.30

Finally, wildlife markets are not the biggest cause of zoonotic epidemics. Research shows that land use changes, such as farmers cutting into forests and moving closer to bat habitats, are a much bigger factor — and the leading cause of new diseases.31

“If you blocked the wildlife trade completely in China you would still get lots of people infected every year by bat coronaviruses,” says Daszak of EcoHealth Alliance.

Is it possible to predict the next pandemic?

In the wake of the 2003-06 H5N1 bird flu that provoked fears of a global pandemic, USAID in 2009 created a program called PREDICT, charged with strengthening “global capacity for detection and discovery of zoonotic viruses with pandemic potential.”

From 2009 to 2019, PREDICT funded research to find viruses among animals in the wild, trained about 5,000 people around the world to identify new diseases and helped develop 60 research labs.32

The program found about 1,000 viruses, including bat coronaviruses similar to the ones that caused SARS and COVID-19, but it did not discover the virus causing the current pandemic. Critics say hunting for the next pandemic virus in nature is like looking for a needle in a haystack, because thousands of zoonotic viruses are present and are frequently mutating in ways that could change their potential to infect and thrive in humans.

“The difficulty with that approach is that there are so many viruses, and the vast majority of them are undescribed and harmless,” says Barbara Han, disease ecologist at the Cary Institute of Ecosystem Studies. She uses a different strategy, one of constructing computer models based on the distinctive traits of animals that have given humans viruses in the past to forecast which animals are most likely to host new zoonotic diseases.

Some prominent scientists have called for reorienting the government's approach.

“Although PREDICT almost certainly discovered hundreds of potential zoonoses [zoonotic diseases], their true zoonotic potential is almost impossible to assess,” wrote Colin J. Carlson, a biologist at Georgetown University who studies newly emerging infectious diseases. “For now, the only real way” to distinguish potentially zoonotic viruses from their low-risk counterparts is to observe a human infection caused by a virus that has spilled over from animals, he said. The government's approach “oversells basic science” and detracts from funding for primary health care, diagnosis and other efforts to catch clusters of human infection early, according to critiques cited by Carlson.33

Daszak's group EcoHealth Alliance is one of the most prominent funded by PREDICT to perform virus-hunting research in the wild. After the SARS outbreak, the group's hunting led it to a group of bat coronaviruses that it concluded were the likely source.34 After 20 years of studying animals that cause zoonotic outbreaks, Daszak says, “it's clear to me there are patterns to disease emergence that are predictable. It doesn't mean that we can predict the next one.” But much like an earthquake forecaster, he says, his research can point to the hotspots where clusters of animal viruses are likely to jump to humans, then take steps to limit people's contact with the host animals.

In 2015, Daszak's group, together with Chinese researchers, found 3 percent of people living near bat caves in Yunnan province, China, where hunting and eating bats is common, had antibodies to a SARS-like coronavirus found in bats. That finding suggested bats could directly infect people, the researchers said.35 (See Short Feature.)

As for the argument that it would be better to focus on early clusters of people infected with a new disease, Daszak says that is essentially what countries are doing now with their public health approach: “We wait for pandemics to emerge and hope we'll get a vaccine. It's not a strategy at all.”

Daszak wants to raise private and public funds for a $1.2 billion project to discover and catalog the majority of the 1.5 million zoonotic viruses — mostly unknown — in mammals, humans and waterfowl. “To prevent the few that could cause a pandemic, we have to discover all of the potential ones,” Daszak says. This proposed atlas of viruses, dubbed the Global Virome Project, would be a logical successor to PREDICT, supporters say.

“The Global Virome Project will begin lowering risk of spillover because we'll have greater granularity about where and what needs to be done,” says Dennis Carroll, the project's chair, who founded PREDICT when he led USAID's emerging pandemic threats program. The new project would expand the kind of research done in Yunnan province that discovered antibodies in people to animal viruses, Carroll says, then use that knowledge as an early-alarm system to work closely with communities and national governments to prevent an epidemic.

But some scientists say the government should shift away from this biomedical approach. “Rather than emphasizing virological research in places where people and wildlife come into dangerously close contact, investments should be dramatically shifted to focus on making such human-wildlife contact much less likely in the first place,” wrote Cornell's Osofsky. The focus, he said, should be on preventing the risky behaviors likely to cause future outbreaks — eating and trading the body parts of wild animals, mixing species in markets and human incursions into wild areas that increase contact with wildlife.36

Governments should focus on catching the disease in animals before it even gets to humans and then act quickly, according to Larry Brilliant, a leading epidemiologist who helped the World Health Organization (WHO) eradicate smallpox and is now board chair of Ending Pandemics, a group that advises governments on the early discovery and containment of pandemics.

He pointed to a Cambodian program where a farmer “can call the government and say, ‘I have 20 dead chickens,’ and they'll come and bring you 30 live ones and clean up your place. That's a phenomenal bi-direction system that cleans up the virus for you, puts you back into business, and the epidemic is aborted. Being able to survey bats, pigs, birds … that's what we're going to have to do in the age of pandemics.”37

The main reason a zoonotic disease emerges “is not biology, it's sociology; it's human,” says Frutos, a molecular microbiologist at CIRAD. “It's not possible,” he says, to predict which virus will cause the next pandemic because that requires a chain of largely accidental events triggered by humans, from destroying wild places to successful spillover to the mutation into a human disease. “We should put the filter at the bottleneck” of human activity, he says. “Whatever the virus, it has to go through the bottleneck.”

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Background

Rodents and Plagues

One of the most notorious early zoonotic diseases was the Black Death, the name given to bubonic plague carried by rodents that devastated Europe in successive waves starting in the 14th century. The plague first reached Europe in 1346, most likely carried by fleas on black rats that inhabited merchant ships. The disease wiped out as much as 30 to 60 percent of Europe's population.38

Recent genomic research has revealed that the plague originated in China, then traveled through Asia, Europe and Africa from 1346 to 1351.39

An artist depicted an outbreak of plague in Florence in the 14th century based on the description of writer Giovanni Boccaccio. A bubonic plague pandemic in that century, which killed between 30 percent and 60 percent of Europe's population, originated from fleas on black rats. (Getty Images/Bettmann)

The bacterium that causes the plague, Yersinia pestis, still resides in rodents indigenous to North and South America, Africa and Central Asia.40 Plague is now treatable with antibiotics. Human plague infections continue to occur in rural areas in the western United States, but significantly more cases occur in Africa and Asia, according to the CDC.41

Zoonotic diseases predated the plague. Today, they account for more than 60 percent of human infectious diseases.42 Zoonoses include diseases that cross routinely from animals to humans, such as rabies, or have recently crossed and now pass from human to human, such as HIV, which originated in a chimpanzee.43

Many diseases that people now consider human-to-human — including smallpox and measles — are believed to have originated with animals in the distant past.44 For example, researchers believe influenza jumped from horses to humans soon after horses were domesticated and then made additional jumps to humans from other domesticated animals, such as poultry and swine.45

The moment when a pathogen leaps from a member of one species into members of another is known as a spillover. Spillover leads to the emergence of a new disease only when the alien pathogen thrives in a new species and spreads among its members.46

Spillovers are actually “fairly common events,” says the Global Virome Project's Carroll: In studies, 10 to 15 percent of communities that have routine exposure to wildlife test positive for antibodies to wildlife viruses. But many animal pathogens that make the jump to humans “fizzle out,” says the Cary Institute's Han, either failing to transmit to another human or infecting only a limited number of people.

Carroll says, “What is less common is a virus that is able to spread human to human after the initial spillover.”

One characteristic that makes zoonotic pathogens so problematic is that they can hide in “reservoir hosts,” animals that carry the pathogen while suffering little or no illness, such as the white-footed mice that carry Lyme disease.47

By contrast, eradicating smallpox worldwide, as the WHO announced had been accomplished in 1980, was feasible because it lacked the ability to live anywhere but in the human body, according to science writer David Quammen in his 2013 book, Spillover. The virus could not hide in animals.

It would be far more difficult to eradicate yellow fever, a zoonotic disease that is infectious to both monkeys and people and is passed by mosquitoes. It will continue to occur in humans unless the WHO “kills every mosquito vector or every susceptible monkey in tropical Africa and South America,” Quammen wrote.48

Zoonotic diseases include several diseases better known in the United States, including Lyme disease (from mice), West Nile virus (mosquitoes), hantavirus pulmonary syndrome (rodents) and monkeypox (monkeys).49

COVID-19 is the third coronavirus (so-called because of its crown-like structure) to cause an outbreak of serious illness in the past 20 years. All three — SARS, MERS and COVID-19 — have been linked to animal origins. Many of the most serious recent zoonotic outbreaks can be traced to environmental causes, often to human contact with animals disturbed from their natural habitats, according to the Wildlife Conservation Society.50

Influenza Outbreaks

Influenza pandemics were first documented about 300 years ago. The 20th century alone saw three such pandemics: Two were comparatively mild, but the 1918-19 “Spanish flu” pandemic infected an estimated 25 to 30 percent of the world's population. About 675,000 Americans died from the flu in 1918 — nearly half of all U.S. deaths that year. Worldwide, 40 million to 100 million people died.51

Red Cross medical personnel transport a victim of the 1918 influenza pandemic in St. Louis. The disease killed 675,000 Americans and at least 40 million people worldwide. (Getty Images/PhotoQuest)

The two milder 20th-century pandemics, in 1957 and 1968, were probably caused by the exchange of genes between human and avian flu viruses. The 1957 and 1968 outbreaks caused about 116,000 and 100,000 U.S. deaths, respectively.52

The 1918 flu was a novel, or new, virus that originated in birds and then spent some time in another host, perhaps pigs or horses, before it emerged as a human disease. Striking during World War I, it was able to spread quickly among soldiers in cramped army barracks and steerage-like transports. The majority of deaths probably resulted from secondary infections, such as bacterial pneumonia, which were deadly before the discovery of antibiotics. The death rate in the 1918 flu was 20 times greater than that for today's influenza, which kills fewer than 0.1 percent of those who catch it.53

In 1939, the newly invented electron microscope took a picture of a virus — the first time in history it could be seen. By the 1940s, scientists had isolated two strains of influenza and had begun to test vaccines. After the discovery of DNA in 1953, scientists were able to identify the building blocks of a virus.54

Ebola, Nipah and AIDS

The Ebola virus causes a hemorrhagic fever that is among the most virulent known diseases.55

It first appeared in two separate outbreaks in 1976 in the African countries of South Sudan and the Democratic Republic of the Congo (formerly Zaire) near the Ebola River with fatality rates of more than 80 percent. Researchers suspect fruit bats are the natural hosts of Ebola virus.56

Although the exact origin of Ebola is unknown, the virus is introduced to humans through contact with the blood, organ or secretions of bats or from chimpanzees, gorillas, monkeys, antelopes or porcupines found ill in the forest.57

Beginning around 1995, Gabon and the Democratic Republic of the Congo reported clusters of the disease — in each case linked to gorilla and chimpanzee carcasses in nearby forests that were sometimes eaten by villagers. As researchers searched for the cause between 2001 and 2005, they discovered that bats, which carried the virus, came into contact with apes during the dry season when fruits become less plentiful and they compete for the same food. A 2007 outbreak in Gabon was linked to hunters eating bats during a massive migration when fruits were plentiful.58

Although the AIDS epidemic was first recognized in 1981 in the United States, researchers say it originated far earlier, as similar immunodeficiency viruses long existed in primates. The first spillover to humans likely occurred in the course of hunting, butchering and eating primates carrying viruses. One of these events likely occurred in Africa between 1910 and 1930, some researchers believe, giving rise to the HIV strain behind AIDS.59

Nipah virus, which can cause severe respiratory infection and encephalitis, broke out among pig farmers in Malaysia in 1999, followed by Bangladesh in 2001. Nipah virus has a fatality rate of 40 to 75 percent, and it has no cure or vaccine.60

Since 2001, Bangladesh has had nearly yearly outbreaks and India has had several. In Malaysia, the virus has been traced to fruit bats that roost above pig sties, with pigs passing the disease via direct contact with people who work in the pork industry.61

Slash-and-burn deforestation, together with drought, initially drove bats into fruit orchards adjoining pig farms that had recently expanded into forests.62

The 2014-16 Ebola outbreak in West Africa was the largest since the virus was discovered in 1976, with more cases and deaths in this outbreak than all others combined. A total of 11,310 deaths were reported in Guinea, Liberia and Sierra Leone.63 Vaccines are under development and have been used to control outbreaks in Guinea and the Democratic Republic of the Congo, according to the WHO.64

Ebola reappeared in the Democratic Republic of the Congo in August 2018, causing more than 2,000 deaths by November 2019 at a 67 percent mortality rate, the second-largest Ebola outbreak in history.65

21st-Century Outbreaks

The first pandemic of the 21st century started in China's southern Guangdong province in 2002 after a patient died from an unusual pneumonia, later identified as SARS.66

SARS has infected at least 8,000 people and killed about 10 percent of them.67

Early cases were linked to wildlife markets and restaurants in Guangdong, where coronaviruses were found in masked palm civets, a cat-like mammal considered a culinary delicacy in China. Chinese authorities responded by imposing a temporary ban on the hunting, sale, transportation and export of all wild animals in southern Chinese provinces. They also culled and quarantined civets in the region's many civet farms.68

Horseshoe bats have been identified as the likely origin of the virus, while farmed civets probably served as an intermediary, passing the disease to humans. The disease spread to four continents (Asia, North and South America and Europe) after a tourist returned to Toronto in February 2003 from a Hong Kong hotel, spurring a planetary public health panic. The WHO declared the outbreak contained on July 5, 2003.69

Bird flu, a highly contagious disease among chickens in Asia, Africa and Europe, raised fears of a worldwide pandemic after the WHO reported the first case of human-to-human transmission in Thailand on Sept. 28, 2004, from the H5N1 flu strain.

In December 2005, in response to an emergency request from President George W. Bush, Congress approved $3.8 billion to develop vaccines and stockpile anti-flu medications.70

Dozens of human cases and some deaths were reported in Turkey in January 2006.71 But the outbreak failed to turn into a transmissible disease between humans. Most of the 648 cases since 2003 have occurred in people who had close contact with poultry.

Currently, human infection is rare, and there is no ongoing transmission in humans, according to the CDC, but the bird flu can be fatal, with a 60 percent mortality rate. The first case in North America occurred almost a decade after the first outbreak, in Canada in 2014, when a person who had recently returned from China died.72

Swine flu (H1N1), meanwhile, killed thousands and infected millions in 2009, when it was declared a pandemic by the WHO in June of that year, the last declared pandemic before COVID. The WHO declared an end to the pandemic on Aug. 10, 2010. The WHO said H1N1 had become much like any other flu strain, no longer causing the majority of flu outbreaks or triggering outbreaks during the summer.73 Globally, an estimated 151,700 to 575,400 people died from swine flu in the first year of the pandemic.74 It has been traced to pig and poultry farming and contact with wild waterfowl.75

MERS, a severe respiratory disease caused by a coronavirus, was first reported after a 60-year-old man died of a novel virus in Saudi Arabia in 2012. Across the globe, 27 countries have reported cases of MERS, but about 80 percent occurred in Saudi Arabia. The disease, which has a fatality rate of about 35 percent, has killed 866 people. There is no specific treatment and no vaccine.76

Although the disease emerged from dromedary camels in Saudi Arabia, some researchers view them as an intermediary, since the virus is found in bats and African dromedaries.77

COVID-19's Emergence

On Dec. 31, 2019, the WHO received a report from China of a cluster of cases in Wuhan with a pneumonia of unknown cause, later identified as COVID-19.78 Of the first 44 patients hospitalized, 27 had been exposed to the local seafood market in December, where live wildlife was also sold.79

Authorities closed the Wuhan market in January. They also reported finding environmental samples of COVID-19 virus (on sewage and surfaces) in the area where wild game was sold.80

Since then, however, cases of COVID-19 have been traced back to November, and some scientists began questioning in early 2020 if the market was the source.81

In late May, George Gao Fu, the director of the Chinese Center for Disease Control and Prevention, said the center had been unable to trace the virus to an animal in the market. “At first, we assumed the seafood market might have the virus, but now the market is more like a victim,” Gao Fu told the state-owned Global Times. 82

It remains unclear how the virus was transmitted to humans. Many scientists believe the virus probably came from a horseshoe bat, where a virus whose genome is 96 percent similar to COVID-19's has been identified. One scientist at the Sorbonne University in Paris has suggested that the virus may be the result of a recombination of two different viruses — one closer to the horseshoe bat's and the other closer to a pangolin virus.83

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Current Situation

International Developments

Moving toward its first permanent national ban on the trade in wildlife food, China's legislature is considering changes to the nation's wildlife law that would outlaw the sale and human consumption of some wild animals; the drafting of new legislation is likely to take at least until the end of the year.84 That change would replace the temporary wildlife ban issued in January in the wake of the coronavirus outbreak in Wuhan, which was to stay in effect until the pandemic ended.85

In April, the Chinese government issued a proposed list of animals that could be sold for meat, drastically curtailed from the species that are currently legal. Notably, the approved list left out some of the animals of most concern for zoonotic disease, such as pangolins, civet cats and bamboo rats — a large rodent that lives in bamboo thickets — as well as dogs, which Chinese markets have long sold for food.86

A pangolin, an endangered species that is the most highly trafficked mammal in the world, was rescued from poachers in Uganda in April. Pangolins are prized in China as a culinary delicacy and for alleged medicinal purposes, and may have been part of the transmission chain of the COVID-19 virus. (AFP/Getty Images/Isaac Kasamani)

Some provinces have begun to offer farmers cash to end the practice of rearing civets and other wild animals.87

In May, Guangdong province, a prime center for wildlife gastronomy where SARS originated, started imposing tough fines for ordering restaurant dishes, such as bat soup, a positive sign that the provinces are prepared to enforce a stronger national law, according to Aili Kang, executive director of the Wildlife Conservation Society's Asia program. But she says some of the biggest industries, such as breeders of bamboo rats, are seeking exemptions from the ban.

Wildlife advocates say the proposed law still has big loopholes — permitting wildlife trade for traditional Chinese medicine, for fur and for exotic pets. Pets such as “rare reptiles or turtles may not be as risky as primates or rodents, but they still have risky pathogens,” says Kang.

China's wildlife ban will have limited effect if nearby countries continue the exotic animal trade, experts say. In March, Vietnamese Prime Minister Nguyen Xuân Phúc requested draft legislation by April 1, 2020, to restrict the trade and consumption of wildlife, but no information about a ban has been made public, raising concerns among conservation groups as to the government's seriousness.88

In May, the WHO said it was not recommending a ban on live animal markets globally, despite urging from some environmental groups and members of the U.S. Congress.89 WHO food safety and animal diseases expert Peter Ben Embarek said live animal markets — which exist in many countries, including in Africa — are essential to providing food and livelihoods to millions around the world and that governments should focus on improving the markets' hygiene and food safety standards.90

The Wildlife Conservation Society and other conservation groups are calling on national governments to issue bans on all wildlife for human consumption, with narrow exceptions for indigenous communities that rely on wildlife for subsistence.91

Some environmentalists are seeking an international ban on all live wildlife trade, including pets, working through existing treaties. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), a legally binding accord agreed to by 183 countries, is one possible avenue, according to Elly Pepper, deputy director of the International Wildlife Conservation Initiative at the Natural Resources Defense Council, a New York-based environmental group.92

The treaty prohibits international commercial trade in about 670 animal species threatened with extinction and regulates trade in more than 5,000 species that could become threatened. But most wildlife species traded for food are not covered.93

“The purpose of CITES is to address unsustainable trade, and this pandemic has made us realize that the wildlife trade has a component we haven't thought about — human health,” says Pepper. She wrote in a blog that the leadership of CITES should be “scouring” the treaty's text to bring changes in that direction and not “shrugging its shoulders.”94

However, the CITES secretariat said recently that “matters regarding zoonotic diseases are outside of CITES's mandate,” and other experts agree that the treaty would have to be amended to make public health a reason for prohibiting trade in a designated species.95

“Amending treaties is really complicated — it would not happen quickly,” says Lieberman of the Wildlife Conservation Society, noting that the last time the treaty was amended it took 30 years, requiring a two-thirds majority.96

Pepper says another possible international forum is the United Nations Convention on Biological Diversity, signed by 150 government leaders at the 1992 Rio Earth Summit, which calls for commitments by nations to prevent the long-term decline of biodiversity. The United States is not a party to that treaty.

The next meeting of the diversity convention in 2021 should pledge to meet the Natural Resources Defense Council's goal of protecting 30 percent of the Earth's land and water by 2030, according to Pepper. “When thousands of acres of the Amazon are destroyed for agriculture, for example, the risk to humans from contact with wildlife increases,” she said.97

But the convention, while filled with commendable recommendations, has “no teeth” to enforce any actions by governments, according to Machalaba, the policy adviser at the EcoHealth Alliance. Machalaba says she wants zoonotic risk made part of risk assessments for new development projects, much like environmental impact statements used by governments, corporations and international agencies such as the World Bank.

U.S. Efforts

To prevent another zoonotic epidemic, leading members of Congress are pushing for more funding to enforce laws against illegal wildlife trafficking and legislation to encourage a ban on overseas markets that sell live and exotic animals.

Sen. Tom Udall, D-N.M., said in April that congressional members were pushing for a “substantial increase” in funding for the U.S. Fish and Wildlife Service to stop illegal wildlife from other countries. Udall is the ranking Democrat on the Senate Appropriations subcommittee that oversees the Fish and Wildlife Service. Subcommittee Chairman Lisa Murkowski, R-Alaska, said she was also concerned about the link between the illegal wildlife trade and public health.98

In early February, in its fiscal 2021 budget request, the Trump administration proposed a 16 percent cut in the Fish and Wildlife Service, the agency charged with enforcing wildlife anti-trafficking laws.99 However, Congress rejected many of Trump's proposed cuts in environmental agencies when it passed the 2020 appropriations package, so it is questionable whether Trump's cuts will make it into the final bill for 2021 intact.100

Several bills seek to prohibit zoonotically dangerous imports from wildlife markets overseas and offer incentives to other countries to ban these markets. Buried in the $3 trillion act passed by the House to deal with the pandemic-caused economic downturn is a section making it illegal to import species designated by Fish and Wildlife as a “biohazard to human health.” It authorizes $111 million to help foreign countries end the trade in animals that pose a disease risk to human health and to strengthen early detection of zoonotic diseases.101

However, the Democratic-controlled House passed the bill in a party line vote, and Senate Majority Leader Mitch McConnell, R-Ky., has said it has “no chance of becoming law” and will not pass in the Republican-controlled Senate.102 Some environmental groups think a bipartisan measure dealing with wildlife may have more chance of success than the Democrats' bill — perhaps as part of a future economic stimulus measure.

In one such effort in the Senate, Republican Graham and Democrat Coons have introduced a measure aimed at banning the sale of “high-risk” wildlife in live animal markets for human consumption. The more than $1 billion bill requires federal agencies to identify which species have a high risk of spreading a zoonotic disease and authorizes the president to use sanctions against nations that continue to permit markets selling those animals, along with aid to help communities that depend on wildlife for subsistence.103

“How can we prevent this from happening again?” Graham asked in a statement referring to the COVID-19 pandemic. “Governments in Asia and elsewhere should immediately shut down markets that sell high-risk wildlife for human consumption and fully enforce laws already on the books to end the global illegal trade in wildlife.”104

Several mainstream conservation groups, including the World Wildlife Fund and the Nature Conservancy, have endorsed the bill.

However, two environmental groups say it does not go far enough. The trade in all live wildlife should be banned, not just those designated “high-risk,” say the Natural Resources Defense Council and the Center for Biological Diversity, based in Tucson, Ariz.

The bill's approach — directing federal agencies to predict a species' risk before banning its import — is “like playing Russian roulette,” considering some 5,000 species are traded internationally, says Brett Hartl, the Center for Biological Diversity's government affairs director: “Every single species on the planet has viruses and bacteria. So the notion that somehow we could ever determine what species and combination of events are likely to cause a disease is extremely low.”

Moreover, he says, the bill ignores the United States' own role in the trade; it is the No. 1 importer of exotic animals for pets and the site of markets selling live reptiles and amphibians for food in large American cities.

The bill also encourages the federal government to use a so-called One Health approach to detection and response to pandemic threats, uniting expertise from animal health, human health and environmental health experts.105

Earlier this year, the Trump administration had planned to shut down USAID's 10-year PREDICT program, which trains science and lab workers in developing countries to identify potential zoonotic diseases. Sens. Elizabeth Warren, D-Mass., and Angus King, I-Maine, protested the shutdown in late January, saying COVID-19 “heightens the need for a robust, coordinated, and proactive response to emerging pandemics — one of the roles that PREDICT played.”106

In an about-face effective April 1, the administration extended the program's funding for six months. With the $2.26 million extension, PREDICT will continue to provide technical expertise to support detection of cases of COVID-19 in Africa, Asia and the Middle East to support the public health response.107

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Outlook

Growing Pressures

Pressure to clear land for agriculture and hunt bush meat for food is expected to increase with an expanding world population, raising worries about increasing spillovers of zoonotic diseases in degraded landscapes.

“The intensity and frequency of outbreaks will continue in China, but we will see parallel events beginning with much greater intensity in areas that were remote and isolated,” predicts the Global Virome Project's Carroll, pointing to Africa, where the population is expected to boom along with a growing middle class. “If they assume the dietary patterns that are prevalent in the U.S., then we will have a huge problem in land use, because they will demand cattle protein.”

Sharing similar concerns, Harvard's Myers says habitat destruction in Africa and the Amazon basin for agriculture could be stemmed by innovations in food production, including artificial milk and eggs, plant-based meat substitutes along the lines of the Impossible Burger, insect-based foods and new crop varieties. “It's not too late, but we absolutely can't continue on our current trajectory without paying enormous human health costs,” he says.

Some scientists hope that advances in interpreting the genome of viruses will help predict and prevent zoonotic pandemics.

“Ultimately, one of our big goals — the holy grail — is to look at the genome of a virus before it's caused even a single human infection and understand whether it will cause disease,” says EcoHealth scientist Epstein, who sees the Global Virome Project's proposed virus library as one step in that direction. Each experience of studying these viruses in animals and people “brings us closer,” to that goal, he says.

For bat coronaviruses, which EcoHealth has studied extensively, “we're five to 10 years from being able to break down the risk of them emerging and disrupt them from emerging,” says EcoHealth President Daszak. “In a few decades, we'll be able to prevent many pandemics.”

Daszak adds, “Fifty years from now, people will look back on this time and say, ‘That was the pandemic era and thank goodness they got to grips with that.’”

In the meantime, COVID-19 has been a reminder of how much faster a disease can spread in the modern world via planes and global trade than in earlier centuries. “The rate of spread of the [bubonic] plague from Central Europe took years; now it's hours,” says Stanford's Lambin, who calls COVID-19's “double whammy” of zoonotic disease plus globalization “a very dangerous cocktail.”

One of the biggest obstacles to attacking the environmental roots of zoonotic epidemics, scientists and advocates agree, is getting the world to listen. Many of them hope that will change because of the current pandemic.

“The issue of high-risk wildlife trade has been around forever,” says the World Wildlife Fund's Vertefeuille. “What's new and different right now is the entire world and the global economy is bearing the costs of that risky wildlife trade. So we really have a moment in time to address this issue — that if we act quickly and aggressively we can try to stop the next pandemic.”

The current pandemic is just one of many signals, along with a changing climate, that our planet is in trouble, says Myers.

“I'm hoping COVID-19 will be the loudest and most immediate of these warning bells that we've been hearing, that it will be a wake-up call,” he says. “We need to pause and address this relationship we have with our natural systems.”

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Pro/Con

Should the trade in wildlife for human consumption be banned?

Pro Susan Lieberman Vice President, International Policy, Wildlife Conservation Society. Written for CQ Researcher, June 2020 In only four months, people everywhere have awakened to the massive global tragedy that can result from zoonotic pandemics, when animals pass on pathogens to humans. If we want to avoid the next COVID, we need to accept that tweaks to current policies or targeted closures of some risky wildlife markets will be irresponsibly insufficient. Business as usual and mere improvements to existing policies will not prevent the next zoonotic pandemic. Global public opinion is moving rapidly to a place where decision-makers can adopt policies that once would have been considered radical but seem sensible now as people experience the impact of this pandemic on their economies, well-being and lives. If governments view the challenges of avoiding a future pandemic through this newly shifted Overton Window, they will see how bold policies that reorder our relationship with wildlife will allow for solutions that reflect local realities. Nuanced changes to current policies or targeted closures of only today's problem markets will not prevent future zoonotic pandemics. This shift in public opinion means we need lawmakers and decision-makers to know that now is the time to make wholesale changes to our fractured relationship with wildlife. For example, we need to stop relentlessly destroying wildlife habitat for logging, mining and agriculture, which increases the possibility of spillover of deadly pathogens from wildlife to humans. Protecting ecological integrity should be a priority within any comprehensive plan to avoid future zoonotic outbreaks. With large-scale reform of the global wildlife trade, we can then support local solutions that will preserve wildlife for those who depend on it for food security or sustainable income-generating enterprises such as wildlife-based tourism. Indeed, under this new framework, locally and socially accepted solutions will be stronger and more sustainable. Globally, the commercial trade in wildlife for human consumption, particularly birds and mammals, poses an enormous risk to humans. This trade for urban consumers is especially unnecessary, because they do not need to eat wildlife; it is neither a dietary nor a cultural necessity for them, as it still is for some rural communities. With bold action for an overarching change in our relationship to wildlife, we can significantly reduce the risk of zoonotic pandemics; help address the world's biodiversity crisis; support local economies through nonconsumptive industries such as ecotourism; and preserve wildlife for those who depend on it for their well-being and cultural identity. It is only through recognizing that we are at a global inflection point with our relationship with wildlife that we will make progress.

Con Amy Hinsley, Stephanie Brittain Senior Research Fellow, Wildlife Conservation Research Unit; Postdoctoral Researcher, Interdisciplinary Centre for Conservation Science, Department of Zoology, University of Oxford. Written for CQ Researcher, June 2020 With the highly publicized links between the coronavirus that caused COVID-19 and wild animal meat, banning wildlife trade and consumption has been widely suggested as the only way to stop future pandemics. This is a simple and powerful message, but this very simplicity means this approach is unlikely to work. Proposed bans ignore the complexity of the wildlife trade and the diversity of both its consumers and of the plant, animal and fungal species being consumed. Wild meat is not just threatened high-disease-risk animal species being traded illegally in the tropics, but also pigs, deer, birds, antelope and rodents hunted globally. Further, while wild meat may be consumed as a luxury in high-income areas, it contributes to the food security and livelihoods of millions of people globally, especially those in rural communities. Banning wildlife consumption presents the real risk of unintended consequences and perverse outcomes. Markets can be driven underground where monitoring and regulation are impossible, potentially increasing zoonotic disease transmission by reducing the potential and incentives for applying food hygiene standards. Where bans are successful, wild-meat traders, who are often women, lose valuable employment. Further, viable alternative sources of food and income are rarely available or provided, which could result in increased malnutrition and poverty. Alternatives such as livestock or poultry are often named but, in the Congo Basin, an estimated additional 4.5 million tons of pigs or chickens would be needed to replace wild meat, requiring millions of hectares of forest clearance. Deforestation would destroy globally important habitats. Further, disease emergence from domestic animals is also a real risk, and agricultural intensification and land use change, particularly in tropical regions where wildlife biodiversity is high, are root causes of disease emergence. It is time to learn from past mistakes, not repeat them. This is not to say that nothing should change following the COVID-19 pandemic. We must dramatically re-evaluate our relationship with animals and with nature more broadly. A priority should be better regulation rather than outright bans, focused on addressing illegal, unsustainable and high-disease-risk trade, whether this involves wild or domestic animals. We should also carefully consider the impact of regulation on food security, and focus efforts on areas where wild meat is a luxury. While a blanket ban may sound good on paper, in reality, long-term policy changes need to be designed with enough nuance to be feasible, to be effective, and to not cause further harm.

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Short Features

Bats Can Harbor and Transmit Many Viruses

In 1998, people started getting sick in northern Malaysia with fever, headache, drowsiness and convulsions. All of them were pig farmers or involved in the pork industry. By the end of the outbreak, at least 283 people had been infected and almost 40 percent had died.

Scientists would later trace the illness — Nipah virus — to bats that had roosted in fruit trees above the pig sties, dropping chewed mango and water apple into the sties. The pigs ate the droppings, contracted the virus and passed it on to the rest of the herd, infecting their human handlers.1

Bats have also been linked to coronaviruses, including severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), two coronaviruses that cause the common cold and the virus behind COVID-19. In a new study, researchers from the EcoHealth Alliance, a New York City-based environmental research group, and China's Wuhan Institute of Virology identified more than 780 new coronaviruses in bats and traced the likely origin of the viruses behind both SARS and COVID-19 to horseshoe bats.2

Why have bats been linked to so many outbreaks of human disease? They are highly social animals, roosting in packed groups as large as millions. The authors of the new study point out that horseshoe bats in southern China often share their roost with other bat species, which may make it easier for coronaviruses to leap to different species.3

The lineage of bats can be traced back about 50 million years, and scientists believe they may have co-evolved with viruses in a way that permits them to carry viruses without being affected by them — a trait that is perhaps related to their ability to fly.4

“They have an interesting immune system,” says Peter Daszak, EcoHealth Alliance president and a co-author of the recent paper. “There's pretty good evidence that bats reduce their natural immune response to viruses. Maybe it's part of the [evolutionary] cost of flight, which is energetic; they have to reduce stress.”

A horseshoe bat takes flight in pursuit of a moth. Bats have been identified as the hosts and transmitters of a wide variety of viruses, including the coronavirus. (Getty Images/De Agostini Picture Library)

Bats “seem to be able to recover from infection from a pathogen but not completely clear it from their system, which they do by suppressing their immune system,” said Kate Jones, professor of ecology and biodiversity at University College London. “[An] over-responsive immune system is sometimes what actually kills you — from organ failure.”5

Bats are attracted to human habitation and farms, especially if the bats have been disturbed from their natural habitat. That is one reason they showed up in such large numbers on pig farms in Malaysia. Booming pork demand contributed to slash-and-burn deforestation as farmers cut into the forests where bats lived to create industrialized pig operations, while vast tracts were logged.6

Light from houses attracts insects, which in turn attract the bats that eat them, says Roger Frutos, a microbiologist with the French government research agency CIRAD, who focuses on infectious diseases. EcoHealth researchers expect as many as 10,000 to 15,000 bat coronaviruses have yet to be discovered in addition to the 781 they recently discovered and the 509 previously known bat coronaviruses.7

“Since we attract bats to human environments, we therefore attract a very large reservoir of viruses,” Frutos says. “After that, it's just a matter of probability for disease to happen: The more contact you have, the higher the presence of bats, the higher the probability to get emergence [of disease] — and contamination of humans.”

The first step to prevention, he says, is to fortify barns and pig sheds against bats — the United Nations recommends applying wire screens to open-sided pig sheds, installing roofing and placing netting over ventilation openings.8 Such steps, along with the Malaysian government's ban on pig farming in high-risk areas following the Nipah outbreak, helped to eradicate the disease from Malaysia, according to Dennis Carroll, who oversaw the pandemics prevention program at the U.S. Agency for International Development.9

The area where southern China converges with Laos, Myanmar and Vietnam is likely to be a future hot spot for emerging disease, EcoHealth researchers predict, because a growing human population, urbanization and intense poultry and livestock farming all provide opportunities for a virus to jump from animals to people.10

One study by Daszak's group found about 3 percent of a human community in southern China living near bat caves had antibodies to SARS-like bat coronaviruses, despite recalling no SARS symptoms.11 He says his organization wants to conduct more such studies to anticipate viruses likely to cause epidemics.

However, EcoHealth's funding for this work was abruptly terminated in April by the U.S. National Institutes of Health (NIH) after EcoHealth's grant got caught up in a political controversy over the Wuhan lab. The $3.7 million grant was canceled a few days after President Trump responded to a question at a press conference from a reporter who erroneously claimed that millions of dollars in grants were going to the Wuhan Institute. Trump told the reporter the grant would be ended immediately, amid mounting but unproven theories targeting the Wuhan lab as the source of the coronavirus.12

In fact, only about 10 percent of that grant was slated for the Wuhan Institute for collecting and analyzing samples, according to EcoHealth's Daszak.13

Thirty-one U.S. scientific societies and 77 Nobel laureates wrote to the NIH calling for an investigation into the grant's cancellation. The Nobel laureates said the termination of the grant “sets a dangerous precedent by interfering in the conduct of science.”14

“Our future plans were to sequence whole genomes” of viruses, EcoHealth said in a statement accompanying the recent study, “particularly … to see if any of these viruses are likely able to infect humans. That work will not happen without the funding from NIH.”15

— Sarah Glazer

[1] David Quammen, Spillover: Animal Infections and the Next Human Pandemic (2012), pp. 314-328.

[2] Alice Latinne et al., “Origin and cross-species transmission of bat coronaviruses in China,” bioRxiv, posted June 1, 2020, https://tinyurl.com/y85f63fc.

[3] Ibid.

[4] Quammen, op. cit.

[5] Kate Jones et al., “FAQs — Relationship between habitat loss, biodiversity, bats and live wildlife markets,” 2020, https://tinyurl.com/yaz2csh9.

[6] Tom Evans et al., “Links between ecological integrity, emerging infectious diseases originating from wildlife, and other aspects of human health — an overview of the literature,” Wildlife Conservation Society, April 2020, https://tinyurl.com/y8dd4ac4.

[7] “Talking points from Latinne et al., Origin and cross transmission of bat CoVs in China,” EcoHealth Alliance, June 1, 2020.

[8] “Nipah Virus Frequently Asked Questions,” Food and Agriculture Organization of the United Nations, https://tinyurl.com/ybhp37p8.

[9] Ferris Jabr, “How Humanity Unleashed a Flood of New Diseases,” The New York Times Magazine, June 17, 2020, https://tinyurl.com/yc26pngc.

[10] Latinne et al., op. cit.

[11] Nin Wang et al., “Serological Evidence of Bat SARS-Related Coronavirus Infections in Humans, China,” Virologica Sinica, March 2, 2018, https://tinyurl.com/ycqze63h.

[12] James Gorman, “Prominent Scientists Denounce End to Coronavirus Grant,” The New York Times, May 21, 2020, https://tinyurl.com/y9vl62de.

[13] Nurith Aizenman, “Why The U.S. Government Stopped Funding A Research Project On Bats And Coronaviruses,” NPR, April 29, 2020, https://tinyurl.com/yc47l3po.

[14] Gorman, op. cit.

[15] “Talking points from Latinne et al., Origin and cross transmission of bat CoVs in China,” op. cit.

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As Deer Population Explodes, Lyme Disease Spreads

The first thing many summer visitors see on the ferry to Martha's Vineyard is the pamphlet warning them to beware of Lyme disease.

Martha's Vineyard, an island off Cape Cod in Massachusetts that is famed for its beaches, has consistently ranked among the top 10 counties in the country for Lyme disease rates.16

But old-timers who grew up on the island in the 1950s or earlier “say they never saw a tick here” of the Lyme variety, the blacklegged or deer tick, says Richard Johnson, director of the Martha's Vineyard Tick Program, a county effort that educates the public about Lyme.17

Many people think of Lyme as a recent invader, because it was first identified in Lyme, Conn., in 1976. Cases have risen steadily from just under 10,000 in 1991 to more than 300,000 a year, according to the U.S. Centers for Disease Control and Prevention (CDC). Initial symptoms include skin rash, headache, fever and fatigue. Lyme can be treated with antibiotics, but if not caught early, the infection can spread to joints, the heart and the nervous system.18

Deer ticks, like this one, can infect humans with Lyme disease through their bite. The disease, which has spread in the Northeast and Midwest in recent years, can cause rash, headache, fever and fatigue; if not caught early, it can damage the joints, heart and nervous system. (Getty Images/Portland Press Herald/Shawn Patrick Ouellette)

It turns out the Lyme bacterium has been in North America for at least 60,000 years, circulating unnoticed in forests, according to recent genomic analysis by Yale University researchers. The researchers concluded that the suburban explosion of the deer population — without predators — allowed the tick population to soar in New England and the Midwest.19

Like many parts of the Northeast, the Vineyard was originally covered by virgin forest, then turned into treeless pastureland for sheep by European colonists starting in the 18th century. With the collapse of the sheep industry in the early 1900s, the trees started growing back.

They provided cover for deer, which carry the adult ticks, and for white-footed mice, which carry the poppy seed-sized tick nymphs, the stage when ticks bite people. Deer ticks reappeared in the 1960s or '70s, Johnson estimates, when second-growth forest blanketed the island's pastures.

While it is true that some forest seems to be a prerequisite for ticks and their hosts, humans have made it worse by cutting up the forest into small fragments, where large predators of mice and deer can no longer survive, says Richard S. Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies, a research center in Millbrook, N.Y.

Ostfeld's research finds more infected ticks in small patches of woods than in undisturbed forest, where predators of mice such as foxes live, as do opossums, which eat most of the ticks on them.20

In suburban developments, “we're placing homes, dogs and kids right in the hot zone we've created,” Ostfeld says. “If you're right next to a bit of forest, that's more dangerous than living next to a big continuous forest.” One solution he proposes is building houses together in clusters.

Yet on the Vineyard, as in much of the Northeast, it would be hard to change the longstanding suburban and rural patterns, where houses abut small patches of woods, observes Johnson.

Traditional approaches to controlling Lyme disease have been to clear vegetation and cull the animals hosting the ticks, says Chelsea L. Wood, an assistant professor at the University of Washington's School of Aquatic and Fishery Sciences in Seattle. “The unfortunate reality is that is the only strategy that's ever worked for us in the past,” she says.

For example, Monhegan Island off Maine employed sharpshooters to kill the entire herd of 100 deer on its four-and-a-half square miles between 1996 and 1999.21 By 2004, no ticks could be found on the island.22

If an adult tick can no longer feed on a deer, she can no longer reproduce, so killing one fed adult female tick is the equivalent of killing 2,000 larvae or several hundred nymphs.23

Looking to Monhegan, Martha's Vineyard has been encouraging more deer hunting, offering bow hunters a bounty of $100 for taking their third doe. It also has been encouraging homeowners to allow hunting on their property.24 Last year, hunters took almost twice as many deer as in 2015, according to Johnson.

But simply reducing the deer population will not necessarily eliminate ticks, cautions Ostfeld. Ticks are constantly seeking a host, he says, noting one case where halving the deer population led to twice as many ticks living on each deer. However, other studies find that reducing the deer population dramatically resulted in a significant reduction in Lyme cases.25

“I don't think there's any doubt that reducing deer will eventually reduce ticks,” says Johnson, explaining his strategy for the Vineyard. “The question is how low do you have to get the numbers.”

Reducing density to eight or fewer deer per square mile might break the cycle of ubiquitous Lyme disease, according to one estimate Johnson cites. That would be an ambitious goal for the Vineyard, which averages 30 to 50 deer per square mile on its approximately 100 square miles.

“No one has tried it on the scale we're doing it on the Vineyard,” Johnson says. As an island, the Vineyard has an advantage: Deer cannot walk over a land border from a neighboring county to replace those that have been killed.

Success, for Johnson, would be to return the island to “the way it used to be 60 years ago” — before the ticks arrived.

— Sarah Glazer

[16] Noah Asimow, “Funding for Tick Program Runs Out; Tick Spread Marches On,” Vineyard Gazette, June 27, 2019, https://tinyurl.com/y6w5hace; Matt Rocheleau, “Mass. counties have some of the highest rates of Lyme disease in the U.S.,” The Boston Globe, May 10, 2018, https://tinyurl.com/y9l8o4s2.

[17] “MV Tick Program,” Dukes County, https://tinyurl.com/ycfk7tol.

[18] “Lyme Disease,” U.S. Centers for Disease Control and Prevention, https://tinyurl.com/yx9fq6n2.

[19] “Ancient History of Lyme Disease in North America Revealed with Bacterial Genomes,” Yale School of Medicine, Aug. 28, 2017, https://tinyurl.com/yakh9mxz.

[20] Felicia Keesing et al., “Hosts as ecological traps for the vector of Lyme disease,” Proceedings Biological Sciences, Aug. 19, 2009, https://tinyurl.com/ycqkl4a3.

[21] George Smith, “Monhegan killed all its deer and eliminated Lyme disease,” George's Outdoor News, Oct. 28, 2016, https://tinyurl.com/yb5r6bs8.

[22] Joseph Piesman, “Strategies for Reducing the Risk of Lyme Borreliosis in North America,” International Journal of Medical Microbiology, May 2006, https://tinyurl.com/y6vsqbn3.

[23] “Could Reducing Deer Populations Reduce Lyme Disease?” Entomology Today, Sept. 28, 2017, https://tinyurl.com/ycl7y4jw.

[24] Julia Wells, “Bow Hunters Offered Financial Incentive to take More Deer,” Vineyard Gazette, Sept. 30, 2019, https://tinyurl.com/yakwamw2.

[25] Howard J. Kilpatrick et al., “The Relationship between Deer Density, Tick Abundance, and Human Cases of Lyme in a Residential Community,” Journal of Medical Entomology, July 1, 2014, https://tinyurl.com/y9ym5k25.

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Bibliography

Books

Andiman, Warren A. , Animal Viruses and Humans, A Narrow Divide: How Lethal Zoonotic Viruses Spill Over and Threaten Us , Paul Dry Books, 2018. A professor emeritus of pediatrics and epidemiology at the Yale University Schools of Medicine and Public Health explains the science behind some of the biggest zoonotic outbreaks in recent years, including MERS, SARS and Ebola.

Brown, Jeremy , Influenza: The Hundred-Year Hunt to Cure the Deadliest Disease in History , Touchstone, 2018. The director of the Office of Emergency Care Research at the National Institutes of Health provides a readable history of flu epidemics, including the 1918 Spanish flu, and traces scientific and governmental efforts to cure the disease.

Quammen, David , Spillover: Animal Infections and the Next Human Pandemic , W.W. Norton, 2012. A science writer accompanies prominent virus hunters into the wild to illustrate how scientists have tried to trace zoonotic diseases such as SARS, Ebola and AIDS back to their animal origins and how animal diseases spill over to humans.

Articles

Areddy, James T. , “China Rules Out Animal Market and Lab as Coronavirus Origin,” The Wall Street Journal, May 26, 2020, https://tinyurl.com/yb7jyb78. In an interview with Chinese state media, the head of China's Center for Disease Control and Prevention said his scientists were unable to trace the virus that caused COVID-19 to an animal at the Wuhan seafood market, originally suspected as a source.

Beitsch, Rebecca , “Two green groups call for end to wildlife trade to prevent next pandemic,” The Hill, May 18, 2020, https://tinyurl.com/yasezlar. Two environmental groups urged Congress to ban the trade in all live wildlife, saying the recent House-passed Heroes Act does not go far enough.

Bell, Diana , “Coronavirus: We still haven't learned the lessons from Sars,” The Conversation, Jan. 24, 2020, https://tinyurl.com/yc5u86el. A professor of conservation biology at the University of East Anglia in England argues that the world should learn the lesson from the 2002-03 SARS outbreak — that the wildlife trade is a “threat to human health.”

Meyers, Steven Lee , “China Vowed to Keep Wildlife Off the Menu, a Tough Promise to Keep,” The New York Times, June 7, 2020, https://tinyurl.com/y9havdyf. A journalist discusses the economic pressures to narrow China's wildlife ban as the government considers permanent legal changes.

Osofsky, Steve , “Emerging ‘dis-ease’: US foreign assistance needs to focus on the root causes of pandemics,” The Hill, May 24, 2020, https://tinyurl.com/ycds8yoa. A wildlife veterinarian at Cornell University argues that the government should reorient its efforts away from hunting for the viruses that could cause the next pandemic and toward stopping root causes such as wildlife trade and deforestation.

Watts, Jonathan , “‘Promiscuous treatment of nature’ will lead to more pandemics — scientists,” The Guardian, May 7, 2020, https://tinyurl.com/yaf3l4gr. A journalist quotes scientists who say human beings' destruction of nature, such as habitat occupied by bats in Asia, will lead to more pandemics of diseases jumping from animals.

Reports and Studies

Evans, Tom , et al., “Links between ecological integrity, emerging infectious diseases originating from wildlife, and other aspects of human health — an overview of the literature,” Wildlife Conservation Society, April 2020, https://tinyurl.com/y8dd4ac4. A global conservation group that also runs the Bronx Zoo summarizes research showing links between human incursions into the environment and outbreaks of infectious diseases.

Keesing, Felicia , et al., “Impacts of biodiversity on the emergence and transmission of infectious diseases,” Nature, Dec. 2, 2010, https://tinyurl.com/yaja4q8j. A Bard College professor and other environmental health researchers conclude that preserving ecosystems “should generally reduce the prevalence of infectious diseases.”

Magnusson, Magnus , et al., “Effect of spatial scale and latitude on diversity-disease relationships,” Ecology, December 2019, https://tinyurl.com/yab8tbbg. This meta-analysis by Swedish and American ecology experts found that high biodiversity was linked to reduced risk of infectious disease in large regions in the temperate zone.

Wood, Chelsea L. , et al., “Human infectious disease burdens decrease with urbanization but not with biodiversity,” Philosophical Transactions of the Royal Society B, April 24, 2017, https://tinyurl.com/ya89fgmg. In this study of 60 countries, researchers from universities in Washington, California and Maryland find that urbanization and growing wealth have been the main drivers in reducing infectious diseases, while biodiversity has had a minimal to negative effect.

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The Next Step

Biodiversity

Hall, Louise , “World Bee Day: Are we ignoring biodiversity risks in the same way we ignored the pandemic?” The Independent, May 20, 2020, https://tinyurl.com/y85s2j6s. Experts warn that losses of biodiversity, especially bees, constitute a crisis that people are unprepared for, much the way many were caught off guard by the coronavirus pandemic.

Rankin, Jennifer , “EU plan for 3bn trees in 10 years to tackle biodiversity crisis,” The Guardian, May 19, 2020, https://tinyurl.com/ybku3t9q. A European Union initiative calls for one-third of the continent to become protected zones, but some scientists say the strategy is not specific enough.

Win, Thin Lei , “Will pandemic push humans into a healthier relationship with nature?” Reuters, May 21, 2020, https://tinyurl.com/yagvjtf8. The coronavirus pandemic has hampered ongoing efforts to preserve biodiversity, according to environmentalists.

Coronavirus and the Environment

Beitsch, Rebecca , “Efforts to rescue recycling complicated by coronavirus,” The Hill, June 17, 2200, https://tinyurl.com/ybnznbzo. Municipalities facing budget shortfalls due to the coronavirus pandemic might be forced to recycle less material, and the recycling industry has turned to Congress for help.

Harvey, Fiona , “Covid-19 pandemic is ‘fire drill’ for effects of climate crisis, says UN official,” The Guardian, June 15, 2020, https://tinyurl.com/ycu6ww4c. A United Nations business chief warns that crises like the coronavirus pandemic will multiply until humans adopt more environmentally sustainable practices.

Miller, Ryan W. , “‘More masks than jellyfish’: Environmental groups worry about coronavirus waste in oceans,” USA Today, June 9, 2020, https://tinyurl.com/ydfe6rlw. Environmentalists warn that masks, gloves and other pandemic-related waste are polluting the ocean.

Regulations

Challender, Dan , et al., “Coronavirus: why a blanket ban on wildlife trade would not be the right response,” The Conversation, April 8, 2020, https://tinyurl.com/y8exr4sf. Environmental researchers argue blanket bans on wildlife consumption would encourage illegal sales, but that targeted regulations would make wildlife trade safer.

Khadka, Navin Singh , “Coronavirus: China wildlife trade ban ‘should be permanent,’” BBC, Feb. 4, 2020, https://tinyurl.com/ybve9hom. Conservationists called on China to make its temporary wildlife trade ban permanent, and state-run media in the country denounced the lack of regulations in the wildlife market.

Londoño, Ernesto, Manuela Andreoni and Letícia Casado , “Amazon Deforestation Soars as Pandemic Hobbles Enforcement,” The New York Times, June 6, 2020, https://tinyurl.com/y9tqce7v. Illegal loggers and miners in the Amazon see little chance of punishment because deforestation regulations are going unenforced during the pandemic.

Wildlife Consumption

Alden, Chris, and Ross Harvey , “A South African proposal to allow the breeding of wildlife for slaughter could end in disaster,” Quartz Africa, June 15, 2020, https://tinyurl.com/y9rbc2q9. South Africa is considering expanding the number of species that can be bred for slaughter, raising the risk of humans contracting zoonotic diseases, according to the authors.

Kays, Roland , “Can Asia end its uncontrolled consumption of wildlife? Here's how North America did it a century ago,” The Conversation, June 17, 2020, https://tinyurl.com/yazbkl3d. North America limited wildlife consumption in the early 1900s, after many species were driven nearly extinct, and China could pursue a similar conservation plan, according to a scientist.

Stanway, David , “China legislators take on wildlife trade, but traditional medicine likely to be exempt,” Reuters, May 20, 2020, https://tinyurl.com/y9h6skc4. Wildlife continues to be used in medicine and in the fur trade in China, because those practices are exempt from the country's ban on consumption.

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Contacts

Center for Biological Diversity
PO Box 710, Tucson, AZ 85702-0710
520-623-5252
biologicaldiversity.org
Advocacy group working to protect endangered species.

Centers for Disease Control and Prevention
1600 Clifton Road, Atlanta, GA 30329
800-232-4636
cdc.gov
Federal government's lead public health agency.

EcoHealth Alliance
520 Eighth Ave., Suite 1200, New York, NY 10018
212-380-4460
ecohealthalliance.org
Research group developing science-based solutions to prevent pandemics and promote conservation.

One Health Commission
PO Box 972, Apex, NC 27502
984-500-8093
onehealthcommission.org
Nonprofit advocating “One Health” approaches, which join experts in animal, plant and human health with ecosystem professionals.

Wildlife Conservation Society
2300 Southern Blvd., Bronx, NY 10460
718-220-5100
wcs.org
Global advocacy and research group dedicated to protecting wildlife and wild places.

World Health Organization
1 Dag Hammarskjold Plaza, 885 Second Ave., 26th floor, New York, NY 10017
646-626-6060
who.int
United Nations agency that is responsible for international public health.

World Wildlife Fund
1250 24th St., N.W., Washington, DC 20037
202-293-4800
worldwildlife.org
Global conservation group dedicated to protecting wildlife and natural habitats.

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Footnotes

[1] Andrew Joseph, “First death from Wuhan pneumonia outbreak reported as scientists release DNA sequence of virus,” STAT, Jan. 11, 2020, https://tinyurl.com/s4wx3nk; Derrick Bryson Taylor, “How the Coronavirus Pandemic Unfolded: a Timeline,” The New York Times, June 9, 2020, https://tinyurl.com/wb48cut; and Chaolin Huang et al., “Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China,” The Lancet, Jan. 24, 2020, https://tinyurl.com/w5qfs4w.

[2] Jeremy Page and Natasha Khan, “On the ground in Wuhan, Signs of China Stalling Probe of Coronavirus Origins,” The Wall Street Journal, May 12, 2020, https://tinyurl.com/ycqtmqkp.

[3] James T. Areddy, “China Rules out Animal Market and Lab as Coronavirus Origin,” The Wall Street Journal, May 26, 2020, https://tinyurl.com/yb7jyb78.

[4] David Cyranoski, “The biggest mystery: what it will take to trace the coronavirus source,” Nature, June 5, 2020, https://tinyurl.com/yd7ooc6a; Alexandre Hassanin, “Coronavirus origins,” The Conversation, March 24, 2020, https://tinyurl.com/rynx542.

[5] Kate E. Jones, “Global trends in emerging infectious diseases,” Nature, Feb. 21, 2008, https://tinyurl.com/y8676bqx; “One Health, Zoonotic Diseases,” Centers for Disease Control and Prevention, last reviewed July 14, 2017, https://tinyurl.com/yaxup36m.

[6] Vincent C.C. Cheng et al., “Severe Acute Respiratory Syndrome Coronavirus in an Agent of Emerging and Reemerging Infection,” Clinical Microbiology Review, October 2007, https://tinyurl.com/w2yjfj6.

[7] Damian Carrington, “Coronavirus: ‘Nature is sending us a message,’ says UN environment chief,” The Guardian, March 25, 2020, https://tinyurl.com/ycvgc7lt.

[8] “Our health depends on our environment,” Planetary Health Alliance, https://tinyurl.com/yaospq78.

[9] “Global Wildlife Health and Pandemic Prevention Act,” Sen. Chris Coons and Sen. Lindsey Graham, https://tinyurl.com/ya72mg34; “Bi-Partisan One Health Congressional Bills introduced in U.S. Senate and House,” One Health Commission, 2020, https://tinyurl.com/yyn8b8vj.

[10] “Reducing Pandemic Risk, Promoting Global Health,” USAID, accessed June 17, 2020, https://tinyurl.com/yad4gotw.

[11] “World Population by Year,” worldometer, https://tinyurl.com/y2nw28sa.

[12] Anthony Cilluffo and Neil G. Ruiz, “World's population is projected to nearly stop growing by end of the century,” Pew Research Center, June 17, 2019, https://tinyurl.com/yd2kw8j2.

[13] Chelsea L. Wood et al., “Human infectious disease burdens decrease with urbanization but not with biodiversity,” Philosophical Transactions of the Royal Society B, April 24, 2017, https://tinyurl.com/ya89fgmg.

[14] “The Wildlife Origins of SARS-COV2 and Employing a One Health Approach,” podcast interview with Dr. Steve Osofsky, Excellsior, April 3, 2020, https://tinyurl.com/yacvagop.

[15] Kate E. Jones et al., op. cit.

[16] “Forest ecology shapes Lyme disease risk in the eastern US,” Science Daily, July 9, 2018, https://tinyurl.com/y7h82kja; Richard S. Ostfeld et al., “Tick-borne disease risk in a forest web,” Ecology, May 8, 2018, https://tinyurl.com/ybskbxce.

[17] Wood et al., op. cit.

[18] Laura S.P. Bloomfield et al., “Habitat fragmentation, livelihood behaviors, and contact between people and nonhuman primates in Africa,” Landscape Ecology, April 1, 2020, https://tinyurl.com/y8uxnems.

[19] “How forest loss leads to spread of disease,” Stanford University, April 8, 2020, https://tinyurl.com/yahrzsuu.

[20] Christine K. Johnson et al., “Global shifts in mammalian population trends reveal key predictors of virus spillover risk,” Proceedings of the Royal Society B, April 8, 2020, https://tinyurl.com/rcjgms2.

[21] Jason R. Rohr et al., “Emerging human infectious diseases and the links to global food production,” Nature Sustainability, June 11, 2019, https://tinyurl.com/y9uuc5y9.

[22] Johnson, op. cit.

[23] “End the Trade: Coalition Invites Global Community to Take a Stand Against Future Pandemics,” WildAid, April 20, 2020, https://tinyurl.com/y7amshwc.

[24] “A Global Call to Action on Covid-19 and Wildlife Trade,” preventpandemics.org, https://tinyurl.com/ybhcdpb7.

[25] Dan Challender et al., “Coronavirus: Why a blanket ban on wildlife trade would not be the right response,” The Conversation, April 8, 2020, https://tinyurl.com/y8exr4sf.

[26] “China Suspends Wildlife Trade to Curb Novel Coronavirus,” Xinhuanet, Jan. 26, 2020, https://tinyurl.com/yag4e22g.

[27] George Wittemyer, “The new coronavirus emerged from the global wildlife trade and may be devastating enough to end it,” The Conversation, March 31, 2020, https://tinyurl.com/spztlfm.

[28] Jesse Bonwitt et al., “Unintended Consequences of the ‘Bushmeat Ban’ in West Africa during 2013-2016 Ebola Virus Disease Epidemic,” Social Science & Medicine, March 2018, https://tinyurl.com/yc4p9bq9.

[29] “Wildlife Crime: Pangolin Scales,” United Nations Office on Drugs and Crime, 2020, https://tinyurl.com/yablpa5e.

[30] Candace Famiglietti and Maria Ivanova, “We must address exotic wildlife consumption to avoid the Next Global Pandemic,” New Security Beat, April 20, 2020, https://tinyurl.com/ybgucocn.

[31] “One Health,” World Bank Group, 2018, p. 15, https://tinyurl.com/t6gbr7e.

[32] “Shutdown of PREDICT Infectious Disease Program Challenged by Senators Warren and King,” Global Biodefense, Feb. 4, 2020, https://tinyurl.com/y8pzml9p.

[33] Colin J. Carlson, “From PREDICT to prevention, one pandemic later,” The Lancet Microbe, March 21, 2020, https://tinyurl.com/yaw424hr.

[34] Cyranoski, op. cit.

[35] Nina Wang et al., “Serological Evidence of Bat SARS-related Coronavirus Infection in Humans, China,” Virological Sinica, March 2, 2018, https://tinyurl.com/y8e4j53b.

[36] Steve Osofsky, “Emerging ‘dis-ease’: US foreign assistance needs to focus on the root causes of pandemics,” The Hill, May 24, 2020, https://tinyurl.com/ycqze63h.

[37] Steven Johnson, “How Data Became One of the Most Powerful Tools to Fight an Epidemic,” The New York Times Magazine, June 10, 2020, https://tinyurl.com/y9mk9vt8.

[38] Christian Nordqvist, “Origins of the Black Death Traced Back to China, Gene Sequencing Has Revealed,” Medical News Today, Nov. 1, 2010, https://tinyurl.com/yd27waez.

[39] Ibid.

[40] “The History of Plague — Part 1. The Three Great Pandemics,” Journal of Military and Veterans Health, https://tinyurl.com/yckb75kl.

[41] “Plague,” Centers for Disease Control and Prevention, https://tinyurl.com/saz8w86.

[42] “One Health, Zoonotic Diseases,” op. cit.

[43] David Quammen, Spillover (2013), p. 427.

[44] Ibid., p. 137.

[45] Jason R. Rohr, op. cit.

[46] Quammen, op. cit., p. 43.

[47] Ibid.

[48] Ibid., pp. 22-23.

[49] Ibid., p. 31; “Monkeypox,” Centers for Disease Control and Prevention, https://tinyurl.com/y726qbrh.

[50] Tom Evans et al., “Links between ecological integrity, emerging infectious disease originating from wildlife, and other aspects of human health,” Wildlife Conservation Society, April 2020, https://tinyurl.com/y8dd4ac4.

[51] Sarah Glazer, “Avian Flu Threat,” CQ Researcher, Jan. 13, 2006, https://tinyurl.com/ycb53he2.

[52] “Influenza; 1957-1958 Pandemic (H2N2 Virus),” Centers for Disease Control and Prevention, Jan. 2, 2019, https://tinyurl.com/ycqqgbqb; “Influenza; 1968 Pandemic (H3N2 virus),” Jan. 2, 2019, https://tinyurl.com/ybxo853d.

[53] Jeremy Brown, Influenza: The Hundred-Year Hunt to Cure the Deadliest Disease in History (2018), p. 60.

[54] Ibid., p. 65.

[55] “Hot Spots for Emerging Diseases,” The New York Times, July 15, 2012, https://tinyurl.com/y5kl5vhu.

[56] Warren Andiman, Animal Viruses and Humans, a Narrow Divide (2018), p. 165, p. 167.

[57] “Ebola Virus Disease,” World Health Organization, Feb. 10, 2020, https://tinyurl.com/y24gcxvg.

[58] Andiman, op. cit., pp. 170-173.

[59] Evans et al., op. cit.

[60] “Nipah virus,” World Health Organization, May 30, 2018, https://tinyurl.com/y8hudome; Paul M. Sharp and Beatrice H. Hahn, “Origins of HIV and the AIDS Pandemic,” Cold Spring Harbor Perspectives in Medicine, September 2011, https://tinyurl.com/y5pftt2w.

[61] “Hot Spots for Emerging Diseases,” op. cit.

[62] Evans et al., op. cit.

[63] “2014-2016 Ebola Outbreak in West Africa,” Centers for Disease Control and Prevention, March 8, 2019, https://tinyurl.com/y7aqqxp2.

[64] “Ebola virus disease,” op. cit.

[65] “Top 9 Infectious Disease Outbreaks of 2018,” Contagion Live, Dec. 31, 2018, https://tinyurl.com/y8los7fp; Grant M. Gallagher, “The Ebola Outbreak Response So Far,” Contagion Live, Jan. 2, 2020, https://tinyurl.com/y8ryuglp; and “Ebola Virus Disease,” op. cit.

[66] “CDC SARS Response Timeline,” Centers for Disease Control and Prevention, April 26, 2013, https://tinyurl.com/vsp9qng.

[67] Brown, op. cit., p. 6.

[68] Diana Bell, “Coronavirus: We still haven't learned the lessons from Sars,” The Conversation, Jan. 24, 2020, https://tinyurl.com/yc5u86el.

[69] “SARS (Severe Acute Respiratory Syndrome),” World Health Organization, 2020, https://tinyurl.com/vnwflw4; “Update 95 — SARS: Chronology of a Serial Killer,” World Health Organization, Nov. 16, 2002, https://tinyurl.com/y8p2uuxy.

[70] Glazer, op. cit.

[71] Ibid.

[72] “Influenza (Flu),” Centers for Disease Control and Prevention, Jan. 8, 2014, https://tinyurl.com/u4jjgh5.

[73] Martin Enserink, “WHO Declares Official End to H1N1 ‘Swine Flu’ Epidemic,” Science, Aug. 10, 2010, https://tinyurl.com/ybxkojbb.

[74] Mackenzie Bean, “A look back at swine flu,” Becker's Hospital Review, March 12, 2020, https://tinyurl.com/t5n5jpk.

[75] “Hot Spots for Emerging Diseases,” op. cit.; Jim Robbins, “The Ecology of Disease,” The New York Times, July 14, 2012, https://tinyurl.com/qpmwpry.

[76] Yella Hewings-Martin, “How do SARS and MERS Compare with COVID-19?” Medical News Today, April 10, 2020, https://tinyurl.com/y77vpj7t.

[77] Roger Frutos et al., “COVID-19, The Conjunction of Events Leading to the Coronavirus Pandemic and Lessons to Learn for Future Threats,” Frontiers in Medicine, May 12, 2020, https://tinyurl.com/yd388hkr.

[78] “Pneumonia of Unknown Cause-China,” World Health Organization, Jan. 5, 2020, https://tinyurl.com/qwxenbk.

[79] Chaolin Huang et al., “Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China,” The Lancet, Jan. 24, 2020, https://tinyurl.com/w5qfs4w.

[80] Hassanin, op. cit.

[81] Daniel Lucey, “Recent Data and Maps to help find origin of COVID-19,” Science Speaks: Global ID News, March 15, 2020, https://tinyurl.com/szykfa2; Frutos, op. cit.; Josephine Ma, “Coronavirus: China's first confirmed COVID-19 case traced back to November 17,” South China Morning Post, March 13, 2020, https://tinyurl.com/sdajymy; and Page and Khan, op. cit.

[82] Jackie Salo, “Wuhan market is the ‘victim’ of coronavirus outbreak,” New York Post, May 27, 2020, https://tinyurl.com/y89u8g3m.

[83] Hassanin, op. cit.

[84] Steven Lee Meyers, “China Vowed to Keep Wildlife off the Menu, a Tough Promise to Keep,” The New York Times, June 7, 2020, https://tinyurl.com/y9havdyf.

[85] David Stanway, “China legislators take on wildlife trade, but traditional medicine likely to be exempt,” Reuters, May 20, 2020, https://tinyurl.com/y8pmgfnj.

[86] Ben Westcott, “Chinese government reveals draft list of animals which can be farmed for meat,” CNN, April 10, 2020, https://tinyurl.com/s9fpupq.

[87] “China offers farmers cash to give up wildlife trade,” AFP, Bangkok Post, May 19, 2020, https://tinyurl.com/ydcwt343.

[88] Michael Tatarski, “Vietnam wildlife trade ban appears to flounder amid coronavirus success,” Mongabay, May 25, 2020, https://tinyurl.com/ya7k2uqy.

[89] Jackie Northam, “Calls to Ban Wildlife Markets Worldwide Gain Steam Amid Pandemic,” NPR, April 19, 2020, https://tinyurl.com/yceea6rd; Helen Briggs, “Coronavirus: WHO developing guidance on wet markets,” BBC News, April 21, 2020, https://tinyurl.com/y7rx5j6x.

[90] “UN: Live Animal Markets Shouldn't Be Closed Despite Virus,” The Associated Press/U.S. News & World Report, May 8, 2020, https://tinyurl.com/y9sjswby.

[91] “End the Trade: New Coalition Invites Global Community to Take a Stand Against Future Pandemics,” WSCNewsroom, April 21, 2020, https://tinyurl.com/yajo6ys8.

[92] “What is CITES?” CITES, https://tinyurl.com/zrccyqb.

[93] Susan Lieberman, “CITES, the Treaty that Regulates Trade in International Wildlife, Is Not the Answer to Preventing Another Zoonotic Pandemic,” National Geographic, May 22, 2020, https://tinyurl.com/y8d5qzk6.

[94] Elly Pepper, “We must prevent future viruses by ending the wildlife trade,” NRDC, April 14, 2020, https://tinyurl.com/ya6gdy99.

[95] “CITES Secretariat's statement in relation to COVID-19,” CITES, https://tinyurl.com/ydgudnxy.

[96] Lieberman, op. cit.

[97] Pepper, op. cit.

[98] Stephen Lee and Dean Scott, “As Lawmakers Push Global Wildlife Market Ban, U.S. Issues Remain,” Bloomberg Law, April 28, 2020, https://tinyurl.com/ybjungch.

[99] “U.S. Fish and Wildlife Service: FY2021 Appropriations,” Congressional Research Service, March 20, 2020, https://tinyurl.com/yclp53wu.

[100] John R. Platt, “Trump's Budget Plan: A Push for Even Greater Environmental Regression,” EcoWatch, Feb. 12, 2020, https://tinyurl.com/y79sor5s.

[101] Rebecca Beitsch, “Two green groups call for end to wildlife trade to prevent next pandemic,” The Hill, May 18, 2020, https://tinyurl.com/yasezlar.

[102] Lauren Frias, “House passes $3 trillion coronavirus relief bill dubbed HEROES Act,” Business Insider, May 15, 2020, https://tinyurl.com/yaccyogl.

[103] “Discussion Draft,” coons.senate.gov, accessed June 17, 2020, https://tinyurl.com/y7wxw5mu.

[104] “Sens. Coons, Graham introduce legislation to shut down high-risk wildlife markets that could ignite another global disease outbreak,” press release, Sen. Chris Coons, May 19, 2020, https://tinyurl.com/y77otomf.

[105] “Global Wildlife Health and Pandemic Prevention Act,” op. cit.

[106] “Senators Warren, King Question USAID on Decision to Shutter Global Infectious Disease Prevention Program,” press release, Elizabeth Warren, Jan. 31, 2020, https://tinyurl.com/y8u6nw7m.

[107] Kristin Burns, “PREDICT Receives Extension for COVID-19 Pandemic Emergency Response,” UCDavis, March 31, 2020, https://tinyurl.com/ybcw8p35.

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About the Author

Sarah Glazer is a New York-based freelancer who contributes regularly to CQ Researcher. Her articles on health, education and social-policy issues also have appeared in The New York Times and The Washington Post. Her recent CQ Researcher reports include “Manipulating Human Genes” and “Global Migration.” She graduated from the University of Chicago with a B.A. in American history.

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