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The reflection in the water of a Trajinera boatman, in Xochimilco, a transportation system created by the indigenous Aztec ethnic group in Mexico City, on March 14, 2020.

RODRIGO ARANGUA/AFP/Getty Images

Since Earth Day was first celebrated in 1970, millions have gathered every April 22 to celebrate the planet and recognize our connection to it.

Now, 50 years since the event was launched, there will be no mass public gatherings as the COVID-19 pandemic forces people around the world to stay safe and stay apart. But humanity’s relationship to the environment and the long-term consequences for our survival and well-being could hardly be more apparent.

Earth Day reads: Books that will help the environmentalist in you grow

Although the sequence of events that allowed a novel and dangerous coronavirus to jump into the human population late last year remains obscure, the broader situation that made the spillover possible is not. Coronaviruses of the type that causes COVID-19 are known to originate in bats, an animal whose microbes are not typically shared with humans. But a thriving wildlife trade can facilitate the journey from bat to human. Wild animals that are captured or raised to be purchased and eaten are potential bridges for pathogens moving from their natural reservoirs into people.

Because of the pandemic, the issue has gained new visibility, prompting China and Vietnam to shut down large swaths of the trade while other countries face pressure to follow suit.

An empty freeway intersection is seen two days before Earth Day, after Los Angeles’ stay-at-home order caused a drop in pollution in Pasadena, California, April 20, 2020.

LUCY NICHOLSON/Reuters

Yet, while this response may seem like an obvious thing to do, given the enormous human and economic cost of COVID-19, conservation biologists warn that the wildlife trade is only one piece of a much bigger crisis. Through habitat loss and climate change – byproducts in the quest for cheap resources, cheap food and cheap energy – humans are pushing nature to its limits while simultaneously crowding it on all sides. In other words, our collective actions are making wild species more susceptible to disease while putting ourselves in closer contact with them than ever before.

“The health of our environment, the health of wildlife, the health of our livestock and our own health are all intimately intertwined,” said EJ Milner-Gulland, director of the interdisciplinary centre for conservation science at Oxford University.

Dr. Milner-Gulland, who has worked for two decades to understand and mitigate the underlying forces that fuel the wildlife trade, said that attempting to enforce a global ban on the practice would be an incomplete response to COVID-19. Instead, she said, the pandemic should be taken as an opportunity for thinking differently about nature and the inequities that drive its exploitation.

View of a heron on the Santa Catarina river, in Monterrey, Nuevo Leon state, Mexico on March 14, 2020.

JULIO CESAR AGUILAR/AFP/Getty Images

“The whole thing needs resetting,” she said. “The kind of change we need to push for is more fundamental.”

Other experts note that last year’s revelation that one million species on the planet are now at risk – a figure released by the United Nations body tasked with monitoring biodiversity – and this year’s COVID-19 pandemic, are actually two parts of the same story.

Story continues below advertisement

By destroying habitat and breeding massive homogeneous populations of livestock, “we have created a world of intensified encounters with animals," said Rosemary Collard a political ecologist at Simon Fraser University. And it is precisely those encounters that put us at risk of more global pandemics.

Evidence for this can be found in a 2017 study published in Nature Communications in which scientists with the EcoHealth Alliance, a global not-for-profit, analyzed the factors that are mostly likely to correlate with the emergence of zoonotic diseases – diseases that originate in animals but can spill over into humans. They found that the risk was most elevated in tropical forest regions that are high in mammal biodiversity and where the land use by humans is changing because of agricultural practices. Land use is similarly implicated as one of the major drivers of wildlife extinction, with climate change emerging as a rising threat that is causing remaining habitat to shrink or shift through long-term changes in temperature and precipitation.

Pine stump is left after deforestation in a forest near the village of Piatrylava, Belarus April 21, 2020.

VASILY FEDOSENKO/Reuters

As humans close in on the wilderness, pathogens can enter the human population through a variety of routes, including transport by insects or other parasites that feed off both animals and people, direct exposure to live pathogens shed by animals and the consumption of wild meat. It is thought that some combination of the last two – exposure to and butchering of wild animals (or farmed wildlife) destined to be consumed – is most likely how COVID-19 found its way into us.

“It’s one of the ways that we most intimately contact other species – by killing them and eating them,” said James Lloyd-Smith, who studies the ecology of infectious disease at the University of California Los Angeles.

PATHWAYS TO SPILLOVER

There are multiple routes by which pathogens

(viruses or micro-organisms that cause disease)

can enter the human population from an animal

host. In each case a combination of pathogen

characteristics and human behaviour can com-

bine to increase the odds that a disease will cross

the barriers between species.

INFECTION VARIABLES

STEPS TO INFECTION

Animal host population

density and distribution

Extent of

host infections

Prevalence of infection

Intensity of infection

Insect or

other vector

Excretion

Slaughter

Rate of

pathogen

release

Shedding rate

Harvest rate

Rate of biting

host aminals

Pathogen sur-

vival and trans-

port of meat

Vector survival

and movement

Pathogen survi-

val and move-

ment

Pathogen

resilience

Amount of pathogen available for contact

Human behav-

iour that leads

to contact with

pathogen

Butchering,

preparation and

eating

Rate of biting

humans

Extent of

human

exposure

Dose and route of exposure

Physical barriers to infection

Effectiveness of immune response

Human

susceptibility

Compatibility with human host

Success of pathogen replication and spread​

Probability of infection

ivan semeniuk and john sopinski/THE GLOBE AND

MAIL, SOURCE: Nature Reviews Microbiology

PATHWAYS TO SPILLOVER

There are multiple routes by which pathogens

(viruses or micro-organisms that cause disease)

can enter the human population from an animal

host. In each case a combination of pathogen

characteristics and human behaviour can com-

bine to increase the odds that a disease will cross

the barriers between species.

INFECTION VARIABLES

STEPS TO INFECTION

Animal host population

density and distribution

Extent of

host infections

Prevalence of infection

Intensity of infection

Insect or

other vector

Excretion

Slaughter

Rate of

pathogen

release

Shedding rate

Harvest rate

Rate of biting

host aminals

Pathogen sur-

vival and trans-

port of meat

Vector survival

and movement

Pathogen survi-

val and move-

ment

Pathogen

resilience

Amount of pathogen available for contact

Human behav-

iour that leads

to contact with

pathogen

Butchering,

preparation and

eating

Rate of biting

humans

Extent of

human

exposure

Dose and route of exposure

Physical barriers to infection

Human

susceptibility

Effectiveness of immune response

Compatibility with human host

Success of pathogen replication and spread​

Probability of infection

ivan semeniuk and john sopinski/THE GLOBE AND MAIL

SOURCE: Nature Reviews Microbiology

PATHWAYS TO SPILLOVER

There are multiple routes by which pathogens (viruses or micro-organisms that cause dis-

ease) can enter the human population from an animal host. In each case a combination of

pathogen characteristics and human behaviour can combine to increase the odds that a dis-

ease will cross the barriers between species.

STEPS TO INFECTION

INFECTION VARIABLES

Animal host population

density and distribution

Extent of

host infections

Prevalence of infection

Intensity of infection

Insect or

other vector

Excretion

Slaughter

Rate of

pathogen

release

Shedding rate

Harvest rate

Rate of biting

host aminals

Pathogen survival

and transport of

meat

Vector survival

and movement

Pathogen survival

and movement

Pathogen

resilience

Amount of pathogen available for contact

Extent of

human

exposure

Human behaviour

that leads to con-

tact with pathogen

Butchering,

preparation and

eating

Rate of biting

humans

Dose and route of exposure

Physical barriers to infection

Effectiveness of immune response

Human

susceptibility

Compatibility with human host

Success of pathogen replication and spread​

Probability of infection

ivan semeniuk and john sopinski/THE GLOBE AND MAIL

SOURCE: Nature Reviews Microbiology

Exactly why the spillover occurred when it did is harder to understand. Viruses can ebb and flow in some animal species just as they do in humans, Dr. Lloyd Smith said. If so, when a virus is on the rise, the chance it will break through the species barrier is higher. At those times, a combination of pathogen characteristics and human behaviour determines the outcome.

A youth walks on the wreckage of a wooden boat, as smog covers North Jakarta, Indonesia, July 26, 2018.

Beawiharta Beawiharta

In February, scientists in China studying the genetic sequence of the COVID-19 virus found similarities with another coronavirus that is found in pangolins, scale-covered anteaters that are endangered but widely traded. Since then, the picture has grown more confusing because a closer genetic match exists between COVID-19 and a bat coronavirus. One possible explanation is that the coronavirus now rampaging through the human population is a chimera that arose from gene exchange between different virus lineages.

But whatever the details, there’s no question that the result was a pathogen that appears to be more robust in the environment and more readily transmitted than its close relative, the 2003 SARS coronavirus.

Underwater scene with acquatic life is seen in Venice's unusual still canals ahead of Earth Day, in Italy April 12, 2020.

ANDREA MANGONI/Reuters

“This one is a little bit sneakier ... It’s actually perfectly adapted to spread in a population like humans,” said Jeffrey Joy, an evolutionary geneticist at the University of British Columbia who is trying to untangle the molecular history of COVID-19.

Experts say there is no evidence to support social-media fuelled speculation that the virus originated in a Chinese lab. For Chris Walzer, a veterinarian and executive director of health for the Wildlife Conservation Society, based in New York, the scenario that remains the most plausible is that the virus was present among animals in the live market in Wuhan that was connected to many of the earliest cases of COVID-19. It then could have jumped into humans, potentially more than once, when animals were handled and then slaughtered and prepared for customers.

“That’s an interface where we have a lot of contact and a lot of opportunities,” Dr. Walzer said.

Aili Kang, who leads the organization’s Asia program, said that China’s actions to ban wildlife consumption and to increase the number of protected species from 406 to more than 2,500 is an important move because the measure targets consumers and not just the provider of the wildlife.

Men give bananas to monkeys gathered on the side of the road as India remains under lockdown over the coronavirus on April 8, 2020 in New Delhi.

Getty Images/Getty Images

While the ban does not cover animal products for medicinal use or exotic pets, Dr. Kang called the ban “a huge step” that is markedly different from the more modest impositions placed on the trader after the SARS outbreak. Despite fears that a ban would drive the trade underground, Dr. Kang said that in China’s case, the new rules are still likely to drastically reduce consumption, although the trade remains a problem in other countries. But, she added, the coming months will reveal whether China is prepared to codify the changes in legislation.

Story continues below advertisement

For her part, Dr. Milner-Gulland said her biggest worry is that once the threat of COVID-19 passes, our troubled relationship with animals, not to mention the bigger threats to biodiversity, will no longer be at the forefront.

“Let’s keep our eyes on the prize,” she said. “And the prize is a transition to humans living in harmony and within our means on this planet.”

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