A burned area of the Amazon rainforest
'Promiscuous treatment of nature' will lead to
more pandemics – scientists
Habitat destruction forces wildlife into human
environments, where new diseases flourish
Jonathan
Watts Global environment editor
@jonathanwatts
Thu 7 May
2020 07.00 BSTLast modified on Thu 7 May 2020 07.02 BST
South America is a key area of concern due to the
rapid clearance of the Amazon.
Humanity’s
“promiscuous treatment of nature” needs to change or there will be more deadly
pandemics such as Covid-19, warn scientists who have analysed the link between
viruses, wildlife and habitat destruction.
Deforestation
and other forms of land conversion are driving exotic species out of their
evolutionary niches and into manmade environments, where they interact and
breed new strains of disease, the experts say.
Three-quarters
of new or emerging diseases that infect humans originate in animals, according
to the US Centers for Disease Control and Prevention, but it is human activity
that multiplies the risks of contagion.
A growing
body of research confirms that bats – the origin of Covid 19 – naturally host
many viruses which they are more likely transfer to humans or animals if they
live in or near human-disturbed ecosystems, such as recently cleared forests or
swamps drained for farmland, mining projects or residential projects.
In the
wild, bats are less likely to transfer the viruses they host to other animals
or come into contact with new pathogens because species tend to specialise
within distinct and well-established habitats. But once land is converted to human
use, the probability increases of contact and viruses jumping zoonotically from
one species to another.
As natural
habitats shrink, wild animals concentrate in ever smaller territories or
migrate to anthropogenic areas, such as homes, sheds and barns. This is
particularly true of bats, which feed on the large number of insects drawn to
lamplight or fruit in orchards.
Two years
ago, scientists predicted a new coronavirus would emerge from bats in Asia,
partly because this was the area most affected by deforestation and other
environmental pressures.
One of the
authors, Roger Frutos, a specialist in infectious diseases at the University of
Montpellier, said multiple studies have confirmed the density and variety of
bat-borne viruses is higher near human habitation.
“Humans
destroy the bats’ natural environment and then we offer them alternatives. Some
adapt to an anthropomorphised environment, in which different species cross
that would not cross in the wild,” he said.
With deforestation and land-use change, you
open a door
Habitat
destruction is an essential condition for the proliferation of a new virus, he
added, but it is only one of several factors. Bats also need to pass the disease
on to humans. There is no evidence of this being done directly for
coronaviruses. Until now there has been an intermediary – either a domesticated
animal or a wild animal which humans came into contact with for food, trade,
pets or medicine. In the 2003 Sars outbreak in China, it was a civet cat. In
the Mers outbreak in the Middle East in 2012, it was a camel. Scientists are
not yet certain of the animal for Covid-19, though Frutos said initial theories
that a pangolin was the intermediary now seem less likely.
In a
soon-to-be-published paper in Frontiers in Medicine, Frutos and his co-authors
argue the key to containing future epidemics is not to fear the wild, but to
recognise that human activities are responsible for the emergence and
propagation of the zoonosis. “The focus must be on these human activities
because they can be properly organised,” notes the paper titled, the
Conjunction of Events Leading to the Pandemic and Lessons to Learn for Future
Threats.
Scientists
have detected about 3,200 different strains of coronavirus in bats. Most are
harmless to humans, but two very closely related sarbecoviruses found in east
Asia were responsible for Sars and Covid-19. The paper says future sarbecovirus
emergence will certainly take place in east Asia, but epidemics of other new
diseases could be triggered elsewhere.
South
America is a key area of concern due to the rapid clearance of the Amazon and
other forests. Scientists in Brazil have found viral prevalence was 9.3% among
bats near deforested sites, compared to 3.7% in pristine woodland. “With
deforestation and land-use change, you open a door,” said Alessandra Nava, of
the Manaus-based Biobank research centre.
She said
diseases were naturally diluted in the wild, but this broke down when humans
rapidly disrupted the ecological balance. As a local example, she pointed to
Lyme disease, which has spread to humans through capybaras. Some municipalities
are culling the giant rodents to prevent contagion, but Nava said this was not
necessary in pristine forests that still had jaguars. “You don’t find Lyme
disease in areas with jaguars because they keep the capybara numbers in check,”
she said.
“The
problem is when you put different species that aren’t naturally close to one
another in the same environment. That allows virus mutations to jump to other
species,” she said. “We have to think about how we treat wild animals and
nature. Right now we deal with them far too promiscuously.”
Her
conclusions were echoed by Tierra Smiley Evans, an epidemiologist at the University
of California who studies virus distributions in the rapidly degrading forests
of Myanmar. She has found that endangered or threatened species are more likely
to have viruses than animals at lower risk of habitat loss and hunting. She
said the connection between environmental stress and human health had been made
more apparent by Covid-19 pandemic.
“I’m
hopeful that one of the most positive things to come out of horrible tragedy
will be the realisation that there is a link between how we treat the forest
and our wellbeing,” she said. “It really impacts our health. It is not just a
wildlife issue or an environmental issue.”
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To prevent
future pandemics, the academics said international cooperation was needed to
encourage monitoring and education at a local level so that virus outbreaks
could be detected and contained at an early stage. Although this would be
expensive, they said it would more economically efficient than waiting for an
outbreak to become a pandemic, which forces the world into lockdown.
They also
emphasised that bat culls and bans on wet markets were likely to be ineffective
and could prove counterproductive because bats play an important role in insect
control and plant pollination. “Living safely with bats is what we should be
focusing on, not eliminating them,” Evans said.
Conservation
groups have also urged greater protection of existing habitats. A recent
Greenpeace report warned the Amazon could see the next spillover of zoonotic
viruses because the Brazilian president, Jair Bolsonaro, is putting a higher
priority on opening up the forest than protecting people’s health.
“It’s
unforgivable. His appetite for destruction is fuelling the current health
crisis and will make future crises we face even worse,” Daniela Montalto,
Greenpeace forests campaigner, said. “He must be stopped and forest protection
prioritised. Without it, we will all pay the price.”
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