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Scientists spend a lot of time studying how the coronavirus and other emerging diseases end up in human populations.
About three-quarters of new diseases are zoonotic, which means they are transmitted by animals.
In the case of the coronavirus, which causes the disease known as COVID-19, many experts suspect it came from bats and likely spread into another animal sold at a wet market in Wuhan, China. But what about the circumstances that allow zoonotic diseases to jump from animals to humans?
There is a growing consensus that human destruction of pristine habitats is driving animals into new environments where once-separated species congregate, spreading viruses and incubating new ones.
The consequences of the human destruction of animal habitats is a classic case of the old phrase, what goes around comes around. Jonathan Watts, a global environment editor at The Guardian, writes about this in his recent article "Promiscuous Treatment of Nature will Lead to More Pandemics.”
“It's basically rushing out, doing exactly what you want, not thinking of the consequences, not thinking of the partner, in this case nature, who is suffering and who's suffering will in turn come back on you,” Watts says.
These emerging viruses like the coronavirus have always existed in few species in the wild, Watts explains, and those species have evolved to live in certain habitats.
“But when mankind comes in, clears the forest for logging or for farmland, it disturbs this balance,” he says. “So they are concentrated in a smaller and smaller area of what's left, or they have the choice to migrate into human-disturbed areas like suburbs, like farmlands, like orchards. And animals are mixing that shouldn't mix or didn't mix before, and as a result, there's all of this potential for zoonotic contagion.”
When humans treat nature promiscuously, it accelerates the ecological balance that naturally dilutes diseases in the wild. For example, scientist Alessandra Nava of the Biobank Research Centre found that Lyme disease in the capybara species of the Mata Atlântica was more prevalent when they lived near human populations.
“By contrast, the capybara in the wild had hardly any cases of Lyme disease,” Watts says. That’s because there were more jaguars in those habitats that naturally kept the capybara species at a stable level.
“So diseases are in the wild, but it's the humans that are increasing the risks of those diseases, spreading out, mutating and crossing over into a form that humans become vulnerable,” Watts says.
Take that same logic and apply it to bats. Scientists found viral prevalence at 9.3% in bats near deforested sites, compared to 3.7% when they were found in pristine areas.
Bats are generally major carriers of viruses when they enter human populations, but scientists have not recorded an instance where they passed a virus directly to humans, Watts says. There have been few cases where bats have contaminated another animal species and that animal species has infected humans, including the 2002 SARS outbreak and the 2012 MERS outbreak.
“It was predicted two years ago that the next big virus would emerge from bats in Asia,” Watts says. “And, of course, that's exactly what's happened now.”
So scientists did see the current pandemic coming, particularly infectious disease specialist Roger Frutos, who wrote a 2018 paper on the link between deforestation and the spread of coronaviruses. Frutos looked specifically at Southeast Asia and East Asia, which has the worst areas of deforestation in the world, Watts says.
Frutos is set to publish a new paper arguing that preventing another outbreak is not so simple as eradicating bats or wet markets.
For one, Frutos argues that shutting down all wet markets is probably “impractical” because they exist all over the world, Watts says. Closing them would likely push them underground.
“The alternative is industrial farming, which also has immense health problems,” Watts says. For example, recent influenza outbreaks emerged on chicken and pig factory farms.
At the same time, Frutos says getting rid of bats altogether could have unintended consequences because bats are important for insect control and pollination.
“It's very important to live with nature, not to replace nature,” Watts says. “The problem really is human activity, and so what needs to be regulated is human activity on the frontline.”
The key to preventing future pandemics is twofold, Watts says.
An international network of health monitoring centers in areas of the developing world would help provide early detection of new viruses. There also needs to be better monitoring of food markets and the forestry industry, he says.
This will cost enormous amounts of money, but the current pandemic has had huge economic consequences, Watts says.
“It will be incredibly expensive to have monitoring and education in all of these remote parts of the world,” he says. “But [Frutos] said, look at the alternative. How much has this one virus, this one pandemic, cost us?”
This segment aired on May 20, 2020.
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