Are human attacks on the environment the cause of the coronavirus?


Covering Climate NowThis article was originally published in The Nation and is republished here as part of Covering Climate Now, a global journalistic collaboration to strengthen coverage of the climate crisis of which UP' Magazine is a member.


It could have been a pangolin. Or a bat. Or, as one now debunked theory that has been debunked and toured the web suggests, a snake. The race to identify the animal source of COVID-19, the coronavirus that currently traps more than 150 million people in quarantines and cordon sanitaire in China and elsewhere, is underway. The animal origin of the virus is a crucial mystery to be solved. But speculation about the wild creature that originally harboured the virus masks a more fundamental source of our growing vulnerability to pandemics: the accelerating rate of habitat loss.

Since 1940, hundreds of microbial pathogens have either emerged or re-emerged in new territories where they had never been seen before. These include HIV, the Ebola virus in West Africa, the Zika virus in the Americas, and a series of new coronaviruses. The majority of them - 60 % - come from the bodies of animals. Some come from pets and livestock. Most of them - more than two-thirds - come from wild animals.

Benign animal microbes transformed into deadly human pathogens.

But the wild animals aren't the real culprits. Although a multitude of publications in the media portrays wild animals as the " source " of deadly epidemics, the truth is that they are not, in fact, particularly infested with deadly pathogens ready to infect us. In fact, most of these microbes live harmlessly in the bodies of these animals.

The real problem is how deforestation and the expansion of cities and industrial activities create pathways for animal microbes to adapt to the human body.

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Habitat destruction threatens many wildlife species with extinction, including the medicinal plants and animals on which we have always depended for our medicine. It also forces clinging wildlife species to crowd into smaller fragments of the remaining habitat, increasing the likelihood that they will come into intimate and repeated contact with human settlements expanding into their newly fragmented habitats. It is this kind of repeated and intimate contact that allows the microbes that live in their bodies to pass into ours, transforming benign animal microbes into deadly human pathogens.

Take Ebola, for example. According to a 2017 study, Ebola epidemics, which have been linked to several bat species, are more likely to occur in areas of central and western Africa that have experienced recent episodes of deforestation. Cutting down bat forests forces bats to take refuge in backyard and farm trees, increasing the likelihood that a human could, for example, take a bite of fruit covered in bat saliva or hunt and kill a local bat, exposing himself to microbes that take shelter in the animal's tissues. Such encounters allow a multitude of viruses carried innocuously by bats - Ebola, Nipah and Marburg, to name a few - to creep into human populations. When these so-called "contagion" events occur with sufficient frequency, animal microbes can adapt to our bodies and evolve into human pathogens.

Deforestation and loss of wildlife habitat

Epidemics of mosquito-borne diseases have been similarly linked to the felling of forests, although less because of habitat loss than habitat conversion. As leaf litter and tree roots disappear, water and sediment flow more easily along the shaved forest floor, newly open to the sun's rays. Malaria-carrying mosquitoes breed in sunny puddles. A study conducted in a dozen countries found that mosquito species carrying human pathogens are twice as common in deforested areas than in intact forests.

Habitat destruction also blurs the population size of different species to increase the likelihood of a pathogen spreading. West Nile virus, a migratory bird virus, is an example. Pressed by habitat loss as well as other stresses, bird populations have declined by more than 25 % over the last 50 years.

But the species are not declining at a uniform rate. Specialized bird species, such as woodpeckers and rails, have been harder hit than generalists such as robins and ravens. This increases the abundance of West Nile virus in our domestic bird flocks because, while woodpeckers are poor carriers of the virus, robins and ravens are excellent carriers. The probability that a local mosquito bites a West Nile virus infected bird and then a human can't help but multiply.

Wild species that would rarely - if ever - be found in the wild are caged together, allowing microbes to pass from one species to another.It's not just the destruction of habitat that increases the risk of disease, it's also what we're replacing wildlife habitat with. To satisfy the carnivorous appetites of our species, we razed an area the size of the African continent to raise animals for slaughter. Some of these animals are then delivered through the illegal wildlife trade or sold on the black market. There, wild species that would rarely - if ever - be found in the wild are caged together, allowing microbes to move from one species to another, a process that gave rise to the coronavirus that caused the SARS outbreak of 2002-2003 and perhaps the new coronavirus that is stalking us today.

Intensive and promiscuous breeding

But many others are raised on factory farms, where hundreds of thousands of individuals are waiting to be slaughtered, crammed side by side, giving the microbes lush opportunities to develop into deadly pathogens. Avian influenza viruses, for example, which originate from the bodies of wild waterfowl, are unleashed in factory farms where captive chickens are crowded together, mutating and becoming more virulent, a process so reliable that it can be reproduced in the laboratory. A strain called H5N1, which can infect humans, kills more than half of those infected. The containment of another strain, which reached North America in 2014, has involved slaughtering tens of millions of poultry.

The avalanche of excrement produced by our livestock provides new opportunities for animal microbes to spread to human populations. Because animal waste is much larger than what the cultivated land can absorb as fertilizer, it is collected in many places in makeshift manure ponds. Shiga toxin-producing Escherichia coli , which lives harmlessly in the intestines of more than half of the cattle in U.S. feedlots, hides in this waste. In humans, this bacterium causes hemorrhagic diarrhea, fever, and can lead to acute kidney failure. Because livestock waste is so common in our food and water, tens of thousands of people are infected each year.

The deadly gifts of our animal friends

This process of transforming animal microbes into human pathogens is now being accelerated, but it is not new. It began with the Neolithic revolution, when we first cleared wildlife habitat to make way for crops and put wild animals under our yoke. The "deadly gifts" we have received from our "animal friends", as Jared Diamond said, include measles and tuberculosis in cows; whooping cough in pigs; and influenza in ducks. It continued during the era of colonial expansion. The Belgian settlers in Congo built the railways and cities that allowed a lentivirus found in local macaques to perfect its adaptations to the human body; British settlers in Bangladesh cut down the Sundarbans wetlands to build rice paddies, exposing humans to the bacteria found in the brackish waters of the wetlands.

The pandemics created by these colonial-era intrusions still plague us today. The lentivirus in the macaque monkey has turned into HIV. The aquatic bacterium from the Sundarbans, now known as cholera, has caused seven pandemics so far, the latest of which occurred in Haiti.

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The good news is that because we are not passive victims of the animal microbes that invade our bodies, but fully empowered agents that transform harmless animal microbes into pandemic pathogens, there is much we can do to reduce the risk that these pathogens will not emerge at all.

We can protect the habitat of wild animals so that animal microbes stay in their bodies and do not spread in ours, an approach advocated by the " One Health"

Epidemics are inevitable, but pandemics are optional We can conduct active surveillance in places where animal microbes are most likely to develop into human pathogens, looking for those that show signs of adaptation to the human body and smothering them before they cause epidemics. This is exactly what scientists funded by USAID's Predict program have been doing for the past decade. As the human footprint has continued to spread across the planet, Predict scientists have identified more than 900 new viruses around the world that has emerged as a result, including new strains of SARS-like coronaviruses.

Epidemiologist Larry Brilliant said one day: " Epidemics are inevitable, but pandemics are optional ». However, pandemics will only remain optional if we have the will to disrupt our policy as easily as we disrupt nature and wildlife. In the end, there is no real mystery as to the animal source of pandemics. It is not a pangolin with pointed scales or a flying fur bat. These are populations of warm-blooded primates: the real animal source is us.

Sonia Shah is a science journalist and the author of Pandemic: Tracking Contagion from Cholera to Ebola and Beyond (Farrar, Straus & Giroux, 2016). His fifth book, The Next Great Migration: The Beauty and Terror of Life on the Movewill be published in June.

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