these animals that we suspect a little quickly

The scene is almost familiar as it has been mentioned. Huanan wet market in Wuhan city, Hubei province, China. One of these open spaces where sellers and buyers alley alongside fish, birds, bats, pangolins, turtles, civets. Some are dead; most of them alive, soon butchered on the spot. If this is not where the epidemic was born, researchers locate the starting point for the spread of the virus. “The structure was quickly dismantled, reports Jean-François Guégan, research director at the Research Institute for Development (IRD). This complicates the search for the source of the coronavirus.”

In their quest to determine the origin of Sars-CoV-2, an essential step to avoid its resurgence, scientists have acquired a certainty: everything started from an animal. It is not a surprise, 75% of the emerging diseases appeared since the beginning of the XXe century are zoonoses, diseases transmitted by the animals. “To determine which ones, it is necessary to conduct a real police investigation, says Serge Morand, researcher at CNRS-Cirad. But going up the track will take time.”

Since the start of the epidemic, several scenarios have been developed. They all start with bats. “The bats are home to around thirty coronaviruses,” explains the health ecologist. “Their various species have existed for millions of years, the time to cohabit with a multitude of diseases!” Excellent reservoirs of virus, they harbor them without developing symptoms.

Scenarios in laboratories around the world

Research has established that the genome of a coronavirus isolated from a bat from Yunnan province had 96% identity with that of the human virus. Since the gene sequences are different, the route of direct transmission from small mammals to humans is explored but not privileged. Scientists are also working on the hypothesis of an intermediate host. It was here that the pangolin arose, an animal that has the unenviable status of the most poached mammal on the planet, hunted for its flesh and scales.

Several studies have established that the insectivore is the only other mammal, with the bat, reported to be infected with a coronavirus related to Sars-Cov-2. Again, scenarios are written in laboratories around the world. Sometimes the roles are even distributed. Bats carrying the virus feed on the nectar of begoniaceae flowers and fruits; in doing so they swallow and, primary reflex in this animal, urinate. The soiled fruit falls to the ground, attracting ants whose pangolins love.

“

What we do know is that the virus circulating in the human population is a recombination from two coronaviruses

“

This is an attractive hypothesis. But, in a last study published in the journal Nature on March 26, researchers estimate that the genome of the coronavirus isolated from pangolin is only similar between 85.5 and 92.4% to that of Sars-Cov-2. If the animal played a role in the ecology of the virus, it is not known whether it transmitted it to humans. “What we do know is that the virus circulating in the human population is a recombination from two coronaviruses, explains Jean-François Guégan, that of a bat and that of a pangolin.” And to continue: “Were both of them reservoirs and transmitted it to other animals? Is one reservoir and the other, intermediate host? It is Too early to say.”

Other researchers are also following the trail of the civet, a mammal halfway between the panther and the badger, already suspected of having played the intermediate hosts between the bat and man in the epidemic of Sras in 2003. “We should also look at the pigs side, believes Serge Morand. There was an alert in 2017 when a bat coronavirus had emerged on pigs on farms in China.”

Intensive use, destruction of forests

Scientists agree that the intermediate host is to be found in a wild animal taken en masse from its original environment or from a farm. “It is indeed the proximity between human activities and wildlife that creates the conditions for the birth of an epidemic,” explains Aleksandar Rankovic, researcher at Iddri. Deprived of their natural habitats and source of food – 13 million hectares of forest disappear each year – wild animals venture out on the outskirts of cities, and in particular animal farms. When they are not directly chased and transported for thousands of kilometers. “It is the man himself who organizes these meetings”, judge Jean-François Guégan, recounting these long journeys by truck during which pangolins, bats and others find themselves in cages soiled with urine and excrement . “The perfect crossroads for building the bed of infectious diseases.”

Intensive farms host animals whose lack of genetic diversity makes them perfect candidates for the epidemic. The influenza pandemics of 2005 and 2009 were also born in pigs and poultry farms in high concentration. “Around the world, the demand for meat, milk and eggs is exploding,” says Aleksandar Rankovic. “This is a real steamroller on ecosystems.”

“Today, 75% of our land is transformed for agriculture and human activities, abounds Hélène Soubelet, director of the Foundation for research on biodiversity. Our development model endangers human, animal and environmental health . ” This is why, judge Serge Morand, it is “necessary to understand the ecological mechanisms of the emergence of the virus”. Otherwise, “it will not be the last of disasters, warns Jean-François Guégan, because we have awakened cycles that were sleeping.”