At the beginning of the 20th century, the most lethal of the three variants of the HIV virus and responsible for the AIDS pandemic spread along the Sangha River, in Cameroon, from chimpanzees that inhabited remote stretches of the country’s jungle. Many of these animals were sold at fairs and consumed by the population, which helped the virus to infect about 75 million people worldwide. The same happened now with bats and SARS-CoV-2.
“It was no longer a question of ‘if’, but of ‘when’ a virus would jump from animals to humans. We were preparing for something like this,” he told the BBC the World Health Organization (WHO) technical chief for covid-19, Maria Van Kerkhove.
It is almost certain that it will never be possible to know who was patient zero in the current pandemic, even though there is a consensus that he was infected by a wild animal.
“These diseases are emerging more frequently in recent years as a result of human encroachment on wild habitat and increased contact with and consumption of wild animals,” explained Zoological Society of London professor Andrew Cunningham.
For infectologists, most diseases now emerging among human communities began with a virus unnoticed leaping the species barrier. Not only SARS-CoV-2, but also the Ebola, rabies and flu viruses SARS and MERS originated from wild bat populations.
the virus smuggler
Bringing the bat virus to the human cell was only possible through an intermediary: the wild animal trade. With evidence gleaned from other outbreaks, scientists believe that one of the ways to prevent a future pandemic is, on a global scale, to fight for an end to the trade in wild animals, a source of disease transmission between species.
In the case of the cause of covid-19, the entry point for the virus into the world of humans was not Wuhan’s popular market, ground zero of the pandemic. “The initial set of infections was associated with the market, but this is circumstantial. The infection could have come from elsewhere and, by chance, be transmitted due to the crowding of people in the market,” explained Cambridge University professor James Wood.
For Professor Cunningham, wildlife markets are warehouses for diseases that live in animals to find new hosts. “Mixing a large number of species that normally do not have contact, and even in precarious conditions of hygiene, is to offer opportunities for pathogens to pass from one species to another.”
everything is eaten
In the case of SARS, humans were contaminated by civets (a small carnivorous animal) marketed as food in southern China. Clues to the missing link in the SARS-CoV-2 transmission chain led scientists to animals as diverse as ferrets and turtles.
Coronaviruses have also been found in pangolins (an animal similar to a hedgehog, widely trafficked). However, the sequencing of the virus genome found in this animal showed a similarity of only 90.3% compared to SARS-CoV-2 (it takes 99.8% to establish a link between the mutations).
The only certainty in this quest is that the trade in wild animals increases the possibility of being contaminated by unknown diseases that are silently searching for a new host.