Recent studies have challenged one of the main hypotheses about the interspecies transmission of the new coronavirus, which made pangolin the initial host of Covid-19.
The culprit was too perfect. Since early February, the pangolin, a small mammal with scales, had emerged as the main suspect in the investigation to identify the animal by which Covid-19 appeared in humans. But several scientific articles published since February 20 have challenged this hypothesis. Two months after the start of an epidemic that killed more than 2,700 people and infected around 80,000 people, mainly in China, the mystery of the interspecies transmission of the new coronavirus remains unresolved.
When researchers from the Agricultural University of South China came to a press conference on February 7, they thought, however, that they had made a great leap forward to identify the animal at the origin of the epidemic in humans. After the civet for the SARS – a coronavirus which had caused a global epidemic between 2002 and 2004 -, and the dromedary in the case of the Mers, which prevailed mainly in the Middle East in 2012, we had to look this time for the side pangolin, said, Chinese scientists.
A partial genome analysis
“By using artificial intelligence programs to browse databases of animal genomes, they had discovered a coronavirus in pangolin specimens which were very similar to Covid-19″”, says Dimitri Lavillette, a researcher at CNRS and specialist in questions of interspecies transmission of pathologies, contacted by France 24. The results of this research suggest a correspondence of 99%. Hard to beat?
The pangolin had, moreover, all of the ideal suspects. It is one of the most poached animals in the world, mainly to satisfy the appetite of the Chinese who lend aphrodisiac virtues to its flesh and also use it in traditional medicine. A specimen carrying the virus could very well have ended up on the market in Wuhan, where the epidemic seems to have started in late December. Quickly, articles on “revenge of the pangolin” began to flourish on the canvas. Hunted down and decimated, it was now the source of one of the biggest health crises of the decade.
But two weeks later, the same researchers behind the “pangolin” hypothesis came forward again to ensure that the presentation of their findings “was the result of an embarrassing miscommunication between [university] laboratories ”. They were no longer at all certain that the small mammal should be blamed for what looked more and more like a pandemic.
In reality, the comparison with Covid-19 “was based only on fragments of genomes in the pangolin”, underlines Dimitri Lavillette. These researchers had simply established that a piece of a coronavirus present in animals was very similar to the virus which is currently raging in more than 40 countries. Two other Chinese studies, published on February 20, refined these results and came to the conclusion that by taking into account the whole genome, the proximity between the two was rather of the order of 90%.
The bat again and again
“It is not enough to say that it is the same genome. 90% may be a completely different coronavirus ”, underlines the French specialist. The genome of the civet specimen that allowed us to trace the source of the SARS epidemic was 99% similar to this coronavirus.
The quest to find the ferryman of Covid-19 in the animal kingdom is thus relaunched. “The pangolin remains, despite everything, a suspect, but in this case, it is not the specimens analyzed so far,” said Arinjay Banerjee, coronavirus specialist at McMaster University in Hamilton (Canada). , interviewed by Nature magazine.
Other avenues have been explored without success. All the animals present on the market in Wuhan were tested without finding any trace of the Covid-19. There was also talk of the snake, and more specifically of the Chinese cobra, but the hypothesis was swept away as quickly as it had been advanced at the end of January. All kinds of animals – from birds to marmots – have been scrutinized, but nothing conclusive has been discovered.
There remains the mammal to which the eyes turn to each new coronavirus discovered: the bat. And, in fact, “we discovered a virus that has a similarity of 96% with the current coronavirus”, recognizes Dimitri Lavillette.
But he does not think that the Man was contaminated in contact with the bat. “It is a reservoir for all kinds of coronavirus, but cases of direct transmission to humans are rare,” he said. The most probable hypothesis remains, in his eyes, the same as in the case of SARS: the bat is the primary source, but there is an intermediate host which, contaminated by the bat, then transmitted it to the man.
The importance of identifying the origin
One of the special features of Covid-19 is the difficulty in identifying the animal that is the source of this virus. In the case of Sras and Mers, the culprit had been found in the days or weeks following the start of the epidemic. “This time, it is not to be excluded that we will never know,” recognizes Dimitri Lavillette.
And this is a problem. The quest for the zero animal patient represents an important health security issue. “This allows us to try to break the link that started the epidemic,” says the CNRS expert. Putting in place a general ban on the trade in an animal carrying a coronavirus can avoid the repetition of an epidemic.
When in doubt, the Chinese authorities introduced a general ban on trade and consumption of wild animals on Monday 24 February. But such a measure is likely to be only temporary given the importance of this sector in the Chinese economy, recalls the South Morning China Post. This is already what had happened during the SARS epidemic. After the lifting of a general ban, Beijing had continued to ban the trade in civet, identified as the initial host. In the meantime, the Chinese could take the opportunity to banish permanently the pangolin trade which is on the list of endangered species of the International Union for the Conservation of Nature.