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This genetic detective job is tracing the coronavirus family tree that has killed tens of thousands in its relentless spread across the planet.
It could also help find out if the virus was spreading in other countries before the first infections were officially registered.
In France, a group of cases was discovered in late January.
But a new study published in the International Journal of Antimicrobial Agents suggested that the virus was already in the country a month earlier.
A retrospective analysis of samples taken from 14 intensive care patients with influenza-like symptoms at the Avicenne and Jean-Verdier hospitals in Paris found a positive COVID-19 case: a 42-year-old French resident who had not visited China. He was hospitalized on December 27.
Olivier Bouchaud, head of Avicenne’s department of infectious diseases, said at the beginning that the virus spreads “silently in the population, without anyone detecting its presence.”
So evidence of previous infections would only confirm what many scientists had suspected, he told AFP.
It could also help explain cases like that of Aicha, a 57-year-old medical secretary who was hospitalized in Marseille in mid-January with severe respiratory symptoms.
At the time, the mysterious outbreak of pneumonia cases in the Chinese city of Wuhan was still seen as a distant problem.
France did not have a single case and the World Health Organization was still weeks away from naming it COVID-19.
Aicha’s husband, Jacques, a doctor, said he had “all the clinical signs” of the disease, including loss of taste and smell. But his evidence has not been conclusive.
Other countries are discovering that they may have had previous infections. In the United States, autopsies on suspicious deaths in California have revealed infections before the first official case on January 21.
But Samuel Alizon of the French National Center for Scientific Research at the University of Montpellier warned that it is important to distinguish between isolated cases and the origin of the “epidemic wave”.
Origins of china
In China, Wuhan health authorities spoke of an initial case on December 8.
A study published in The Lancet in January said the first identified patient in the city began showing symptoms on December 1.
The timeline has been roughly corroborated by research that maps the genetic evolution of the virus.
So far, the genomes of more than 15,000 samples of the new coronavirus have been sequenced. As it replicates, it produces multiple mutations, although none have been found to change its virulence.
Alizon said that about twice a month a mutation occurs that remains in the genetic sequence, giving researchers a trail to follow.
So “if you compare two viruses, you can count how many mutations separate them,” he said. Following the chain we find the “ancestor common to all infections”.
Using publicly shared genome sequences, Andrew Rambaut of the University of Edinburgh found that “the lack of diversity is indicative of a relatively recent common ancestor for all of these viruses.”
He estimated that this ancestor could have emerged around November 17 of last year (with a range of uncertainty between August 27 and December 29).
Imperial College London, in collaboration with the WHO, has also traced the family tree of the virus, estimating that it appeared in China on December 5 (with a margin of uncertainty between November 6 and December 13).
Erik Volz, an epidemiologist at Imperial College, said that all of the first genetic sequences of the virus collected in Wuhan in December and January “have almost identical genomes.”
“And all the viruses currently circulating in other parts of the world are descended from these closely related lineages in Wuhan,” he told AFP.
But experts don’t think an epidemic has a single starting point in time, he added: rather, they are planted “multiple times from multiple points of origin.”
He said estimates of the dates of these “planting events” suggest that epidemics in many European and North American cities began in mid-January or early February.
‘We will never know’
Italian research suggests that the virus reached Lombardy between the second half of January and the beginning of February, weeks before the first infections were confirmed on February 20.
Soccer players at Inter Milan have said they suffered symptoms of the virus earlier this year. Could they have had it?
“We had a week off in December and then we went back to work and I swear 23 out of 25 players were sick,” Belgian Inter Milan striker Romelu Lukaku said in a recent radio interview.
The players were not tested for the virus at the time.
Even if serological tests were done now and antibodies were found in their blood, it would not confirm when they became infected.
“We will never know,” said Lukaku.
