Washington (AFP)

A genetic analysis published on Tuesday reveals that one person is undoubtedly at the origin of the 700 contaminations aboard the liner Diamond Princess, one of the very first foci of the Covid-19 pandemic, which has become an ideal subject of study and rich in lessons for the global scientific community.

In a study published in the American journal PNAS, a team from the Japanese Institute of Infectious Diseases reports having sequenced the genome of viruses taken from 148 of the passengers and crew of the ship, which was quarantined for 14 days by the Japanese authorities on February 3 in the port of Yokohama, after an 80-year-old passenger disembarked in Hong Kong previously tested positive on February 1.

The quarantine saga of more than 3,600 passengers and crew had been followed around the world, with Japan criticized for not evacuating the boat instead, while countries whose risks the United States debated relative to repatriate their nationals.

Ultimately, around 700 of the 3,711 people on board were infected with the coronavirus, seven of whom died. The study of data drawn from this environment of closed contamination had led to the first estimates of the mortality of the coronavirus (1.2%), and of the proportion of asymptomatic people (18%), and at least thirty studies using the ship have been carried out since February, according to the covid19primer.com website.

The new genetic analysis shows that all the viruses shared the same mutation, which suggests that "the spread of SARS-CoV-2 aboard the Diamond Princess originated from a single introductory event, before the start of quarantine", Japanese scientists conclude.

The contagions probably started with large gatherings in the common areas, "where passengers danced, sang, went shopping and attended performances".

According to the authors of the study, this demonstrates the value of genetic surveys for understanding the pathway of infections, with viruses constantly mutating by replicating, which always makes it possible to reconstruct the equivalent of a family tree and to understand which precautions might have helped reduce contagion.

© 2020 AFP