La grippe saisonnière, possible descendante directe de la grippe espagnole

Seasonal flu, possible direct descendant of the Spanish flu

Preserved in formalin, deciphered by genetics, European lung tissue from the early 20th century provides new insights into the Spanish flu, from which one of the seasonal flu viruses may be a direct descendant, according to a study published Tuesday in the Nature magazine.

The most devastating respiratory pandemic of the 20th century, the 1918-1919 flu, known as “Spanish” – a misleading term because this pandemic was far from concentrated in Spain – killed an estimated 50 to 100 million people. Its viral origin was not confirmed until the 1930s. Further investigation identified the culprit: an influenza A virus of the H1N1 subtype. But there are still mysteries about the Spanish flu. Geneticists have been trying to dispel them for twenty years, but their task is limited by the small number of victim specimens to be analyzed.

After fifteen failed steps, Sébastien Calvignac-Spencer, a viral evolution specialist at the Robert Koch Institute in Germany, says he and his colleagues were “extremely lucky.” They had access to 13 lung samples, dating from 1901 to 1931, including six from 1918-1919, preserved in formalin in museums in Berlin and Vienna. And they detected RNA fragments from the Spanish flu virus in three samples from 1918.

These researchers managed to sequence much of the virus that infected two people, but also an entire genome in the third case. Previously, “there were only sequences of 18 specimens in the world, two complete genomes, in the United States”, and “no genetic information on the first phases of the pandemic”, stressed Sébastien Calvignac-Spencer during a press conference. The Spanish flu has experienced three major waves. The second and third were especially lethal, more so than the first, which had developed in the spring of 1918. His work detected, in particular, genomic variations throughout the pandemic and its round trip around the world favored by transfers of soldiers at the end of the First World War. Since the early days of the Spanish flu, a gene in the virus appears to have evolved to counter the human immune response.

Above all, “these new analyzes are compatible with the scenario of a purely pandemic origin of seasonal influenza viruses”, a direct affiliation, according to the study. This undermines other hypotheses about the emergence of seasonal flu, in particular the idea – known as “rearrangement” – that current viruses are made up of several fragments from heterogeneous ancestors.

However, it’s hard to describe how the 1918 influenza pandemic gradually became a seasonal virus “due to lack of data,”, especially in the 1920s, explained Thorsten Wolff, a virologist at the Robert Koch Institute. Can this research give some clues about the evolution of Covid? If we cannot compare these two pandemics, due to “different viruses, very different propagation conditions, differently organized and connected humans,” certain similarities may exist, according to Sébastien Calvignac-Spencer. “For example, the 1918 flu had several waves, like Covid, but unlike the Covid pandemic, where the waves are associated with new variants, the 1918 pandemic probably didn’t, according to our study,” he noted. The Nature study, however, has a limit, its “very small sample size”, acknowledge its authors, stressing that its results are still “preliminary”. “Additional genomes from samples surrounding the pandemic period, as well as phenotypic characterization of various 1918 viruses in vitro and in vivo, will certainly allow for more robust analysis,” they say. It remains to find new preserved pathological specimens.

Isabelle Cortes/AFP

Preserved in formalin, deciphered by genetics, European lung tissue from the early 20th century provides new insights into the Spanish flu, from which one of the seasonal flu viruses may be a direct descendant, according to a study published Tuesday in the Nature magazine. the devastating respiratory pandemic of the 20th century, the…


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