Medicine: the Spanish flu would be the ancestor of the seasonal flu

PostedMay 10, 2022, 7:34 p.m.

German researchers have successfully sequenced the RNA of the 1918 virus in period lung samples preserved in museums. Their work was published Tuesday in “Nature”.

The seasonal flu virus is said to be the direct descendant of the Spanish flu which killed between 50 and 100 million people in 1918-1919.

Photo d’illustration/Getty Images

Preserved in formalin, deciphered by genetics, European lung tissue from the beginning of the 20th century brings new knowledge about the Spanish flu”, of which one of the seasonal flu viruses could be a direct descendant, according to a study published Tuesday in the magazine “Nature”. This work undermines other hypotheses on the emergence of seasonal influenza, in particular the idea that current viruses are made up of several fragments from heterogeneous ancestors.

The most devastating respiratory pandemic of the 20th century, the 1918-1919 flu, known as “Spanish”, killed an estimated total of 50 to 100 million people. Its viral origin was not confirmed until the 1930s. Subsequent research identified the culprit: an influenza A virus of the H1N1 subtype. Sébastien Calvignac-Spencer, specialist in viral evolution at the Robert Koch Institute (Germany) and his colleagues had access to 13 lung samples kept in formalin in museums in Berlin and Vienna, dating from 1901 to 1931, including six of 1918-1919. And they detected RNA fragments from the Spanish flu virus in three samples from 1918.

A whole genome

These researchers managed to sequence large parts of the virus that infected two people, but also an entire genome in the third case. Previously, “there were only sequences of 18 specimens worldwide, two complete genomes, in the United States”, and “no genetic information on the first phases of the pandemic”, underlined Sébastien Calvignac-Spencer during a press briefing.

Their work notably detected genomic variations over the course of the pandemic, favored by the transfers of soldiers at the end of the First World War. From the earliest 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 pure pandemic origin of seasonal influenza viruses”, a direct filiation, according to the study. Difficult to describe, however, how the 1918 pandemic gradually turned into a seasonal virus, “due to lack of data”, according to Thorsten Wolff, virologist at the Robert Koch Institute.

Commonalities with the Covid-19 pandemic

Can this research give some keys to the evolution of Covid? If we cannot compare these two pandemics, given “different viruses, very different propagation conditions, humans organized and connected differently”, certain similarities may exist, according to Sébastien Calvignac-Spencer. “For example, the 1918 flu had several waves like the Covid, but unlike the Covid pandemic, where the waves are associated with new variants, this was probably not the case for the 1918 pandemic, according to our study,” he notes.

The study in “Nature”, however, has a limit, its “very small sample size”, recognize its authors, stressing that their results remain “preliminary”. “Additional genomes from samples surrounding the pandemic period, as well as phenotypic characterization of several 1918 viruses in vitro and in vivo, will undoubtedly allow for more robust analysis,” they say. It remains to find new preserved pathological specimens.




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