Seasonal flu, possible descend directly from the “Spanish” flu

published Tuesday, May 10, 2022 at 6:35 p.m.

Formulated, genetically decrypted, early twentieth-century European lung tissue provides new insights into “Spanish” flu, one of the seasonal flu viruses of which could be a direct descendant, according to a published study Tuesday in Nature.

The most devastating respiratory pandemic of the 20th century, the 1918-1919 flu, known as “Spanish” – a misleading term because this pandemic is far from focused on Spain – has killed an estimated 50 to 100 million people. of people.

Its viral origin was not confirmed in the 1930s. Subsequently, research has identified the culprit: an H1N1 subtype influenza A virus.

But there are still mysteries about the Spanish flu. Geneticists have been trying to dispel them for about 20 years, but their work is limited by the small number of victim specimens to be analyzed.

After about 15 unsuccessful steps, Sébastien Calvignac-Spencer, a viral development specialist at the Robert Koch Institute (Germania), said that he and his colleagues were “extremely lucky”. They had access to 13 samples of formalin-stored lungs in museums in Berlin and Vienna, from 1901 to 1931, including six from 1918-19.

And they found RNA fragments of the Spanish flu virus in three 1918 samples.

These researchers were able 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 in the world, two complete genomes, in the United States,” and “no genetic information on the early stages of the pandemic,” said Sébastien Calvignac-Spencer in a statement. pressing the dot.

The Spanish flu has indeed seen three major waves. The second and third were particularly deadly, more so than the first, which developed in the spring of 1918.

Among other things, their work has detected genomic variations over the course of the pandemic and its journey around the world through round trips facilitated by the transfers of soldiers at the end of the First World War.

From the earliest times of the Spanish flu, a virus gene appears to have evolved to counteract the human immune response.

– “Very limited” sample –

Above all, “these new analyzes are compatible with the scenario of a pure pandemic origin of seasonal influenza viruses”, a direct affiliation, according to the study.

This dispels other hypotheses about the emergence of seasonal flu, especially the idea – the so-called “reassortment” – that today’s viruses are made up of several fragments from heteroclite ancestors.

On the other hand, it is difficult to describe how the 1918 flu pandemic gradually turned into a seasonal virus, “due to a lack of data”, especially in the 1920s, said Thorsten Wolff, a virologist at the Robert Koch Institute.

Can this research shed some light on the evolution of Covid?

If I can’t compare these two pandemics, given “different viruses, very different spread conditions, differently organized and connected humans,” certain similarities may exist, according to Sébastien Calvignac-Spencer.

„For example, the 1918 flu experienced 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 noted.

The study in Nature, however, has one limitation, its “very small sample size,” its authors acknowledge, noting that their results remain “preliminary.”

“Additional genomes of samples surrounding the pandemic period, as well as phenotypic characterization of several 1918 viruses in vitro and in vivo, will no doubt allow for more robust analysis,” they said.

New preserved pathological specimens remain to be found.

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