H1N1 may be descended from virus that caused flu pandemic in 1918

When the world was ravaged by influenza at the beginning of the last century, there was not the technology available today to quickly make a genetic study of the viruses that are causing the deaths of thousands of people – something very different from what happened with the coronavirus that caused the pandemic. current.

But scientists are dedicating themselves to putting together a kind of “time tunnel” to understand, with current tools, how the virus that caused the influenza A pandemic that started in 1918 behaved – which became popularly known, erroneously, as the Spanish flu. Knowing this past can prepare us for future pandemics, as they are predicted by scientists.

This Tuesday (10), new results of this effort were published in the scientific journal Nature Communications. Working with genetic material from the remains of people who lost their lives in 1918, the researchers point out that the H1N1 subtype currently responsible for seasonal flu may be a direct descendant of the strain of influenza A virus that caused the last century’s pandemic.

This possibility contrasts with another hypothesis, that H1N1 is the result of a rearrangement process, that is, when there is an exchange of genetic segments from virus subtypes over time.

The possibility of a direct link between the 1918 strain and the H1N1 subtype that circulates today was raised thanks to a method called the molecular clock, which allows estimating the number of genetic changes that accumulate over time — and that eventually lead to division of lineages or species, for example.

The authors of the study published on Tuesday, led by researchers at the Robert Koch Institute in Germany, say that it was only in the 1930s that it was confirmed that the 1918 pandemic had its origins in a virus, and that recent research had already shown that it was caused by an influenza A virus and H1N1 subtype. What the team brings is the demonstration of the similarities between segments of the genetic material of that time with the seasonal influenza of today.

Differences about variants

It is important to remember that H1N1 also caused a pandemic in 2009. The current pandemic is caused by a family of viruses other than influenza (Orthomyxoviridae), the Coronaviridae.

On the other hand, the authors say that “all reported results (in the study) remain preliminary”, since they worked with a small number of samples. Very few remains of that time are preserved for study. Some, mainly from the United States, had already been partially or completely genetically sequenced.

In the study published in Nature Communications, the authors provide information on three more bodies whose lung tissues revealed infection with influenza A. These samples are part of a histopathological collection at the Museum of Medical History in Berlin, Germany.

In a virtual press conference, researcher Sébastien Calvignac-Spencer said that the few samples of the remains of people who died in the 1918 pandemic are difficult to work with, due to challenges for the conservation of the material, among other factors. So when he started studying the samples in Berlin, Calvignac-Spencer said he wasn’t very “hopeful”.

“Five years ago, the first thing I did was knock on the door of the nearest pathology collection in Berlin. I really just wanted to get a first technical view,” he said. “So I looked with the (museum) staff at the lung tissue that they had stored, and we were very lucky because they had a handful of very very rare 1918 flu samples.”

“We want to find more samples and reconstruct more genomes,” added Calvignac-Spencer, whose lab has been studying the evolution of respiratory viruses over the past two centuries.

According to the team, there are no samples from the years immediately before or after the last century’s pandemic. Therefore, it is difficult to determine how the virulence of H1N1 declined, until it went from a pandemic to a seasonal influenza. On the other hand, scientists were able to detect signs that there was local transmission combined with a spread of the virus between continents.

In the interview, Calvignac-Spencer was cautious when comparing the 1918 pandemic with the one that started in 2020: “They are two very different pandemics. They are different viruses, and the conditions for the virus to spread are also different: populations are not organized in the same way, nor connected in the same way.”

“In that (1918) pandemic, there were many waves (of infection cases), just as we see now,” he said. “But contrary to what we see in the Covid pandemic, where different waves are usually associated with new variants, during the 1918 pandemic it probably wasn’t like that. The little data we have does not suggest that there was a substitution (of different variants). “