Shedding light on the past is sometimes difficult. This is the case when science tries to work with certain historical genomes, such as the Spanish flu. RNA viruses, like those of the flu, decompose quickly and pose tough challenges to making them talk. But for the first time, a team has managed to sequence a Swiss strain of the Spanish flu, more than 100 years old.
“ It was a complete surprise", recalls Dr. Christian Urban, a specialist in genomics at the University of Zurich (Switzerland) with Science and Future and first author of the study published in the journal BMC Biology. “ We took three lungs and three livers dating from 1918 from the medical collection of the Institute for Evolutionary Medicine in Zurich. » Originally, the researcher thought he would work on cases of pneumonia and hepatitis. But one of the lungs tested positive for the 1918 Spanish flu! "Without waiting, the team sequences the virus to reveal its secrets." And immediately we see that it has three key mutations", the researcher enthuses.
Three transfers from July 1918
The appearance of the Spanish flu is not clearly documented. In Europe, as early as 1916 and 1917, a " pneumonia » wreaked havoc in France, leading to the deaths of workers and soldiers of Indochinese origin. But on the continent, the Spanish flu, the nickname given to the H1N1 influenza A pandemic, was not documented for the first time until April 1918 in Rouen. The epidemic then spread to Great Britain in May, then to the United States, Italy, and Germany in June. In Switzerland, it had its first wave in July 1918. The virus had therefore already had time to adapt to its new host, humans." explains Dr. Urban.
By comparing the Swiss strain with a German strain and a North American strain, the researchers observed the appearance of three new mutations. The first two concern interactions with their host's immune system. These are very common mutations in zoonoses, infectious diseases that are transmitted from animals to humans. They make it easier to infect patients.. » The third mutation concerns a protein located on the surface of the virus. It has the effect of facilitating the passage of the virus from birds to humans. It was absolutely crazy to discover all this in the space of two weeks. ! »
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RNA difficult to reconstruct
After this July wave, Switzerland and Europe more broadly would experience two more waves. The deadliest first, in the autumn of 1918; then that of early 1919. In all, the pandemic caused more than 50 million deaths worldwide, according to estimates by the World Health Organization (WHO). 2.3 million people are estimated to have died in Europe, including 25,000 in Switzerland (and 400,000 in France according to recent estimates). While research has already largely documented the dynamics of the virus across the world and the severity of the waves of contamination, the adaptation of the virus and its mutations have still received little attention.
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The researcher emphasizes the rarity of such a result. Indeed, unlike adenoviruses, which cause the common cold and are composed of stable DNA, influenza viruses carry their genetic information in the form of RNA. However, the latter degrades much more quickly. It is only preserved for long periods under specific conditions. This is why we don't have that many sequenced strains of the 1918 flu virus.", explains the researcher. It is only thanks to very specific methods of recovering ancient DNA that this feat was possible. " For the other strains, we did classic sequencing, piece by piece. In total, we had to cut the virus into 8! "To speak of certain diseases of the past, all that remains today are the collections of samples from natural history museums and medical schools. This is a crucial heritage for learning more about past pandemics... and equipping us for future ones.
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