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HEALTH – He is an imposing parent to say the least. Researchers have found that the 1918 Spanish flu pandemic may be an ancestor of current seasonal flu infections. Published in the journal Nature on Tuesday, May 10, this new study looks at the deadliest pandemic of the 20th century, the Spanish flu.
Started in the United States, it then spread throughout Europe between 1918 and 1921, causing between 50 and 100 million deaths worldwide. To compare, the current covid-19 pandemic reportedly claimed 15 million lives at the end of last year.
This is the result of painstaking investigation, as much of the pathogen of the 1918 influenza virus remains mysterious. For example, scientists only demonstrated that influenza was caused by a virus in the 1930s, and few samples of the pandemic virus remain.
Relationship to the Spanish flu
Today, Thorsten Wolff of the Robert Koch Institute in Berlin, Germany, and his colleagues shed additional light on this pandemic. To do this, the researchers genetically sequenced the Spanish flu viruses.
In particular, they used 13 lung samples kept in museums in Berlin and Vienna, from people who died of lung infections between 1901 and 1931. Three of these samples were from people who died in 1918, and two of these samples were taken before the height of the pandemicin the last months of 1918.
The comparison of the genomes before and during the pandemic peak shows a variation on two elements of the nucleoprotein. This is the gene associated with the resistance of the host antiviral response. The latter can be (roughly) seen as the crowbar of the virus to force our immune systems. These elements show that the 1918 flu adapted to humans, evolving to last.
Mutate to survive
The virus mutated, in order to survive: this joins previous work on cells, which suggests that these mutations might help the virus to escape the defenses of the human immune system triggered by chemicals called interferons (a kind of alarm system of our body), which target the nucleoprotein.
This suggests that the virus has evolved to better evade the immune system. Although it is established that the 1918 virus was very virulent, the number of deaths has gradually decreased. The cause of this development might be herd immunity, but also the fact that the virus has become less virulent (and deadly) for spread better.
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