What scientists discovered when they “resurrected” the Spanish flu virus
One of the most surprising conclusions reached by a group of scientists from the Universities of Basel and Zurich, after decoding the genome of the virus responsible for the Spanish flu (preserved from a patient in the Swiss city), was that the pathogen had already adapted to humans at the very beginning of the pandemic. This adaptation, in the form of genetic mutations, allowed it to be simultaneously more infectious and more resistant, which helps explain how that pandemic, between 1918 and 1920, became the deadliest influenza pandemic in history and one of the most devastating of all: worldwide, between 20 and 100 million people died (COVID-19 is estimated to have claimed over 7 million lives).
Always on the lookout for the next major threat, scientists around the world continue to try to find ways to contain it, even though no one knows how, when, or through what agent it will arrive. To do this, it's crucial to understand how viruses evolve and, by analyzing past pandemics, how they behave.
Until now, little was known about the influenza responsible for the Spanish flu. Only now have researchers been able to reconstruct the virus's first genome, thanks to a specimen preserved at the Institute of Evolutionary Medicine at the University of Zurich.
The victim was an 18-year-old from the Swiss city who died during the first wave of the pandemic in the country and was autopsied in July 1918.
"This is the first time we've had access to the genome of the 1918-1920 influenza virus in Switzerland. This opens up new insights into the dynamics of how the virus adapted in Europe at the beginning of the pandemic," says Verena Schünemann, one of the authors of the study, published in BMC Biology .
By comparing the Swiss genome with the few influenza virus genomes previously published in Germany and North America, researchers were able to prove that the Swiss strain already had three key adaptations to humans that would persist until the end of the pandemic.
Two of these mutations made the virus more resistant to an antiviral component of the human immune system—a key barrier against the transmission of viruses, such as bird flu, from animals to humans. The third mutation involved a protein in the virus's membrane that increased its ability to bind to receptors on human cells, making the virus more resistant and infectious.
Unlike other viruses, such as adenoviruses, whose DNA is stable, influenza stores its genetic information in the form of RNA, or ribonucleic acid, which degrades much more quickly. Hence, it has only now been possible to decode its genome: scientists have developed a new method to recover RNA fragments from preserved specimens.
How useful is this discovery for dealing with future pandemics? Verena Schünemann explains: "A better understanding of the dynamics of how viruses adapt to humans during a pandemic over a long period of time allows us to develop models for future pandemics." "Thanks to our interdisciplinary approach that combines historical-epidemiological and genetic transmission patterns, we can establish a proven basis for calculations," adds Kaspar Staub, co-author of the research.
