The development of the influenza virus H1N1, which caused the deadly Spanish flu pandemic in 1918 and 1919, has been mapped using lungs from 1918 that have been stored in spirits for over a century.
Researchers have learned a lot about the coronavirus that is causing the Covid-19 pandemic. New variants were quickly identified. The analysis techniques required for this were not yet available during the Spanish flu. That is why researchers are now trying to find remnants of this H1N1 virus in preserved tissue from flu victims.
Lungs in spirits
It was pure coincidence that molecular virologist Sébastien Calvignac-Spencer of the Robert Koch Institute in Berlin came across tissue from victims of the Spanish flu. He is interested in all the respiratory infections viruses that have come along over the past two centuries, including several flu viruses.
But studying viruses that no longer exist is difficult. That is why the virologist knocked on the door of the medical history museum of the nearby Charité hospital. “We were really lucky,” Calvignac-Spencer said during an online press conference. In the basement, the hospital turned out to have the lungs in spirit of two soldiers, aged 17 and 18, who had died in 1918 from the Spanish flu. Lung tissue from a 17-year-old woman who died of the disease in Munich that same year also turned up.
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Calvignac-Spencer was given small pieces of the lungs to study. His expectations were low. ‘But the analysis went fantastic from day one’, he says enthusiastically. They succeeded in uncovering large parts of the genetic code of the fatal virus. The researchers themselves found the complete genome of the virus that had affected the young woman. That had only happened twice before, and never with a victim from the start of the pandemic.
Image: Navena Widulin, Berlin
Millions of deaths
With this genetic information, Calvignac-Spencer and his colleagues were able to better map the deadliest pandemic of the twentieth century. This flu virus killed 50 to 100 million people worldwide. Strikingly, it affected many healthy, young people between the ages of 20 and 40.
In 1918 it was already suspected that a virus caused the disease. This was confirmed in the 1930s. It was not until the late 1990s that molecular analysis techniques had developed sufficiently to tamper with the virus from victims’ tissues. To do this, researchers used lungs that had been kept in labs all along, and lung tissue from the deceased buried in the icy permafrost floor of Alaska. Based on this, it was determined that it was an H1N1 flu virus.
There is little information about how the virus developed in the 1920s. In the 1930s it seemed to have been watered down to a much less deadly variant, which circulated until at least the 1950s.
In the past thirty years, due to the limited information, questions arose mainly about this flu virus. As we are now seeing with the covid-19 pandemic, there were several waves. But were there also different variants that took over from each other at the time? The new research found the answer: There is no indication that new variants of the virus replaced the old ones in 1918. The virus seems to have gone through few major changes at all.
Descendants of Spanish flu
The flu virus is genetically very similar to bird flu viruses, and does not appear to have mixed with swine flu viruses since 1918. It was suspected that this flu virus, like some others, could get genetically mixed with other flu viruses in pigs and then transfer to humans. This did happen with the H1N1 virus that caused swine flu or swine flu in 2009 and has been resurfacing every now and then. The researchers’ genetic analyzes suggest that the H1N1 seasonal flu prevalent today may well be descended from the 1918 flu.
But Calvignac-Spencer and colleagues emphasize that even with their new findings, there is still too little information to draw firm conclusions about the Spanish flu. The researchers are therefore looking for more hidden treasures, such as the lungs in spirits they found in Berlin. With this they hope to further unravel the Spanish flu.