The swine flu pandemic (S-OIV) currently sweeping the world is the result of an influenza H1N1 virus that made the leap from pigs to humans. But this jump is just the latest leg of a journey that has taken over 90 years and shows no signs of finishing.
Today’s pandemic is a fourth-generation descendant of the 1918 flu virus that infected around a third of the world’s population. This original virus is an incredible survivor and one that has spawned a huge legacy of daughter viruses. By importing and exporting its genes, it has contributed to several new strains that have been responsible for at least three further pandemics, including the current one.
In an editorial in the New England Journal of Medicine, David Morens says, “We are living in a pandemic era that began around 1918.” This is one of two papers that narrate the incredible story of the 1918 virus and its descendants – a thrilling tale of survival, adaptation, extinction and resurrection.
All influenza A viruses contain 8 different genetic segments that they can freely exchange with one another. Morens beautifully compares each virus to a squad of eight players, rather than a single entity. For the viral team to be successful, its eight-person genetic team has to work together. Their individual skills become more or less useful with time and the team will often swap its members for fresh faces that add something new to the mix. In technical terms, they “reassort”.
To do that, viruses need to infect the same cell and they find communal ground in the internal passages of birds, pigs and humans. Animal bodies are essentially viral networking events where different squads can meet and exchange players.
In 1918, one such squad of players went on an infamous world tour. H1N1 influenza viruses had been around for a long time, but the story of the current “pandemic era” really begins in that year. While H1N1 was busy killing humans in our millions, pig farmers at the Cedar Rapids Swine Show in Iowa also noticed something unusual. Even though H1N1 had never been described in pigs before, their herds were suffering from an unusual respiratory illness, whose symptoms were very similar to those afflicting the world’s humans. Swine flu had landed.