Orgin of Swine Flu

A better understanding of how the new strain of influenza arose

YOU are now officially permitted to blame the pigs. When a strain of influenza with pandemic potential struck in April, it was generally referred to as “swine flu” because it seemed similar to an existing group of strains, known as A/H1N1, which are commonly found in pigs. But when it became clear that the new bug was being spread by people, not porkers, the pig-breeding industry complained that it was being unfairly maligned. It also became apparent that the new virus contains bits and pieces derived from avian and human strains of influenza, as well as porcine ones, further muddying its origins.

A new study, however, suggests pigs really were to blame. Several dozen researchers, led by Rebecca Garten of America’s Centres for Disease Control and Prevention (CDC), sequenced full or partial genomes of 76 samples of the new virus, which has afflicted almost 13,000 people around the world so far. In a paper published in Science, they confirm that the closest genetic relatives of the new virus are swine-flu strains from both North America and Eurasia. The virus is made of eight gene segments of known provenance but which have not previously been seen in this combination. The genetic material in them is indeed a hotchpotch derived from avian, human and swine sources, but all eight segments come most recently from pigs.