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The Spanish flu suspect
Genes point to birds
  
By Birgit Hofmann

Scientists have come one step closer to discovering the genetic makeup of the worst infectious pandemic in human history—the "Spanish" flu. In 1918, the Spanish influenza epidemic spread around the globe in just a few months, killing an estimated 20 million persons worldwide, among them half a million Americans. Not only was the Spanish flu strikingly contagious, but its unprecedented virulence struck especially hard among young healthy adults. Spain reported it first, and so it was called Spanish influenza.


80-year-old clues

To find more about the genetic nature and origin of this lethal virus, molecular biologist Jeffery K. Taubenberger, of the Armed Forces Institute of Pathology in Washington, DC, and his team examined the frozen lung tissues of exhumed 1918 flu victims, which had been buried in permafrost. The team isolated influenza RNA fragments from these 80-year-old clues.

The scientists have now completed the sequencing of one of the key genes—the gene for neuraminidase (NA), a protein responsible for influenza's infectiousness. The coding sequence of the 1918 NA gene, published in the current early edition of the Proceedings of the National Academy of Sciences USA, bears strong similarity to those found in bird flu viruses, thus sustaining the assumption that the 1918 virus originated in birds.

A previous study by the same research team of another 1918 protein called hemagglutinin (HA) supports this link. Yet the NA and HA gene sequences in the 1918 sample not only resemble the corresponding sequences in birds but also those seen in pig flu viruses. Therefore it is also possible that these genes could have been adapting in a mammalian host for some time before they emerged in humans. Final evidence is difficult to obtain as there is no frozen 1918 bird tissue available. Further studies are required to shed additional light on the nature of the 1918 influenza virus to understand and ultimately prevent the emergence of future influenza viruses with pandemic potential.

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Reid, A.H.; Fanning, T.G., Janczewski, T.A., & Taubenberger, J.K. Characterization of the 1918 "Spanish" influenza virus neuraminidase gene. Proc Natl Acad Sci USA (Early Edition), (May 23, 2000).
 

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