Eyes on the Swine

Editor's Note: This article will appear in the July issue of Scientific American. We are posting it early in light of a report today in the journal Science that bears on similar themes. The study, led by Nancy J. Cox of the Centers of Disease Control and Prevention describes a molecular analysis of the novel influenza A (H1N1) virus infecting humans in several parts of the world. The authors confirm that the new strain is comprised of segments from swine flu strains known to circulate in Europe, Asia and North America, but that this combination has not previously been seen and appears to have been evolving independently from its parent strains for some time. Noting the "relative lack of surveillance for swine influenza viruses," the authors suggest, "this virus might have been circulating undetected among swine herds somewhere in the world." The study also confirms that the "H1" hemagluttinin protein of the new virus derives from the classical swine H1N1 strain, which shares a close common ancestor with the human H1N1 strain circulating before 1957 and several lines of evidence show that older people exposed to that virus may have some immunity to the new H1N1. Finally, the study finds that genetic changes associated with adaptation to a new host seen in other flu viruses that have breached the species barrier--such as the avian H5N1 flu strain--are not seen in the novel H1N1, suggesting that unknown changes in the new virus account for its ability to replicate and transmit in humans. [More]

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