Swine flu may have been spreading in August
By MALCOLM RITTER, AP Science Writer
NEW YORK – As early as last August, the swine flu virus may have been spreading among people — long before it was first recognized in April, scientists reported Thursday.
Through genetic analysis, researchers came up with several possibilities for when the virus might have first spread to humans. This past January is their best estimate. It's also possible it jumped as early as last August — or maybe even before then, said Oliver Pybus of
The research involved a genetic analysis of various strains of the virus and construction of a sort of family tree to see when the flu strains last shared a common ancestor. The study was published online Thursday by the journal Nature.
Raul Rabadan of
The new analysis also concluded that ancestors of the swine flu virus had circulated in pigs for years undetected. The researchers called for better surveillance of flu viruses in swine, although Pybus said scientists don't have the ability yet to identify strains in pigs that will lead to human epidemics.
Rabadan also has called for better surveillance and recently published a similar conclusion about ancestors of the human virus circulating unnoticed in pigs.