Scientists say the swine flu virus may have jumped from pigs to people as early as last August. That's several months before it was reported in Mexico in April.

Scientists came up with a range of possible times for when the virus showed up in people. Their best estimate was that it happened this past January, but they also said it could have been last August.

Oliver Pybus of Oxford University, a co-author of the study, said it's also possible that the germ jumped to humans even before then. The study was published online Thursday by the journal Nature.