Judging by the rate of evolutionary change in the virus, Hurt and his colleagues estimate that the virus has been evolving on its own in Antarctica for between 49 and 80 years.
Migratory birds that travel to and from Antarctica, such as skuas and giant petrels, may be responsible for carrying flu viruses to penguin populations, the researchers wrote in mBio. Marine mammals such as seals could spread the viruses, too. Another possibility, they wrote, is that avian flu circulates among penguins and other birds in the summer and becomes frozen in ice over the winter, only to reactivate during the summer thaw.
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