  In March and early April 2013, a new avian-origin influenza A (H7N9) virus
(A-OIV) emerged in the eastern China. During the first week of April, the 18
infection cases have been confirmed and 6 people have died since March. This
virus has caused global concern as a potential pandemic threat. Here we use
evolutionary analysis to reconstruct the origins and early development of the
A-OIV viruses. We found that A-OIV was derived from a reassortment of three
avian flu virus strains, and substantial mutations have been detected. Our
results highlight the need for systematic surveillance of influenza in birds,
and provide evidence that the mixing of new genetic elements in avian can
result in the emergence of viruses with pandemic potential in humans.
