BEIJING - A top Chinese biology lab has ascribed the H7N9 avian influenza to genetic reassortment of wild birds from East Asia and chickens from East China.

The researchers found that no genes in H7N9 were traceable to pigs, thus excluding pigs as intermediate hosts for the deadly new strain of bird flu, the Chinese Academy of Sciences' Key Laboratory of Pathogenic Microbiology and Immunology said on Wednesday.