Chinese scientists working with the bird flu virus (H9N2) and H1N1 virus have found that eight of the 127 potential hybrids discovered so far are more virulent than either of the original viruses on their own.

"The main message is that the H1N1 can combine in certain ways with the H9N2 to create reassortants and some of the viruses had an increased pathogenicity comparing with the parent viruses in mice," said lead author Jinhua Liu, of the College of Veterinary Medicine at the China Agricultural University in Beijing. Mice infected with the eight hybrid viruses experienced pneumonia, edema and hemorrhaging. These findings, said Liu, underscore the importance of tracking and monitoring hybrid viruses that result from the combination of H9N2 and H1N1.

Full findings were published in the Proceedings of the National Academy of Sciences.