H1N1 and bird flu virus produce dangerous hybrids

The scientists made 127 hybrid viruses by mixing genes of the H1N1 and the avian H9N2 virus in a laboratory, and eight of the hybrids turned out to be more virulent than either parents when tested in mice.

The H1N1 pandemic of 2009 turned out to be milder than feared and human infections of H9N2 in China in the past are not known to have caused severe disease. But the experts said their hybrid offspring - or "reassortants" - cannot be casually dismissed.

"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," lead author Jinhua Liu, of the College of Veterinary Medicine at the China Agricultural University in Beijing, wrote in an email to Reuters.

Liu and his colleagues, who published their findings in the Proceedings of the National Academy of Science, warned in their paper: "The possibility of novel pandemic strains being generated from reassortment between avian H9N2 and H1N1/2009 influenza viruses exists."

Flu viruses have eight gene segments and one of the segments is called the PA gene. Interestingly, all eight dangerous hybrids carried the PA gene belonging to the H1N1 parent virus.

The eight hybrid viruses caused severe pneumonia, edema and hemorrhaging in infected mice, the experts wrote.

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