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Scientists in China trace new bird flu strain H7N9 back to market chicken

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Scientists in China say they have pinpointed a likely source of a new strain of avian influenza (bird flu) that's killed 23 people in the country so far: chicken sold in the markets of Zhejiang, China. In a study fast-tracked into online publication in the international medical journal the Lancet yesterday, 30 scientists from hospitals and universities around China took samples of the H7N9 virus strain from human patients and compared it to samples of viruses grown from chicken in a Zhejiang market and found that "viral isolate from the patient was closely similar to that from an epidemiologically linked market chicken." Yet the human version of the virus also seems to be a compilation of sorts: The scientists found that the H7 portion was similar to domestic ducks from Zhejiang, while the N9 portion more closely resembled viruses in wild birds in South Korea.

"We are quite certain...the poultry is really giving the virus to humans."

"We are quite certain they very closely related and that the poultry is really giving the virus to humans," said microbiology professor K.Y. Yuen of the University of Hong Kong, describing the study results in a podcast. The study reveals more important information on the virus, such as that incubation takes around six days. In a separate comment on the findings published by the Lancet, the researchers note that the virus can evade detection in human patients if doctors only take samples from their upper-throat. But even in those cases, it can be detected in samples from lower in the the throat. The comment also cautions against thinking that the source has been definitively identified, noting further studies should be done to "possibly look for other sources of infection."

Unfortunately, the study also found that the virus has been transmitted among poultry for some time without many ill effects in those animals, but has now "more adapted to mammalian infection," because it has mutated to thrive at mammal body temperature, particularly that of humans. "Person-to-person transmission fortunately seems negligible so far,"the Lancet comment adds, but, warns: "vigilance is needed, however, as just a few mutations could change this behavior."