An international team of researchers led by a university professor from Japan has discovered a biochemical signal in flu virus that indicates whether it would infect humans and spread, the US science journal PLoS Pathogens has said.

Professor Yoshihiro Kawaoka of University of Tokyo found out that if either of two particular amino acids, lysine or arginine, is observed in position 591 in PB2 protein of flu viruses, it will lead to efficient replication of highly pathogenic H5N1 bird flu virus or the pandemic new-type H1N1 virus in humans.

“Even the H5N1 virus, which rarely spreads to humans, would be able to replicate in humans if the amino acids are observed in this area (position 591),” said Kawaoka, a Director of the Institute of Medical Science at the University of Tokyo.

Findings are expected to help public health authorities predict the spread of H5N1 in humans, which had killed 299 of 503 confirmed cases in 15 countries, mostly in Asia, since 2003 as of Tuesday, according to the World Health Organisation.

The new H1N1 has spread to over 214 countries and territories with at least 18,398 fatal cases as of July 25, after its outbreak in April 2009, the WHO said.

Up until now, amino acids lysine and asparagine in two other positions in PB2 protein were considered critical for adaptation of bird flu viruses in humans, prompting scientists to question why the H1N1, which lacked the amid acids, spread in humans.

With the findings by Kawaoka’s team, which comprises scientists from Japanese, American and Indonesian universities and research institutes, human infection has become more predictable since if relevant type of amino acids is found in any of the three positions in a flu virus’ PB2 protein, it is likely to infect humans and spread.

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