But so far the evidence seems to suggest this mutation does not make the new H1N1 virus more virulent, the researchers said Tuesday.
The change, at position 627 on the PB2 gene of the virus, is known to increase the ability of flu viruses to replicate; prolonged viral replication can lead to more serious illness. The mutation has been found in all known human flu viruses, including the three that caused the pandemics of the last century.
"Everybody predicted that this mutation is going to have a big impact on virus replication of the new H1N1," said Dr. Ron Fouchier, one of the authors of the report and a molecular virologist at Erasmus Medical Centre in Rotterdam.
"If you would have asked me three months ago, I would have bet my car on it. But nobody placed that bet because everybody was sure that it would increase (virulence)."
If they had, it seems they might have been able to claim the keys to Fouchier's SUV.
Three people either known or suspected of having been infected with the mutated H1N1 viruses suffered only mild disease. And ferrets infected with a laboratory synthesized H1N1 virus with this change also did not suffer more severe disease. Ferrets are the standard animal model for human flu.
"Given the information that we have at present, we have no indication for increased virulence," said Dr. Marion Koopmans, chief of virology in the infectious diseases laboratory of the National Institute of Public Health, The Netherlands.
"This is a mutation that is in the textbooks as something to look out for, but whether it really confers something to these (H1N1) viruses remains to be seen."
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