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January 19, 2006

Turkish virus better adapted to humans

Scientists studying virus samples from the human outbreak of avian flu in Turkey have identified three mutations in the virus's sequence. They say that at least two of these look likely to make the virus better adapted to humans.

[...] The first mutation found, announced last week, involves a substitution in one sample of an amino acid at position 223 of the haemoagglutinin receptor protein. This protein allows the flu virus to bind to the receptors on the surface of its host's cells.

[...] It increases the virus's ability to bind to human receptors, and decreases its affinity for poultry receptors, making strains with this mutation better adapted to infecting humans.

The same sample also contained a mutation at position 153 of the haemoagglutinin protein, Nature has learned. Cheng says this information was not included in WHO statements, because "it is not clear what role this particular change plays".

Finally, both samples from the Turkish teenagers show a substitution of glutamic acid with lycine, at position 627 of the polymerase protein, which the virus uses to replicate its genetic material. This mutation has been seen in other flu sequences from Eurasian poultry over the past year. It was also present in the one person who died during an outbreak of H7N7 in the Netherlands in 2003, and in a few people in Vietnam and Thailand.

The polymerase mutation is one of the ten genetic changes that gave rise to the 1918 pandemic flu virus. Like the 223-haemoagglutinin mutation, it signals adaptation to humans, says Alan Hay, director of a WHO influenza laboratory at the NIMR. "There is this glutamic acid–lysine flip," he explains. "Glutamic acid is associated with flu-virus replication in birds, and lycine is in primates."

Read the entire article at Nature.com.

Posted by dymaxion at January 19, 2006 09:33 PM

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