H5N1 has already been mutating rapidly in Vietnam, where few chickens are vaccinated. Cao Bao Van, head of the Pasteur Institute in Ho Chi Minh City in Vietnam, told the Vietnamese press this week that 24 isolates of H5N1 from poultry and humans, taken between December 2003 and March 2005, show “significant variation”.
Cao was also quoted as saying a mutation had been observed in the PB2 gene of a virus isolated from a human case in March, which “allows more effective breeding of the virus in mammals”. PB2 codes for part of the polymerase enzyme which replicates the virus.
That mutation, at amino acid number 627 of the protein, changes the glutamic acid of bird flu to the lysine typical of human flu. The change allows the virus to replicate in the human respiratory tract, which is cooler than the bird guts where bird flu normally replicates.
The same mutation has been turning up since 2004 in several isolates of H5N1 from humans and other mammals in east Asia and shows the virus is adapting to mammals while infecting them. It was also a feature of the 1918 pandemic virus, which was a bird flu virus that adapted to humans.
From a New Scientist article that also informs us of a Chinese plan to vaccinate all poultry against bird flu.