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Maintain Dominance Polymorphisms
December 23, 2008
The CDC has
deposited HA and NA sequences at Genbank, which will be available
shortly (see list below). As expected, all are clade IIB
(Brisbane) and have H274Y. One sequence from August, A/Missouri/06/2008,
was also released and it is the only oseltamivir sensitive
isolate. However, it is clade IIC, and like the clade IIC
isolates in the US last season and over the summer,
it is adamantidine resistant and oseltamivir sensitive.
The new sequences have evolved from the dominant sub-clade in
circulation last season, and have changes that led to dominance last
season and in the 2008 season for the southern hemisphere. As
noted earlier, one US sequence from the summer had the clustered
changes near the position 190 receptor binding domain. The
current sequences have one
of the polymorphisms in that cluster A193T.
Most of the new sequences formed a branch that included Memphis/03/2008
and Hawai/02/2008. The new isolates on this branch were from
Hawaii, Texas, and Pennsylvania, so more samples are required to see
the full distribution of this sub-clade.
However, the sequences from these initial isolates indicate that the changes
that initiated dominance last season, have been maintained over the
summer and into the new season. These dominance changes were
acquired via recombination
from clade IIC sequences.
at Nature Precedings