- Four complete sequences from tree sparrows in Henan,
China (A/Tree sparrow/Henan/1/2004(H5N1), A/Tree sparrow/Henan/2/2004(H5N1),
A/Tree sparrow/Henan/3/2004(H5N1), A/Tree sparrow/Henan/4/2004(H5N1))
have been deposited at GenBank. These 2004 isolates are reassortants
with H5and N1 on the outside and sequences related to H9N2 on the inside,
similar to the 1997 isolates linked to the Hong Kong outbreak. Thus,
although 1.5 million birds were culled in Hong Kong in 1997, related sequences
were circulating in wild birds in China.
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- The four sequences share polymorphisms with the 1997
isolates as well as 2000-2001 H5N1 isolates from Hong Kong. These
"older" sequences however are present in 2004 tree sparrow isolates.
One of the 2004 isolates also has the 20 amino acids in NA that are deleted
in the Z genotype.
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- These isolates also still have PB2 E627 and although
they are pathogenic to chickens, they are not pathogenic in ducks or mice.
However, these sequences may be endemic in China, offering genetic variations
used in the evolution of H5.
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- Indeed there are also polymorphisms found in LPAI H's
recently deposited. These H5N3 and H5N2 serotypes are from ducks
and swans in Mongolia and Japan. They also share polymorphisms with
H5 isolates from Primorie and northern Europe, which identify an additional
northern migratory pathway stretching from Sweden to Japan.
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- The presence of HPAI H5N1 in tree sparrows also raises
the possibility that the dominant wild bird serotype in Asia, LPAI H9N2,
is being replace by HPAI H5N1. Moreover, this indigenous HPAI H5N1
is assuming several configurations via reassortment, and acquiring novel
polymorphisms via recombination. These genetic changes may be contributing
to the lack of effectiveness of vaccines in China and the mismatches may
be driving genetic diversity.
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- These new sequences from China also highlight the need
for wider surveys of wild bird populations, including water fowl and well
as local terrestial birds. Screening and publishing of these sequences
will aid in the development of effective vaccines to better control the
accelerating evolution of H5 in Asia and throughout the world.
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