- The HA sequence of A/mallard/BC/317/2005(H5N2) has been
released. This isolate was obtained via an expanded banding project by
the Canadian Cooperative Wildlife Health Centre. Last year the agency
reported that H5 had been found in live healthy wild birds throughout southern
Canada. A remarkable 24% of the birds tested in British Columbia were
H5 positive. The latest breakdown by species indicates bird flu was detected
in 1165/2657 of the mallards tested and H5 was detected in 187/811. The
update report by region indicates H5 was detected in 167/380 birds tested
in British Columbia.
-
- Analysis of the above sequence indicates it has a HA
cleavage site consistent with low path H5. However, analysis of individual
polymorphisms indicates the H5 has acquired two tandem polymorphisms, C1367T
and C1377T.
-
- Other isolates in the Los Alamos flu database having
these two polymorphisms are listed below. The only H5 or avian isolate
in the list is the H5N1 sequence from British Columbia. All other isolates
are mammalian H1 isolates, including recent isolates from Canadian swine
as well as a fatal human case in Maryland
-
- The most extensive homology is identified with a 25 bp
probe which identifies the recent isolate A/swine/Ontario/11112/2004(H1N2),
which was among a group of Canadian swine showing both extensive recombination
as well as extreme conservation of sequences. As noted below, the 25 bp
probe identifies A/Wilson-Smith/33 and A/WSN/33, the first human flu isolate
as well as its neurotropic derivative.
-
- The acquisition of these polymorphisms in a health wild
bird population is cause for concern. Recent data from Prince Edward Island
suggests the Qinghai strain of H5N1 has already entered North America.
Recombination between low path H5 and high path H5N1 is common and provides
a mechanism for acquisition of these mammalian polymorphisms by the Qinghai
strain of H5N1 bird flu.
-
- The initial H5N1 human isolates from Vietnam and Thailand
had acquired a number of mammalian polymorphisms that were not found in
other H5N1,s. The acquisition of swine polymorphisms in H5 in wild birds
in Canada, and presumably the United States, is cause for concern.
|
