- The detection of H5 avian influenza is not unexpected:
the virus is commonly seen in migratory bird populations around the world
and various types and strains have been detected in North America over
the last 30 years, with no impact on human health. The birds tested in
this national survey were healthy, and there is no evidence of influenza-related
illness among domestic or wild birds in the test areas.
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- Tests to confirm the H5 type and tests to determine the
N type of the virus are ongoing. Definitive findings may not be possible
if there is insufficient live virus remaining in the original samples.
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- The above comments form the Public Health Agency of Canada
offer little assurance that the H5 detcted in two provinces is not H5N1.
Sincethere is no data on the precise location of the H5 positive birds,
it is hard to evaluate the lack of reported illness in the test areas.
Moreover, since the species of positive birds were nit given, it is hard
to say how widespread the H5 infections are.
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- Russia has reported HPAI in healthy wild waterfowl, so
the health of the H5 positive birds also does not address the serotype.
The H5N1 wild bird flu has been well characterized and full sequences
of genes from isolates from Qinghai Lake and Novosibirsk are publicly available,
so determining the relationship between the H5 in Canada and those isolates
in Asia or Europe should not be difficult. All of the H5N1 wild bird flu
described recently in China, Russia, Kazakhstan, Mongolia, Romania, Turkey,
and Croatia appear to be closely related. They all have the signature RRRKKR
sequence in their HA cleavage site, so even a partial sequence would determine
if it was HPAI and if the signature sequences was present, the isolate
would almost certainly be H5N1 because RRRKKR has not been detected in
any other serotype.
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- Although H5N1 has been widely detected recently in Asia
and Europe, HPAI H5N1 has never been reported the Americas. In Canada,
there have been few H5 isolates of any serotype. Surveillance of avian
influenza in Cnada has led to the sequencing of a large number of influenza
isolates and the published sequences are publicly available at GenBank.
These sequences however, show little evidence for H5 in Canada.
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- Most of the sequences on deposit are from Alberta. There
are 91 isolates, yet only one is H5. The H5N2 isolate was from 1980.
Other serotypes were deposited more frequently. There are 12 H4N6, 9 H3N8,
8 H6N8, 6 H2N3, 5 H2N9 and 4 H10N7, H1N1, H6N2, H7N3. There are 15 isolates
from Ontario and again only one is H. The H5N9 isolate is from 1966. The
other provinces did not have any H5, including 13 isolates from British
Columbia and 2 each from Manitoba and Quebec.
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- Thus, H5 serotypes in Canada a rare, raising concerns
that the 33 H5 isolates are HPAI H5N1. Recent data suggest H5N1 wild bird
flu may be linked to human infections in Hunan, Vietnam, Thailand, and
Indonesia. Sequencing of the HA cleavage site is routine and should be
available in hours. Since RRRKKR is specific for H5N1 wild bird flu from
Asia, an answer on the concerns linked to H5 in Canada should be answered
soon.
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