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Initial Analysis of H5 in Wild Birds in Canada Causes Concern
November 19, 2005
Two wild ducks in Manitoba have tested positive for H5N1 avian flu viruses, but not the dangerous form of the virus circulating in Southeast Asia, federal officials announced Saturday.
Two birds in British Columbia carried H5N9 viruses and five carried H5N2s. Two birds in Quebec carried H5N3 viruses. All were low-path viruses.
"None of these results, based on assessment to date, are of significant human or animal health concern," Dr. Evans said.
Analysis of the viruses carried by birds sampled in Quebec, Manitoba and British Columbia have been completed, Evans said. Findings from Ontario, Alberta, New Brunswick and Nova Scotia have yet to be reported.
The above comments on intial data out of Canada clearly show that H5 in wild birds is widespread. So far all three reporting provinces are positive and the details above only describe 11 of the 207 birds positive for H5. The initial results were delayed because many isolates were mixtures, so there is more data being developed on other serotypes.
The above data indicates the current database of wild bird sequences isolated in Canada as represented by deposited sequences at GenBank is a poor representation of the current situation. Although there are over 100 sequences from Canada, only two are H5 (H5N9 from 1966 and H5N2 from 1980).
The presence of HPAI H5N1 in Canada remains unclear. The initial data does not provide information on the 196 H5 positive samples not included in the initial data. Much attention has been focused on H5N1 HPAI in wild birds in Asia and Europe. Full sequences from isolates at Qinghai Lake in China, Chany Lake in Russia, and Erhel Lake in Mongolia are at GenBank. All sequences are closely related to each other, but the sequences also have regional differences. In addition partial sequence data from H5N1 isolates in Turkey, Romania, and Croatia indicate the European isolates are also closely related to the sequences at GenBank.
The H5N1 wild bird sequences have several features in common with Z genotype isolates from domestic poultry and people in Asia. These features included a multi-basic HA cleavage site as well as a 20 amino acid deletion in NA. Thus, HPAI H5N1 can be identified and distinguished from LPAI by simply sizing the inserts from a PCR assay that spans the insertions in HA or deletions in NA. It is unclear of all 207 H5 positive samples have been tested and lack the above insertions or deletions. Thus, it is unclear if the 11 reported isolates represent the full spectrum of H5 positive samples.
The initial results indicate that similar studies should be done over a longer time frame. The samples tested were part of a wild bird banding study and all swabs were collected in August. Recent outbreaks in Europe and China indicate many of the H5N1 positive wild birds have recently left their summer locations and these migrating birds from Russian and Mongolia would not have been tested in the August collections.
Similarly, H5 in a large number of wild birds in August in southern Canada would mean that the number of H5 positive birds in the United States at this time would be high. Although the US has announced increased surveillance of wild birds, there are no reports of H5 detections in the US. Moreover, the recent announcement of H5 in a farm duck in British Columbia suggests more recent infections in Canada, which would also migrate to the US. There have been no reports on recent H5 isolations in the US.
The high frequency of H5 detection across Canada suggests that many countries in Europe, Asia, the Middle East, and Africa that are testing wild or suspect birds are reporting false negatives. Countries have announced negative data on hundreds or thousands of birds. The failure of these countries to detect any avian influenza or H5 avian influenza suggests that false negatives are being generated or reported.
Thus, at this time the initial H5 result from Canada raises questions about the status HPAI H5N1 in a variety of countries, including Canada, that are reporting negative H5N1 results.