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Fatal H5 Infections in Farm Ducks in Abottsford British Columbia?
November 21, 2005
The Canadian Food Inspection Agency said yesterday that tests on a "small number" of dead ducks at the Chilliwack farm showed they were infected with an H5 virus, considered "low-pathogenic."
"It does not cause serious disease in birds," said agency veterinarian Dr. Con Kiley.
The dead infected birds were "probably not" killed by the virus, he said.
The above comments add to the confusion surround detection of H5 among wild birds in 3 provinces in Canada as well as a duck farm in Frazer Valley, British Columbia.
The spread of HPAI (highly pathogenic avian influenza) H5N1 by migratory birds in Asia and Europe has led to increased surveillance in Canada. As part of this increased surveillance, Canada swabbed approximately 4800 wild birds in 6 provinces in association with a banding study. Although the swabs were collected in August, the finding of H5 was announced at the end of last month.
The data from the first three provinces was alarming. H5 had been detected in 5 birds in Manitoba, 28 in Quebec, and 170 in British Columbia. Initial results from the analysis of these positives were released this weekend. 11 of the 207 had been serotyped and characterized. All were LPIA (low pathogenic avian influenza) and four serotypes were identified, H5N1 in Manitoba, H5N3 in Quebec, and H5N2 and H5N9 in British Columbia.
The announcement of the initial results indicate that all of the H5 sequences in the 11 isolates were closely related to H5 found in North America and distance from H5 in Asia or Europe. These data made it clear that the 11 isolates were not due to migratory birds carrying H5N1 from Asia, but the reports did not address the relationship of the 11 characterized isolates to the 196 uncharacterized isolates.
The finding of H5 in 207 birds in Canada was unexpected. Although over 100 sequences from Canadian bird flu isolates were at GenBank, only two were H5, suggesting H5 was rare among migratory birds in North America and the most recent isolate was from 1980. The survey of ducks in British Columbia found that 24% were positive. Although the initial isolates were H5N2 and H5N9, H5 or H7 in domestic birds is a problem because both H5 and H7 have been shown to convert from LPAI to HPAI via non-homologous recombination. Such a conversion was seen in British Columbia last year when LPAI H7N3 converted to HPAI H7N3 and caused the death and culling of millions of birds.
The detection of H5 at high frequencies in migratory birds raises questions about H5 in domestic birds in Canada and the United States. Although both countries claimed to have increased surveillance because of the threat of H5N1 from Asia, there were no reports of any H5 in any farm in the US or Canada, although the H5 in healthy birds in Canada in August would likely lead to more infections of wild and domestic birds in Canada and the United States.
Late last week a farm duck did test positive for H5 in Abbotsford. The detection was said to be linked to increased surveillance, but it remains unclear why the H5 positive duck was selected. Initial reports indicated that all ducks on the associated farm were healthy.
However, the above comments indicate some of the ducks on the farm were dead, and these ducks tested positive for H5. These findings raise the possibility that some H5 LPAI has already converted to H5 HPAI. In addition, the dead ducks raise the possibility that there is H5N1 from Asia, because ducks usually are resistant to HPAI H5N1.
The current level of concern regarding H5N1 in Asia as driven in large part by the finding of H5N1 in dead bar headed geese at Qinghai Lake in May. H5N1 had been causing problems in poultry and people in southeast Asia, but that version of H5N1 was generally not lethal to waterfowl. The H5N1 at Qinghai Lake had the unusual property of being able to kill waterfowl. This property made it easier to track the H5N1 because of the associated deaths of domestic ducks and geese.
Recently China has announced human infections and fatalities linked to the H5N1 in poultry outbreaks linked to migratory birds. This H5N1 is generating new outbreaks in China at the rate of 1-2 per day and the situation has been described as grave.
Finding dead H5 positive dead ducks on the Abbotsford farm raises the possibility that in addition to LPAI H5 from North America, there is H5N1 from Asia in British Columbia.
To clarify these possibilities, Canada needs to provide more information about the 196 wild birds not included in the 11 that were characterized and reported. In addition, more detail is needed on the H5 in the dead ducks and the status of ducks at neighboring farms.
Similarly, the US needs to explain why increased surveillance has not detected H5 in wild or domestic birds in the US. Clearly H5 is present in the US, and failure to detect the H5 reveals serious flaws in the surveillance network in the US.