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H5 Wild Bird Flu In the United States?
November 7, 2005
The announcement last week in Canada on frequent detection of H5 in wild birds in Canada is cause for concern. This weekend additional information raised questions about the monitoring of H5 in wild birds in the United States.
The initial announcement in Canada indicated H5 had been detected in 28 wild birds in Quebec and in 3 in Manitoba. This was followed by an announcement that 24% of wild birds tested in British Columbia were H5 positive. 14 were strong positives and the weaker positives were being retested.
Media services provide some additional information this weekend. No sequence or N subtype data has been released. The characterizations to date have been based on the lack of sick birds, either amount the wild population swabbed, or domestic poultry on nearby farms.
The samples tested thus far show evidence of dual infection. More than one H serotype have been identified in some birds. Therefore the viral isolates are being plaque purified to allow for testing of individual isolates, eliminating confusion that be come from mixed samples. These additional steps have delayed release of the sub-typing data until the end of this week.
Moreover, the weak positives from British Columbia are being re-tested and results from the other provinces are expected in two weeks.
Most if not all of the swabs were collected in August as part of a banding exercise and the birds tested were young. After swabbing and banding, the birds were released.
The widespread detection of H5 in August in southern Canada in young wild birds would suggest that some or most of those birds would now have migrated in the United States.
Although the US has described increased surveillance, there have been no reports on H5 detected in the United States. The lack of such reports raise questions about the sensitivity of the US surveillance
Currently H5 and H7 HPAI are notifiable diseases. Soon all H5 and H7 will be reportable.
Based on the data from Canada, it seems likely that H5 is well represented in the wild bird population in the US. It is unclear why such infections have not been detected and reported.