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H5 Test Failure in Winnipeg Raises Pandemic Concerns
June 21, 2006
The fact that the H5 virus was not detected in testing at the Winnipeg lab, along with the absence of clinical signs of disease in the birds depopulated in the flock, indicates that only a very small amount of low pathogenicity virus may have been present in the index bird. A finding of incidental contamination in the index bird would not be unexpected given that it spent time out of doors and other birds on the farm were confirmed to have co-mingled with wild migratory birds which commonly carry AI viruses.
The above comments from the Canadian Food Inspection Agency provide additional evidence that the dead geese on Prince Edward Island (PEI) were killed by the Qinghai strain of H5N1. Since H5 was detected in the only dead bird tested, the chance that the infection was incidental is low.
The four dead birds had classical H5N1 symptoms. The H5 was detected in a free range backyard goose, which is more likely to interact with wild migratory birds, as indicated above. The four geese were said to be "walking oddly" on Sunday, June 4, another classical symptom of H5N1 infection. All four birds were found dead the next morning. Rapid death is another classical sign of H5N1 infection. The autopsied dead goose also had organ damage, which was also consistent with H5N1 infection.
The only aspect of the goose that was not consistent with the Qingahi strain of H5N1 was the delay in sending the sample to Winnipeg for sequencing and sero-typing. Since the announcement on Friday, June 16 indicated that H5 had been confirmed, the sample must have been positive at least twice prior to shipment. The long delay between death on June 5 and announcement of the H5 result on June 16 raises concerns over the handling of the sample, including sample degradation.
Since the four dead birds had a number of symptoms consistent with Qinghai H5N1 infection, it is unclear why only one of the dead birds was tested. Determining the sequence of the HA cleavage site is routine, so it is unclear why that test was not be done locally on PEI. The Qinghai strain of H5N1 is quite distinctive, so a small amount of sequence data across any of the eight gene segments would have provided conclusive data on the relationship between the H5 in the dead goose, and the Qinghai stain of H5N1.
The failure to find spread of the H5 provided little data on the relationship to the Qinghai strain. Since symptoms were observed Sunday and the geese were dead Monday morning, the interactions with other birds whie the infected geese were contagious may have been limited. Since all four birds developed symptoms and died at the same time, a common source was likely. However, if the common source was wild birds, they may have flown away and limited exposure of the other birds on the farm.
The failure of Winnipeg to detect the H5, which had been confirmed on PEI, is cause for concern. The testing of only one goose and delay in testing and/or shipping of samples on PEI indicates pandemic H5N1 bird flu testing in Canada is inadequate.