H5N1 in Tenth Swan Highlights Surveillance Flaws in England
Recombinomics Commentary 09:11
February 6, 2008
The confirmation of H5N1 in a tenth mute swan in Dorset raises serious surveillance concerns. Although DEFRA continues to claim that H5N1 in wild birds in England is limited and has not spread, the basis of their statement is negative results from a fatally flawed surveillance program.
H5N1 in dead mute swans in the swannery in Dorset was reported over a month ago in mute swans that were collected as early as December 27, 2007 (see satellite map) . The first two swans were euthanized because they were near death, and all subsequent positives have been from dead mute swans. The most recent positive swan was collected February 4, 2008. Thus, although H5N1 has been in the region for well over a month, the surveillance program has yet to detect H5N1 in a live healthy mute swan, and has failed to detect H5N1 in any other species.
H5N1 levels in mute swans are higher than other species, which may explain the failure to detect H5N1 in other species. Similarly, the failure to detect the Qinghai strain (clade 2.2) in live wild birds is fairly common because the levels are lower. Thus, the surveillance failures are not limited to the DEFRA program.
However, these major limitations are ignored in DEFRA reports, which continue to claim that there has been no evidence of spread. This lack of evidence is due to the insensitive assay, not to the absence of spread.
The recent DEFRA report described the identity levels in the H5N1 from the first four positive swans. The differences between the isolates indicated the introductions into the swan population were independent, and not do to a common source. This genetic diversity supports a varied reservoir in the mute swan population, or repeated infections from a local source. However, neither has been identified in the surveillance program, even though it has been in the ”enhanced” mode since H5N1 was first detected, in early January.
The failure to detect H5N1 in live birds or any wild birds other than the mute swans. signals flawed surveillance. H5N1 is readily transmitted to a wide range of avian species which would have contact with H5N1 infected birds in and around the swannery. However, these H5N1 infected birds continue to circulate undetected.
The failures should be acknowledged by DEFRA, and the misleading statements about “lack of evidence” should cease.
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