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H7N3 Bird Flu False Negatives in UK?
April 30, 2006
Dr Reynolds admits the surveillance - testing wild birds for flu - failed to find any carrying the virus affecting the farms, despite the greatest bird flu monitoring exercise ever carried out in Britain…….
The Department for Environment, Food and Rural Affairs says its tests are valid, but plans a trial to see if the methods used abroad are better.
DEFRA has already published its results, demonstrating that their methodology is fatally flawed. Over 3000 samples from dead birds identified only one positive, the H5N1 infected whooper swan. Only two positives were found in live birds, but virus was not isolated. This low rate of positive results indicates that the methodology is generating false negatives because low pathogenic influenza is common in wild birds.
H5N1 has been detected throughout Europe. The strain identified has been the Qinghai strain which was initially reported a year ago at Qinghai Lake in China. The strain has subsequently migrated to Russia, Mongolia, and Kazakhstan in the summer of 2005 and then onto Europe, the Middle East, and Africa in the fall and winter. H5N1 is undoubtedly widespread in Britain also, yet the surveillance has detected just one positive case. No H7 was found, although it has now been detected in at least three farms in Britain and four poultry workers have conjunctivitis symptoms.
Although the H7N3 has been characterized as low pathogenic, H7 can quickly evolve into high pathogenic, especially as it spreads through densely populated poultry farms. The sequence of events in Britain is quite similar to the H7N3 outbreak in British Columbia in 2004. That outbreak was initially characterized as low pathogenic, which was confirmed by sequence analysis of the HA cleavage site. However, the site evolved via non-homologous recombination to generate a multi-basic HA cleavage site, and the H7N3 infections spread quickly. The increased spread was associated with cases of conjunctivitis in poultry workers. Like the 2003 H7N7 outbreak in the Netherlands, the conjunctivitis cases were mild. However, a sensitive assay for H7 antibodies indicated that over 2000 human contacts were infected, demonstrating efficient human-to-human transmission. These cases were also mild. However, there was one fatality, and H7N7 from the fatal case had acquired PB2 E627K. All H5N1 Qinghai strain isolates to date have had E627K and reassortment between H5 and H7 in Europe has been documented in several northern countries, including Denmark and Sweden.
The detection of H7N3 in a poultry worker linked to the current outbreak is cause for concern. The infection indicates the H7N3 in Britain is readily transmitted to humans. Three additional workers have symptoms of conjunctivitis and initial negative results for H7N3 remain suspect.
The co-circulation of H7 which is readily transmitted to humans, with H5N1 which is poorly transmitted but frequently fatal, is cause for concern. This concern is compound by the poor surveillance in Britain and throughout Europe. Only Russia has detected H5N1 in live wild birds. The poor surveillance of bird flu worldwide remains a cause for concern.