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H7N3 Bird Flu Confirmed in UK Poultry Worker
April 28, 2006
the worker, who does not want to be named, has the H7N3 strain of bird flu which is not highly infectious
The above comments acknowledge that H7N3 has caused at least one case of conjunctivitis in Great Britain. This case is not a surprise. H7 infections in poultry frequently result in conjunctivitis cases in human contacts. The most recent example was in British Columbia in 2004 where several poultry workers developed conjunctivitis from H7N3. However the H7N7 outbreak in the Netherlands in 2003 produced over 80 cases of conjunctivitis in poultry cullers.
However, a sensitive assay was developed to detect H7 antibodies and hundreds or thousands of culler contacts had H7 antibodies, indicating human-to-human transmission of H7 is efficient. The cases had mild symptoms or were asymptomatic. However, a veterinarian developed pneumonia and died. This is the only reported fatality from bird flu linked to a serotype other than H5N1. The H7N7 isolated from the fatal case had PB2 E627K.
E627K was first reported in H5N1 from birds in the 16 isolates from Qinghai Lake, almost 1 year ago. All Qinghai H5N1 PB2 sequences to date have also had E627K. This polymorphism is liked to enhanced polymerase activity at lower (33 C) temperatures. It is also associated with increased virulence in mammals.
Although the has been only one report of H5N1 in the UK, the Qinghai strain has been detected throughout Europe, raising serious issues about the sensitivity of the assay in the UK. The UK surveillance failed to detect significant infections by H5N1 or low pathogenic serotypes, even though over 7000 birds were tested. The surveillance failed to detect any H7 infections.
The co-circulation of H7 and the Qinghai strain of H5N1 is cause for concerns. E627K could be acquired by H7N3 via recombination or reassortment. This acquisition would likely increase virulence in an H7 which is probably readily transmitted between humans.