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H5N1 Antibodies in Korean Poultry Workers
Recombinomics Commentary
February 24, 2006
The Korea Center for Disease Control and Prevention (KCDC) confirmed Korea's first human bird flu infections without symptoms in an announcement yesterday.
According to the KCDC, the cases were confirmed after it carried out an antibody test on the blood serum of 318 soldiers and workers who took part in a poultry cull from December 2003 to March 2004. Four tested positive for H5N1, a mutated bird flu strain.
The above data on antibodies on asymptomatic poultry workers is similar to earlier data on farm workers in Japan. H5N1 isolates from South Korea and Japan form a clade that includes a HA cleavage site that has lost an R. The cleavage site recombined with H5N1 in northern Vietnam to create and H5N1 in northern Vietnam in 2005 that was associated with milder cases.
The data from Japan and South Korea suggest the number of mild cases that have gone undected is high. The acquisition of the Korea/Japan cleavage site in northern Vietnam was also associated with more efficient transmission. Although 1000 serum samples were collected from patients and contacts in northern Vietnam approximately one year ago, WHO has yet to release details of those results. Media reports had indicated that many of the samples were positive, confirming that mild cases of H5N1 were widespread. This notion was supported by the results from the family of five in Haiphong last year. Although all five family members were positive for H5N1, all had mild cases and were discharged after a brief hospital stay.
The Korea/Japan clade of H5N1 has been associated with additional H5N1's. The Qinghai strain of H5N1, which is circulating widely in Europe, the Middle East, and Africa is closely related to to Korea/Japan clad.
Similarly, the H5N1 that is being detected in Hong Kong is most closely related to the H5N1 clade from Korea/Japan. If this version is associated with human infections, then the number of current infections by H5N1 may be markedly higher than the number being reported and recorded by WHO.
These milder versions of H5N1 in humans allow for silent spread and provide provocative targets for additional recombination with season flu. H5N1 acquisition of mammalian polymorphism has been noted in Vietnam and Thailand as well as Qinghai versions of H5N1.
Monitoring of the mild cases is scandalously poor. Reports of mild cases in Turkey stopped abruptly and updates on serum tests of patients in Turkey not been forthcoming. Patents in northern Vietnam and Indonesia suggest mild versions of H5N1 can be efficiently transmitted human to human. The current status of H5N1 in people in these regions is unclear, because testing for H5N1 usually requires contact with poultry, which would reduce or eliminate infections by humans.
A serious survey on antibody levels in contacts of H5N1 patients and people in areas of high incidence of H5N1 detection is long overdue,
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