About 40 people in Ibaraki Prefecture linked to chicken farms are suspected of having been infected with the H5N2 strain of bird flu in the past, informed sources said Saturday.
They showed no symptoms and there is no possibility of secondary infection, the sources said.
The health ministry and National Institute of Infectious Diseases have reportedly been testing farm workers.
Chickens at some 40 farms in Ibaraki Prefecture have been infected with the H5N2 strain of bird flu since June, but the ministry and the institute suspect farm workers might have been infected before then, the sources said.
A former employee of a farm in Kyoto Prefecture was found in February 2004 to be infected with the H5N1 strain of bird flu, which is more harmful than H5N2 and could be fatal to humans.
If the latest cases of avian flu are confirmed, they would be the first involving humans since that incident.
Because the antibody of the H5N2 strain is weak, there are no defining marks of infection, such as birds dying en masse.
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