The weak strain of avian influenza recently detected at more than a dozen farms in Ibaraki Prefecture may have been brought about by artificial contamination, including by the use of vaccines, a farm ministry panel said Friday.

The use of vaccines to prevent bird flu is currently banned by law, and the Agriculture, Forestry and Fisheries Ministry said it would probe the matter further.

According to panel head Hiroshi Kida, a professor at Hokkaido University, the genetic makeup of the virus found at the Ibaraki farms was strikingly similar to that of a bird flu virus found in Guatemala and Mexico, too far for a migrating bird to carry into Japan. It is also different from other Central American strains of the virus previously found in other parts of Asia.

This led the panel to suspect that a vaccine developed using the Central American virus was brought into Japan and used on some birds, infecting the animals around them, he said.

The ministry has a stock of vaccines to be used in the event of a massive bird flu outbreak, but has banned its general use because vaccinated birds will develop the antibody and be indistinguishable from animals that have really come down with the disease.

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