The Environment Ministry and the Oita Prefectural Government launched an ecological study of migratory birds Tuesday to determine whether they brought in avian influenza.
Experts said the bird flu virus found earlier this month in Oita and in January in nearby Yamaguchi Prefecture are believed to have derived from the same "ancestor" virus, and that the two viruses are not the same types as those found in other parts of Asia, including Vietnam and Hong Kong.
However, they also said it is difficult to imagine that the virus spread directly from Yamaguchi to Oita. It is necessary to look into the possibility of the virus being brought in from overseas, including the role of migratory birds, the experts said.