No poultry have been sickened so far, said Shigeki Oda, a farm official in the northern island prefecture (state) of Hokkaido. He said, however, that health authorities plan to inspect three nearby poultry farms and to disinfect 180,000 chickens as a precaution.
Scientists at Hokkaido University were conducting gene tests to determine more information about the cases, Oda said.
The most recent case reported was that of a wild swan found dead May 5 near Saroma Lake, with final test results Saturday confirming the presence of the virus. H5N1 was also confirmed in dead swans in another location in Hokkaido on May 5, and in northeastern Akita prefecture on April 29.
The virus remains hard for people to catch, but scientists are concerned it could mutate into a form that spreads more easily between humans, with the potential to kill millions worldwide.
At least 240 people have died from bird flu since 2003, according to the World Health Organization. Most human cases have been linked to contact with infected poultry.
Japan has reported no human cases of the bird flu virus.
