TOKYO, April 28 (Reuters) - Japan has detected a strain of bird flu in four wild swans after stepping up checks following major outbreaks of the disease in neighbouring South Korea, local and government officials said on Monday.
The birds, three of which had died, were found on the shores of Lake Towada in Akita prefecture in the north on April 21, the prefectural government said in a news release.
Inspectors detected the H5 strain of bird flu in the swans, the prefectural government said, but they were still checking whether it was the highly virulent H5N1 strain.
Authorities have patrolled the area but have not found any incidents of large numbers of deaths or unnatural deaths in wild fowl.
There are no chicken farms within a 10 km radius of the area where the swans were found, and no unusual incidents were noted at other farms.
"We’ve asked to step up surveillance measures at poultry farms in the prefectures of Aomori, Akita and Iwate," a farm ministry official said, referring to the prefectures in the area.
"Japan has asked poultry farms to strengthen surveillance after the case in South Korea in early April," he said.
The official said Japan’s last case of bird flu was found in a wild bird in March 2007 in Kumamoto prefecture on Japan’s southern island of Kyushu.
Prior to that, Japan reported cases of bird flu at four poultry farms in January 2007. (Reporting by Chikafumi Hodo and Miho Yoshikawa; Editing by Hugh Lawson)