Authorities found that 10 ducks in Osaka Prefecture suspected of bird flu had a less harmful type of the virus, but they were still conducting tests on another 47 birds that also showed signs of infection, officials said Tuesday.

Tests at the National Institute of Animal Health confirmed that the 10 birds from a duck farm were infected with the H4 flu virus, which has no history of human transmission, according to Katsunori Tanaka, an Osaka livestock farming official.

Officials were testing another 47 ducks at the farm, after preliminary tests showed some may be infected with bird flu, Tanaka said. It was not clear exactly how many of the 47 birds may be infected.

Officials have completed their inspection of the farm, which raises ducks for human consumption, and of another eight chicken farms within a 10-km radius, Tanaka said.

The farms in the area had been asked not to sell or move birds and eggs while authorities carry out their tests, but Osaka was planning to end that policy soon, he said.

The latest case follows the announcement Monday that authorities detected signs of bird flu at a farm in Ibaraki Prefecture and planned to kill 82,000 chickens.

Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus, hemagglutinin, or H, and neuraminidase, or N.

The deadly H5N1 strain has ravaged Asia since 2003 and killed at least 62 people there.

If the remainder of the ducks test positive for types H5 or less acute H7, the farm will be ordered to kill its 780 birds, said Tadayoshi Nakai, another Osaka official.