On April 21st, 2008, four whooper swans were found dead at Lake Towada, Akita prefecture, Japan. Highly pathogenic avian influenza virus (HPAIV) of the H5N1 subtype was isolated from specimens of the affected birds. The HA gene of the isolate belongs to clade 2.3.2 in the HA phylogenic tree. The isolate is antigenically distinguishable from the HPAIVs causing previous outbreaks in Japan. Genetic and antigenic analysis clearly demonstrated that the virus is distinguishable from the strains causing previous poultry outbreaks in Japan, ruling out the possibility of a resurgence of previously introduced HPAIV in Japan. Studies of the migratory route of whooper swans suggested that whooper swans infected with the viruses have contacted with possible sources that had been introduced from overseas in Japan.
(Research Team for Zoonosis, TEL +81-29-838-7708)
Uchida, Y., et al. (2008) Emerg. Infect. Dis. 14: 1427-1429.