Highly Pathogenic H5N1 Avian Influenza Virus Infections in Wild Birds in Japan

Abstract

There have been four times since 2004 that infections of highly pathogenic H5N1 avian influenza virus (HPAIV) were detected in wild birds in Japan. The HPAIV infection of jungle crows in 2004 was considered as secondary infection from chickens. However, infections of a mountain hawk eagle in 2007 and whooper swans in 2008 suggested that HPAIV infection existed among wild birds. From October 2008, a nationwide survey of wild birds on HPAIV, including monitoring of abnormal mortality and HPAIV detection from wild waterfowl feces and from dead birds, has started. As a result of this survey, HPAIV was isolated from 63 birds of 17 species of waterfowl and raptors in 17 prefectures of Japan from December 2010 to March 2011. Among the 63 birds infected, there were three exotic swans kept in open water under captivity. In all four occasions, epidemiological relationships of HPAIV infections between Japan and Korea, Mongolia and central Russia were indicated from the genetic feature of the viruses. For the HPAIV monitoring in Japan, swans and tufted ducks looked like suitable species for early detection. It was suspected that the dead birds examined were only a small part of the actually infected wild birds. If birds in captivity are sharing environments with wild birds, it will not be possible to prevent infection. Those who are responsible for keeping wild bird species in captivity, especially in open water, will need fundamental reconsideration of management methods.