Giuseppe
Emeritus
Highly Pathogenic Avian Influenza Virus (H5N1) Isolated from Whooper Swans, Japan
Yuko Uchida, Masaji Mase, Kumiko Yoneda, Atsumu Kimura, Tsuyoshi Obara, Seikou Kumagai, Takehiko Saito, Yu Yamamoto, Kikuyasu Nakamura, Kenji Tsukamoto, and Shigeo Yamaguchi
Author affiliations: National Institute of Animal Health, Kannondai, Japan (Y. Uchida, M. Mase, T. Saito, Y. Yamamoto, K. Nakamura, K. Tsukamoto, S. Yamaguchi); Japan Wildlife Research Center, Taito-ku, Tokyo, Japan (K. Yoneda); Akita Animal Hygiene Service Center of Akita Prefecture, Akita, Japan ( A. Kimura, T. Obara, S. Kumagai)
On April 21, 2008, four whooper swans were found dead at Lake Towada, Akita prefecture, Japan. Highly pathogenic avian influenza virus of the H5N1 subtype was isolated from specimens of the affected birds. The hemagglutinin (HA) gene of the isolate belongs to clade 2.3.2 in the HA
phylogenetic tree. (...)
Conclusions
Whooper swans breed in northern Eurasia and winter in Europe and eastern Asia i.e., China, the Korean peninsula, and Japan.
In Japan, ≈35,000–38,000 whooper swans spend every winter primarily in Hokkaido, Tohoku, and the Hokuriku area (10).
In the Lake Towada area, ≈300 whooper swans arrive beginning in late October; they leave the area between late March and late April (11).
In late March, summer birds begin to arrive.
According to results of satellite tracking of 8 swans (12), as well as the results of banding studies since 1961 (13), whooper swans that winter in Japan migrate from the northern end of Honshu Island to eastern Hokkaido, by means of Sakhalin, and reach eastern Siberia, where they breed.
To our knowledge, there have been no reports of whooper swans that winter on the Eurasian continent migrating north through Japan.
In light of the migratory route mentioned above, the whooper swans found dead at Lake Towada were most likely recently infected with HPAIV (H5N1) in Japan.
It is unlikely that the swans were infected before they flew to Japan in autumn, maintained the virus within the flock, and then suddenly developed the disease after no apparent infections for several months.
Although the susceptibility of a certain species of birds to a subtype H5N1 virus may be different depending on the virus strain (14), whooper swans as well as mute swans have been considered to be susceptible species to HPAIV (H5N1), as they showed a fulminant course of disease at the outbreak in Germany in 2006 (7).
The possibility that the swans were infected by domestic fowl is low because there has been no report of HPAI among domestic fowl in Japan since the beginning of 2008.
One possible explanation is that other wild birds brought the virus from outside the country.
Although it is not known whether any birds wintering on the continent migrate north through Japan, passage visitor birds such as wader birds migrate from south to north through Japan in spring; summer birds, e.g., egrets, swallows, songbirds, and some raptors, come to Japan from the south in spring for breeding.
Also, the possibility of anthropogenic introduction of virus, such as by inappropriate importation of birds, meats, or materials, cannot be excluded.
In conclusion, genetic analysis demonstrates that the virus that killed the 4 swans in Japan in 2008 is genetically distinguishable from the strains that caused previous poultry outbreaks in Japan, ruling out a possibility of resurgence of previously introduced HPAIV in Japan.
After the incident we describe, 2 other whooper swan cases of HPAIV (H5N1) infection were confirmed in eastern Hokkaido in early May.
Possible involvement of wild birds in the introduction of the virus to Japan requires further scrutiny.
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http://www.cdc.gov/eid/content/14/9/pdfs/08-0655.pdf
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Yuko Uchida, Masaji Mase, Kumiko Yoneda, Atsumu Kimura, Tsuyoshi Obara, Seikou Kumagai, Takehiko Saito, Yu Yamamoto, Kikuyasu Nakamura, Kenji Tsukamoto, and Shigeo Yamaguchi
Author affiliations: National Institute of Animal Health, Kannondai, Japan (Y. Uchida, M. Mase, T. Saito, Y. Yamamoto, K. Nakamura, K. Tsukamoto, S. Yamaguchi); Japan Wildlife Research Center, Taito-ku, Tokyo, Japan (K. Yoneda); Akita Animal Hygiene Service Center of Akita Prefecture, Akita, Japan ( A. Kimura, T. Obara, S. Kumagai)
On April 21, 2008, four whooper swans were found dead at Lake Towada, Akita prefecture, Japan. Highly pathogenic avian influenza virus of the H5N1 subtype was isolated from specimens of the affected birds. The hemagglutinin (HA) gene of the isolate belongs to clade 2.3.2 in the HA
phylogenetic tree. (...)
Conclusions
Whooper swans breed in northern Eurasia and winter in Europe and eastern Asia i.e., China, the Korean peninsula, and Japan.
In Japan, ≈35,000–38,000 whooper swans spend every winter primarily in Hokkaido, Tohoku, and the Hokuriku area (10).
In the Lake Towada area, ≈300 whooper swans arrive beginning in late October; they leave the area between late March and late April (11).
In late March, summer birds begin to arrive.
According to results of satellite tracking of 8 swans (12), as well as the results of banding studies since 1961 (13), whooper swans that winter in Japan migrate from the northern end of Honshu Island to eastern Hokkaido, by means of Sakhalin, and reach eastern Siberia, where they breed.
To our knowledge, there have been no reports of whooper swans that winter on the Eurasian continent migrating north through Japan.
In light of the migratory route mentioned above, the whooper swans found dead at Lake Towada were most likely recently infected with HPAIV (H5N1) in Japan.
It is unlikely that the swans were infected before they flew to Japan in autumn, maintained the virus within the flock, and then suddenly developed the disease after no apparent infections for several months.
Although the susceptibility of a certain species of birds to a subtype H5N1 virus may be different depending on the virus strain (14), whooper swans as well as mute swans have been considered to be susceptible species to HPAIV (H5N1), as they showed a fulminant course of disease at the outbreak in Germany in 2006 (7).
The possibility that the swans were infected by domestic fowl is low because there has been no report of HPAI among domestic fowl in Japan since the beginning of 2008.
One possible explanation is that other wild birds brought the virus from outside the country.
Although it is not known whether any birds wintering on the continent migrate north through Japan, passage visitor birds such as wader birds migrate from south to north through Japan in spring; summer birds, e.g., egrets, swallows, songbirds, and some raptors, come to Japan from the south in spring for breeding.
Also, the possibility of anthropogenic introduction of virus, such as by inappropriate importation of birds, meats, or materials, cannot be excluded.
In conclusion, genetic analysis demonstrates that the virus that killed the 4 swans in Japan in 2008 is genetically distinguishable from the strains that caused previous poultry outbreaks in Japan, ruling out a possibility of resurgence of previously introduced HPAIV in Japan.
After the incident we describe, 2 other whooper swan cases of HPAIV (H5N1) infection were confirmed in eastern Hokkaido in early May.
Possible involvement of wild birds in the introduction of the virus to Japan requires further scrutiny.
-
http://www.cdc.gov/eid/content/14/9/pdfs/08-0655.pdf
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