Arch Virol (1998) 143: 1773–1782
Continued circulation of reassortant H1N2 inﬂuenza viruses
in pigs in Japan
, Y. Kawaoka
, A. Vines
, H. Ishikawa
, T. Asai
, and H. Kida
Department of Veterinary Public Health, Faculty of Agriculture,
Tottori University, Tottori, Japan
Department of Virology and Molecular Biology, St. Jude Children’s Research Hospital,
Memphis, Tennessee, U.S.A.
Department of Pathology, University of Tennessee, Memphis, Tennessee, U.S.A.
Kanagawa Laboratory of Animal Health, Yamato, Kanagawa, Japan
Zen-Noh Institute of Animal Health, Sakura, Ciba, Japan
Laboratory of Microbiology, Department of Disease Control,
Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
Accepted May 6, 1998
Summary. In 1991 and 1992, H1N2 inﬂuenza A viruses were isolated from the
lungs of pigs with overt signs of respiratory disease at farms in the Chiba and
Kanagawa prefectures of Japan. To determine the genetic origin of these isolates,
we phylogenetically analyzed partial nucleotide sequences of their genes. The
results indicate that inﬂuenza viruses possessing the N2 of human inﬂuenza virus
and seven other gene segments of classical H1N1 swine inﬂuenza virus, which
were ﬁrst isolated in 1980, have become established in Japanese pigs.
The genome of inﬂuenza A viruses consists of eight single-stranded RNA seg-
ments of negative sense . Mixed infection with different inﬂuenza viruses in a
single cell can lead to reassortment of the genomic segments, as demonstrated by
experimental co-infection of ducks  and pigs . In nature, the H2N2 Asian
and H3N2 Hong Kong pandemic inﬂuenza strains provide striking examples
of genetic reassortants involving human and avian viruses [41, 46]. Pigs are
Present address: Department of Pathobiological Sciences, School of Veterinary
Medicine, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.