Virus Research 125 (2007) 98–103
Isolation and phylogenetic analysis of H1N1 swine inﬂuenza
virus isolated in Korea
, C.S. Lee
, K. Jung
, B.K. Kang
, J.S. Oh
, J.H. Lee
, B.K. Park
Research Unit, Green Cross Veterinary Products, Yong-In 449-903, Republic of Korea
Department of Veterinary Medicine Virology Lab, College of Veterinary Medicine and BK21 Program for Veterinary Science,
Seoul National University, Seoul, 151-742, Korea
Research and Development Center, Daewoong Pharmaceutical Co., Ltd., 501-2, Samgye-Ri, Pogok-Myun,
Kyounggi-Do 449-814, Republic of Korea
Animal Genetics, Suwon, Republic of Korea
Interdisciplinary Program in Bioinformatics, Seoul National University, Republic of Korea
Received 22 August 2006; received in revised form 7 November 2006; accepted 17 November 2006
Available online 15 December 2006
A swine inﬂuenza H1N1 virus was isolated from a pig during a severe outbreak of respiratory disease in Korea. All genes of the H1N1 isolate,
including hemagglutinin (HA), neuraminidase (NA), matrix (M), nucleoprotein (NP), non-structural (NS), PA, PB1 and PB2, were of swine origin.
Also, all these genes showed a close phylogenic relationship with those of H1N1 viruses previously isolated from pigs in the United States. These
results suggest that North American swine inﬂuenza virus has actually been transmitted to pigs in Korea.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Swine inﬂuenza virus; H1N1 subtype; Genetic characterization
Inﬂuenza virus is a member of the genus Orthomyxovirus,
family Orthomyxoviridae, and contains negative sense single-
stranded RNA (Lamb and Krug, 1996). There are 16 different
subtypes of hemagglutinin (HA) and 9 different subtypes of
neuraminidase (NA) that can be differentiated both antigeni-
cally and genetically (Choi et al., 2004; Fouchier et al., 2005;
Ma et al., 2006). Currently, three main subtypes of inﬂuenza
A virus circulate in different swine populations throughout the
world: H1N1, H1N2, and H3N2 (Jung and Chae, 2004). The
ﬁrst inﬂuenza A virus isolated from pigs was of the H1N1 sub-
type and related viruses of this subtype are reported to have
infected pigs in many countries (Robert et al., 1987). H1N2
viruses were isolated previously in the United States in 1999, in
France in 1987, in Japan from 1978 to 1980, and in the United
Kingdom in 1994. Furthermore, since 1998, H3N2 viruses have
Corresponding author. Tel.: +82 2 880 1255; fax: +82 2 885 0263.
E-mail address: email@example.com (B.K. Park).
These authors contributed equally to this work.
caused widespread outbreaks of respiratory disease and, in some
cases, abortion among pigs in the USA (Webby et al., 2000). In
Korea, H3N2 and H1N2 swine inﬂuenza viruses were isolated
in 1998 and 2003 (Song et al., 2003; Jung and Chae, 2004),
while H1N1 viruses were isolated from pigs in 2004 (Choi et al.,
2004). Although inﬂuenza A virus infection has been reported
in Korean pigs, there have been no phylogenetic analyses of
H1N1 swine inﬂuenza virus isolates. In this study we describe,
for the ﬁrst time, the isolation of H1N1 inﬂuenza virus from
a pig in Korea and provide a phylogenetic analysis of Korean
In January 2005, an outbreak of acute respiratory disease
occurred in a commercial pig farm with 300 breeding sows
in Kyounggi Province, South Korea. Most of the weanling
and grower pigs in the herd showed typical clinical signs of
inﬂuenza (sneezing, coughing, and abdominal breathing). The
outbreak progressed through the entire facility within 2 weeks.
The pigs had been routinely vaccinated against atrophic rhinitis
and mycoplasmal pneumonia, according to their veterinarian’s
recommendation. Three 45-day-old pigs with severe respiratory
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