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Journal of Clinical Microbiology, December 2003, p. 5770-5773, Vol. 41, No. 12
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.12.5770-5773.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Cocirculation and Evolution of Two Lineages of Influenza B Viruses in Europe and Israel in the 2001-2002 Season
X. Sherry Chi, Trentice V. Bolar, Ping Zhao, Ruth Rappaport, and Sheau-Mei Cheng*
Clinical Immunology and Virology Department, Applied Immunology and Microbiology Division, Wyeth Vaccine Research, Pearl River, New York 10965
Received 18 July 2003/
Returned for modification 22 August 2003/
Accepted 11 September 2003

ABSTRACT
Forty-nine influenza B virus isolates collected in Belgium,
Finland, Spain, and Israel during the 2001-2002 winter season
were categorized into either of two lineages, B/Yamagata/16/88
or B/Victoria/2/87, based on the phylogenetic studies of HA1
sequences. The data trace the geographic spread of B/Victoria/2/87-like
viruses and support the emergence of B/Hong Kong/1351/02-like
viruses, possibly due to selective advantages of reassortment.

TEXT
Influenza epidemics are caused by rapid evolution of the viral
genome and continue to play a significant role in the annual
frequency of mortality and morbidity as a result of respiratory
tract infection. Both influenza A virus and influenza B virus
undergo antigenic drift, and influenza A virus is capable of
antigenic shift resulting from genetic reassortment between
different subtypes (
2). On the other hand, reassortment of influenza
B viruses has been observed between cocirculating influenza
B virus strains of different lineages (
5,
6,
12,
17). Monitoring
antigenic and genetic variations of circulating influenza viruses
is critical for the selection of annual vaccine strains. Recent
isolates of influenza B viruses, for example, fall into two
major phylogenetic lineages: the B/Victoria/2/87 lineage or
the B/Yamagata/16/88 lineage (
12). The former group of viruses
was found primarily in East Asia during the last decade. In
contrast, the B/Yamagata/16/88-like viruses have been found
worldwide during the same period (
11). Increased incidence of
B/Victoria/2/87 viruses in the regions beyond Asia in the 2001-2002
season resulted in the World Health Organization recommendation
of B/Hong Kong/330/01 (a member of the B/Victoria/2/87 lineage)
for the vaccine strain for both the Northern and Southern Hemispheres
in the 2002-2003 season (
14,
15).
The hemagglutinin (HA) of an influenza virus surface antigen is synthesized as a single polypeptide, which is subsequently cleaved into two chains, HA1 and HA2. The antigenic variation of the HA protein of influenza viruses occurs predominantly in the HA1 domain (13). In this report, we determined the nucleotide sequence of the HA1 gene segment of 49 influenza B viruses circulating in Europe and Israel during the 2001-2002 winter season. The isolates were derived from respiratory specimens in the placebo group, collected during an experimental influenza vaccine efficacy trial conducted concurrently in three European countries, Spain, Belgium, and Finland, as well as in Israel. Briefly, viral RNA was extracted from influenza viruses propagated once in MDCK cells with the aid of a 6700 automatic nucleic acid workstation (Applied Biosystems Inc., Foster City, Calif.). The type and quantities of the viruses were determined for all the specimens using a real-time PCR method (data not shown). Coinfection of influenza A and B was found only in a very few cases (S.-M. Cheng, unpublished data), and the dominant type was chosen to be characterized further. HA1 fragments were amplified by reverse transcription (RT)-PCR using the Titan One tube RT-PCR system (Roche Diagnostics Corp., Indianapolis, Ind.) with oligonucleotides conserved in several influenza B virus strains: 5'-ATAACATCGTCAAACTCACC-3' and 5'-GCACCATGTAATCAACAACA-3'. DNA sequencing was performed using a 3100 genetic analyzer and BigDye Terminator Mix v3.0 (Applied Biosystems Inc.) with both PCR primers and two additional primers, 5'-GTTCTGTCGTGCATTATAGG-3' and 5'-GCAACAATGGCTTGGGCTGT-3'. This fragment (from nucleotide 98 to 836) corresponds to the coding region of amino acids 7 to 253 of the HA1 protein. We also selectively amplified and sequenced HA1 fragments directly from five nasal swab specimens, and the result shows a 100% match of the nucleotide sequence with that from cultures (data not shown).
Alignment of multiple sequences was performed by the ClustalV method, which groups sequences into clusters by examining sequence distances between all pairs (4). The phylogenetic tree was then constructed by a neighbor-joining method using MegAlign5.03 software (DNASTAR, Inc., Madison, Wis.). The result indicated that there were two genetically distinct lineages of influenza B viruses among the specimens (Fig. 1). The majority of the B viruses (63%) belonged to the B/Yamagata/16/88 lineage (represented by our reference strain, B/Victoria/504/00, to which the nucleotide sequence identity of the specimens ranged from 94.9 to 99.7%). The remaining viruses (37%) belonged to the B/Victoria/2/87 lineage (represented by our two reference strains B/Hong Kong/330/01 and B/Hong Kong/1351/02, to which the sequence identity of the specimens ranged from 98.9 to 99.7%).
The appearance of B/Victoria/2/87 lineage in these European
countries and Israel documented the spread of this lineage beyond
Asia during the 2001-2002 influenza season. This was also observed
in Northern Italy (
1) and several other countries in Europe
(
10) as well as in North America (
12). It is noteworthy that
Israel, the country with the earliest and greatest incidence
of B/Hong Kong-like viruses, is located closest to East Asia.
On the other hand, the countries with lower incidences (Spain
and Belgium) or even an absence (Finland) of B/Hong Kong-like
viruses are progressively farther away from East Asia, suggesting
the geographic trail of viral spreading. These data suggest
that Israel may have been one possible route accounting for
the spread of the B/Hong Kong viruses through Europe. Among
the B/Victoria/2/87-like group of specimens (
n = 18), B/Hong
Kong/1351/02-like viruses (
n = 14) were found to be at least
three times more prevalent than B/Hong Kong/330/01-like viruses
(
n = 4). We also observed that as the flu season progressed,
B/Hong Kong/1351/02-like viruses became more dominant (data
not shown). Although the number of specimens in this study is
relatively small, we have data from other regions of the world
that suggested a similar trend (X. S. Chi, unpublished data).
We also selectively analyzed neuraminidase gene segments from seven clinical specimens, amplified by RT-PCR with oligonucleotides 5'-GCTACCTTCAACTATACAAACG-3' and 5'-AACGAGGGTATGTCCACTCC-3' and found that B/Hong Kong/1351/02 is a reassortant of two influenza B lineages, B/Victoria/2/87 and B/Yamagata/16/88 (Table 1). The HA gene of B/Hong Kong/1351/02 derives from the B/Victoria/2/87 lineage, similar to its predecessor, B/Hong Kong/330/01, whereas the neuraminidase gene derives from the B/Yamagata/16/88 lineage, similar to its predecessor, B/Victoria/504/00. These results are in agreement with those reported by Shaw et al. (12). The reassortment between two lineages of influenza B viruses has been reported previously (6, 16), and it is thought that such influenza reassortants have selective advantages in viral growth, replication, or stability. The pattern of spreading of B/Hong Kong/1351/02-like viruses in our study and others (10) suggests that this reassortant may become more dominant worldwide in the 2002-2003 season.
In recent years, molecular methods have been developed and successfully
applied in the diagnosis and surveillance of influenza viruses
(
3). Here, we employed a high-throughput molecular method combining
RT-PCR and DNA sequencing, which provides an alternative to
the classical hemagglutinin inhibition assay with specific antisera
for determining the phylogenetic relationship of influenza virus
isolates. Furthermore, our results reveal detailed genetic information
of viral surface protein. We found, for example, some variations
in the deduced amino acid sequence of the HA1 protein in our
specimens compared to that of reference strains obtained from
the Influenza Sequence Database of the Los Alamos National Laboratory.
Table
2 shows a summary of all the amino acid variations and
the estimated frequencies of the dominant changes in the HA1
sequence of our clinical specimens. Among the B/Victoria/504/00-like
group of specimens, there are 28 variations in the HA1 sequence
compared with that of the reference strain, with 6 of them being
dominant (>35%). One particular specimen, WV5, has the most
variations compared to the reference strain. A BLAST search
in the database revealed that WV5 has a close relationship with
a subgroup of the Yamagata/16/88 lineage, which includes recent
circulating strains, such as B/New York/47/01, B/Hong Kong/557/00,
and B/Argentina/69/01. It is apparent that there are more variations
in the HA1 sequence of the B/Victoria/504/00-like group than
in the two B/Hong Kong-like groups, indicating more extensive
antigenic drift in the former group of viruses. This observation
is in agreement with the hypothesis that new antigenic variants
are generated in order to escape existing human immunity (
5,
8). A notable variation among the sequences of the B/Yamagata
lineage (group 1) is Asp126, which was found in 58% of the isolates
studied. The amino acid residue Asn at position 126 had been
conserved in B/Yamagata strains for 10 years (
5), and a previous
study by Nakagawa et al. suggested that a point mutation at
position 126 resulted in altered viral antigenicity (
9). The
variations at position 58, 126, and 175 were also reported recently
by Ansaldi et al. (
1). However, the variation at position 88
was not found in their specimens. In the group of B/Victoria
lineage, nearly all sequences from clinical specimens contain
the amino acid Asn at position 197. Interestingly, as a result
of this substitution, the stretch of three amino acid residues
changes from XXT to NXT (where X is any amino acid), and the
latter becomes a possible
N-glycosylation site. Such an amino
acid substitution at position 197 has also been observed before
and was suggested to play an important role in the determination
of antigenicity (
5,
7). In addition, a predominant change at
position 159 in the B/Hong Kong/1351/02 group was also detected,
which has not been reported previously. Three signature amino
acids, Arg116, Asn121, and Glu164 of B/Hong Kong/330/01 (
12),
are all conserved in our specimens.
Nucleotide sequence accession numbers.
Nucleotide sequences of the HA gene can be found in GenBank
with the following accession numbers: B/Victoria/2/87,
M22943;
B/Yamagata/16/88,
M36105; B/Victoria/504/00, ISDN20057; B/Hong
Kong/330/01,
AF532549; B/Hong Kong/1351/02,
AF532545; B/Hong
Kong/557/00,
AF532553; B/Argentina/69/01,
AF532525; B/New York/47/01,
AY139048. Clinical isolates: WV106, AY375988; WV107, AY375989;
WV109, AY375990; WV114, AY375991; WV122, AY375992; WV124, AY375993;
WV126, AY375994; WV133, AY375995; WV135, AY375996; WV137, AY375997;
WV142, AY375998; WV143, AY375999; WV145, AY376000; WV146, AY376001;
WV150, AY376002; WV153, AY376003; WV158, AY376004; WV161, AY376005;
WV166, AY376006; WV169, AY376007; WV170, AY376008; WV174, AY376009;
WV183, AY376010; WV187, AY376011; WV194, AY376012; WV22, AY376013;
WV26, AY376014; WV27, AY376015; WV29, AY376016; WV33, AY376017;
WV34, AY376018; WV36, AY376019; WV4, AY376020; WV41, AY376021;
WV42, AY376022; WV43, AY376023; WV45, AY376024; WV5, AY376025;
WV50, AY376026; WV51, AY376027; WV56, AY376028; WV57, AY376029;
WV65, AY376030; WV66, AY376031; WV67, AY376032; WV69, AY376033;
WV70, AY376034; WV73, AY376035; WV78, AY376036.

ACKNOWLEDGMENTS
We thank Giuseppe Palladino for providing wild-type influenza
reference strains and Fenglan Li for technical assistance.

FOOTNOTES
* Corresponding author. Mailing address: Wyeth Vaccine Research, 401 N. Middletown Rd., Bldg. 180, Pearl River, NY 10965. Phone: (845) 602-5115. Fax: (845) 602-5296. E-mail:
chengsm{at}wyeth.com.


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Journal of Clinical Microbiology, December 2003, p. 5770-5773, Vol. 41, No. 12
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.12.5770-5773.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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