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Published on: April 4, 2011
Molecular analysis of isolates from influenza B outbreaks in the U.S. and Nepal, 2005
L T Daum1, L C Canas, A I Klimov
1Air Force Institute for Operational Health, Brooks City Base, TX 78235, USA. luke.daum@brooks.af.mil
Abstract:
Currently circulating influenza B viruses can be divided into two antigenically and genetically distinct lineages referred to by their respective prototype strains, B/Yamagata/16/88 and B/Victoria/2/87, based on amino acid differences in the hemagglutinin surface glycoprotein. During May and July 2005, clinical specimens from two early season influenza B outbreaks in Arizona and southeastern Nepal were subjected to antigenic (hemagglutinin inhibition) and nucleotide sequence analysis of hemagglutinin (HA1), neuraminidase (NA), and NB genes. All isolates exhibited little reactivity with the B/Shanghai/361/2002 (B/Yamagata-like) vaccine strain and significantly reduced reactivity with the previous 2003/04 B/Hong Kong/330/2001 (B/Victoria-like) vaccine strain. The majority of isolates were antigenically similar to B/Hawaii/33/2004, a B/Victoria-like reference strain. Sequence analysis indicated that 33 of 34 isolates contained B/Victoria-like HA and B/Yamagata-like NA and NB proteins. Thus, these outbreak isolates are both antigenically and genetically distinct from the current Northern Hemisphere vaccine virus strain as well as the previous 2003-04 B/Hong Kong/330/2001 (B/Victoria lineage) vaccine virus strain but are genetically similar to B/Malaysia/2506/2004, the vaccine strain proposed for the coming seasons in the Northern and Southern Hemispheres. Since these influenza B outbreaks occurred in two very distant geographical locations, these viruses may continue to circulate during the 2006 season, underscoring the importance of rapid molecular monitoring of HA, NA and NB for drift and reassortment.
Insights
Influenza B virus outbreaks in 2005 showed genetic and antigenic divergence from vaccine strains. Monitoring hemagglutinin (HA), neuraminidase (NA), and NB genes is crucial for tracking influenza B evolution.
Area of Science:
- Virology
- Molecular Biology
- Epidemiology
Background:
- Influenza B viruses circulate in two distinct lineages: B/Yamagata and B/Victoria.
- Vaccine strains are selected based on prototype strains like B/Yamagata/16/88 and B/Victoria/2/87.
- Antigenic and genetic drift in influenza viruses necessitate ongoing surveillance.
Purpose of the Study:
- To analyze the antigenic and genetic characteristics of influenza B virus isolates from 2005 outbreaks.
- To compare these isolates with contemporary vaccine strains.
- To assess the potential for future circulation and the need for molecular monitoring.
Main Methods:
- Antigenic analysis using hemagglutinin inhibition tests.
- Nucleotide sequence analysis of hemagglutinin (HA1), neuraminidase (NA), and NB genes.
- Comparison of isolate sequences and reactivity with vaccine strains.
Main Results:
- 2005 influenza B isolates showed reduced reactivity to both B/Yamagata-like and B/Victoria-like vaccine strains.
- The majority of isolates were antigenically similar to B/Hawaii/33/2004 (B/Victoria-like).
- Sequence analysis revealed a mix of B/Victoria-like HA and B/Yamagata-like NA and NB genes in most isolates.
- Outbreak isolates were genetically similar to the proposed 2006 vaccine strain B/Malaysia/2506/2004.
Conclusions:
- The 2005 influenza B outbreaks involved viruses antigenically and genetically distinct from current vaccine strains.
- These viruses possess genetic similarities to the proposed 2006 vaccine strain.
- Widespread geographical occurrence suggests continued circulation, highlighting the importance of molecular surveillance for HA, NA, and NB gene variations.
