Reassortment between human A(H3N2) viruses is an important evolutionary mechanism
ABSTRACT Phylogenetic relationships of whole genomes of H3N2 viruses circulating in Germany during a 6-year period from 1998 to 2005 revealed the co-circulation of different lineages of viruses. Multiple reassortment events occurred during this time between viruses belonging to different lineages or different subgroups. Strains isolated during 1998-1999 were characterised by a surprisingly high heterogeneity and multiple reassortment events. Seventy percent of the examined 1998-1999 viruses had completely different genome compositions. To our knowledge, such an exceptional high proportion of different reassortant strains, encompassing all eight genome segments, have not been described before. In contrast, only one reassortant virus was prevalent during 1999-2000 even though two of the three 1998-1999 lineages were co-circulating. Reassortant viruses were isolated also in each of the other seasons. However, the proportion of H3N2 viruses with different genome compositions varied from season to season. Strains with a reassortant NA played an important role and were also detected during 2003-2004 and 2004-2005 accounting for 45% and 70% of the circulating H3N2 viruses, respectively. Moreover, different reassortment events occurring during these seasons included also the PB1, PB2 and NP genes. The results presented here emphasize that genetic reassortment is an important factor in the evolution of H3N2 viruses and highlight the need for a comprehensive analysis of influenza viruses, especially with regard to the annual vaccine composition.
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ABSTRACT: Reassortment is an important evolutionary route for influenza A viruses to generate pandemic strains. The pre-requisite for reassortment to occur is co-infection of different influenza virus strains in the same host population. Empirical evidence suggests that co-circulation of influenza A virus strains is common and co-infection in patients has been reported. Whether a novel virus can successfully spread among a host population is determined by its life-history (infectivity and infectious period). It is also well known that different influenza A strains interfere through the immune response of human body cells. The reassortant virus strain generated from co-infections deviates dramatically in antigenic and genetic properties from its parental strains such that human populations have limited immunity against it. We consider a mathematical model which includes two strains of influenza virus within a standard SIR model and integrate life history and cross-immunity into the evolutionary dynamics of influenza virus. We assume that, following primary infection by one strain and recovery, individuals are susceptible to secondary infection by the other strain only but with reduced probability due to cross-immunity. Co-infection is included to examine how life-history and cross-immunity interplay to regulate the co-circulation and co-infection of different influenza A virus strains in human populations. Further, we introduce novel strains via reassortment and investigate how the opportunities of a reassortant strain developing into a pandemic are constrained by its life-history and the residual immunity within human populations. We find that though the probability of pandemic emergence via reassortment increases with transmissibility of reassortant strains and the rate of reassortment, the existence of cross-immunity acquired through previous infections or vaccination can greatly constrain pandemic emergence.03/2013; 5(1):20-33. DOI:10.1016/j.epidem.2012.10.003
- Epidemics 01/2013; 5:20-33. · 2.38 Impact Factor
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ABSTRACT: Analyses and visualizations by the ISSCOR method of the influenza virus hemagglutinin genes of three different A-subtypes revealed some rather striking temporal (for A/H3N3), and spatial relationships (for A/H5N1) between groups of individual gene subsets. The application to the A/H1N1 set revealed also relationships between the seasonal H1, and the swine-like novel 2009 H1v variants in a quick and unambiguous manner. Based on these examples we consider the application of the ISSCOR method for analysis of large sets of homologous genes as a worthwhile addition to a toolbox of genomics-it allows a rapid diagnostics of trends, and possibly can even aid an early warning of newly emerging epidemiological threats.Comptes rendus biologies 03/2012; 335(3):180-93. DOI:10.1016/j.crvi.2012.01.001 · 1.68 Impact Factor