The study of influenza virus evolution is not new. In fact, humans have been studying influenza viruses since the beginning of the 18th century. Three types of influenza viruses exist: A, B and C. Influenza B is a strain of influenza virus with the ability to cause severe epidemics. Although influenza A and B have similar structure, genome organization, and epidemiology, they have several important differences which imply that their evolutionary dynamics differ. Unlike influenza A viruses, influenza B viruses almost exclusively affect humans. Influenza B tends to be prominent every 2–3 years. It is important to study influenza B evolution, as research in this area can be used to track epidemics and assist in the creation of effective vaccines.
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Research has shown that evolutionary rates of influenza B are 2–3 times lower than influenza A. Lower evolution rates of influenza B viruses may be because new influenza B strains are not introduced as regularly as new influenza A strains, or because influenza B strains are not as genetically diverse as those of influenza A. Further research must be done on these topics in order to accurately determine the cause of the difference of evolutionary rates between the two strains. Two distinct lineages characterize influenza B viruses. These lineages are named Vic87 and Yam88, and may circulate individually or simultaneously in particular areas and time periods. Vic87 and Yam88 are antigenically and genetically distinct, suggesting that divergent evolution occurred early on in influenza B virus evolution. The separation of influenza B strains into two distinct lineages represents a large-scale genomic event. However, frequent reassortment within lineages complicates …show more content…
These branches are more likely to diverge into various lineages with different genotypes. This allows gene segment exchange between lineages. Occasionally, minor lineages of influenza B virus exist which maintain and increase the diversity to gene pools available for future strains. Analysis of influenza B shows that viral HA in Vic87 lineages experience a higher rate of nucleotide substitution compared to other segments. This suggests influenza B is subject to positive selection as a contributing factor for its evolution. Another aspect that is important in determining influenza B evolution patterns includes immune selection on the HA, NA, and NS proteins. Amino acid fixation rates are high in these proteins, which again suggests positive selection plays a role in the evolution of influenza B viruses. Antigenic drift, a common means of antigenic variation, allows viruses to avoid host immune pressures. Although influenza B strains cause worldwide epidemics frequently, there is no established pattern. Differences in antigenicity between lineages are likely due to amino acid differences within antigenic sites of influenza B viruses. These differences occur both in the HA and NA sequences. Over time, reassortment generates genome configurations that are advantageous and removes deleterious ones, leading influenza B viral
Research has shown that evolutionary rates of influenza B are 2–3 times lower than influenza A. Lower evolution rates of influenza B viruses may be because new influenza B strains are not introduced as regularly as new influenza A strains, or because influenza B strains are not as genetically diverse as those of influenza A. Further research must be done on these topics in order to accurately determine the cause of the difference of evolutionary rates between the two strains. Two distinct lineages characterize influenza B viruses. These lineages are named Vic87 and Yam88, and may circulate individually or simultaneously in particular areas and time periods. Vic87 and Yam88 are antigenically and genetically distinct, suggesting that divergent evolution occurred early on in influenza B virus evolution. The separation of influenza B strains into two distinct lineages represents a large-scale genomic event. However, frequent reassortment within lineages complicates …show more content…
These branches are more likely to diverge into various lineages with different genotypes. This allows gene segment exchange between lineages. Occasionally, minor lineages of influenza B virus exist which maintain and increase the diversity to gene pools available for future strains. Analysis of influenza B shows that viral HA in Vic87 lineages experience a higher rate of nucleotide substitution compared to other segments. This suggests influenza B is subject to positive selection as a contributing factor for its evolution. Another aspect that is important in determining influenza B evolution patterns includes immune selection on the HA, NA, and NS proteins. Amino acid fixation rates are high in these proteins, which again suggests positive selection plays a role in the evolution of influenza B viruses. Antigenic drift, a common means of antigenic variation, allows viruses to avoid host immune pressures. Although influenza B strains cause worldwide epidemics frequently, there is no established pattern. Differences in antigenicity between lineages are likely due to amino acid differences within antigenic sites of influenza B viruses. These differences occur both in the HA and NA sequences. Over time, reassortment generates genome configurations that are advantageous and removes deleterious ones, leading influenza B viral