Influenza viruses: High rate of mutation and evolution

Influenza viruses can be classified into three types: A, B, and C. These viruses are similar in morphology, composition, and in their replication processes and are clearly evolutionarily related. Nevertheless, they exhibit major differences in their epidemiology, genetic variability, and evolution. The most dramatic differences are seen on a comparison of influenza A and C viruses. This chapter will review briefly the epidemiology and genetic variability of these two influenza virus types, contrast their rates and patterns of evolution, and consider mechanisms which could account for the differences.