Genetic Characterizations and Molecular Evolution of the Measles Virus Genotype B3's Hemagglutinin (H) Gene in the Elimination Era.

Measles virus (MeV) genotype B3 is one globally significant circulating genotype. Here, we present a systematic description of long-term evolutionary characterizations of the MeV genotype B3's hemagglutinin (H) gene in the elimination era. Our results show that the B3 H gene can be divided into two main sub-genotypes, and the highest intra-genotypic diversity was observed in 2004. MeV genotype B3's H gene diverged in 1976; its overall nucleotide substitution rate is estimated to be 5.697 × 10 substitutions/site/year, and is slowing down. The amino acid substitution rate of genotype B3's H gene is also decreasing, and the mean effective population size has been in a downward trend since 2000. Selection pressure analysis only recognized a few sites under positive selection, and the number of positive selection sites is getting smaller. All of these observations may reveal that genotype B3's H gene is not under strong selection pressure, and is becoming increasingly conservative. MeV H-gene or whole-genome sequencing should be routine, so as to better elucidate the molecular epidemiology of MeV in the future.