Molecular characterization and evolutionary dynamics of measles virus sequences isolated from children in Lagos and Ibadan, South Western, Nigeria.

Measles infection is endemic in Nigeria, with outbreaks occurring yearly. Genotype B3 is the dominant genotype and the only genotype characterized from Nigeria. The current study investigated the phylogenetic and Bayesian evolutionary dynamics of Nigerian measles virus Nucleoprotein (N) sequences isolated from Lagos and Ibadan, Nigeria. A total of 120 throat swab samples were analysed by RT-PCR and Sanger sequencing. Phylogenetic analysis and Bayesian demographic reconstructions were done using MEGA and BEAST software. Measles RNA positivity was 14.2% (17/120), age range 0-1 recorded the highest rate with 40.83%. Study sequences clustered within clade B3.1. The evolutionary rate of analysed B3 sequences was 1.108×10, higher posterior density HPD interval (1.462×10 - 7.886×10)subs/site/year. The time to most recent common ancestor (T), was 1991. The Bayesian skyride analysis(BSP) of West African MV cladeB3.1, showed a stable, steady state population demography. This study has reemphasised the dominance of clade B3.1 in Nigeria. We have shown that clade B3.1 was recently introduced into circulation and has a slow population expansion. We advocate for the institution of molecular surveillance country wide in order to help monitor strain diversity and genetic evolution of Measles in Nigeria.