BAYESIAN COALESCENT INFERENCE DEMONSTRATES DIFFERENCES IN EVOLUTIONARY DYNAMICS AMONG NOROVIRUS GII GENOTYPES

The high incidence of Norovirus (NoV) infections seems to be related with a pattern of continuous lineage turnover of NoV GII.4, with emerging new variants replacing those previously predominant. It has been proposed that other NoV genotypes evolved similarly to GII.4, suggesting the future emergence and widespread of other epidemic genotype variants. In this work, evolutionary rates and population dynamics of different genotypes of NoV GII were inferred by Bayesian coalescent approach. This study provides an insight into the complex evolutionary patterns of different NoV GII genotypes and reports for the first time the evolutionary rates of GII.7, GII.13 and GII.14. The estimated mean evolutionary rate for NoV GII.14 was 10-2 substitution/site/year. For the other NoV genotypes included in the study, GII.3, GII.7 and GII.13, the estimated mean evolutionary rates were lower, with values of 10-3 substitution/site/year. The MCC (maximum clade credibility) tree, showing a time measured phylogenetic relationship among the different genotypes analysed, revealed that GII.4 and GII.14 are the most ancient genotypes, diverging respectively from common TMRCAs (Time to Most Recent Common Ancestor) dated 83 and 54 years ago. Results obtained for GII.4 BSP (Bayesian Skyline Plot) revealed an increment in Net values coincident with the appearance of 2006 and 2009 variants. GII.14 BSP shows a high increase in Net values from year 2009, with peaks in 2010 and 2011. The high evolutionary rate of NoV GII.14, together with its observed population dynamics might be correlated with the current widespread of new genotype variants.