Inferring Evolutionary Timescale of Omsk Hemorrhagic Fever Virus.

Until 2020, there were only three original complete genome (CG) nucleotide sequences of Omsk hemorrhagic fever virus (OHFV) in GenBank. For this reason, the evolutionary rate and divergence time assessments reported in the literature were based on the E gene sequences, but notably without temporal signal evaluation, such that their reliability is unclear. As of July 2022, 47 OHFV CG sequences have been published, which enables testing of temporal signal in the data and inferring unbiased and reliable substitution rate and divergence time values. Regression analysis in the TempEst software demonstrated a stronger clocklike behavior in OHFV samples for the complete open reading frame (ORF) data set (R = 0.42) than for the E gene data set (R = 0.11). Bayesian evaluation of temporal signal indicated very strong evidence, with a log Bayes factor of more than 5, in favor of temporal signal in all data sets. Our results based on the complete ORF sequences showed a more precise OHFV substitution rate (95% highest posterior density (HPD) interval, 9.1 × 10-1.8 × 10 substitutions per site per year) and tree root height (416-896 years ago) compared with previous assessments. The rate obtained is significantly higher than tick-borne encephalitis virus by at least 3.8-fold. The phylogenetic analysis and past population dynamics reconstruction revealed the declining trend of OHFV genetic diversity, but there was phylogenomic evidence that implicit virus subpopulations evolved locally and underwent an exponential growth phase.