Molecular evolution of the tick-borne encephalitis and Powassan viruses |
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Authors: | E L Subbotina V B Loktev |
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Institution: | 1.Vector State Research Center of Virology and Biotechnology,Koltsovo, Novosibirsk oblast,Russia;2.Institute of Cytology and Genetics,Siberian Branch of the Russian Academy of Sciences,Novosibirsk,Russia |
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Abstract: | Issues associated with newly emerging viruses, their genetic diversity, and viral evolution in modern environments are currently
attracting growing attention. In this study, a phylogenetic analysis was performed and the evolution rate was evaluated for
such pathogenic flaviviruses endemic to Russia as tick-borne encephalitis virus (TBEV) and Powassan virus (PV). The analysis
involved 47 nucleotide sequences of the TBEV genome region encoding protein E and 17 sequences of the PV NS5-encoding region.
The nucleotide substitution rate was estimated as 1.4 × 10−4 and 5.4 × 10−5 substitutions per site per year for the E protein-encoding region of the TBEV genome and for the NS5 genome region of PV,
respectively. The ratio of non-synonymous to synonymous nucleotide substitutions (dN/dS) in viral sequences was calculated
as 0.049 for TBEV and 0.098 for PV. The highest dN/dS values of 0.201–0.220 were found in the subcluster of Russian and Canadian
PV strains, and the lowest value of 0.024 was observed in the cluster of Russian and Chinese strains of the Far Eastern TBEV
genotype. Evaluation of time intervals between the events of viral evolution showed that the European subtype of TBEV diverged
from the common TBEV ancestor approximately 2750 years ago, while the Siberian and Far Eastern subtypes emerged approximately
2250 years ago. The PV was introduced into its natural foci of the Russian Primorskii krai only approximately 70 years ago;
these strains were very close to Canadian PV strains. The pattern of PV evolution in North America was similar to the evolution
of the Siberian and Far Eastern TBEV subtypes in Asia. The moments of divergence between major genetic groups of TBEV and
PV coincide with historical periods of climate warming and cooling, suggesting that climate change was a key factor in the
evolution of flaviviruses in past millennia. |
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