Distribution of Far-Eastern TBEV subtype strains in the former Soviet UnionArchived
European and Asian viruses within the tick-borne encephalitis Flavivirus complex are known to show temporal, spatial and phylogenetic relationships that imply a clinal pattern of evolution.
Belyaeva, IV and Kovalev, SY (Laboratory of Molecular Genetics, Department of Biology, Ural State University, Yekaterinburg, Russia); Kokorev, VS (Arbovirus Laboratory, Yekaterinburg Research Institute of Viral Infections, Yekaterinburg, Russia)Journal of General Virology, 2010, 91: 2941-2946; doi:10.1099/vir.0.023879-0
European and Asian viruses within the tick-borne encephalitis Flavivirus complex are known to show temporal, spatial and phylogenetic relationships that imply a clinal pattern of evolution. However, the isolation of recognized Far-Eastern TBEV strains in the European region of the former Soviet Union (SU), i.e. thousands of kilometers west of the region in which they are considered endemic, appears to contradict this concept. Here, we present a parsimonious explanation for this apparent anomaly based on analysis of the dates and regions in which these non-endemic strains were isolated, together with their phylogenetic relationships and the records of re-distribution of animals under the All-Union Programme for acclimatisation of game animals within the former SU. Our evidence supports the concept that the anomalous distribution of Far-Eastern strains in Europe and Siberia arose primarily as the result of large-scale westward re-distribution of game animals for economic purposes.
VBORNET comment: 2010-12-07
This is an interesting study since many investigations have been conducted these last decades on European TBEV (EU-TBEV) transmitted by Ixodes ricinus but little information is available on other Eurasian strains like Far-Eastern TBEV (FE-TBEV) and Siberian TBEV (S-TBEV) transmitted by Ixodes persulcatus. In this paper, a nice effort is done to link molecular epidemiological data obtained by genotyping and localizing these virus strains and possible environmental factors explaining such observed patterns (natural animal migrations versus anthropogenic changes acting on vertebrate host location for ticks). The authors show that most FE-TBEV emergence events have been located in the western part of Europe, where S-TBEV is commonly endemic. Such emergence could be explained by the all-Union program of acclimatization and resettlement of game mammals and birds (reservoir hosts of FE-TBEV) from east to west, from the beginning of the 1930s until the middle of the 1990s. Although this explanation is the most likely there is no evidence of such phenomenon like the analysis of isolates from wild transferred animals. In addition, since the program finished in the 1990s, the existence of recent foci of FE-TBEV in the Sverdlovsk region remains unexplained. Far eastern TBE viruses have been also detected in Estonia, and their presence was not explained (see e.g. Golovljova et al., 2004. 74(4): 580-588; Golovljova et al., 2008. Int. J. Med. Microbiol., 298: 108-120). The article brings however some piece of evidence.
