Molecular epidemiology of tick-borne encephalitis virus inIxodes ricinus ticks in Lithuania

Abstract

In Lithuania, 171-645 serologically confirmed cases of tick-borne encephalitis occurred annually [Mickiene et al. (2001): Eur J Clin Microbiol Infect Dis 20:886-888] in 1993-1999, and the tick-borne encephalitis virus (TBEV) seroprevalence in the general population was found previously to be 3.0% [Juceviciene et al. (2002): J Clin Virol 25:23-27]. To assess the risk for TBEV virus infection in Lithuania and to characterize the agent a panel of 3,234 ticks combined into 436 pools [Juceviciene et al., 2005] were tested for presence of TBEV RNA by a nested RT-PCR targeting at the NS5 gene. Six pools were confirmed positive and the prevalence of the infected ticks was 0.2% (if one tick per pool [Juceviciene et al., 2005] was considered positive) and the proportion of positive tick pools was 1.4%. The prevalence of the infected ticks in the Panevezys, Siauliai, and Radviliskis regions (in central Lithuania) was 0.1%, 0.4%, and 1.7% corresponding with a higher TBE disease burden in these regions. The 252-nucleotide NS5-region amplicons, and a longer sequence (737 nucleotides) obtained from one sample from the PrM-E gene region, were sequenced. Phylogenetic analysis of the latter showed that all western type TBEV PrM-E sequences, including the Lithuanian strains, were monophyletic, showed no clustering and had very little variation. The NS5 sequences, although identical within one locality, did not show any mutations common to strains from the two Lithuanian regions, nor could any geographical clustering be found among western type TBEV strains from other areas.

Phylogeographic Characterization of Tick-Borne Encephalitis Virus from Patients, Rodents and Ticks in Slovenia

“…Previous studies of genetic diversity of TBEV have also shown that multiple sequence variants are present in relatively small geographical areas. Genetic variability of the Slovenian TBEV variants is similar to those reported in previous studies (nucleotide sequence identity 96.1 to 100%) [6], [7], [10], [15], [16]. Our results also revealed that TBEV variants in Slovenia show correlation between geographical and phylogenetic clustering which is in concordance with previous reports [8].…”

Detection and Characterization of Tick-Borne Encephalitis Virus in Baltic Countries and Eastern Poland

“…In other European countries the overall reported prevalence rates of TBEV in I. ricinus were 0.5%–2.0% in Bavaria [25], 0.2%–1% in Finland [26], and 0.47% in Slovenia [27]. Infection rates of 0.1%–1.7% and similar to the ones in the present study were previously reported from Lithuania [28], while a higher prevalence of 2.4%–3.7% and 1.6% were reported from Latvia and Poland, respectively [14], [24]. The differences in TBEV prevalence rates in different countries may, however, be explained by different methods of virus detection in ticks as well as fluctuations in TBEV prevalence during collection seasons and years.…”

Prevalence of tick‐borne encephalitis virus in Ixodes Ricinus from a novel endemic area of North Eastern Italy

“…The nucleotide identity, as evaluated by the E gene analysis, was as high as 97.7-98% among Swedish strains [Haglund et al, 2003], while the deduced amino acidic sequences were 100% identical. Similar figures were obtained in Finland [Han et al, 2001], in Lithuania [Han et al, 2005], and in Estonia, where a 98.1-98.7% identity was confirmed in the E gene [Golovljova et al, 2004]. Thus, it is expected that, under usual circulation conditions, a low degree of genetic variability should be detected.…”