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32 A. Bormane, A. Zeltiņa, I. Lucenko et al. Table 1. Number of ticks (samples) removed from patients for TBE tests in 2002 (Vaccination service, by dates of registration) Month Adult TBEV TBEV Nymphs TBEV TBEV Larvae TBEV imagos positive prevalence positive prevalence positive imagos in imagos nymphs in nymphs larvae (% ± SD) (% ± SD) April 10 2 20.0 ± 13.3 7 1 14.3 ± 14.3 0 - May 72 37 51.4 ± 5.9 39 21 53.9 ± 8.1 0 - June 101 41 40.6 ± 4.9 88 49 55.7 ± 5.3 6 4 July 125 31 24.8 ± 3.9 96 28 29.2 ± 4.7 3 2 August 47 16 34.0 ± 7.0 38 17 44.7 ± 8.2 3 0 September 35 10 28.6 ± 7.8 21 11 52.4 ± 11.2 0 - October 5 2 40.0 ± 24.5 4 1 25.0 ± 25.0 0 - total 395 139 35.2 ± 2.4 293 128 43.7 ± 2.9 12 6 of patients were likely to be bitten in the whole territory of Latvia (including eastern regions). About 1 % of patients received a tick bite abroad. TBE virus investigations with ELISA TBE virus prevalence in adult questing ticks collected from vegetation was 9.2 ± 1.5 % (34/369) in 2002 and 5.1 ± 1.2 % (17/336) in 2003. In 2002, the TBEV prevalence in I. persulcatus was higher than in I. ricinus (accordingly 29.0 ± 5.8 % and 5.2 ± 1.3 %), but in 2003 only one (0.9 ± 0.9 %) I. persulcatus tick (female) and 5.2 ± 1.8 % of I. ricinus ticks were TBEV positive. The results of both years indicate a higher TBEV prevalence in females of both species than in males. In 2002, the TBEV prevalence in I. ricinus females was 6.1 ± 1.9 % (in males – 4.2 ± 1.7 %); the TBEV prevalence in I. persulcatus females was 60 ± 9.1 % (in males – 0 %). In 2003, the TBEV prevalence in I. ricinus females was 13 ± 3.2 % (in males – 0.9 %); the TBEV prevalence in I. persulcatus females was 1.6% (in males – also 0 %). However, as the number of investigated ticks was low, the standard deviation was too high to show statistical significance. The TBE virus prevalence rate in ticks (samples per patient) removed from patients in the Vaccination service was higher: in 2002, 35.0 % (136/385) of adults, 42.7 % (127/303) of nymphs and 6 of 12 larvae were TBE positive. However, in 2003, the TBEV prevalence in ticks was 23.9 % (240/1005) for adults, 14.8 % (203/1374) for nymphs and 12 % (3/25) for larvae. The TBEV prevalence in tested ticks changed during the whole tick activity season: the highest numbers of infected adults and nymphs brought to the Vaccination service were registered in the first part of season with the peak prevalence levels in June and July (accordingly 46 % to 59 % and 27 % to 28 %). TBE virus investigations with RT-PCR Twelve tick pools (five ticks per pool) and 22 tick homogenates from patients were investigated. Seventeen samples of 22 tick homogenates were previously identified as TBEV-positive by the ELISA test. The RT-PCR targeted TBEV 5'NCR gene fragment pointed to TBEV prevalence in
Tick-borne encephalitis in Latvia 2002 - 2003 33 Table 2. Number of ticks (samples) removed from patients for TBE tests in 2003 (Vaccination service, by dates of registration) Month Adult TBEV TBEV Nymphs TBEV TBEV Larvae TBEV imagos positive prevalence positive prevalence positive imagos in imagos nymphs in nymphs larvae (% ± SD) (% ± SD) April 6 2 33.3 ± 21.8 3 0 0 0 - May 92 36 39.1 ± 5.1 63 5 7.9 ± 3.6 1 0 June 132 61 46.2 ± 4.4 173 46 26.6 ± 3.4 0 - July 153 90 58.8 ± 4.0 295 83 28.1 ± 2.6 2 0 August 200 35 17.5 ± 2.7 213 25 11.7 ± 2.2 12 1 September 394 13 3.3 ± 0.9 595 38 6.4 ± 1.0 9 2 October 27 3 11.1 ± 6.2 32 6 18.8 ± 7.0 1 0 December 1 0 0 0 0 0 0 - total 1005 240 23.9 ± 1.4 1347 203 14.8 ± 1.0 25 3 seven tick pools (of 12), but only in one sample of previously positive tick homogenates from patients. The RT-PCR targeted TBEV NS5 gene fragment pointed to TBEV prevalence in three tick pools (of 12). The 5'NCR-RT-PCR method results indicated different PCR product lengths for the positive control-containing K23 TBEV strain and for the one containing the Sofjyn strain (accordingly ~178 bp and ~215 bp). The length of amplicone from the K23-containing sample was identical to that described in the literature (Han et al. 2001), but the PCR amplicone from the Sofjyn-containing sample was longer than theoretically expected (Fig. 3). Lengths of amplification products of the NS5 gene fragment from the positive controlcontaining K23 TBEV strain was also identical to those given in literature but the positive control-containing Sofjyn TBEV strain did not show any positive results. Fig. 3. Tick pools detected by nested 5'NCR-RT-PCR.
Page 1 and 2: Acta Universitatis Latviensis, Biol
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