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Table 1 Summary of published and unpublished data on I. ricinus ticks collected in Sweden, Norway, Finland and Denmark analysed for TBE virus infection

From: Prevalence of tick-borne encephalitis virus in Ixodes ricinus ticks in northern Europe with particular reference to Southern Sweden

    Number of collected ticks Number of TBEV-positive Prevalence estimate (%)   
Country Collection year Locality Nymphs Males Females Total Pools Positive pools Positive nymphs Positive adults MIR nymphs MIR adults MIR all Method Reference
Sweden 1958 96 km NE of Stockholm (9 sites) 35 898 933 24 4 1 3 2.86 0.33 0.42 MBI* [43]
Sweden 2003 Torö 106 9 115 1 1 0.87 RT-PCR [17]
Sweden 2003 Combined central Sweden (3 sites) 167 23 190 1 1 0.53 RT-PCR [17]
Sweden 2006 3 sites south of Vänern (T1-T3) 4380 220 220 4820 263 11 9 2 0.21 0.45 0.23 RT-PCR [29]
Sweden 2004 South-western Sweden (T4) 2740 70 2810 144 7 6 1 0.22 1.43 0.25 RT-PCR [29]
Sweden 2008 Hudiksvall (1) 30 6 5 41 14 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Stenö/Källskär (2) 300 90 92 482 202 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Gävle (3) 4 1 0 5 2 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Trödje (4) 3 2 2 7 4 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Skutskär (5) 29 11 15 55 27 1 0 1 0 3.85 1.82 RT-PCR This study
Sweden 2008 Älvkarleby (6) 10 6 13 29 20 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Borlänge (7) 7 4 4 15 9 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Vikmanshyttan (8) 15 2 4 21 7 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Östhammar (9*) 94 10 15 119 31 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Norbo Finnmark (10) 11 11 12 34 24 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Väddö (11*) 32 10 6 48 18 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Skebobruk (12*) 40 13 19 72 34 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Morga (13*) 300 31 55 386 114 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Rimbo (14*) 8 2 4 14 7 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Kapellskär (15*) 373 59 70 502 151 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Kolarvik (16*) 158 57 49 264 115 1 1 0 0.63 0 0.38 RT-PCR This study
Sweden 2008 Västerås (17*) 137 11 24 172 47 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Strängnäs (18*) 37 27 22 86 51 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Eskilstuna (19*) 27 4 7 38 13 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Karlstad (20) 9 5 3 17 9 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Värmdö (21*) 46 3 6 55 16 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Askersund (22) 36 0 5 41 9 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Herrhamra (23*) 196 31 36 263 99 4 1 3 0.51 4.48 1.52 RT-PCR This study
Sweden 2008 Kapellängen, GS (24) (P) 24 21 2 47 25 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Gamla gården, GS (25) (P) 5 2 2 9 4 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Jönköping (26) 30 2 1 33 5 1 0 1 0 33.33 3.03 RT-PCR This study
Sweden 2008 Västervik (27) 14 4 5 23 10 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Änggårdsbergen (28) 31 0 1 32 3 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Särö Västerskog (29) (P) 68 0 2 70 8 0 0 0 0 0 0 RT-PCR This study
Sweden 2008 Combined central Sweden, 12 sites* 1448 258 313 2019 258 5 2 3 0.14 0.53 0.25 RT-PCR This study
Sweden 2008 Combined Sweden, 29 sites 2074 425 481 2980 1074 7 2 5 0.10 0.55 0.23 RT-PCR This study
Sweden 1958–2008 Combined Sweden, 4 studies, 45 sites 9396 2337 11733 1510 30 18 11 0.19 0.47 0.26 */PCR [17, 29, 43], this study
Finland 1957–1960, 1964 Archipelago of southern-western Finland 4932 391 389 8131 249 18 0.22 MBI** [44]
Finland 1957-1960, 1964 Southern Finland 124 9 0 133 7 0 0 MBI** [44]
Finland 1957–1960, 1964 South-eastern Finland 1308 39 84 1643 51 1 0.06 MBI** [44]
Finland 1996–1997 Isosaari (Mjölö) island, Helsinki 69 70 139 20 1 0.72 RT-PCR [45]
Finland 1996–1997 Åland islands 203 247 450 48 1 0.22 RT-PCR [45]
Finland 1996–1997 Helsinki city parks 74 123 726 130 0 0 RT-PCR [45]
Finland 2004 Kokkola (Karleby) archipelago (10 sites) 72 539 570 1181 122 13 1.10 RT-PCR [13]
Finland 2003 Kumlinge 454 46 4 0.88 RT-PCR [21]
Finland 2005 Isosaari (Mjölö) island, Helsinki 96 11 1 1.04 RT-PCR [21]
Finland 2007 Turku (Åbo) archipelago 1039 315 1 0.10 RT-PCR [21]
Finland 2005 Lappeenranta (Villmanstrand) 292 29 2 0.68 RT-PCR [21]
Finland 2008 Närpiö (Närpes) 36 0 0 RT-PCR [21]
Finland 1957–2008 Combined Finland, 4 studies, ≥ 27 sites     14320 2490 42 0.29 **/PCR [13, 21, 44, 45]
Norway 2003 Vest-Agder and Hordaland county 360    1 0.28 RT-PCR [19]
Norway 2004 Vest-Agder and Hordaland county 450    1 0.22 RT-PCR [19]
Norway 2009 Risør, Dalen (S1) 900 900 90 1 1 0.11 0.11 RT-PCR [46]
Norway 2009 Arendal (S2–S3) 1350 1350 135 8 8 0.59 0.59 RT-PCR [46]
Norway 2009 Mandal (S4–S5) 1520 1520 152 9 9 0.59 0.59 RT-PCR [46]
Norway 2009 Lyngdal (S6–S7) 1860 1860 186 6 6 0.32 0.32 RT-PCR [46]
Norway 2003–2009 Combined Norway, 2 studies, 9 sites     6440 ≥ 563 26 0.40 RT-PCR [19, 46]
Denmark 1999 Bornholm (7 sites) 3843 215 4058   2 0.05 RT-PCR [47]
Denmark 2002–2003 Northern Zealand 50 25 30 105 3 1 1 2.00 0.95 RT-PCR [48]
Denmark 2002–2003 3 different sites 62 62 9 0   RT-PCR [48]
Denmark 2011 Tokkekøb (3 sites, Jun.) 854 22 20 896 24 3 2 1 0.23 2.38 0.33 RT-PCR [20]
Denmark 2011 Tokkekøb (3 sites, Sept.) 700 15 15 730 8 5 5 0 0.71 0.68 RT-PCR [20]
Denmark 2011 Grib Forest 183 9 6 198 13 0 0 0 RT-PCR [20]
Denmark 2011 Bornholm (3 sites) 738 37 41 816 13 0 0 0 RT-PCR [20]
Denmark 1999–2011 Combined Denmark, 3 studies , ≥ 18 sites     6865 ≥ 70 11 0.16 RT-PCR [20, 47, 48]
All four countries 1957–2011 All sites (≥ 99) included in references     39358 3171 109      0.28   [13, 17, 1921, 29, 4348], this study
  1. Numbers within parenthesis for the present study correspond to sampling localities in Figure 1.
  2. MIR, Minimum Infection Rate (%). P, adult ticks were pooled.
  3. MBI*, Mouse brain inoculation and tissue cultures followed by neutralization tests and complement fixation tests [43].
  4. MBI**, Mouse brain inoculation followed by haemagglutination and haemagglutination-inhibition tests [44].