TBE in Lithuania

Auksė Mickienė

E-CDC risk status: endemic

(data as of end 2022)

History and current situation

The first case of tick-borne encephalitis (TBE) in Lithuania, diagnosed by clinical and epidemiologic criteria only, was reported in 1953. A forest worker became ill with the disease in April after a tick bite, had a typical clinical presentation with shoulder girdle muscle paralysis and bulbar syndrome, and died after 12 days from the start of clinical symptoms. Autopsy data were compatible with viral encephalitis.¹ Serological diagnosis of TBE in Lithuania was started in 1970.²

In Lithuania, Ixodes ricinus is the main vector of tick-borne encephalitis virus (TBEV), which is spread throughout the entire country. In addition, Dermacentor reticulatus is also found in Lithuania.^3,4,5 In 1974, 142 of 13,726 field-collected ticks in two northeastern districts of Lithuania (Rokiškis and Biržai) located near the Latvian border were identified as Ixodes persulcatus.⁶ The most recent entomological studies have also detected I. persulcatus in the Rokiškis district.,⁷ Sequence analysis of Lithuanian TBEV strains isolated from humans and field-collected ticks has shown that the virus belongs to the European TBEV subtype.⁴^,⁸ The minimum infection rate of I. ricinus ticks in Lithuania varies from 0.1% to 1.84%.⁴^,⁹

TBEV is found from ticks collected in all administrative districts of Lithuania and in 3 urban parks in the country.³ The density of I. ricinus ticks during the spring peak of activity increased three-fold from 1995 (19 ticks per 1 km) to 2008 (57 ticks per 1 km),³ and this increase has been correlated to increased numbers of TBE cases in humans.

TBEV seroprevalence in non-vaccinated healthy permanent residents in Lithuania is 3%. TBEV antibodies have been more frequently found in people who regularly visit the countryside or who consume unpasteurized goat milk, and the risk for seropositivity increases with age.¹⁰ Also, a general correlation has been noted between seropositivity among domestic animals, TBEV prevalence in ticks, and cases of TBE in humans in some regions of Lithuania.¹¹

From 1998 to 2012, the highest annual incidence of TBE was recorded in the northern and central parts of the country, mainly in the municipalities of Kaunas, Panevėžys, and Šiauliai. Between 1998 and 2011, when the average incidence of TBE in Lithuania was 11.5 cases per 100,000 people, the average incidence rate in Panevėžys, Šiauliai and Radviliškis districts was 52.1, 45.6, and 33.3, respectively (3–5 times higher than the average incidence in the country). In 2012, 4.1% of the Lithuanian population lived in these three districts (123,255 of 3,003,641 permanent inhabitants of Lithuania); however, the total number of TBE cases in these districts comprised 17% (1,230 of 7,409) of all TBE cases registered in Lithuania between 1993 and 2011.¹² Since 2013, a new trend in the epidemiology of TBE in Lithuania could be observed. While the incidence in the three aforementioned districts remains high, an increase in Vilnius, Alytus and Utena counties is gradually but steadily recorded up to 2018. During the last 3 years, the highest TBE incidence rate in Lithuania was observed in Utena county, in the northeastern part of Lithuania and on the border to Latvia (2016 – 42.8/100,000, 2017 – 40.3/100,000, 2018 – 27.3/100,000).¹³

Presently, TBE is the most common viral infection of the CNS in Lithuania, with an average number of 395 cases per year; a total of 10,611 TBE cases was reported between 1990 and 2018.¹³ Children (mainly school children and adolescents) comprise 8.7% of all TBE cases in the country. In the period from 1999 to 2018, children 0–3 years of age comprised 5.4% of all TBE cases in children (n=38), 4–6-year-old children – 11.2% (n=79), and 7–16-year-old children 83.4% (n=589).¹³ Retired and unemployed people are the major risk group for infection with TBEV in Lithuania; 56.4% of TBE patients are infected in the immediate areas surrounding their homes.¹⁴

Overview of TBE in Lithuania

Table 1: Virus, vector, transmission of TBE in Lithuania
Viral subtypes, distribution	European TBEV subtype⁴ ^,8
Reservoir animals	Main reservoir animals – Apodemus agrarius, Apodemus flavicollis, Myodes glareolus¹⁵
Infected tick species (%)	I. ricinus (0.1%–1.84%), D.reticulatus (0,58%)⁴^,⁹
Dairy product transmission	Rare¹³

Table 2: TBE reporting and vaccine prevention in Lithuania
Mandatory TBE reporting	All hospitalized patients with CNS form of TBEV infection confirmed by serological methods (TBEV IgM ± IgG) are reported to the Lithuanian Center for Communicable Diseases and AIDS¹³
Other TBE-surveillance	N/A
Special clinical features	Biphasic disease in 72.2% Risk groups: retired people, unemployed people, and permanent inhabitants of highly endemic areas¹⁴ Moderate and severe sequelae in 30.8%. Mortality 0.75%¹⁴
Available vaccines	Encepur, Ticovac¹³ Total number of doses sold 2010–2015: 308,969
Vaccination recommendations and reimbursement	Vaccination of adults: the joint recommendations by Lithuanian Societies for Infectious Diseases, Internal and Family Medicine (2013; no reimbursement). Reimbursed for military recruits and forestry workers*
Vaccine uptake by age group/ risk group/ general population	Total number of doses sold 2010–2015:¹³ Children (0–17 years) – 101,651 Adults (>18 years) – 207,318
Name, address/website of TBE National Reference Center	The Lithuanian Center for Communicable Diseases and AIDS¹³

Figure 1: Burden of TBE in Lithuania

Source data

Year	Number of Cases	Incidence / 10⁵
1969	9	0.3
1970	21	0.7
1971	38	1.12
1972	44	1.14
1973	40	1.12
1974	28	0.8
1975	51	1.5
1976	65	1.9
1977	70	2.1
1978	30	0.9
1979	41	1.1
1980	32	0.9
1981	13	0.3
1982	16	0.4
1983	18	0.5
1984	21	0.3
1985	10	0.2
1986	12	0.3
1987	9	0.2
1988	17	0.5
1989	8	0.2
1990	9	0.2
1991	14	0.4
1992	17	0.4
1993	198	5.3
1994	284	7.6
1995	427	11.5
1996	310	8.4
1997	645	17.4
1998	548	14.8
1999	171	4.6
2000	419	11.3
2001	298	8.5
2002	168	4.8
2003	763	22
2004	425	12.2
2005	243	7.1
2006	462	13.5
2007	234	6.9
2008	220	6.5
2009	605	17.9
2010	612	18.3
2011	365	11.1
2012	495	16.5
2013	501	16.9
2014	353	12
2015	336	11.5
2016	633	22.1
2017	474	16.8
2018	384	13.7
2019	711	25.8
2020	679	24.3
2021	365	12.8
2022	377	13.4

Figure 2: Age and gender distribution of TBE in Lithuania

Source data

2010
Age group (years)	Males	Females	All
0-9	17	7	24
10-19	30	20	50
20-29	43	19	62
30-39	34	31	65
40-49	59	59	118
50-59	71	56	127
60-69	41	57	98
>70	38	30	68
2011
Age group (years)	Males	Females	All
0-9	7	1	8
10-19	20	12	32
20-29	20	17	37
30-39	29	24	53
40-49	35	33	68
50-59	34	31	65
60-69	30	39	69
>70	14	19	33
2012
Age group (years)	Males	Females	All
0-9	9	5	14
10-19	21	13	34
20-29	37	21	58
30-39	34	17	51
40-49	52	33	85
50-59	59	43	102
60-69	42	37	79
>70	30	42	72
2013
Age group (years)	Males	Females	All
0-9	4	8	12
10-19	16	10	26
20-29	36	16	52
30-39	39	21	60
40-49	53	35	88
50-59	67	53	120
60-69	36	43	79
>70	24	40	64
2014
Age group (years)	Males	Females	All
0-9	4	2	6
10-19	17	12	29
20-29	25	14	39
30-39	19	13	32
40-49	27	22	49
50-59	53	39	92
60-69	26	30	56
>70	16	34	50
2015
Age group (years)	Males	Females	All
0-9	5	3	8
10-19	16	9	25
20-29	29	9	38
30-39	27	15	42
40-49	33	29	63
50-59	31	26	57
60-69	33	29	62
>70	17	25	42

TBEV-isolation and TBE cases in Lithuania

No information available

Contact:

amickiene@gmail.com

Citation:

Mickiene A. TBE in Lithuania. Chapter 12b. In: Dobler G, Erber W, Bröker M, Schmitt, HJ, eds. The TBE Book. 6th ed. Singapore: Global Health Press;2023. doi:10.33442/26613980_12b20-6

References

Motiejunas L, Regaliene, G. [The outbreak of cow milk origin tick-borne encephalitis]. Sveikatos apsauga. 1982;10:28-31.
Motiejunas L, Sapranauskaite D, Regaliene G. [Concerning the causes of a different morbidity of tick-borne encephalitis and the quality of patient’s laboratory testing in the cities and districts of Lithuanian SSR]. Sveikatos apsauga. 1978;1o:20-3.
Zygutiene M. [Tick-Borne Pathogens and spread of Ixodes ricinus in Lithuania]. EpiNorth. 2009;10:63-71.
Han X, Juceviciene A, Uzcategui NY, et al. [Molecular epidemiology of tick-borne encephalitis virus in Ixodes ricinus ticks in Lithuania]. J Med Virol. 2005;77:249-56.
Katargina O, Russakova S, Geller J, et al. [Detection and characterization of tick-borne encephalitis virus in Baltic countries and eastern Poland]. PLoS One. 2013;8(5):e61374. doi:10.13711/journal.pone.0061374.
Motiejunas L, Podenaite B. [Tick species and abundance of ticks in forest landscape in Lithuanian SSR]. Medical Parasitology and Parasitic Diseases. 1972;41(2):235-7.
Paulauskas A, et al. New localities of Dermacentor reticulatus ticks in the Baltic countries. Ticks and Tick Borne Dis. 2015;6(5):630-5.
Mickiene A, Vene S, Golovljova I, et al. [Tick-borne encephalitis virus in Lithuania]. Eur J Clin Microbiol Infect Dis. 2001;20:886-8.
Sidorenko M, Radzijevskaja J, Paulauskas, A. Prevalence of Tick-borne encephalitis virus in Ixodes ricinus and Dermacentor reticulatus ticks in Lithuania. In: ISTTBD – XIII : 13th international symposium on Ticks and Tick-borne diseases, 28–30 March 2019, Weimar, Germany: programme and abstract book. Zwickau: Förster & Borries GmbH, 2019: 124-5. Available at: https://www.vdu.lt/cris/handle/20.500.12259/101497
Juceviciene A, Vapalahti O, Laiskonis A, Ceplikiene J, Leinikki P. [Prevalence of tick-borne encephalitis virus antibodies in Lithuania]. J Clin Virol. 2002;25(1):23-7.
Juceviciene A, Zygutiene M, Leinikki P, et al. [Tick-borne encephalitis virus infections in Lithuanian domestic animals and ticks]. Scand J Infect Dis. 2005;37(10):742-6.
Mickiene A. Tick-Borne Encephalitis – Clinical and Pathogenetic Aspects. University dissertation from Stockholm: Karolinska Institutet, Department of Medicine at Huddinge University Hospital. 2015. Available at: https://openarchive.ki.se/xmlui/bitstream/handle/10616/44938/Thesis_Aukse_Mickiene.pdf?sequence=1&isAllowed=y
The Center for Communicable Diseases and AIDS (2014). Available at: http://www.ulac.lt/ataskaitos (Accessed: March 13 2014).
Mickienė A, Laiškonis A, Günther G, Vene S, Lundkvist Ă, Lindquist L. Tickborne Encephalitis in an Area of High Endemicity in Lithuania: Disease Severity and Long-Term Prognosis. Clin Infect Dis. 2002;35(6):650-8.
Paulauskas A, Radzijevskaja J, Turcinaviciene J, Ambrasiene D, Galdikaite E. Data on some ixodid tick species (acari, ixodidae) in the Baltic countries. New and Rare For Lithuania Insect Species. 2010:22.