Temporal trends in Lyme borreliosis and tick-borne encephalitis in Nordic countries, 2018-2024: a descriptive epidemiological analysis of European surveillance data

Ixodes ricinus ticks are one of the most important vectors and reservoirs of infectious diseases in Europe, and tick-borne encephalitis (TBE) is one of the most dangerous human diseases transmitted by these vectors. The aim of the present study was to investigate the TBE incidence in some European countries during the COVID-19 pandemic. To this end, we analyzed the data published by the European Center for Disease Prevention and Control (ECDC) and Eurostat on the number of reported TBE and COVID-19 cases in 2020 and TBE cases in 2015–2019 (reference period). Significant differences in the TBE incidence were found between the analyzed countries. The highest TBE incidence was found in Lithuania (25.45/100,000 inhabitants). A high TBE incidence was also observed in Central European countries. In 12 of the 23 analyzed countries, there was significant increase in TBE incidence during the COVID-19 pandemic during 2020 compared to 2015–2019. There was no correlation between the incidence of COVID-19 and TBE and between the availability of medical personnel and TBE incidence in the studied countries. In conclusion, Central Europe and the Baltic countries are areas with a high risk of TBE infection. Despite the COVID-19 pandemic and imposed restrictions, the incidence of TBE is increasing in more than half of the analyzed countries.

Tick-borne encephalitis (TBE): An underestimated risk…still: Report of the 14th Annual Meeting of the International Scientific Working Group on Tick-Borne Encephalitis (ISW-TBE)

Tick-borne encephalitis (TBE) is a potentially life-threatening infectious disease caused by the tick-borne encephalitis virus (TBEV). In recent years, TBE-endemic areas have expanded in Europe and the incidence of surveillance-reported TBE cases has increased. TBE is preventable through vaccination, with vaccines available and recommended for residents of, and travellers to, TBE-endemic regions. We summarized the published literature on international travel-associated TBE cases and country-specific TBE vaccine recommendations for travellers. We conducted a systematic literature review using PubMed and Web of Science and reviewed public health surveillance online sources to identify reports of travel-associated TBE cases published from 1978 to 2024. We also analysed the European Centre for Disease Prevention and Control (ECDC) TBE Annual Epidemiological Reports from 2015 to 2022 for travel-associated cases and collected information on TBE vaccination recommendations by national public health authorities for travellers to Europe. Thirty-nine international travel-associated TBE cases were identified from 24 articles and one public health report. Of the 34 travel-associated TBE cases with clinical information, 33 (97.0%) were hospitalized for a median of 9days. Travel-associated cases departed from the USA, Israel and several countries in Europe; the most frequently visited countries were Austria, Russia, Sweden and Switzerland. Of the 22 191 surveillance-reported TBE cases reported to ECDC from 2015 to 2022, 376 (1.7%) were international travel-associated cases. Recommendations for TBE vaccination for travellers were identified in 32 countries. Despite recommendations for TBE vaccination for travellers to TBE-endemic areas in Europe, international travel-associated TBE cases among travellers to Europe continue to occur. Most of the published travel-associated TBE cases are associated with severe clinical illness. When considering the increasing geographic spread of the TBE-endemic areas and increasing TBE incidence in Europe, enhanced efforts are needed to inform appropriate international travellers about the risk of TBE and to promote vaccination of travellers to TBE-endemic areas in Europe.

Purpose: to conduct a comparative analysis and to identify the epidemiological and clinical features of tick-borne encephalitis (TBE) and Lyme borreliosis as a mono- and coinfections in St. Petersburg. Materials and methods. 718 cases of TBE, 4353 cases of Lyme borreliosis and 127 combined diseases registered by the St. Petersburg epidemiological bureau in 2006-2017 were studied. Identification of combined diseases was carried out by a special software that allows to identify co-morbid diseases from the array of monoinfections. To identify clinical and epidemiological features, 144 cases of TBE, 286 Lyme borreliosis, and 43 cases of co-infection were studied. Age and sex characteristics, places of human contagion, infection rates of ticks, clinical forms of mono- and associated diseases, morbidity dynamics changes and patients’ IgM seropositivity were studied. Results. The long-term dynamics of TBE and Lyme borreliosis incidence had did not have significant upward or downward trends, it was characterized by synchronous fluctuations. The priority of the incidence of men over women is revealed. 61–69% cases of TBE and Lyme borreliosis occurred in Leningrad region, 19–30% – in the adjacent territories of Russia, 5,7–6,7% of cases were imported from other countries. High tick infection rates of TBE virus and Borrelia was revealed. Borrelia аnd virus of TBE and were detected in 81,6–87,5% of the examined ticks removed from patients with a later established diagnosis. Seasonal distribution of Lyme borreliosis was shifted by a month to the right in comparison with TBE. The clinical forms of both diseases did not differ in their structure from the country data, however after 2012 subclinical forms were more common in women. The proportion of non-erythematous forms of Lyme borreliosis in 2011–2015 compared with the 2006–2010 observation period increased almost 1,5-fold mainly forms, including those with co-infection. The IgM seropositivity rate in the dynamics of the disease testifies to the incomplete rehabilitation of patients. Conclusion. The clinical and epidemiological characteristics of TBE, Lyme borreliosis and combined infection in the North-West region of Russia, with the example of St. Petersburg, have certain distinctive features. The reasons for the revealed features need further study.

The regional characteristics of the epidemic process and the incidence rates of tick-borne encephalitis (TBE) in the Arkhangelsk region have been examined in the paper. In the period 2005 -2015 the annual TBE incidence rates per 100 thousand population were from 2,0 to 5,4 times higher as compared to the corresponding averages reported for the whole population of the Russian Federation. The most possible causes of the increased incidence rates of tick-borne viral encephalitis in the Arkhangelsk region and temporal trends in its changes as well as potential risk factors of TBE extension have been stated. The vectors of viral encephalitis in the Arkhangelsk region are represented by two types of ixodic ticks: Ixodes persulcatus (the "taiga" tick) and Ixodes ricinus ("forest" tick), the Ixodes persulcatus constitutes over 99 % of their total number. Spring-summer season is typical for TBE cases occurrence which is associated with higher tick activity in this area. The average tick infection rate for the period was 7.8 %. The cases of TBE are reported to occur mainly in urban citizens; and lethality rate due to TBE reached 4.3%. Since 2010 decrease in the TBE morbidity has being observed in the Arkhangelsk region. Reducing morbidity can be connected to the increase in the proportion of vaccinated persons, which reached 6.3 % of the total population of the Arkhangelsk region. The main indices of the acaricide treatment volume which increased since 2005 nearly 6 times, from 128.2 to 740.0 hectares have been stated. Considering the fact that the area of acaricide treatment in the region increases every year, and the number of persons seeking medical advice concerning tick bites remains high it is necessary to control the effectiveness of acaricide treatment regularly. Core measures to decrease the tick-borne viral encephalitis conducted by the Regional Office of Federal Service for Consumers' Rights Protection and Human Wellbeing as well as ways for further research have been introduced.

Background In the face of ongoing climate warming, vector-borne diseases are expected to increase in Europe, including tick-borne diseases (TBD). The most abundant tick-borne diseases in Germany are Tick-Borne Encephalitis (TBE) and Lyme Borreliosis (LB), with Ixodes ricinus as the main vector. Methods In this study, we display and compare the spatial and temporal patterns of reported cases of human TBE and LB in relation to some associated factors. The comparison may help with the interpretation of observed spatial and temporal patterns. Results The spatial patterns of reported TBE cases show a clear and consistent pattern over the years, with many cases in the south and only few and isolated cases in the north of Germany. The identification of spatial patterns of LB disease cases is more difficult due to the different reporting practices in the individual federal states. Temporal patterns strongly fluctuate between years, and are relatively synchronized between both diseases, suggesting common driving factors. Based on our results we found no evidence that weather conditions affect the prevalence of both diseases. Both diseases show a gender bias with LB bing more commonly diagnosed in females, contrary to TBE being more commonly diagnosed in males. Conclusion For a further investigation of of the underlying driving factors and their interrelations, longer time series as well as standardised reporting and surveillance system would be required.

Our study was aimed at analyzing data combining objective epidemiological, zoological and entomological research intended to determine the environmental and epidemiological patterns of tick-borne encephalitis (TBE) and Lyme borreliosis (LB) foci, as well as the role of anthropogenic factors in epidemic manifestations to improve anti-epidemic activities. Long-term data on the abundance of ticks flagged from vegetation in various districts of the Komi Republic (RK) have been analyzed. The prevalence of tick-borne encephalitis virus (TBEV) and Borrelia burgdorferi (agent of LB) in ticks picked from vegetation, humans and domestic animals in various districts of the RK was measured by using enzyme-linked immunosorbent assay and polymerase chain reaction (PCR-ELISA). In addition, the data on 1994–2017 tick-bite incidence in RK, 1970–2017 TBE incidence, and 1997–2017 LB incidence were also examined and correlated with the impact of forest transformation on the TBE incidence. The rise of tick population in the southern districts of RK and its northward expansion were noted. It is also shown that the RK territory, where tick bites are registered, expanded significantly. Mean annual tick-bite incidence rate in 2006–2017 vs. 1994–2005 timeframe was increased by 4-fold. RK regions where deforestation took place, the tick-bite incidence was increased, and the local TBE incidence elevated distinctly. In recent years, there was a rise in TBEV prevalence in ticks, collected either from vegetation or from humans and animals. In 2006–2017 and 1970–1981, mean annual TBE incidence rate increased by a 11- and 36-fold as compared to that one registered in 1982–1993. In recent years, the most severe focal TBE forms began to be recorded. In 1996–2017, the TBE mortality rate was 2.3%. The main features of LB epidemiology mimic those found in TBEV. In particular, the prevalence of Borrelia burgdorferi in ticks flagged from vegetation increased from 9.5% to 34.7% in 2010 vs. 2017, respectively. A sharp rise in LB incidence rate and profound northward shift for bacterial range, where this infection started to be registered only in recent years, were noted. Both TBE and LB demonstrated marked occupation-related pattern. The need in conducting task-oriented prophylaxis of tick-borne infections is necessitated by taking into account geographic specifics. The RK northern regions should be considered as potentially endemic, where tick bites in human population has recently begun to be reported.

Comparison of the number of Lyme neuroborreliosis cases in European Centre for Disease Prevention and Control (ECDC) data and national public surveillance reports, 2018-2023.

Relevance. Hemorrhagic fever with renal syndrome (HFRS) and tick-borne encephalitis (TBE) are the most common natural focal diseases of viral etiology in Russia. The medical and social significance of these two infections is determined by the extensive foci of their spread, high annual morbidity rates, and the presence of severe forms of the disease can lead to permanent disability and even death. Aim. To assess the current epidemiological situation of HFRS and TBE in the Russian Federation. Conclusions. Over 23 years (from 2000 to 2022), 164,582 cases of HFRS were identified in Russia with an average annual rate of 4.9 cases per 100 thousand population, as well as 71,579 cases of TBE with an average annual rate of 2.5 cases per 100 thousand population; 668 (0.4%) and 1136 (1.6%) deaths from HFRS and TBE, respectively; 4030 (2.5%) and 9414 (13%) children under the age of 14 years among patients with HFRS and TBE, respectively. The incidence of HFRS and TBE per 100 thousand population of Russia was higher among rural residents than among urban residents. Most cases of HFRS were registered in the autumn-winter period, and TBE – at the end of June – the first half of July. Of the 85 administrative regions of Russia, cases of HFRS and TBE are registered in 42, in 18 – only HFRS, in 13 – only TBE, and in 12 regions no clinically diagnosed cases of HFRS and TBE have been identified.

BackgroundWhy human tick-borne encephalitis (TBE) cases differ from year to year, in some years more 100%, has not been clarified, yet. The cause of the increasing or decreasing trends is also controversial. Austria is the only country in Europe where a 40-year TBE time series and an official vaccine coverage time series are available to investigate these open questions.MethodsA series of generalized linear models (GLMs) has been developed to identify demographic and environmental factors associated with the trend and the oscillations of the TBE time series. Both the observed and the predicted TBE time series were subjected to spectral analysis. The resulting power spectra indicate which predictors are responsible for the trend, the high-frequency and the low-frequency oscillations, and with which explained variance they contribute to the TBE oscillations.ResultsThe increasing trend can be associated with the demography of the increasing human population. The responsible GLM explains 12% of the variance of the TBE time series. The low-frequency oscillations (10 years) are associated with the decadal changes of the large-scale climate in Central Europe. These are well described by the so-called Scandinavian index. This 10-year oscillation cycle is reinforced by the socio-economic predictor net migration. Considering the net migration and the Scandinavian index increases the explained variance of the GLM to 44%. The high-frequency oscillations (2–3 years) are associated with fluctuations of the natural TBE transmission cycle between small mammals and ticks, which are driven by beech fructification. Considering also fructification 2 years prior explains 64% of the variance of the TBE time series. Additionally, annual sunshine duration as predictor for the human outdoor activity increases the explained variance to 70%.ConclusionsThe GLMs presented here provide the basis for annual TBE forecasts, which were mainly determined by beech fructification. A total of 3 of the 5 years with full fructification, resulting in high TBE case numbers 2 years later, occurred after 2010. The effects of climate change are therefore not visible through a direct correlation of the TBE cases with rising temperatures, but indirectly via the increased frequency of mast seeding.

A survey was made over a two-year period (September 1987 to August 1989) of a population living in an area endemic for Lyme borreliosis and tick-borne encephalitis in Sweden. For each patient a blood sample was collected and a questionnaire completed annually. All sera were tested for an antibody response to Borrelia burgdorferi in an EIA using sonicated antigen and for an antibody response to the tick-borne encephalitis virus using an EIA and a haemagglutination inhibition test. Antibodies to Borrelia burgdorferi and tick-borne encephalitis virus were detected in 89 (25.7%) and 40 (11.6%) respectively of 346 samples collected in August 1987. In the first year of the study 14 of 303 subjects (4.6%) developed Lyme borreliosis and in the second year 9 of 277 subjects (3.2%). A significant increase in the antibody titre for Borrelia burgdorferi was seen in 14 of 303 (4.6%) subjects in the first year and 8 of 277 (2.9%) subjects in the second year. An earlier episode of Lyme borreliosis or an elevated antibody titre did not seem to protect against reinfection. One case of tick-borne encephalitis was seen each year. Seroconversion for tick-borne encephalitis virus was found in 3 of 258 (1.2%) subjects in the first year and 5 of 211 (2.4%) in the second year, excluding subjects who had undergone successful immunisation or had earlier been hospitalised for tick-borne encephalitis. The study thus demonstrated a high yearly incidence of tick-borne infections in a population at risk.

To the Editor: Tickborne encephalitis virus (TBEV) is focally distributed in Europe and Asia (between 42a nd 63 north latitude). Recently, 5 human tickborne encephalitis cases have been reported, and anti-tickborne encephalitis antibody prevalence in dogs has been observed in southern Norway (1). In the last 2 decades, mild winters may have favored a northbound spread and increased tickborne encephalitis incidence (2). Tickborne encephalitis is endemic in southern Germany, but no cases had been reported in northeast Germany since 1985 (3,4).

Slovenia has a high tick-borne encephalitis (TBE) incidence and TBE vaccination is recommended for all residents ≥1 year-of-age. Despite widespread TBE vaccine use in Slovenia, TBE vaccine effectiveness (VE) has not been reported for Slovenia. We defined individuals who received ≥3 TBE vaccine doses in accordance with the recommended vaccination schedule as fully vaccinated. Using the screening method, TBE VE was determined by comparing the proportions of TBE cases and survey respondents who were fully vaccinated. TBE incidence and VE were used to estimate the number of TBE cases prevented by TBE vaccination. Of 637 surveillance-reported TBE cases in 2019–2024, 332 (52.1%) had a known vaccination history. Of these 332 TBE cases, 322 (97.0%) were unvaccinated and 10 (3.0%) received ≥1 doses of a TBE vaccine. Among 25,242 persons surveyed with known TBE vaccination history, 57.9% were unvaccinated. VE of ≥3 TBE doses for the prevention of TBE was 93.4% (84.0–97.3%). TBE vaccination prevented 426 TBE cases in 2019–2024. If the entire population was vaccinated against TBE, vaccination would have prevented 994 TBE cases in 2019−2024. TBE vaccination in Slovenia was highly effective, preventing hundreds of TBE cases a year. Most of the Slovenian population, however, is not vaccinated against TBE. To prevent additional TBE cases in Slovenia, further efforts are needed to enhance TBE vaccine uptake.

Background In the face of ongoing climate warming, vector-borne diseases are expected to increase in Europe, including tick-borne diseases (TBD). The most abundant tick-borne diseases in Germany are Tick-Borne Encephalitis (TBE) and Lyme Borreliosis (LB), with Ixodes ricinus as the main vector. Methods In this study, we display and compare the spatial and temporal patterns of reported cases of human TBE and LB in relation to some associated factors. The comparison may help with the interpretation of observed spatial and temporal patterns. Results The spatial patterns of reported TBE cases show a clear and consistent pattern over the years, with many cases in the south and only few and isolated cases in the north of Germany. The identification of spatial patterns of LB disease cases is more difficult due to the different reporting practices in the individual federal states. Temporal patterns strongly fluctuate between years, and are relatively synchronized between both diseases, suggesting common driving factors. Based on our results we found no evidence that weather conditions affect the prevalence of both diseases. Both diseases show a gender bias with LB bing more commonly diagnosed in females, contrary to TBE being more commonly diagnosed in males. Conclusion For a further investigation of of the underlying driving factors and their interrelations, longer time series as well as standardised reporting and surveillance system would be required.

BACKGROUND: Among the spectrum of the tick-borne infections, Lyme borreliosis and tick-borne encephalitis are most often recorded in the Tomsk region, however it is obviously that possible range of the pathogens is not limited to these ones. AIM: To make epidemiological and clinical characteristics of cases and detect frequencies of pathogen’s markers of tick-borne infections among adult patients applying serological and molecular genetic techniques in the Tomsk region during 2020–2023. METHODS: A single-center prospective sample study was conducted applying a comprehensive approach in peripheral blood specimens obtained from 197 patients with suspected tick-borne infections hospitalized during 2020–2023. To verify the diagnoses of tick-borne encephalitis or Lyme borreliosis, specific immunoglobulins of classes M and G to the antigens of virus of tick-borne encephalitis and Borrelia burgdorferi s.l. were determined in paired blood serum samples applying enzyme-linked immunosorbent assay. Additionally, the polymerase chain reaction was used to detect genetic markers of virus of tick-borne encephalitis, B. burgdorferi s.l., B. miyamotoi, Rickettsia spp., Coxiella burnetii, and Francisella tularensis. Epidemiological surveillance data of incidence rates of tick-borne infections obtained from official reports were analyzed as well. MS Office Excel 2010 software was used to calculate frequency morbidity measures. RESULTS: We verified the final diagnosis of tick-borne encephalitis in 52 (26.4%) patients, Lyme borreliosis in 116 (58.9%) patients, co-infection of tick-borne encephalitis and Lyme borreliosis 15 (7.6%) patients, hard tick relapsing fever caused by B. miyamotoi in 8 (4.1%) patients, coinfection of Q fever caused by C. burnetii with tick-borne encephalitis or Lyme borreliosis in 4 (2.0%) patients, and coinfection of tularemia with tick-borne encephalitis or Lyme borreliosis in 2 (1.0%) cases. We identified markers of tick-borne encephalitis and Lyme borreliosis pathogens by polymerase chain reaction in 3.6% and 4.1% of the patients. Most number of individuals with tick bites, and the highest incidence rates of Lyme borreliosis and tick-borne encephalitis were recorded in the suburbs of Tomsk. The age groups of 40–59 years, and elderly people 60 years and older were predominated among the patients. CONCLUSIONS: It was found out that, in addition to Lyme borreliosis and tick-borne encephalitis, there were such tick-borne infections as tick relapsing fever, Q fever, and tularemia in the Tomsk region in the 2020–2023 period.