Incidence Of Tick-borne Encephalitis Research Articles

The Study of Community Immunity to the Tick-Borne Encephalitis Virus in One of the Non-Endemic Areas of the Khabarovsk Krai (the Tuguro-Chumikansky District)

Introduction. At present, the areas endemic for tick-borne encephalitis (TBE) tend to expand. Monitoring of TBEV antibody detection rates in the population of non-endemic areas in order to adopt timely measures for specific and non-specific disease prevention thus acquires particular importance. The Tuguro-Chumikansky District is not among the endemic areas of the Khabarovsk Krai. Yet, the rise in the number of people seeking medical attention for an ixodes tick bite and TBE rates in the local population has been registered recently. Our purpose was to establish the level of natural herd immunity to the tick-borne encephalitis virus in the population of the Tuguro-Chumikansky District. Materials and methods. We conducted a serological survey among unvaccinated permanent residents of 6 villages of the study district. Results. The highest TBEV antibody detection rates were registered in the examined residents of the villages of Tugur (61.3 ± 8.75%) and Udskoye (51.4 ± 8.22%). On the whole, specific immunoglobulins for the tick-borne encephalitis virus were found in 29.4 ± 2.26% of the subjects, thus indicating that the locals have contacts with infected vectors or have possibly suffered from the inapparent (subclinical) infection. Discussion. The established immunoglobulin G detection rates and immunity levels to TBEV may show that the population of the Tuguro-Chumikansky District is involved in the epidemic process. A further increase in the number of people bitten by ticks can lead to an increase in the registered TBE incidence in the district making it yet another regional area endemic for the disease.

Ecological and epidemiological characteristics of tick-borne encephalitis in St. Petersburg

Here, we provide an analysis on 1996–2016 St. Petersburg tick-borne encephalitis (TBE) epidemiological and ecological data. In particular, two main TBE transmission vectors were observed in St. Petersburg: Ixodes persulcatus Ixodes ricinus. TBE tick contamination was 0.61% as shown by ELISA and polymerase chain reaction data. It is found that number of subjects seeking for medical aid due to tick bites rises, whereas TBE incidence declines. In particular, a mean 1996–2002 vs. 2010–2016 tick-bite incidence rate increased from 141.9 up to 288.9, respectively. Despite that the Leningrad region is a major area for TBE spread, however, a risk of exposure to tick bites as well as TBE infection exists even in the city of St. Petersburg. In connection with this, around 1,000 subjects undergo tick bites within the city limits. Moreover, whereas a 1996–2002 mean TBE incidence rate was 1.66, it decreased in 2010–2016 down to 1.17. A peak TBE incidence was documented in St. Petersburg Kurortny, Pushkinsky and Primorsky districts. In addition, males vs. females suffered from TBE at higher frequency in Russian Federation, with its peak incidence rate being reported in children under 14 that differs St. Petersburg from the most of other regions in the Russian Federation. A seasonal distribution of TBE cases in St. Petersburg does not differ from that one for the remainder of Russian regions, which displays a spring-summer seasonality lasting from April to September. Of note, 1996–2016 St. Petersburg TBE mortality was 1.37%. A coverage of TBE vaccinated population tends to rise but still remains at low level (0.25–0.58%). Lack of reported TBE cases in occupationally threatened human cohorts evidences about efficient preventive measures. Detection of TBE virus-specific serum antibodies in 5.0% apparently healthy and unvaccinated residents in St. Petersburg significantly complements the official TBE recording data and provides a more accurate understanding of its actual spread.

Abundance of <i>Ixodes persulcatus</i> ticks in Komi Republic as a function of an air temperature

The sharp rising incidence of tick-borne encephalitis (TBE) in Komi Republic at the North-east of European Russia was recorded last decades. Tick-bite incidence also was grown. Rapid rise of TBE incidence growth and Ixodidae ticks depends on a number of factors, and the impact of climate change being one of them. Ixodes persulcatus ticks is considered as a main vector of TBE in Komi. Our objective is to estimate the influence of air temperature change on the tickbite incidence and Ixodes persulcatus population in Komi. Komi Republic is located near the Polar circle where the northern frontier of Ixodes persulcatus ticks situated and we expected the growth of tick’s population. The number of Komi inhabitants seeking medical care after tick bites in 1992–2014 was considered. Gridded monthly air temperature data with grid size 0.5 degree were recalculated to temperature referred to Komi administrative units. The time series of annual number of tick victims from 1992 till 2014 and model air temperature from 1948 till 2016 for all Komi administrative units were compiled. We analyzed the data on tick-bite incidence in Komi administrative units in relation to changes in local annual average air temperature within the study area. The linear dependence of the tick-bite incidence on air temperature was established when of the tick-bite incidence is represented in logarithm form. The tick population depends not only on temperature but humidity, landcover and hosts. Described areas of Komi belong to humid climate, where precipitations exceed evaporation. Most of the Komi territory is covered by taiga with underwood, grass and bush. Hosts of the first and the major levels are represented by birds and rodents. The dependence of tick-bite incidence and temperature looks like “Malthus’s law”, but the development of population depends on temperature not on time. The exponential growth in the nearest future will ceased and the population will proceed to stable phase. Ticks population in Komi Republic is moving to the North and the air temperature determines the dynamics of population.

The potential impact of climate change on the transmission risk of tick-borne encephalitis in Hungary

BackgroundImpact of climate change on tick-borne encephalitis (TBE) prevalence in the tick-host enzootic cycle in a given region depends on how the region-specific climate change patterns influence tick population development processes and tick-borne encephalitis virus (TBEV) transmission dynamics involving both systemic and co-feeding transmission routes. Predicting the transmission risk of TBEV in the enzootic cycle with projected climate conditions is essential for planning public health interventions including vaccination programs to mitigate the TBE incidence in the inhabitants and travelers. We have previously developed and validated a mathematical model for retroactive analysis of weather fluctuation on TBE prevalence in Hungary, and we aim to show in this research that this model provides an effective tool for projecting TBEV transmission risk in the enzootic cycle.MethodsUsing the established model of TBEV transmission and the climate predictions of the Vas county in western Hungary in 2021-2050 and 2071-2100, we quantify the risk of TBEV transmission using a series of summative indices - the basic reproduction number, the duration of infestation, the stage-specific tick densities, and the accumulated (tick) infections due to co-feeding transmission. We also measure the significance of co-feeding transmission by observing the cumulative number of new transmissions through the non-systemic transmission route.ResultsThe transmission potential and the risk in the study site are expected to increase along with the increase of the temperature in 2021-2050 and 2071-2100. This increase will be facilitated by the expected extension of the tick questing season and the increase of the numbers of susceptible ticks (larval and nymphal) and the number of infected nymphal ticks co-feeding on the same hosts, leading to compounded increase of infections through the non-systemic transmission.ConclusionsThe developed mathematical model provides an effective tool for predicting TBE prevalence in the tick-host enzootic cycle, by integrating climate projection with emerging knowledge about the region-specific tick ecological and pathogen enzootic processes (through model parametrization fitting to historical data). Model projects increasing co-feeding transmission and prevalence of TBEV in a recognized TBE endemic region, so human risk of TBEV infection is likely increasing unless public health interventions are enhanced.

Tick-borne encephalitis foci in northeast Italy revealed by combined virus detection in ticks, serosurvey on goats and human cases

ABSTRACT Tick-borne encephalitis (TBE) is a severe zoonotic neurological disease endemic in northeast Italy since 1992. In the Province of Trento, a sharp increase in TBE incidence has been recorded since 2012, despite the vaccination efforts. To assess current TBE infection hazard in this area, we applied an integrated approach combining the distribution of human cases, the seroprevalence of tick-borne encephalitis virus (TBEV) in sentinel hosts and the screening of questing ticks for TBEV. A total of 706 goat sera from 69 farms were screened for TBEV-specific antibodies resulting in 5 positive farms, while the location of human cases was provided by the local Public Health Agency. Tick sampling was concentrated in areas where TBEV circulation was suggested by either seroprevalence in goats or human cases, resulting in 2,410 Ixodes ricinus collected and analyzed by real-time RT–PCR. Four tick samples from 2 areas with record of human cases were positive to TBEV corresponding to a 0.17% prevalence in the region, while risk areas suggested by serology on goats were not confirmed by tick screening. Our results revealed an increase in TBEV prevalence in ticks and the emergence of new active TBE foci, compared to previous surveys, and demonstrated the importance of an integrated approach for TBE risk assessment. A phylogenetic analysis of the partial E gene confirmed that the European TBEV subtype is circulating in northeast Italy and suggested that the different Italian TBEV strains originated independently as a result of different introductions from neighbouring countries, presumably through migratory birds.

Epidemiology of tick-borne encephalitis in China, 2007- 2018.

Tick-borne encephalitis (TBE) is endemic to Europe and some Asian countries and is prevalent in northeast China. We analyzed the epidemiology of TBE in China from 2007 to 2018. A total of 3,364 TBE cases were reported in mainland China from 2007 to 2018, for an annual incidence of 0.09 to 0.44/100,000. Among the TBE cases, 89.92% were reported in forest areas (41.94% in DaXingAnLing, 8.70% in XiaoXingAnLing, and 39.21% in ChangBaiShan) in northeast China. The TBE cases were primarily male with a proportion of 67.15% (2,259/3,364 cases) and in 40–49-year age group with a proportion of 31.89% (1,073/3,364 cases). The epidemiology of TBE differed slightly among the three forest regions. Domestic workers and forestry workers accounted for the most of the TBE cases in DaXingAnLing, and domestic workers and farmers in XiaoXingAnLing and ChangBaiShan, respectively. The TBE cases mainly occurred from April to August with a peak in June. The TBE laboratory confirmed rate in DaXingAnLing (84.14%, 1,189/1,413 cases) was highest, compared with XiaoXingAnLing and ChangBaiShan (13.99% and 11.37%, respectively). Moreover, the hospital with the highest laboratory confirmed rate (88.01%, 1,336/1,518 cases) was Inner Mongolia Forestry General Hospital of DaXingAnling region. Systematic enhanced TBE surveillance and a vaccination program are needed to improve the laboratory confirmed rate and reduce the incidence of TBE in northeast China.

Impact of specific prevention on epidemic process of tick-borne viral encephalitis in Siberian Federal District's regions

The article presents an assessment of the effectiveness of the effect of specific prevention measures on the incidence of tick-borne viral encephalitis in the population of the regions of the Siberian Federal District. The data on the incidence of Rospotrebnadzor of the Russian Federation and the regions of the Siberian Federal District for 2000–2017 years were used, the reporting of regional health services, the conditions and cause-effect relationships of the incidence of tick-borne encephalitis were assessed in the analysis of epidemiological survey maps of outbreaks. The study found that the analysis of the potential risk of contact with the foci of this infection in the regions of the Siberian Federal District, based on the ranking of regions by the level of population’s appeal for tick bites, can be considered as a prognostic criterion in planning the volume of preventive measures. Vaccination, having a significant impact on reducing morbidity (r = –0.89; p < 0.001) and mortality (r = –0.86; p < 0.001) from this infection, together with seroprophylaxis, can be one of the leading factors in epidemiological forecasting the incidence of tick-borne viral encephalitis in endemic areas.

Evaluation of the epidemiological and clinical characteristics of central nervous system infections in adults in the West Pannonian region

Introduction: Despite advancements in diagnostic capabilities and the availability of effective antimicrobial agents, community-acquired infections of the central nervous system (CNS) are still associated with high mortality rates. Aim: To assess the epidemiological and clinical characteristics of community-acquired CNS infections treated in the West Pannonian region between 2010 and 2016. Method: Clinical data of 176 patients were retrospectively analysed in two age cohorts: 15 to 65 and more than 65 years of age. Results: Neuroinfections were found to be bacterial in 81, viral in 91, parasitic in 1 and mixed in 3 cases during the observation period. The most frequent bacterial pathogens isolated were Streptococcus pneumoniae (20%) and Borrelia burgdorferi (16%). The most frequent viral pathogens isolated were tick-borne encephalitis virus (37%), herpes simplex virus (10%) and enterovirus (7%). Aetiology was unknown in 40 percent of all cases. The average incidence rate was 9.8/100 000 person/year with a mortality rate of 12%. In the cohort of patients aged >65 years, significantly higher frequencies of immunocompromising factors, lower Glasgow Coma Scale values at admission and confusion were observed (p-values: 0.008, 0.017, and 0.050, respectively). Prognosis was negatively influenced by low Glasgow Coma Scale values at admission (OR = 1.6 CI95%: 1.3-1.9; p<0.001), old age (OR = 6.5 CI95%: 2.5-17.1; p<0.001) and immunodeficiency (OR = 3.1 CI95%: 1.2-8.1; p = 0.019). Conclusions: S. pneumoniae remains the most frequently observed causative bacterial pathogen associated with community-acquired CNS infections. Incidence of tick-borne encephalitis in our county is higher than the national average (2.3 versus 0.35/100 000 person/year). Orv Hetil. 2019; 160(40): 1574-1583.

Knowledge, habits and attitudes towards TBE and other tick-borne diseases in German forestry trainees

Tick-borne encephalitis (TBE) is an occupational hazard for forestry workers. We measured knowledge levels, misbeliefs, and vaccination rates in forestry trainees in order to tailor specific measures aimed at reducing occupational TBE incidence. A paper-based survey was performed at a central training site for forestry workers in the state of Baden-Wuerttemberg. The questionnaire contained items regarding vaccination status against tick-borne encephalitis virus (TBEV), self-reported tick-borne diseases, knowledge of and attitudes towards tick-borne disease, and practices in the context of ticks and tick bites. All trainees in the period June-December 2018 were surveyed. Statistical analyses were conducted using Mann-Whitney-Rank sum test and one-way ANOVA tests. Two-hundred-twenty-five trainees participated in the survey. Almost all (>99%) were aware of living in a TBE high-risk area. Eighty-three percent of respondents were vaccinated in line with current recommendations. Seventeen percent had no effective vaccination status. Twenty-seven percent believed that ticks can transmit only TBEV and Borrelia spp. Sixty-two percent knew that TBEV infections can be fatal. Only 8% of respondents use tick repellents and only 17% wear long sleeves and pants. Trainees who graduated from a six and (eight or) nine secondary school (Realschule and Abitur respectively) had more knowledge on ticks and tick-borne disease compared to graduates from a five year school (Hauptschule) (p = 0.002 and p = 0,037 respectively). Overall, the TBE vaccination rate is not high enough in this high-risk occupational group. We identified gaps in knowledge and practices that could have an impact on TBE incidence in this group if addressed. Further epidemiological research is needed on knowledge, attitudes, and practices in different high-risk populations.

Assessing systemic and non-systemic transmission risk of tick-borne encephalitis virus in Hungary.

Estimating the tick-borne encephalitis (TBE) infection risk under substantial uncertainties of the vector abundance, environmental condition and human-tick interaction is important for evidence-informed public health intervention strategies. Estimating this risk is computationally challenging since the data we observe, i.e., the human incidence of TBE, is only the final outcome of the tick-host transmission and tick-human contact processes. The challenge also increases since the complex TBE virus (TBEV) transmission cycle involves the non-systemic route of transmission between co-feeding ticks. Here, we describe the hidden Markov transition process, using a novel TBEV transmission-human case reporting cascade model that couples the susceptible-infected compartmental model describing the TBEV transmission dynamics among ticks, animal hosts and humans, with the stochastic observation process of human TBE reporting given infection. By fitting human incidence data in Hungary to the transmission model, we estimate key parameters relevant to the tick-host interaction and tick-human transmission. We then use the parametrized cascade model to assess the transmission potential of TBEV in the enzootic cycle with respect to the climate change, and to evaluate the contribution of non-systemic transmission. We show that the TBEV transmission potential in the enzootic cycle has been increasing along with the increased temperature though the TBE human incidence has dropped since 1990s, emphasizing the importance of persistent public health interventions. By demonstrating that non-systemic transmission pathway is a significant factor in the transmission of TBEV in Hungary, we conclude that the risk of TBE infection will be highly underestimated if the non-systemic transmission route is neglected in the risk assessment.

Generation of Databases and Visualization of Current Epidemiological Information for Purposes of a Medical-Ecological Monitoring of a Region

The geo-ontology principles of identifying the functional connectivity of all components of the socio-biological system have been used as the basis for developing a unified and scientifically rigorous methodology of preprocessing epidemiological information and its preparation for further use. The specific features in epidemiological information are highlighted as well as the need for territorial linkage of the objects and situations under study in order to ensure the adequacy of management decisions. According to the principles of designing relational databases, an integrated epidemiological database has been generated, which includes the geographical coordinates of the objects and situations under study. Such a territorial linkage when implemented using GIS technologies provides a means of solving regional problems of estimating the probability of disease with due regard for the specific features of the location, which ensures competent and targeted work of the system of medical and environmental monitoring. The continually updated databases have been created and patented, which are compatible with ArcGIS and contain basic epidemiological data on the incidence of tick-borne encephalitis and tick-borne borreliosis, based on information received from hospitals in Irkutsk. For updating the integrated database with information on the occurrence of infections across landscapes, annual (since 2005) expeditions have been conducted in several key areas of Irkutsk oblast which are distinguished by landscape diversity, vector size, attendance and morbidity of the population. Ticks and their hosts are collected and analyzed for the presence of pathogens of natural focal infections. More than 25 thousand ticks were caught, whose infection with tick-borne encephalitis virus averaged 1.5%. Visualization of epidemiological information used the methods of end-to-end geographical mapping of the territory, the logic of which formulates the principles of geoinformation mapping and naturally includes a natural territorial component.

Epidemiology of Tick-Borne Encephalitis (TBE) in Germany, 2001⁻2018.

We reviewed tick-borne encephalitis (TBE) surveillance and epidemiology in Germany, as these underlie public health recommendations, foremost vaccination. We performed descriptive analyses of notification data (2001–2018, n = 6063) according to region, demographics and clinical manifestations and calculated incidence trends using negative binomial regression. Risk areas were defined based on incidence in administrative districts. Most cases (89%) occurred in the federal states of Baden-Wurttemberg and Bavaria, where annual TBE incidence fluctuated markedly between 0.7–2.0 cases/100,000 inhabitants. A slight but significantly increasing temporal trend was observed from 2001–2018 (age-adjusted incidence rate ratio (IRR) 1.02 (95% confidence interval (CI): 1.01–1.04)), primarily driven by high case numbers in 2017–2018. Mean incidence was highest in 40–69-year-olds and in males. More males (23.7%) than females (18.0%, p = 0.02) had severe disease (encephalitis or myelitis), which increased with age, as did case-fatality (0.4% overall; 2.1% among ≥70-year-olds). Risk areas increased from 129 districts in 2007 to 161 in 2019. Expansion occurred mainly within existent southern endemic areas, with slower contiguous north-eastern and patchy north-western spread. Median vaccination coverage at school entry in risk areas in 2016–2017 ranged from 20%–41% in 4 states. Increasing TBE vaccine uptake is an urgent priority, particularly in high-incidence risk areas.

Recent establishment of tick-borne encephalitis foci with distinct viral lineages in the Helsinki area, Finland

ABSTRACT Number of tick-borne encephalitis (TBE) cases has increased and new foci have emerged in Finland during the last decade. We evaluated risk for locally acquired TBE in the capital region inhabited by 1.2 million people. We screened ticks and small mammals from probable places of TBE virus (TBEV) transmission and places without reported circulation. The TBEV positive samples were sequenced and subjected to phylogenetic analysis. Within the study period 2007–2017, there was a clear increase of both all TBE cases and locally acquired cases in the Helsinki area. The surveillance of ticks and small mammals for TBEV confirmed four distinct TBEV foci in the Helsinki area. All detected TBEV strains were of the European subtype. TBEV genome sequences indicated that distinct TBEV lineages circulate in each focus. Molecular clock analysis suggested that the virus lineages were introduced to these foci decades ago. In conclusion, TBE has emerged in the mainland of Helsinki area during the last decade, with at least four distinct virus lineages independently introduced into the region previously. Although the overall annual TBE incidence is below the threshold for recommending general vaccinations, the situation requires further surveillance to detect and prevent possible further emergence of local TBE clusters.

Urgent natural foci infections transmitted by ticks in Saint-Petersburg

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.

Learning to live with ticks? The role of exposure and risk perceptions in protective behaviour against tick-borne diseases.

The purpose of this study is to analyse the role of risk perceptions and exposure for protective behaviour against tick bites and the related diseases Lyme borreliosis (LB) and tick-borne encephalitis (TBE), both of which are growing health concerns. We use data from a national survey in Sweden with respondents in geographical areas with substantial differences in both abundance of ticks and incidence of LB and TBE. We find that the share of respondents who frequently use protective clothing (64%), perform tick checks (63%) or avoid tall grass while in areas with ticks (48%) is relatively high. However, the use of protective measures is uneven and a considerably lower share tuck their trousers into their socks (18%), use repellent against ticks (16%) or use a combination of protective measures. Thirty-one per cent of the respondents report one or more tick bites in the last year and 68% report one or more lifetime tick bites, indicating that it is difficult to protect oneself from tick bites. There is a strong positive association between exposure and checking the skin for ticks, but exposure is only weakly associated with other protective measures. Tick bites are perceived as a serious health risk by as many as 43% of the respondents. The perception that a single tick bite is serious is negatively associated with actual exposure to ticks, while the opposite is true for the perception that tick bites constitute a serious lifetime health risk. This indicates a learning effect in relation to risk perceptions and the performance of tick checks, but not in relation to other protective measures. Recommendations include informing people of the risks associated with tick bites, the efficacy of various protective measures and the importance of combining multiple types of protection. Given the high exposure to tick bites, the growing incidence of TBE and LB, and the difficulties in preventing tick bites, other preventive measures should be further discussed, including vaccination programmes.

A Predictive Model Has Identified Tick-Borne Encephalitis High-Risk Areas in Regions Where No Cases Were Reported Previously, Poland, 1999-2012.

During 1999–2012, 77% of the cases of tick-borne encephalitis (TBE) were recorded in two out of 16 Polish provinces. However, historical data, mostly from national serosurveys, suggest that the disease could be undetected in many areas. The aim of this study was to identify which routinely-measured meteorological, environmental, and socio-economic factors are associated to TBE human risk across Poland, with a particular focus on areas reporting few cases, but where serosurveys suggest higher incidence. We fitted a zero-inflated Poisson model using data on TBE incidence recorded in 108 NUTS-5 administrative units in high-risk areas over the period 1999–2012. Subsequently we applied the best fitting model to all Polish municipalities. Keeping the remaining variables constant, the predicted rate increased with the increase of air temperature over the previous 10–20 days, precipitation over the previous 20–30 days, in forestation, forest edge density, forest road density, and unemployment. The predicted rate decreased with increasing distance from forests. The map of predicted rates was consistent with the established risk areas. It predicted, however, high rates in provinces considered TBE-free. We recommend raising awareness among physicians working in the predicted high-risk areas and considering routine use of household animal surveys for risk mapping.

Analysis of Efficacy and Safety of Tick-Borne Encephalitis Vaccines

This article provides a review on efficacy and safety of tick-borne encephalitis vaccines licensed in the Russian Federation. It highlights that both Russian and imported tick-borne encephalitis vaccines demonstrate high immunogenicity, safety and epidemiological effectiveness in regions with high vaccine coverage. All licensed tick- borne encephalitis vaccines meet interchangeability criteria in terms of indications for use (with due regard to age limits), medical contraindications, vaccination schedules, vaccine composition, as well as safety, immunological activity and efficacy parameters. Timely and specific prophylaxis help reduce the incidence of tick-borne encephalitis in endemic regions.

Increased Relative Risk of Tick-Borne Encephalitis in Warmer Weather.

Tick-borne encephalitis (TBE) is a serious acute neuroinfection of humans caused by a tick-borne flavivirus. The disease is typically seasonal, linked to the host-seeking activity of Ixodes ricinus (predominantly nymphs), the principal European tick vector species. To address the need for accurate risk predictions of contracting TBE, data on 4,044 TBE cases reported in the Czech Republic during 2001–2006 were compared with questing activity of I. ricinus nymphs monitored weekly at a defined location for the same 6-year period. A time shift of 21 days between infected tick bite and recorded disease onset provided the optimal model for comparing the number of cases of TBE with numbers of questing nymphs. Mean annual distribution of TBE cases and tick counts showed a similar bimodal distribution. Significantly, the ratio of TBE cases to questing nymphs was highest in the summer-autumn period even though the number of questing nymphs peaked in the spring-summer period. However, this pattern changed during a period of extreme meteorological events of flooding and abnormally high temperatures, indicating that changes in climate affect the incidence of TBE. Previous studies failed to link human behavior with changes in incidence of TBE but showed extrinsic temperature impacts arbovirus replication. Hence, we hypothesize the apparent discrepancy between peak nymphal tick activity and greatest risk of contracting TBE is due to the effect of temperature on virus replication in the tick vector. Relative proportions of questing nymphs and the numbers of weeks in which they were found were greater in summer-autumn compared with spring-summer at near-ground temperatures >5°C and at standard day and weekly average temperatures of >15°C. Thus, during the summer-autumn period, the virus dose in infected tick bites is likely greater owing to increased virus replication at higher microclimatic temperatures, consequently increasing the relative risk of contracting TBE per summer-autumn tick bite. The data support the use of weather-based forecasts of tick attack risk (based on daytime ambient temperature) supplemented with weekly average temperature (as a proxy for virus replication) to provide much-needed real-time forecasts of TBE risk.

Geographical Distribution of Tick-borne Encephalitis and Its Vectors in Mongolia, 2005-2016

Objectives: In the last several years, the incidence and fatality rates of tick-borne encephalitis (TBE) in Mongolia have been increasing with new cases being registered in areas without the main tick vector. Therefore, we sought to determine the geographical distribution of TBE in Mongolia. Methods: Data were analyzed on TBE virus prevalence of collected ticks and seroprevalence rate of TBE and TBE incidence rate among the human population from 2005 to 2016. Results: During this time, TBE incidence was 0.75 per 10,000 populations in Mongolia. Among 2,182 people investigated, seroprevalence rate was 14.6±10.9% (n=312) in 10 provinces and Ulaanbaatar city. The seroprevalence rate among the populations of Selenge, Bulgan and Khuvsgul provinces, which are home to the main tick vector I.Persulcatusis, were 1.8 times (CI 95% 1.5-2.3, p&lt; 0.001) higher than other provinces where the tick species D.nuttalli and D.silvarumare found. The TBE virus prevalence of I.Persulcatus was 3.18%, D.nuttalli was 0.61% and D.silvarum was 2.9% among the 10,464 ticks sampled. Conclusion: Endemic areas of TBE are expanding from northern parts of the country where the main vector I. persulcatus is more common to steppe areas where the vector D. nuttalli is abundant.

Molecular Detection and Serological Evidence of Tick-Borne Encephalitis Virus in Serbia.

Tick-borne encephalitis (TBE) is a zoonotic flaviviral infection that is a growing public health concern in European countries. The aims of this research were to detect and characterize tick-borne encephalitis virus (TBEV) in Ixodes ricinus ticks at presumed natural foci in Serbia, and to determine seroprevalence of TBEV IgG antibodies in humans and animals. A total of 500 I. ricinus ticks were examined for the presence of TBEV by real-time RT-PCR, and conventional nested PCR and sequencing. To determine TBEV seroprevalence, 267 human sera samples were collected, as were 200 sera samples from different animal species. All sera samples were examined by ELISA for the presence of anti-TBEV antibodies. To exclude cross-reactivity, all sera samples were tested for anti-West Nile virus (WNV) antibodies and all human sera samples were also tested for anti-Usutu virus antibodies by ELISA. Results of this preliminary study indicated TBEV activity in Serbia at two microfoci. Several decades after the previous documentation of TBEV in Serbia, we have demonstrated the presence of TBEV in I. ricinus questing nymphs (prevalence 2% and 6.6% at the two different localities) and anti-TBEV antibodies in humans (seroprevalence 0.37%). Moreover, we show for the first time TBEV seroprevalence in several animal species in Serbia, including dogs (seroprevalence 17.5%), horses (5%), wild boars (12.5%), cattle (2.5%), and roe deer (2.5%). None of the goats tested was positive for anti-TBEV IgG antibodies. TBEV isolate from I. ricinus tick in this study belonged to the Western European subtype. To understand the true public health concern in Serbia, detailed epidemiological, clinical, virological, and acarological research are required. This is important for implementation of effective control measures to reduce the incidence of TBE in Serbia.