The current perspective on tick-borne encephalitis awareness and prevention in six Central and Eastern European countries: report from a meeting of experts convened to discuss TBE in their region

Human Tick-Borne Diseases and Advances in Anti-Tick Vaccine Approaches: A Comprehensive Review

This comprehensive review explores the field of anti-tick vaccines, addressing their significance in combating tick-borne diseases of public health concern. The main objectives are to provide a brief epidemiology of diseases affecting humans and a thorough understanding of tick biology, traditional tick control methods, the development and mechanisms of anti-tick vaccines, their efficacy in field applications, associated challenges, and future prospects. Tick-borne diseases (TBDs) pose a significant and escalating threat to global health and the livestock industries due to the widespread distribution of ticks and the multitude of pathogens they transmit. Traditional tick control methods, such as acaricides and repellents, have limitations, including environmental concerns and the emergence of tick resistance. Anti-tick vaccines offer a promising alternative by targeting specific tick proteins crucial for feeding and pathogen transmission. Developing vaccines with antigens based on these essential proteins is likely to disrupt these processes. Indeed, anti-tick vaccines have shown efficacy in laboratory and field trials successfully implemented in livestock, reducing the prevalence of TBDs. However, some challenges still remain, including vaccine efficacy on different hosts, polymorphisms in ticks of the same species, and the economic considerations of adopting large-scale vaccine strategies. Emerging technologies and approaches hold promise for improving anti-tick vaccine development and expanding their impact on public health and agriculture.

Tick-Borne Encephalitis Virus Prevalence in Sheep, Wild Boar and Ticks in Belgium

Tick-borne encephalitis virus (TBEV) is the most important tick-borne zoonotic virus in Europe. In Belgium, antibodies to TBEV have already been detected in wildlife and domestic animals, but up-to-date prevalence data for TBEV are lacking, and no studies have assessed its seroprevalence in sheep. Serum samples of 480 sheep from all over Belgium and 831 wild boar hunted in Flanders (northern Belgium) were therefore screened for TBEV antibodies by ELISA and plaque reduction neutralization test (PRNT), respectively. The specificity of positive samples was assessed by PRNTs for TBEV and the Louping Ill, West Nile, and Usutu viruses. TBEV seroprevalence was 0.42% (2/480, CI 95%: 0.11-1.51) in sheep and 9.27% (77/831, CI 95%: 7.48-11.43) in wild boar. TBEV seroprevalence in wild boar from the province of Flemish Brabant was significantly higher (22.38%, 15/67) compared to Limburg (7.74%, 34/439) and Antwerp (8.61%, 28/325). Oud-Heverlee was the hunting area harboring the highest TBEV seroprevalence (33.33%, 11/33). In an attempt to obtain a Belgian TBEV isolate, 1983 ticks collected in areas showing the highest TBEV seroprevalence in wild boars were tested by real-time qPCR. No TBEV-RNA-positive tick was detected. The results of this study suggest an increase in TBEV prevalence over the last decade and highlight the need for One-Health surveillance in Belgium.

Food-Borne Transmission of Tick-Borne Encephalitis Virus—Spread, Consequences, and Prophylaxis

Tick-borne encephalitis (TBE) is the most common viral neurological disease in Eurasia. It is usually transmitted via tick bites but can also occur through ingestion of TBEV-infected milk and dairy products. The present paper summarises the knowledge of the food-borne TBEV transmission and presents methods for the prevention of its spread. The incidence of milk-borne TBE outbreaks is recorded in central, eastern, and north-eastern Europe, where Ixodes ricinus, Ixodes persulcatus, and/or Dermacentor reticulatus ticks, i.e., the main vectors of TBEV, occur abundantly. The growing occurrence range and population size of these ticks increases the risk of infection of dairy animals, i.e., goats, sheep, and cows, with viruses transmitted by these ticks. Consumers of unpasteurised milk and dairy products purchased from local farms located in TBE endemic areas are the most vulnerable to alimentary TBEV infections. Familial infections with these viruses are frequently recorded, mainly in children. Food-transmitted TBE can be monophasic or biphasic, and some of its neurological and psychiatric symptoms may persist in patients for a long time. Alimentary TBEV infections can be effectively prevented by consumption of pasteurised milk and the use of TBEV vaccines. It is recommended that milk and dairy products should be checked for the presence of TBE viruses prior to distribution. Protection of dairy animals against tick attacks and education of humans regarding the epidemiology and prophylaxis of TBE are equally important.

Broad and potent neutralizing human antibodies to tick-borne flaviviruses protect mice from disease

Tick-borne encephalitis virus (TBEV) is an emerging human pathogen that causes potentially fatal disease with no specific treatment. Mouse monoclonal antibodies are protective against TBEV, but little is known about the human antibody response to infection. Here, we report on the human neutralizing antibody response to TBEV in a cohort of infected and vaccinated individuals. Expanded clones of memory B cells expressed closely related anti-envelope domain III (EDIII) antibodies in both groups of volunteers. However, the most potent neutralizing antibodies, with IC50s below 1 ng/ml, were found only in individuals who recovered from natural infection. These antibodies also neutralized other tick-borne flaviviruses, including Langat, louping ill, Omsk hemorrhagic fever, Kyasanur forest disease, and Powassan viruses. Structural analysis revealed a conserved epitope near the lateral ridge of EDIII adjoining the EDI-EDIII hinge region. Prophylactic or early therapeutic antibody administration was effective at low doses in mice that were lethally infected with TBEV.

Human plasmacytoid dendritic cells at the crossroad of type I interferon-regulated B cell differentiation and antiviral response to tick-borne encephalitis virus

The Tick-borne encephalitis virus (TBEV) causes different disease symptoms varying from asymptomatic infection to severe encephalitis and meningitis suggesting a crucial role of the human host immune system in determining the fate of the infection. There is a need to understand the mechanisms underpinning TBEV-host interactions leading to protective immunity. To this aim, we studied the response of human peripheral blood mononuclear cells (PBMC) to the whole formaldehyde inactivated TBEV (I-TBEV), the drug substance of Encepur, one of the five commercially available vaccine. Immunophenotyping, transcriptome and cytokine profiling of PBMC revealed that I-TBEV generates differentiation of a sub-population of plasmacytoid dendritic cells (pDC) that is specialized in type I interferon (IFN) production. In contrast, likely due to the presence of aluminum hydroxide, Encepur vaccine was a poor pDC stimulus. We demonstrated I-TBEV-induced type I IFN together with Interleukin 6 and BAFF to be critical for B cell differentiation to plasmablasts as measured by immunophenotyping and immunoglobulin production. Robust type I IFN secretion was induced by pDC with the concerted action of both viral E glycoprotein and RNA mirroring previous data on dual stimulation of pDC by both S. aureus and influenza virus protein and nucleic acid that leads to a type I IFN-mediated sustained immune response. E glycoprotein neutralization or high temperature denaturation and inhibition of Toll-like receptor 7 signalling confirmed the importance of preserving the functional integrity of these key viral molecules during the inactivation procedure and manufacturing process to produce a vaccine able to stimulate strong immune responses.

Though vaccination is generally considered effective in reducing tick-borne encephalitis (TBE) incidence, several studies have shown that the antibody response to TBEV vaccination declines with age resulting in more frequent TBE cases among 50+ year-old vaccinees. These observations together with the lack of a specific antiviral drug impose to pinpoint novel host- and pathogen-directed therapies and to improve the control of vaccine efficacy. Thus, we interrogated in vitro human PBMC, whose response to TBEV may provide a picture closer to what occurs in vivo in humans after vaccination or natural infection compared to animal models. The role of E glycoprotein and viral RNA in promoting antiviral and B cell-mediated responses was investigated. Thus, these key viral molecules should be considered, in future, for novel subunit vaccine formulations than the current whole inactivated TBEV-based vaccines, which require laborious manipulation in biosafety level-3 laboratory and animal testing for manufacturing and batch release.

Characterization and in vitro assembly of tick-borne encephalitis virus C protein

Tick-borne encephalitis virus (TBEV), a member of flaviviruses, represents a serious health threat by causing human encephalitis mainly in central and eastern Europe, Russia, and northeastern Asia. As no specific therapy is available, there is an urgent need to understand all steps of the TBEV replication cycle at the molecular level. One of the critical events is the packaging of flaviviral genomic RNA by TBEV C protein to form a nucleocapsid. We purified recombinant TBEV C protein and used a combination of physical-chemical approaches, such as size-exclusion chromatography, circular dichroism, NMR spectroscopies, and transmission electron microscopy, to analyze its structural stability and its ability to dimerize/oligomerize. We compared the ability of TBEV C protein to assemble in vitro into a nucleocapsid-like structure with that of dengue C protein.

Prevalence of tick-borne encephalitis virus and Borrelia burgdorferi sensu lato in Ixodes ricinus ticks in Lower Bavaria and Upper Palatinate, Germany

Lyme borreliosis and tick-borne encephalitis (TBE) are the most common tick-borne diseases in Germany. We collected Ixodes ricinus ticks from 16 high-risk and four low-risk sites distributed in Lower Bavaria and Upper Palatinate based on the number of human TBE cases recorded at the Robert Koch Institute from 2001 to 2009. A total of 8805 questing ticks (8203 nymphs, 602 adults) were collected in 2010 and examined in pools for the presence of tick-borne encephalitis virus (TBEV) using real-time RT-PCR. Overall TBEV prevalence evaluated as the minimum infection rate (MIR) was 0.26 % (23 positive pools/8805 ticks in 1029 pools). TBEV was detected at seven of the 16 high-risk sites, where MIR ranged from 0.16 to 2.86 %. A total of 3969 ticks were examined by PCR for infection with Borrelia burgdorferi sensu lato (s.l.) targeting the 5 S-23 S rRNA intergenic spacer (IGS) region. IGS nucleotide sequences were used to determine genospecies. Selected positive Borrelia samples were subjected to PCR and sequencing targeting the OspA gene, providing 46 sequences for molecular phylogenetic analysis. Of the 3969 questing ticks, 506 (12.7 %) were positive for B. burgdorferi s.l. Seven B. burgdorferi s.l. genospecies were identified: B. afzelii (41.3 %), B. garinii (19 %), B. valaisiana (13.8 %), B. burgdorferi sensu stricto (11.1 %), B. spielmanii (0.4 %), B. lusitaniae (0.2 %), and Candidatus B. finlandensis (0.6 %). Mixed infections were identified in 13.6 % of the ticks. The rate of infection in questing ticks varied among sites from 5.6 % (72 examined, four positive) to 29.5 % (88 examined, 26 positive). B. burgdorferi s.l. occurred at all 20 sites, whereas TBEV was detected only at the high-risk sites where more human TBE cases were reported compared to low-risk sites.

Cross-sectional study on vaccination coverage in newly diagnosed HIV-infected persons in the Czech Republic

OBJECTIVES

Individuals with HIV infection are at an increased risk for a number of infectious diseases, some of which are preventable by vaccination. Unfortunately, little is known about the attitudes of this population group to vaccination, therefore, we decided to find out vaccination coverage against 5 infections among newly diagnosed HIV-infected patients in the Czech Republic.

METHODS

This cross-sectional study was conducted on newly diagnosed patients who started their follow-up care at the HIV Clinic of Na Bulovce Hospital during the two following years. Vaccination history data and results of serological tests were collected from all participants.

RESULTS

Enrolled were 269 HIV-positive subjects (94.1% males) with a mean age of 34.4 years, 64 subjects (23.8%) had tertiary education, 229 (85.1%) were men having sex with men, 32 (11.9%) were heterosexual, and 8 (3.0%) were injection drug users. The mean CD4+ T-lymphocyte count was 556.2/µL, with 149 persons (55.4%) who had a CD4+ T-lymphocyte count > 500/µL, and 68 (25.3%) individuals were late presenters with CD4+ T-lymphocyte count < 350/µL. A vaccination against tetanus was reported by 262 subjects (97.4%), against influenza by 18 subjects (6.7%), against tick-borne encephalitis by 18 subjects (6.7%), against viral hepatitis A by 78 persons (29.0%), and against hepatitis B by 104 subjects (38.7%). For influenza, tick-borne encephalitis and hepatitis A, a significant positive impact of tertiary education was found (p-values < 0.001-0.044). Vaccination coverage against both types of hepatitis was significantly lower in late presenters (p = 0.044 and p = 0.004, respectively).

CONCLUSIONS

Vaccination rates found in our cohort were except tetanus and hepatitis B in young people low, especially for influenza and tick-borne encephalitis. Higher level of education and less advanced HIV infection were associated with higher vaccination rates. To improve this unsatisfactory situation, more attention should be paid to vaccination.

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.

Model of Risk of Exposure to Lyme Borreliosis and Tick-Borne Encephalitis Virus-Infected Ticks in the Border Area of the Czech Republic (South Bohemia) and Germany (Lower Bavaria and Upper Palatinate)

In Europe, Lyme borreliosis (LB) and tick-borne encephalitis (TBE) are the two vector-borne diseases with the largest impact on human health. Based on data on the density of host-seeking Ixodes ricinus ticks and pathogen prevalence and using a variety of environmental data, we have created an acarological risk model for a region where both diseases are endemic (Czech Republic-South Bohemia and Germany-Lower Bavaria, Upper Palatinate). The data on tick density were acquired by flagging 50 sampling sites three times in a single season. Prevalence of the causative agents of LB and TBE was determined. Data on environmental variables (e.g., altitude, vegetation cover, NDVI, land surface temperature) were obtained from various sources and processed using geographical information systems. Generalized linear models were used to estimate tick density, probability of tick infection, and density of infected ticks for the whole area. A significantly higher incidence of human TBE cases was recorded in South Bohemia compared to Bavarian regions, which correlated with a lower tick density in Bavaria. However, the differences in pathogen prevalence rates were not significant. The model outputs were made available to the public in the form of risk maps, indicating the distribution of tick-borne disease risk in space.

Reviewing estimates of the burden in disability-adjusted life years (DALYs) of tick-borne encephalitis in Slovenia

INTRODUCTION

Tick-borne encephalitis (TBE) reflects an increasing burden and can affect public health policy. Vaccination could be the most effective option to reduce the disease burden, this review can support national recommendations for TBE vaccination in Slovenia.

AREAS COVERED

This burden is relatively high in Slovenia and can be estimated by using an incidence-based disability-adjusted life years (DALYs) methodology. Notably, DALYs have been estimated for Slovenia in various studies. The present study summarizes the main differences and conclusions between two studies that dealt with the calculation of DALYs for TBE in Slovenia. The databases of PubMed and Embase were used to get information about publications that dealt with the TBE burden, using an incidence-based DALYs methodology, in Slovenia.

EXPERT OPINION

Permanent sequelae contribute the most to the total burden in DALYs. Increasing vaccination in all ages and age groups can be the most effective and efficient strategy to reduce the burden of TBE and protect the whole population health.

Sequelae of tick-borne encephalitis in retrospective analysis of 1072 patients

Tick-borne encephalitis (TBE) is an emerging vector-borne disease in Europe. The aim of the study was to evaluate sequelae and to analyse the potential risk factors predisposing to sequelae development. We performed a retrospective analysis of medical records of 1072 patients who received a 1-month follow-up appointment after hospital discharge. Medical data, such as patients’ age, gender, place of living, subjective complaints, neurological and psychiatric sequelae were evaluated twice: at the moment of discharge and at follow-up visits 1 month after discharge. We observed that sequelae may affect 20.6% of TBE patients. Subjective sequelae were more frequent than subjective complaints during the hospitalisation (P < 0.001), while objective neurological symptoms during the hospitalisation were more pronounced than neurological sequelae (P < 0.001). Patients with meningoencephalomyelitis were predisposed to neurological complications, while subjective symptoms were more common in meningoencephalitis. Independent risk factors for sequelae development were: age and cerebrospinal fluid (CSF) protein concentration. The risk of late neurological complications persisting was increased in patients with higher CSF protein concentration. Based on the results of our study we concluded that, there is a need for a better vaccination program, which would prevent the development of sequelae.

Tick-Borne Encephalitis Virus: A Structural View

Tick-borne encephalitis virus (TBEV) is a growing health concern. It causes a severe disease that can lead to permanent neurological complications or death and the incidence of TBEV infections is constantly rising. Our understanding of TBEV’s structure lags behind that of other flaviviruses, but has advanced recently with the publication of a high-resolution structure of the TBEV virion. The gaps in our knowledge include: aspects of receptor binding, replication and virus assembly. Furthermore, TBEV has mostly been studied in mammalian systems, even though the virus’ interaction with its tick hosts is a central part of its life cycle. Elucidating these aspects of TBEV biology are crucial for the development of TBEV antivirals, as well as the improvement of diagnostics. In this review, we summarise the current structural knowledge on TBEV, bringing attention to the current gaps in our understanding, and propose further research that is needed to truly understand the structural-functional relationship of the virus and its hosts.

Impact of air temperature variation on the ixodid ticks habitat and tick-borne encephalitis incidence in the Russian Arctic: the case of the Komi Republic

BACKGROUND

The causes of the recent rise of tick-borne encephalitis (TBE) incidence in Europe are discussed. Our objective was to estimate the impact of air temperature change on TBE incidence in the European part of the Russian Arctic.

METHODS

We analysed the TBE incidence in the Komi Republic (RK) over a 42-year period in relation to changes in local annual average air temperature, air temperature during the season of tick activity, tick abundance, TBE-prevalence in ticks, tick-bite incidence rate, and normalised difference vegetation index within the area under study.

RESULTS

In 1998-2011 in RK a substantial growth of TBE virus (TBEV) prevalence both in questing and feeding ticks was observed. In 1992-2011 there was 23-fold growth of the tick-bite incidence rate in humans, a northward shift of the reported tick bites, and the season of tick bites increased from 4 to 6 months. In 1998-2011 there was more than 6-fold growth of average annual TBE incidence compared with 1970-1983 and 1984-1997 periods. This resulted both from the northward shift of TBE, and its growth in the south. In our view it was related to local climate change as both the average annual air temperature, and the air temperature during the tick activity season grew substantially. We revealed in RK a strong correlation between the change in the air temperature and that in TBE incidence. The satellite data showed NDVI growth within RK, i.e. alteration of the local ecosystem under the influence of climate change.

CONCLUSIONS

The rise in TBE incidence in RK is related considerably to the expansion of the range of Ixodes persulcatus. The territory with reported TBE cases also expanded northward. Climate change is an important driver of TBE incidence rate growth.

Compliance with vaccination against tick-borne encephalitis virus in Germany

OBJECTIVES

The goal of this study was to analyse patients' compliance with vaccination against tick-borne encephalitis (TBE) virus in Germany.

METHODS

The present study included 7266 patients from 638 general practices and 4194 patients from 114 paediatric practices. Patients were included if they had received the first dose of one of two vaccines against TBE virus (FSME-Immune^® and Encepur^®). The immunization schedule of these vaccines consisted of three injections. Patients were considered compliant if they received the second and third doses at the recommended time or within a period of ±25% around the recommended time (tolerance period).

RESULTS

Of the recruited patients, 28% received both the second and the third injections within the tolerance period. Individuals treated in paediatric practices had a higher likelihood of receiving vaccine doses within the tolerance period compared with individuals treated in general practices (OR 2.15; 95% CI 1.92-2.41). Moreover, patients <18 years old were more likely to be compliant than patients >65 years old (OR 1.22; 95% CI 1.02-1.46), whereas patients aged between 18 and 30 years were least likely to be compliant (OR 0·77; 95% CI 0.61-0.96).

CONCLUSIONS

Compliance with vaccination against the TBE virus was low. This compliance was significantly associated with age and the type of practices in which patients were treated.

The Burden of Tick-Borne Encephalitis in Disability-Adjusted Life Years (DALYs) for Slovenia

BACKGROUND

Tick-borne encephalitis (TBE) presents an increasing burden in many parts of Europe, Asian Russia, Siberia, Asian former USSR and Far East. Incidence can be considered as one way to express the burden. A more comprehensive measure concerns disability-adjusted life years (DALYs), better characterizing the full burden of TBE. TBE burden in DALYs has not yet been estimated, nor has it been specified by the Global Burden of Disease (GBD) studies.

OBJECTIVE

The purpose of the present study is to estimate the burden of TBE in Slovenia, expressed in DALYs, both from the population and individual perspectives. We discuss the impact of TBE burden on public health and potential strategies to reduce this burden in Slovenia.

METHODS

The burden of TBE is estimated by using the updated DALYs' methodology first introduced in the GBD project. The DALYs᾽ calculations are based on the health outcomes of the natural course of the disease being modelled. Corrections for under-reporting and under-ascertainment are applied. The impact of uncertainty in parameters in the model was assessed using sensitivity analyses.

RESULTS

From the population perspective, total DALYs amount to 3,450 (167.8 per 100,000 population), while from the individual perspective they amount to 3.1 per case in 2011. Notably, the consequences of TBE present a larger burden than TBE itself.

CONCLUSIONS

TBE presents a relatively high burden expressed in DALYs compared with estimates for other infectious diseases from the GBD 2010 study for Slovenia. Raising awareness and increasing vaccination coverage are needed to reduce TBE and its consequences.

Tick borne encephalitis (TBE)-vaccination coverage and analysis of variables associated with vaccination, Sweden

To estimate the tick borne encephalitis (TBE)-vaccination coverage in the greater Stockholm region, we sent a questionnaire to a randomized sample of 8000 individuals in 2013. Fifty-three percent of all respondents (n=4307) reported being vaccinated against TBE at least once. Reasons for not vaccinating included: no perceived risk (28.6%), too expensive (25.6%), did not have the time or opportunity (23%) and worried about vaccine side-effects (20.5%). Multiple logistic regression revealed that the probability of being vaccinated was higher among those who reported ≥2 weeks outdoor exposure in a known high risk area (OR 4.13 95% CI 3.54-4.81) and in individuals ≥60 years of age compared to all other age groups (OR 0.67 95% CI 0.55-0.81). A high net household income was associated with a higher probability of being vaccinated (OR 2.10 95% CI 1.6-2.73). Being born outside Europe was negatively correlated (OR 0.57 95% CI 0.39-0.83). Based on our findings the estimated TBE-incidence in the unvaccinated regional population was 8.5-12/100,000 which is comparable with high endemic areas as the Baltic region and Central Europe. We suggest targeted vaccination and reimbursement strategies in high-endemic areas of Sweden. Our results indicate a need for improved public information about TBE.

Emergence of tick-borne encephalitis in new endemic areas in Austria: 42 years of surveillance

Human infections with tick-borne encephalitis (TBE)virus are a public health concern in certain regions of Europe, central and eastern Asia. Expansions of endemic areas and increased incidences have been associated with different factors including ecological changes supporting tick reproduction, socioeconomic changes increasing human outdoor activities and climatic changes favouring virus circulation in natural foci. Austria is among the most strongly affected countries in Central Europe, but the annual number of cases has strongly declined due to vaccination. Here,we have analysed changes of the incidence of TBE in the unvaccinated population of all federal states of Austria over a period of 42 years. The overall incidence in Austria has remained constant, but new strongly affected endemic regions have emerged in alpine valleys in the west of Austria. In parallel, the incidence in low-land regions in the north-east of the country is decreasing. There is no evidence for a shift to higher altitudes of infection sites in the traditional TBE zones,but the average altitudes of some newly established endemic areas in the west are significantly higher. Our analyses underscore the focal nature of TBE endemic areas and the potential of TBE virus to emerge in previously unaffected regions.

Attenuation of tick-borne encephalitis virus using large-scale random codon re-encoding

Large-scale codon re-encoding (i.e. introduction of a large number of synonymous mutations) is a novel method of generating attenuated viruses. Here, it was applied to the pathogenic flavivirus, tick-borne encephalitis virus (TBEV) which causes febrile illness and encephalitis in humans in forested regions of Europe and Asia. Using an infectious clone of the Oshima 5–10 strain ("wild-type virus"), a cassette of 1.4kb located in the NS5 coding region, was modified by randomly introducing 273 synonymous mutations ("re-encoded virus"). Whilst the in cellulo replicative fitness of the re-encoded virus was only slightly reduced, the re-encoded virus displayed an attenuated phenotype in a laboratory mouse model of non-lethal encephalitis. Following intra-peritoneal inoculation of either 2.10⁵ or 2.10⁶ TCID50 of virus, the frequency of viraemia, neurovirulence (measured using weight loss and appearance of symptoms) and neuroinvasiveness (detection of virus in the brain) were significantly decreased when compared with the wild-type virus. Mice infected by wild-type or re-encoded viruses produced comparable amounts of neutralising antibodies and results of challenge experiments demonstrated that mice previously infected with the re-encoded virus were protected against subsequent infection by the wild-type virus. This constitutes evidence that a mammalian species can be protected against infection by a virulent wild-type positive-stranded RNA virus following immunisation with a derived randomly re-encoded strain. Our results demonstrate that random codon re-encoding is potentially a simple and effective method of generating live-attenuated vaccine candidates against pathogenic flaviviruses.

The arbovirus Tick-borne encephalitis virus (TBEV; genus Flavivirus) is transmitted by ticks of the Ixodes genus. TBEV causes febrile illness and encephalitis in humans in forested regions of Europe and Asia. The incidence of TBE is increasing across Central and Eastern European countries despite the availability of several licensed inactivated vaccines and appropriate vaccination programmes. Large-scale codon re-encoding, a recently developed attenuation method that modifies viral RNA nucleotide composition of large coding regions without alteration of the encoded proteins, has been successfully applied to a variety of RNA viruses. In contrast with previous empirical methods of generating live attenuated vaccines, large-scale codon re-encoding facilitates rapid generation of vaccine candidates using reverse genetics methods, by direct control of the attenuation phenotype. Additional benefits include reduced costs and induction of long-term immunity. Here, we have applied the large-scale codon re-encoding method to the TBEV to demonstrate the principle of developing a live attenuated virus vaccine which protects mice against subsequent infection with the wild type virulent virus. This study therefore illustrates that codon re-encoding is potentially an easily derived and effective method of producing live attenuated vaccine candidates against positive-stranded RNA viruses.

Lyme disease: Current issues, implications, and recommendations for tourism management

Lyme disease is a bacterial infection spread through the bite of an infected tick. In the last few decades, the number and spatial reach of new cases has increased globally and in the United States, Lyme disease is now the most commonly reported vector-borne disease. Despite this evolving public health crisis, there has been little-to-no discussion of the implications for tourism supply and demand. This paper reviews the scientific literature to identify Lyme disease risk factors and the implications for tourism management are discussed. The major contribution of this paper is a set of recommendations for tourism managers who may be tasked with mitigating the risks for visitors and employees as well as the potential impacts of Lyme disease on destination sustainability.

Prevalence of tick-borne encephalitis virus in a highly urbanized and low risk area in Southern Poland

The knowledge of the exact distribution of tick-borne encephalitis virus (TBEV) endemic foci is crucial to plan and implement the optimal prevention of tick-borne encephalitis (TBE), including a vaccination program. In Poland, however, there is still no data on the local distribution of TBEV in many areas of the country. Silesian agglomeration area (Southern Poland) is a highly urbanized and industrialized region of the country, where TBE cases are only sporadically recorded. In this study, a total of 4350 adult Ixodes ricinus were collected between September 2010 and June 2012 at twelve locations. The screening using real-time PCR was carried out on 854 tick pools of five specimens, and the positive pools were verified by pyrosequencing. TBEV was identified in 13 pools (1.52%) at 4 sites, of which 9 pools were verified by pyrosequencing. An overall pool prevalence was estimated at 0.31% ranging from 0.19% to 1.11% for positive locations [95% CI 0.16-0.52], which is comparable with regions with high number of TBE cases reported annually.

Immunoproteomic identification of antigenic salivary biomarkers detected by Ixodes ricinus-exposed rabbit sera

Ixodes ricinus, the primary vector of tick-borne disease in Europe, is currently expanding its distribution area and its activity in many countries. Antibody responses to tick salivary antigens have been proposed as an alternative marker of exposure to tick bites. However, the identification of the I. ricinus corresponding antigens remains elusive. Using rabbits artificially exposed to I. ricinus and 2 other European tick species (Rhipicephalus sanguineus and Dermacentor reticulatus) as controls, a cross-comparison of IgG profiles was performed against protein salivary gland extracts (pSGE) from these 3 tick species using immunoblots. Immunoblot analysis highlighted a singularity in the immune patterns according to tick species exposure and pSGE antigen source. Two protein bands were detected against I. ricinus pSGE only in rabbits exposed to I. ricinus bites. An immunoproteomic approach based on a fluorescence detection method was developed to unambiguously identify corresponding antigenic spots on 2-D gels. Among the unique I. ricinus salivary antigenic proteins detected by sera from rabbits exposed to this tick species, I. ricinus calreticulin was identified. Although tick calreticulin was previously proposed as a potential antigenic marker following exposure to ticks (particularly in North American tick species), the present study suggested that Ixodes calreticulin does not appear to be cross-recognized by the 2 other tick genera tested. Additional experiments are needed to confirm the use of I. ricinus calreticulin salivary protein as a potential discriminant antigenic biomarker to Ixodes tick exposure.

Epidemiology of tick-borne encephalitis (TBE) in Europe and its prevention by available vaccines

Tick-borne Encephalitis (TBE), which is caused by a Flavivirus, is the most common tick-transmitted disease in Central and Eastern Europe and Russia. Today, TBE is endemic in 27 European countries, and has become an international public health problem. The epidemiology of TBE is changing owing to various factors, such as improvements in diagnosis and case reporting, increased recreational activities in areas populated by ticks, and changes in climatic conditions affecting tick habitats. Vaccination remains the most effective protective measure against TBE for people living in risk zones, occupationally exposed subjects and travelers to endemic areas. The vaccines currently in use are FSME-Immun(®), Encepur(®), EnceVir(®) and TBE vaccine Moscow(®). The numerous studies performed on the efficacy and safety of these vaccines have shown a high level of immunogenicity and an excellent safety profile. Several studies have also shown a high level of cross-protection among strains belonging to different subtypes.   In the present paper we attempted to describe the continuously changing epidemiology of TBE in European States and to overview clinical development of available vaccines paying particular attention on cross-protection elicited by the vaccines.

Vaccines and vaccination against tick-borne encephalitis

Tick-borne encephalitis (TBE) is an emerging viral zoonosis and is endemic from Japan, China, Mongolia and Russia, to Central Europe and France. There is no specific treatment and TBE can be fatal. The four licensed prophylactic vaccines are produced according to WHO manufacturing requirements. Large clinical trials and postmarketing surveillance demonstrated safety and efficacy of the two European vaccines. The two Russian vaccines showed their effectiveness in daily use, but limited published data are available on controlled clinical trials. Vaccination recommendations in endemic areas vary significantly. In some countries, public vaccination programs are implemented. The WHO has recently issued recommendations on evidence-based use of TBE vaccines. However, more data are needed regarding safety, efficacy and long-term protection after vaccination.

Prevalence of tick-borne pathogens in adult Dermacentor spp. ticks from nine collection sites in France

The importance of Dermacentor spp. in the transmission of tick-borne pathogens is not well recognized in Europe. To investigate the role of Dermacentor spp. in the transmission of tick-borne pathogens, questing ticks were collected in 9 sites from southern to northwestern France (Camargue Delta to Eastern Brittany) where Dermacentor spp. exist and tick-borne diseases had occurred previously. Three tick species were collected during the spring and autumn of 2009. Collected ticks (both males and females) included D. marginatus (n=377), D. reticulatus (n=74), and I. ricinus (n=45). All ticks were analyzed by PCR or reverse line blot for the presence of pathogens' DNA. Pathogens analyzed were based on veterinarian reports and included Anaplasma phagocytophilum, Coxiella burnetii, Anaplasma marginale, Borrelia burgdorferi, Bartonella spp., Babesia spp., Theileria spp., and Francisella sp. Francisella tularensis was not detected in any of the analyzed ticks. In D. marginatus, infection prevalence for A. phagocytophilum (3%) was similar to that found in I. ricinus in Europe. Other pathogens present in D. marginatus included A. marginale (0.5%), Bartonella spp. (9%), C. burnetii (12%), F. philomiragia (1.3%), and Theileria annulata/Babesia bovis (0.3%), which were detected for the first time in France. Pathogens detected in D. reticulatus included A. marginale (1%), Bartonella spp. (12%), C. burnetii (16%), Borrelia spp. (1.5%), and F. philomiragia (19%). Pathogens detected in I. ricinus included A. phagocytophilum (41%), Bartonella spp. (9%), C. burnetii (18%), A. marginale (1%), Borrelia spp. (4.5%), and Babesia sp. (7%). This study represents the first epidemiological approach to characterize tick-borne pathogens infecting Dermacentor spp. in France and that may be transmitted by ticks from this genus. Further experiments using experimental infections and transmission may be now conducted to analyze vector competency of Dermacentor spp. for these pathogens and to validate such hypothesis.

Recommendations for tick-borne encephalitis vaccination from the Central European Vaccination Awareness Group (CEVAG)

Tick-borne encephalitis (TBE) is a viral neurological zoonotic disease transmitted to humans by ticks or by consumption of unpasteurized dairy products from infected cows, goats, or sheep. TBE is highly endemic in areas of Central and Eastern Europe and Russia where it is a major public health concern. However, it is difficult to diagnose TBE as clinical manifestations tend to be relatively nonspecific and a standardized case definition does not exist across the region. TBE is becoming more important in Europe due to the appearance of new endemic areas. Few Central European Vaccination Awareness Group (CEVAG) member countries have implemented universal vaccination programmes against TBE and vaccination coverage is not considered sufficient to control the disease. When implemented, immunization strategies only apply to risk groups under certain conditions, with no harmonized recommendations available to date across the region. Effective vaccination programmes are essential in preventing the burden of TBE. This review examines the current situation of TBE in CEVAG countries and contains recommendations for the vaccination of children and high-risk groups. For countries at very high risk of TBE infections, CEVAG strongly recommends the introduction of universal TBE vaccination in children > 1 y of age onwards. For countries with a very low risk of TBE, recommendations should only apply to those traveling to endemic areas. Overall, it is generally accepted that each country should be free to make its own decision based on regional epidemiological data and the vaccination calendar, although recommendations should be made, especially for those living in endemic areas.

Phylogeographic characterization of tick-borne encephalitis virus from patients, rodents and ticks in Slovenia

Tick-borne encephalitis virus (TBEV) is the most important arboviral agent causing infections of the central nervous system in central Europe. Previous studies have shown that TBEV exhibits pronounced genetic variability, which is often correlated to the geographical origin of TBEV. Genetic variability of TBEV has previously been studied predominantly in rodents and ticks, while information about the variability in patients is scarce. In order to understand the molecular relationships of TBEV between natural hosts, vectors and humans, as well as correlation between phylogenetic and geographical clustering, sequences of TBEV E and NS5 protein genes, were obtained by direct sequencing of RT-PCR products from TBE-confirmed patients as well as from rodents and ticks collected from TBE-endemic regions in Slovenia. A total of 27 partial E protein gene sequences representing 15 human, 4 rodent and 8 tick samples and 30 partial NS5 protein gene sequences representing 17 human, 5 rodent and 8 tick samples were obtained. The complete genome sequence of TBEV strain Ljubljana I was simultaneously obtained. Phylogenetic analysis of the E and NS5 protein gene sequences revealed a high degree of TBEV variability in patients, ticks and rodents. Furthermore, an evident correlation between geographical and phylogenetic clustering was shown that was independent of the TBEV host. Moreover, we show the presence of a possible recombination event in the TBEV genome obtained from a patient sample, which was supported with multiple recombination event detection methods. This is the first study that simultaneously analyzed the genetic relationships of directly sequenced TBEV samples from patients, ticks and rodents and provides the largest set of patient-derived TBEV sequences up to date. In addition, we have confirmed the geographical clustering of TBEV sequences in Slovenia and have provided evidence of a possible recombination event in the TBEV genome, obtained from a patient.

Multiple tick-associated bacteria in Ixodes ricinus from Slovakia

Eighty Ixodes ricinus ticks collected in the Rovinka forest in Slovakia were tested by real-time and routine single-step PCR for the presence of different pathogenic and endosymbiotic bacteria. No evidence of Coxiella burnetii, Diplorickettsia massiliensis, or Bartonella spp. was found. However, we identified, as the pathogenic bacteria, Anaplasma phagocytophilum in 8%, Rickettsia helvetica in 11%, Borrelia afzelii in 9%, Bo. garinii in 8%, Bo. burgdorferi sensu stricto in 5%, Bo. valaisiana in 3%, and Bo. miyamotoi in 1% of ticks. Other bacteria with unknown or suspected pathogenicity for humans were also identified: Arsenophonus nasoniae in 25%, Spiroplasma ixodetis in 3%, Candidatus Midichloria mitochondrii in 4%, Wolbachia aff. pipientis in 14%, and Ehrlichia muris in 3% of ticks. A. nasoniae was found almost exclusively in nymphs, and E. muris was only found in adult ticks. In total, 65% of ticks contained at least one species of bacteria, and 16% contained 2 or more species.

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)

Today, the risk of getting tick-borne encephalitis (TBE) is still underestimated in many parts of Europe and worldwide. Therefore, the 14th meeting of the International Scientific Working Group on Tick-Borne Encephalitis (ISW-TBE) - a group of neurologists, general practitioners, clinicians, travel physicians, virologists, pediatricians, and epidemiologists - was held under the title "Tick-borne encephalitis: an underestimated risk…still". Among the discussed issues were: TBE, an underestimated risk in children, a case report in two Dutch travelers, the very emotional report of a tick victim, an overview of the epidemiological situation, investigations to detect new TBE cases in Italy, TBE virus (TBEV) strains circulation in Northern Europe, TBE Program of the European Centre for Disease Prevention and Control (ECDC), efforts to increase the TBE vaccination rate in the Czech Republic, positioning statement of the World Health Organization (WHO), and TBE in dogs. To answer the question raised above: Yes, the risk of getting TBE is underestimated in children and adults, because awareness is still too low. It is still underestimated in several areas of Europe, where, for a lack of human cases, TBEV is thought to be absent. It is underestimated in travelers, because they still do not know enough about the risk, and diagnostic awareness in non-endemic countries is still low.

Tick-borne Encephalitis Vaccines

Tick-borne encephalitis (TBE) is a disease that is found from western Europe across Asia and into Japan. In recent years the incidence rate has been increasing as has the endemic range of the virus. Tick-borne encephalitis is caused by three genetically distinct sutypes of viruses within a single TBE virus (TBEV) serocomplex. These three subtypes consist of Far-eastern subtype TBEV (TBEV-FE), Siberian subtype (TBEV-Sib) and European subtype (TBEV-Eu). Each of these subtypes cause clinically distinct diseases with varying degrees of severity. Development of the first vaccines for TBEV began in the late 1930s shortly after the first isolation of TBEV-FE in Russia. In the 1970s Austria began large scale vaccine production and a nationalized vaccine campaign that significantly reduced the incidence rate of TBE. Currently there are four licensed TBE vaccines, two in Europe and two in Russia. These vaccines are all quite similar formalin-inactivated virus vaccines but the each use a different virus strain for production. Published studies have shown that European vaccines are cross-protective in rodent studies and elicit cross-reactive neutralizing antibody responses in human vaccines. European vaccines have been licensed for a rapid vaccine schedule that could be used in response to a significant outbreak and reasonable neutralizing antibody titers can be achieved after a single dose although a second dose provides nearly complete and long-lasting protection. This review focuses on the current status of licensed TBE vaccines and provides a brief summary of technology currently being developed for new vaccines.