Vaccines and vaccination against tick-borne encephalitis

The structure and behavioral patterns of the human population affected by ixodid tick bites in Irkutsk Region, Eastern Siberia, Russia

The bites of hard ticks are the major route of transmission of tick-borne infections to humans, causing thousands of cases of diseases worldwide. However, the characteristics of the human population that is exposed to tick bites are still understudied. This work is aimed at characterizing both the structure of the population directly contacting ticks and the human behavioral features associated with tick bites. We studied 25,970 individuals who sought medical help after a tick bite at the Centre for Diagnostics and Prevention of Tick-borne Infections (CDPTBI) in Irkutsk City (Russian Federation). The demographic and behavioral characteristics of the human population were analyzed using z-tests for proportions, the Mann-Whitney U test, and the Spearman rank correlation coefficient. The majority of bitten people were urban residents (70 %), and most of them were either of active ages between 30 and 74 years old (62 %), or children between 0 and 9 years old (approximately 20%). Tick bites occurred mostly in the range of 150 km around the location of the diagnostic facility (83 %). In comparison to the general population, significant differences were revealed in the representation of different age groups among bitten people. The population affected by tick bites included fewer men and women in the ages of 10-29 and over 75 years old than would be predicted based on the demographics of the general population. Vice versa, the proportions of people in the ages of 5-9 and 60-74 increased among bitten people. Among men, such activities (in order of occurrence) as "leisure and recreation", "visiting allotments", "foraging for forest food", and "fulfilling work duties" tend to be more associated with tick bites. Among women, tick bites occurred mainly during "visiting allotments", "leisure and recreation", "visiting cemeteries" and "contact with pets and plants at home". The overall vaccination rate was 12 %; however, significantly more men than women were vaccinated against tick-borne encephalitis (up to 20 % vs. approximately 7 % respectively). The structure of the tick bite - affected population suggests that it is age-specific human behavior that mainly determines the frequency of contact between people and ticks. However, in several age groups, especially among children from 5 to 9 and people aged 30-39 years old, gender-related factors could significantly change the exposure of people to tick bites.

A systematic literature review of the effectiveness of tick-borne encephalitis vaccines in Europe

BACKGROUND

Tick-borne encephalitis (TBE) is an infectious disease caused by the tick-borne encephalitis virus (TBEV) in patients with symptoms of central nervous system (CNS) inflammation. More than 25 European countries have one or more TBE-endemic areas. Although two TBE vaccines, FSME-IMMUN® and Encepur®, are commonly used in Europe, there are no published reviews of the real-world effectiveness of TBE vaccines in Europe or elsewhere.

METHODS

We searched PubMed for TBE vaccine effectiveness (VE) articles and extracted information on country, study design, study period, study population, number of TBEV-infected cases, number of participants, and VE against TBEV infection and outcomes.

RESULTS

We identified 13 studies, conducted in Austria, the Czech Republic, Latvia, Germany, and Switzerland, published in 2003-2023. One study was a cohort investigation of a milk-borne outbreak. In the other studies, 11 (91.7%) used the screening method and two (16.7%) used a case-control design (one study used both). TBE vaccines were highly effective (VE estimates >92%) against TBEV infection in all age groups. Vaccines were also highly protective against mild infections (i.e., infections in patients without symptoms of CNS inflammation), and against infections resulting in TBE and hospitalization. Vaccines were also highly protective against the most serious outcomes such as hospitalization greater than 12 days. Product-specific VE estimates were also high, though limited data were available. Studies in Austria, the Czech Republic, Latvia, and Switzerland estimated that TBE vaccines prevented >1,000 TBE cases a year, avoiding many hospitalizations and deaths, in these countries combined.

CONCLUSIONS

Published VE studies demonstrate a high real-world effectiveness of the commercially available TBE vaccines in Europe. Although cases averted have been estimated in only four countries, TBE vaccination prevents thousands of cases in Europe each year. To prevent life-threatening TBE, TBE vaccine uptake and compliance with the vaccination schedule should be increased in residents of, and travelers to, TBE-endemic countries in Europe.

DNA Vaccine Encoding the Artificial T-Cell Polyepitope Immunogen of Tick-Borne Encephalitis Virus

A promising approach to the development of new means for preventing infection caused by tick-borne encephalitis virus can be DNA vaccines encoding polyepitope T-cell immunogens. A DNA vaccine pVAX-AG4-ub encoding an artificial polyepitope immunogen that includes cytotoxic and T-helper epitopes from the NS1, NS3, NS5, and E proteins of the tick-borne encephalitis virus has been obtained. The developed construct ensured the synthesis of the corresponding mRNAs in transfected eukaryotic cells. Immunization of mice with pVAX-AG4-ub induced the formation of a virus-specific T-cell response providing 50% protection from lethal infection with the virus.

Tick-Borne Encephalitis-Review of the Current Status

The tick-borne encephalitis virus (TBEV) is the arboviral etiological agent of tick-borne encephalitis (TBE), considered to be one of the most important tick-borne viral diseases in Europe and Asia. In recent years, an increase in the incidence of TBE as well as an increasing geographical range of the disease have been noted. Despite the COVID-19 pandemic and the imposition of restrictions that it necessitated, the incidence of TBE is rising in more than half of the European countries analyzed in recent studies. The virus is transmitted between ticks, animals, and humans. It seems that ticks and small mammals play a role in maintaining TBEV in nature. The disease can also affect dogs, horses, cattle, and small ruminants. Humans are incidental hosts, infected through the bite of an infected tick or by the alimentary route, through the consumption of unpasteurized milk or milk products from TBEV-infected animals. TBEV infections in humans may be asymptomatic, but the symptoms can range from mild flu-like to severe neurological. In Europe, cases of TBE are reported every year. While there is currently no effective treatment for TBE, immunization and protection against tick bites are critical in preventing this disease.

Addressing vaccine-preventable encephalitis in vulnerable populations

PURPOSE OF REVIEW

Vaccinations have been pivotal in lowering the global disease burden of vaccine-preventable encephalitides, including Japanese encephalitis, tick-borne encephalitis, measles encephalitis, and rabies encephalitis, among others.

RECENT FINDINGS

Populations vulnerable to vaccine-preventable infections that may lead to encephalitis include those living in endemic and rural areas, military members, migrants, refugees, international travelers, younger and older persons, pregnant women, the immunocompromised, outdoor, healthcare and laboratory workers, and the homeless. There is scope for improving the availability and distribution of vaccinations, vaccine equity, surveillance of vaccine-preventable encephalitides, and public education and information.

SUMMARY

Addressing these gaps in vaccination strategies will allow for improved vaccination coverage and lead to better health outcomes for those most at risk for vaccine-preventable encephalitis.

Increased Vaccination Diversity Leads to Higher and Less-Variable Neutralization of TBE Viruses of the European Subtype

Tick-borne encephalitis (TBE) is an infectious disease of the central nervous system. The causative agent is the tick-borne encephalitis virus (TBEV), which is most commonly transmitted by tick bites, but which may also be transmitted through the consumption of raw dairy products or, in rare instances, via infected transfusions, transplants, or the slaughter of infected animals. The only effective preventive option is active immunization. Currently, two vaccines are available in Europe-Encepur^® and FSME-IMMUN^®. In Central, Eastern, and Northern Europe, isolated TBEV genotypes belong mainly to the European subtype (TBEV-EU). In this study, we investigated the ability of these two vaccines to induce neutralizing antibodies against a panel of diverse natural TBEV-EU isolates from TBE-endemic areas in southern Germany and in regions of neighboring countries. Sera of 33 donors vaccinated with either FSME-IMMUN^®, Encepur^®, or a mixture of both were tested against 16 TBEV-EU strains. Phylogenetic analysis of the TBEV-EU genomes revealed substantial genetic diversity and ancestry of the identified 13 genotypic clades. Although all sera were able to neutralize the TBEV-EU strains, there were significant differences among the various vaccination groups. The neutralization assays revealed that the vaccination using the two different vaccine brands significantly increased neutralization titers, decreased intra-serum variance, and reduced the inter-virus variation.

Spatiotemporal spread of tick-borne encephalitis in the EU/EEA, 2012 to 2020

BackgroundTick-borne encephalitis (TBE) is a vaccine-preventable disease involving the central nervous system. TBE became a notifiable disease on the EU/EEA level in 2012.AimWe aimed to provide an updated epidemiological assessment of TBE in the EU/EEA, focusing on spatiotemporal changes.MethodsWe performed a descriptive analysis of case characteristics, time and location using data of human TBE cases reported by EU/EEA countries to the European Centre for Disease Prevention and Control with disease onset in 2012-2020. We analysed data at EU/EEA, national, and subnational levels and calculated notification rates using Eurostat population data. Regression models were used for temporal analysis.ResultsFrom 2012 to 2020, 19 countries reported 29,974 TBE cases, of which 24,629 (98.6%) were autochthonous. Czechia, Germany and Lithuania reported 52.9% of all cases. The highest notification rates were recorded in Lithuania, Latvia, and Estonia (16.2, 9.5 and 7.5 cases/100,000 population, respectively). Fifty regions from 10 countries, had a notification rate ≥ 5/100,000. There was an increasing trend in number of cases during the study period with an estimated 0.053 additional TBE cases every week. In 2020, 11.5% more TBE cases were reported than predicted based on data from 2016 to 2019. A geographical spread of cases was observed, particularly in regions situated north-west of known endemic regions.ConclusionA close monitoring of ongoing changes to the TBE epidemiological situation in Europe can support the timely adaption of vaccination recommendations. Further analyses to identify populations and geographical areas where vaccination programmes can be of benefit are needed.

Tick-Borne Encephalitis in Vaccinated Patients: A Retrospective Case-Control Study and Analysis of Vaccination Field Effectiveness in Austria From 2000 to 2018

BACKGROUND

There are discrepant observations on the severity of tick-borne encephalitis (TBE) in vaccinated persons. We, therefore, analyzed the occurrence of severe and mild disease in hospitalized vaccinated and nonvaccinated patients with TBE and determined the field effectiveness (FE) of vaccination against these forms of disease.

METHODS

The study covered all patients hospitalized with TBE in Austria from 2000 to 2018. Clinical diagnoses in vaccinated and age- and sex-matched nonvaccinated patients were compared in a nested case-control study. FE was calculated based on vaccination coverage and incidences in the nonvaccinated and vaccinated population.

RESULTS

Of 1545 patients hospitalized with TBE, 206 were vaccinated. In those, a higher proportion of severe TBE was observed, especially in children. FE was high in all age groups and against all forms of disease. The higher proportion of severe TBE can be explained by a lower FE against severe than against mild disease, a difference especially pronounced in children (FE, 82.7% for severe vs 94.7% for mild disease).

CONCLUSIONS

The FE of TBE vaccination is excellent. The observed higher proportion of severe disease in vaccinated persons with TBE does not reflect a higher risk associated with vaccination but is rather due to a somewhat lower FE against severe TBE. Because this effect was more pronounced in children, we recommend adapting the immunization schedule.

Vaccine uptake in 20 countries in Europe 2020: Focus on tick-borne encephalitis (TBE)

Vaccination as a highly effective measure to protect against tick-borne encephalitis (TBE) comes into new focus as known risk areas are expanding across Europe and Asia. Here we present an online household survey conducted in 20 European countries spanning endemic and non-endemic regions of TBE in 2020. With a comprehensive and standardized list of questions, this survey provided a unique opportunity to compare TBE/TBE vaccine awareness, TBE severity perception, vaccine uptake, vaccination completeness/compliance and motivators/barriers for vaccination across Europe. Among the 51,478 participants, tetanus- (72-92%), influenza- (83-98%), and measles-awareness (79-96%) were highest, but awareness was low for Lyme borreliosis, bacterial meningitis and pneumococcal pneumonia. Awareness towards TBE and a TBE vaccine was 74% and 56% in endemic countries, respectively, compared to 30% and 12% in non-endemic countries. Vaccine uptake defined as at least one TBE vaccination was found to be highly heterogenous across both endemic (range 7-81%) and non-endemic countries (range 1-8%). Compliance with the recommended vaccination schedule was 21% for the primary vaccination series and dropped to 7% for the first booster vaccination in endemic countries. The percentage of participants protected against TBE by vaccination at the time of the survey ranged from 21% in Slovakia to 69% in Lithuania. The perception of personal risk or lack thereof was found to be the most influencing factor for and against TBE vaccination. Overall, these data indicate highly heterogenous responses in different European countries regarding not only awareness towards a TBE vaccine, but also regarding TBE vaccine uptake and compliance. Regionally focused strategies to increase diagnostic completeness as well as TBE vaccination are needed across Europe.

Use of Wild Ungulates as Sentinels of TBEV Circulation in a Naïve Area of the Northwestern Alps, Italy

Wild and domestic animals can be usefully employed as sentinels for the surveillance of diseases with an impact on public health. In the case of tick-borne encephalitis virus (TBEV), the detection of antibodies in animals can be more effective than screening ticks for detecting TBEV foci, due to the patchy distribution of the virus. In the Piedmont region, northwestern Italy, TBEV is considered absent, but an increase in tick densities, of Ixodes ricinus in particular, has been observed, and TBEV is spreading in bordering countries, e.g., Switzerland. Therefore, we collected sera from wild ungulates during the hunting season (October-December) from 2017 to 2019 in the Susa Valley, Italian western Alps, and screened them for TBEV antibodies by a commercial competitive ELISA test. We collected 267 serum samples by endocranial venous sinuses puncture from red deer, roe deer and northern chamois carcasses. The animals were hunted in 13 different municipalities, at altitudes ranging between 750 and 2800 m a.s.l. The serological survey for TBEV yielded negative results. Borderline results for five serum samples were further confirmed as negative for TBEV by a plaque reduction neutralisation test. To date, our results indicate that TBEV is not circulating in western Piedmont. However, monitoring of TBEV should continue since TBEV and its vector are spreading in Europe. The wide-range distribution of wild ungulates and their role as feeding hosts, make them useful indicators of the health threats posed by Ixodid ticks.

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.

Recommendations to Improve Tick-Borne Encephalitis Surveillance and Vaccine Uptake in Europe

There has been an increase in reported TBE cases in Europe since 2015, reaching a peak in some countries in 2020, highlighting the need for better management of TBE risk in Europe. TBE surveillance is currently limited, in part, due to varying diagnostic guidelines, access to testing, and awareness of TBE. Consequently, TBE prevalence is underestimated and vaccination recommendations inadequate. TBE vaccine uptake is unsatisfactory in many TBE-endemic European countries. This review summarizes the findings of a scientific workshop of experts to improve TBE surveillance and vaccine uptake in Europe. Strategies to improve TBE surveillance and vaccine uptake should focus on: aligning diagnostic criteria and testing across Europe; expanding current vaccine recommendations and reducing their complexity; and increasing public education of the potential risks posed by TBEV infection.

Epidemiological Trends of Trans-Boundary Tick-Borne Encephalitis in Europe, 2000-2019

Tick-borne encephalitis is a neuroinfection widely distributed in the Euro-Asia region. Primarily, the virus is transmitted by the bite of infected ticks. From 2000-2019, the total number of confirmed cases in Europe reported to the European Centre for Disease Prevention and Control was 51,519. The number of cases decreased in 2014 and 2015; however, since 2015, a growing number of cases have been observed, with the involvement of countries in which TBE has not been previously reported. The determinant factors for the spread of TBE are host population size, weather conditions, movement of hosts, and local regulations on the socioeconomic dynamics of the local and travelling people around the foci areas. The mean incidence rate of tick-borne encephalitis from 2000-2019 in Europe was 3.27, while the age-adjusted mean incidence rate was 2.19 per 100,000 population size. This review used several articles and data sources from the European Centre for Diseases Prevention and Control.

Burden of Tick-Borne Encephalitis, Sweden

In recent decades, the incidence of tick-borne encephalitis (TBE) in Sweden has increased. To calculate the burden of disease over a 17-year period, we analyzed data from the Swedish National Health Data Register for TBE cases diagnosed during 1998–2014. We compared healthcare use and sick leave associated with 2,429 persons with TBE with a referent cohort of 7,287 persons without TBE. Patients with TBE were hospitalized for significantly more days during the first year after disease onset (11.5 vs. 1.1 days), logged more specialist outpatient visits (3.6 vs. 1.2 visits), and logged more sick leave days (66 vs. 10.7 days). These differences generally increased over time. The case-fatality rate for TBE was 1.1%. Our calculated cost of TBE to society provides a baseline for decisions on immunization programs. Analyzing register data, our study adds to clinical studies of smaller cohorts and model-based studies that calculate disease burden.

Travel vaccines throughout history

Vaccinations are an important component of travel medicine. Beyond protection of travelers, vaccines are administered to prevent the importation of vaccine-preventable diseases at home and at destination. Proof of immunization to travel dates back to the first smallpox vaccine, developed by Edward Jenner in 1796. However, it took one century to generate the next vaccines against cholera, rabies, and typhoid fever. During the 20th century the armamentarium of vaccines used in travelers largely expanded with yellow fever, poliomyelitis, tetravalent meningococcal, and hepatitis A vaccines. The International Certificate of Inoculation and Vaccination was implemented in 1933. Currently there are vaccines administered to travelers following risk assessment, but also vaccines required according to the 2005 International Health Regulations and vaccines required at certain countries. Finally, within less than one year after the declaration of the coronavirus disease 2019 (COVID-19) pandemic, the first COVID-19 vaccines were launched and approved for emergency use to control the pandemic. Despite practical and ethical challenges, COVID-19 vaccine verifications have been widely used since spring 2021 in many activities, including international travel. In this article, we review the course of development of travel vaccines focusing on those for which a proof of vaccination has been or is required.

Immunoinformatics and Immunogenetics-Based Design of Immunogenic Peptides Vaccine against the Emerging Tick-Borne Encephalitis Virus (TBEV) and Its Validation through In Silico Cloning and Immune Simulation

Pegivirus, HPgV, earlier known as Gb virus and hepatitis G virus, is an enveloped, positive-stranded RNA and lymphotropic virus classified into the Flaviviridae family. The transmission routes primarily involve blood products, with infections worldwide, leading up to 25% of persistent infections. To date, no effective therapeutic means are available to resolve Pegivirus infections. Effective vaccine therapeutics are the best alternative to manage this disease and any associated potential pandemic. Thus, whole proteome-based mining of immunogenic peptides, i.e., CTL (cytotoxic T lymphocytes), HTL (helper T lymphocytes) and B cell epitopes were mapped to design a vaccine ensemble. Our investigation revealed that 29 different epitopes impart a critical role in immune response induction, which was also validated by exploring its physiochemical properties and experimental feasibility. In silico expression and host immune simulation using an agent-based modeling approach confirmed the induction of both primary and secondary immune factors such as IL, cytokines and antibodies. The current study warrants further lab experiments to demonstrate its efficacy and safety.

Humoral and cellular immune response to tick-borne-encephalitis (TBE) vaccination depends on booster doses in patients with Juvenile Idiopathic Arthritis (JIA)

Juvenile Idiopathic Arthritis (JIA) patients living in areas with high prevalence of tick-borne-encephalitis-virus-(TBEV)-infection are recommended for administration of inactivated TBE-vaccination. However, there are serious concerns regarding protective vaccine-induced immune responses against TBEV in immunocompromised patients. The present study aimed to analyze the humoral and cellular immune response to TBE-vaccination in previously TBE-vaccinated JIA patients compared to healthy controls (HC) including investigation of IgG-anti-TBEV avidity, neutralization capacity, cellular reactivity by IFNgamma-ELISPOT and cytokine secretion assays. Similar IgG-anti-TBEV antibody concentrations, neutralization titers and cellular reactivity were found between JIA and HC. The number and the early timing of booster vaccinations after primary vaccination had the most prominent effect on neutralizing antibodies in JIA and on IgG-anti-TBEV concentrations in both JIA and HC. Administration of booster vaccinations made it more likely for JIA patients to have IgG-anti-TBEV concentrations ≥165 VIEU/ml and avidities >60%. TNF-alpha inhibitors had a positive and MTX administration a negative effect on humoral immune responses. In conclusion, irrespective of having JIA or not, vaccinated children showed similar humoral and cellular immunity against TBEV several years after primary TBE-vaccination. However, in JIA, booster vaccinations mounted a significantly higher humoral immune response than in JIA without boosters. Our results highlight the need for timely administration of boosters particularly in JIA. Although immunosuppressive treatment at vaccinations in diagnosed JIA had a negative effect mainly on TBEV-specific cellular immunity, most JIA patients mounted a favorable humoral immune response which was maintained over time. Thus, successful TBE-vaccination seems highly feasible in JIA patients with immunosuppressive regimens.

Can the booster interval for the tick-borne encephalitis (TBE) vaccine 'FSME-IMMUN' be prolonged? - A systematic review

Tick-borne encephalitis (TBE) vaccines are effective and well tolerated. However, their acceptance and use by the public in endemic areas are suboptimal. To some extent this is due to the complicated dosing schedule requiring frequent boosters at variable intervals that even change with age. Simplification of the dosing schedule has failed so far as it is debated if the persistence of TBE virus (TBEV) antibodies is the only relevant factor for protection or if immune memory plays a decisive role as well. The objective here is to present the available evidence to determine the need for boosters and their interval after a primary series of three doses of FSME-IMMUN. A systematic literature review was conducted with a focus on serology, particularly seropersistence, immune memory, effectiveness, and vaccine breakthroughs (VB) of FSME-IMMUN. While after a 3-dose primary series seropositivity persisted for more than 10 years in >90% of younger subjects, it dropped to 37.5% in those 60 years or older. In contrast, field effectiveness of FSME-IMMUN remains high in irregularly vaccinated subjects and thus does not correlate well with the percentage of subjects achieving an arbitrarily defined threshold of persisting antibodies. FSME-IMMUN booster doses led to increases in antibody responses within 7 days. VB are rare and remain poorly understood. VB did not increase, and vaccine effectiveness did not significantly decrease with time since completion of the primary vaccination series or with the time since administration of the last vaccine dose. For all these reasons, data identified from this systematic review suggest that seropersistence alone does not explain the high effectiveness of FSME-IMMUN irrespective of the time since the last vaccine dose was administered. Induction of immunological memory characterized by a rapid and sustained secondary immune response is proving to be an alternative mechanism of action for protection against TBE. In this context Switzerland and Finland have adopted a longer booster interval (i.e., 10 years) following the three-dose primary immunization schedule without any evidence of harm at a population level. Longer booster intervals will likely drive up vaccine uptake. There is a lack of data to base an interval recommendation beyond 10 years.

Experimental Assessment of Possible Factors Associated with Tick-Borne Encephalitis Vaccine Failure

Currently the only effective measure against tick-borne encephalitis (TBE) is vaccination. Despite the high efficacy of approved vaccines against TBE, rare cases of vaccine failures are well documented. Both host- and virus-related factors can account for such failures. In this work, we studied the influence of mouse strain and sex and the effects of cyclophosphamide-induced immunosuppression on the efficacy of an inactivated TBE vaccine. We also investigated how an increased proportion of non-infectious particles in the challenge TBE virus would affect the protectivity of the vaccine. The vaccine efficacy was assessed by mortality, morbidity, levels of viral RNA in the brain of surviving mice, and neutralizing antibody (NAb) titers against the vaccine strain and the challenge virus. Two-dose vaccination protected most animals against TBE symptoms and death, and protectivity depended on strain and sex of mice. Immunosuppression decreased the vaccine efficacy in a dose-dependent manner and changed the vaccine-induced NAb spectrum. The vaccination protected mice against TBE virus neuroinvasion and persistence. However, viral RNA was detected in the brain of some asymptomatic animals at 21 and 42 dpi. Challenge with TBE virus enriched with non-infectious particles led to lower NAb titers in vaccinated mice after the challenge but did not affect the protective efficacy.

Distribution of Dermacentor silvarum and Associated Pathogens: Meta-Analysis of Global Published Data and a Field Survey in China

Dermacentor silvarum is an obligate blood sucking arthropod and transmits various pathogens to humans and domestic animals. Recently several new viruses were detected in D. silvarum as an emerging disease threat. In this study, we aimed to analyze its geographical distribution and associated pathogens. Data were collected from multiple sources, including a field survey, reference book, and literature review. We searched various electronic databases with the terms “Dermacentor silvarum” OR “D. silvarum” for studies published since 1963 and the positive rates for Dermacentor silvarum-associated pathogens were estimated by meta-analysis. D. silvarum was found only in four countries in Eurasia, ranging from 22° N to 57° N latitude. At least 20 human pathogens were associated with D. silvarum, including five species of spotted fever group rickettsiae, three species in the family of Anaplasmataceae, three genospecies in the complex Borrelia burgdorferi sensu lato, Francisella tularensis, Babesia venatorum, Coxiella buenetii, Borrelia miyamotoi, and five species of virus. Among them, Rickettsia raoultii was widely detected in D. silvarum, showing the highest pooled positive rate (25.15%; 95% CI 13.31–39.27). Our work presents the most comprehensive data and analysis (to our knowledge) for the geographical distribution of D. silvarum and associated pathogens, revealing an emerging threat to public health and stocking farming. Continued surveillance and further investigations should be enhanced.

Evervac: phase I/II study of immunogenicity and safety of a new adjuvant-free TBE vaccine cultivated in Vero cell culture

Approximately 10,000 cases of tick-borne encephalitis (TBE), a serious disease of the central nervous system caused by tick-borne encephalitis virus (TBEV), are registered worldwide every year. Vaccination against TBE remains the most essential measure of preventing the disease. Unlike available TBE vaccines, a new inactivated lyophilized candidate vaccine Evervac is produced in Vero continuous cell culture and its final formulation does not include aluminum-based adjuvants. To study the safety and immunogenicity of Evervac, healthy adults 18-60 y of age were immunized twice at 30-d intervals. The study was single-blind, randomized, comparative, controlled, and was conducted in TBE-endemic areas. The commercial lyophilized vaccine TBE-Moscow was used as a comparison treatment. The subjects were observed for incidence, severity, and duration of adverse reactions. It was shown that the severity of local and systemic reactions in the Evervac vaccine group was mild to moderate. There were no significant differences in the incidence of adverse reactions between the Evervac and TBE-Moscow vaccine groups. Immunization with Evervac produced a significant increase in geometric mean titer (GMT) of anti-TBEV antibodies in both initially seronegative and seropositive recipients. The seroconversion rate for the initially seronegative recipients was 69% (GMT = 1:214) after the first dose and reached 100% after the second dose. In these parameters, there were no significant differences between the study and control vaccine groups. Thus, the adjuvant-free Vero-based vaccine Evervac was well tolerated, had low reactogenicity, induced a pronounced immune response, and was overall non-inferior to the commercial adjuvanted TBE vaccine used as a control.

Tick-Borne Encephalitis Virus: A Quest for Better Vaccines against a Virus on the Rise

Tick-borne encephalitis virus (TBEV), a member of the family Flaviviridae, is one of the most important tick-transmitted viruses in Europe and Asia. Being a neurotropic virus, TBEV causes infection of the central nervous system, leading to various (permanent) neurological disorders summarized as tick-borne encephalitis (TBE). The incidence of TBE cases has increased due to the expansion of TBEV and its vectors. Since antiviral treatment is lacking, vaccination against TBEV is the most important protective measure. However, vaccination coverage is relatively low and immunogenicity of the currently available vaccines is limited, which may account for the vaccine failures that are observed. Understanding the TBEV-specific correlates of protection is of pivotal importance for developing novel and improved TBEV vaccines. For affording robust protection against infection and development of TBE, vaccines should induce both humoral and cellular immunity. In this review, the adaptive immunity induced upon TBEV infection and vaccination as well as novel approaches to produce improved TBEV vaccines are discussed.

Tick-Borne Encephalitis Virus Vaccines Contain Non-Structural Protein 1 Antigen and may Elicit NS1-Specific Antibody Responses in Vaccinated Individuals

Vaccination against tick-borne encephalitis (TBE) is based on the use of formalin-inactivated, culture-derived whole-virus vaccines. Immune response following vaccination is primarily directed to the viral envelope (E) protein, the major viral surface antigen. In Europe, two TBE vaccines are available in adult and pediatric formulations, namely FSME-IMMUN^® (Pfizer) and Encepur^® (GlaxoSmithKline). Herein, we analyzed the content of these vaccines using mass spectrometry (MS). The MS analysis revealed that the Encepur vaccine contains not only proteins of the whole virus particle, but also viral non-structural protein 1 (NS1). MS analysis of the FSME-IMMUN vaccine failed due to the high content of human serum albumin used as a stabilizer in the vaccine. However, the presence of NS1 in FSME-IMMUN was confirmed by immunization of mice with six doses of this vaccine, which led to a robust anti-NS1 antibody response. NS1-specific Western blot analysis also detected anti-NS1 antibodies in sera of humans who received multiple doses of either of these two vaccines; however, most vaccinees who received ≤3 doses were negative for NS1-specific antibodies. The contribution of NS1-specific antibodies to protection against TBE was demonstrated by immunization of mice with purified NS1 antigen, which led to a significant (p < 0.01) prolongation of the mean survival time after lethal virus challenge. This indicates that stimulation of anti-NS1 immunity by the TBE vaccines may increase their protective effect.

Efficacy, immunogenicity and safety of vaccination in adult patients with autoimmune inflammatory rheumatic diseases: a systematic literature review for the 2019 update of EULAR recommendations

Aim

To present a systematic literature review (SLR) on efficacy, immunogenicity and safety of vaccination in adult patients with autoimmune inflammatory rheumatic diseases (AIIRD), aiming to provide a basis for updating the EULAR evidence-based recommendations.

Methods

An SLR was performed according to the standard operating procedures for EULAR-endorsed recommendations. Outcome was determined by efficacy, immunogenicity and safety of vaccination in adult patients with AIIRD, including those receiving immunomodulating therapy. Furthermore, a search was performed on the effect of vaccinating household members of patients with AIIRD on the occurrence of vaccine-preventable infections in patients and their household members (including newborns). The literature search was performed using Medline, Embase and the Cochrane Library (October 2009 to August 2018).

Results

While most investigated vaccines were efficacious and/or immunogenic in patients with AIIRD, some were less efficacious than in healthy control subjects, and/or in patients receiving immunosuppressive agents. Adverse events of vaccination were generally mild and the rates were comparable to those in healthy persons. Vaccination did not seem to lead to an increase in activity of the underlying AIIRD, but insufficient power of most studies precluded arriving at definite conclusions. The number of studies investigating clinical efficacy of vaccination is still limited. No studies on the effect of vaccinating household members of patients with AIIRD were retrieved.

Conclusion

Evidence on efficacy, immunogenicity and safety of vaccination in patients with AIIRD was systematically reviewed to provide a basis for updated recommendations.

Characterizing the cellular attachment receptor for Langat virus

Tick-borne encephalitis infections have increased the last 30 years. The mortality associated to this viral infection is 0.5 to 30% with a risk of permanent neurological sequelae, however, no therapeutic is currently available. The first steps of virus-cell interaction, such as attachment and entry, are of importance to understand pathogenesis and tropism. Several molecules have been shown to interact with tick-borne encephalitis virus (TBEV) at the plasma membrane surface, yet, no studies have proven that these are specific entry receptors. In this study, we set out to characterize the cellular attachment receptor(s) for TBEV using the naturally attenuated member of the TBEV complex, Langat virus (LGTV), as a model. Inhibiting or cleaving different molecules from the surface of A549 cells, combined with inhibition assays using peptide extracts from high LGTV binding cells, revealed that LGTV attachment to host cells is dependent on plasma membrane proteins, but not on glycans or glycolipids, and suggested that LGTV might use different cellular attachment factors on different cell types. Based on this, we developed a transcriptomic approach to generate a list of candidate attachment and entry receptors. Our findings shed light on the first step of the flavivirus life-cycle and provide candidate receptors that might serve as a starting point for future functional studies to identify the specific attachment and/or entry receptor for LGTV and TBEV.

Seropersistence and booster response following vaccination with FSME-IMMUN in children, adolescents, and young adults

BACKGROUND

Tick-borne encephalitis (TBE) is a viral disease that can have a severe clinical course and considerable long-term morbidity. As no curative treatment exists, vaccination is the primary means of prevention. Long-term antibody seropersistence 2-5 years after the 3-dose primary immunization and 3-10 years after first booster was evaluated, as well as booster responses in children, adolescents and young adults.

METHODS

Subjects who participated in these phase 4 prospective, open-label follow-up studies received all vaccinations with FSME-IMMUN. After 3-dose primary immunization, subjects were followed for 2-5 years. Overall, 205 out of 358 subjects (57%) received the first booster and 179 of these subjects (87%) enrolled in a further 10-year follow-up. Antibody seropersistence was assessed annually. Subjects with a TBE antibody titer below a pre-specified cut-off at the yearly blood draw received a booster. Seropositivity rates and geometric mean fold rises (GMFRs) were assessed.

RESULTS

In children who received their 3-dose primary immunization between 1 and 15 years of age, the seropositivity rate 5 years after the 3rd dose was 84.9% by NT and 72.0% by ELISA. One month post-first booster, all subjects were seropositive by NT and 98.5% by ELISA. Response to first booster by GMFR ranged from 3.7 to 11.4. At 5 years post-first booster, seropositivity was 99.4% by NT and 97.5% by ELISA, and at 10 years, was 90.3% by NT and 87.7% by ELISA. Although seropositivity rates differed between age groups, all subjects (100%) who received a second booster responded with a robust increase of TBEV antibodies.

DISCUSSION

Long-lasting seropersistence of TBEV antibodies after the 3-dose primary immunization and first booster was demonstrated as well as a competent immune memory response in those who received a first or second booster at any time during the 15-year follow-up. Therefore, an extension of FSME-IMMUN booster interval up to 10 years after the 3-dose primary immunization seems warranted. ClinicalTrials.gov Identifier: NCT00894686.

Perceptions of tick-borne encephalitis risk: a survey of travellers and travel clinics from Canada, Germany, Sweden and the UK

BACKGROUND

While the worldwide endemicity of tick-borne encephalitis (TBE) has been increasing, a lack of awareness of the risks of this life-threatening disease may be leading to an underutilization of preventive measures among travellers to TBE-endemic regions. This study's objectives were to assess travellers' awareness of TBE and advice-seeking attitudes, and to evaluate practices of travel clinics regarding pre-travel advice.

METHODS

We used an online questionnaire to identify individuals aged 18-65 years residing in the UK, Germany, Canada and Sweden, who had travelled to TBE-endemic countries between 2013 and 2016. This sample was defined as the visit-risk sample. Of these, the first 375 respondents who reported that they had engaged in pre-defined at-risk activities (e.g. hiking in forests) were asked to complete an additional online survey and were included in the activity-risk sub-sample. We also used an online/phone questionnaire to interview travel clinic personnel.

RESULTS

The TBE visit-risk sample included 4375 individuals; 69% had heard of the disease and 32% had heard of a TBE vaccine. Before travelling, travellers most commonly sought information online (26%); fewer travellers consulted family doctors (8%) or travel clinics (5%). In the activity-risk sample, 79% of the travellers were aware of at least one correct TBE prevention measure; however, only 15% reported being vaccinated within the past 3 years, with 11% of vaccinated travellers doing so following a clinic's recommendation. One hundred and eighty travel clinic representatives responded and reported that TBE vaccination was recommended to an average of 61% of travellers to endemic regions. Vaccination-reminder services such as follow-up appointments, e-mail and text reminders were offered by 50% of the clinics.

CONCLUSIONS

There is a need to increase awareness of the risk and prevention of TBE among travellers to endemic countries, and travel clinics could play an important role in this process. 5975671594001tay062media15975671594001.

Tick-borne encephalitis: A 43-year summary of epidemiological and clinical data from Latvia (1973 to 2016)

Background

The incidence of tick-borne encephalitis (TBE) varies significantly over time. To better understand the annual incidence of all TBE cases in Latvia we investigated the disease burden in the country from 1973–2016 using several available sources and case definitions.

Methods

We identified cases of TBE from an electronic database (maintained by the Centre for Disease Prevention and Control of Latvia [CDPC]) by the use of ICD-10 diagnosis codes for TBE (A84; A84.0; A84.1; A84.8; A84.9). In addition, previously unreported TBE cases were found by review of TBE diagnoses according to ICD-10 codes in four hospital databases.

Results

From 1973 to 2016 a total of 15,193 TBE cases were reported to the CDPC, 2,819 of which were reported from January 2007 through December 2016, additionally for this time period, 104 cases were identified via hospital survey. From all 2,923 reported cases (2007–2016), 1,973 met TBE case definition criteria and were included in the TBE study analysis. The highest average 10 year incidence was observed from 1990–1999 (27.9 cases per 100,000; range 4.6–53.0), however, the average 10-year incidence from 2007–2016 using officially adopted TBE case definition was 9.6 cases per 100,000 (range 5.8–14.6). For this 10-year time period most cases were adults (95.1%) and male (52.2%). The most common clinical form of TBE was meningitis (90.6%). A tick bite prior to TBE onset was reported in 60.6% of TBE cases and 98.2% of cases were not vaccinated against TBE.

Conclusion

The data demonstrate that the incidence of TBE varies by about one third based on the case definition used. TBE occurs almost entirely in the unvaccinated population. Regular TBE awareness campaigns could encourage the population in Latvia to use protective measures to further control TBE in the country, either via vaccination or tick avoidance.

Memory T Cells in Flavivirus Vaccination

Flaviviruses include many medically important viruses, such as Dengue virus (DENV), Japanese encephalitis (JEV), tick-borne encephalitis (TBEV), West Nile (WNV), yellow fever (YFV), and Zika viruses (ZIKV). Currently, there are licensed human vaccines for DENV, JEV, TBEV and YFV, but not for WNV or ZIKV. Memory T cells play a central role in adaptive immunity and are important for host protection during flavivirus infection. In this review, we discuss recent findings from animal models and clinical trials and provide new insights into the role of memory T cells in host protective immunity upon vaccination with the licensed flavivirus vaccines.

Immunogenicity and Protective Activity of a Chimeric Protein Based on the Domain III of the Tick-Borne Encephalitis Virus E Protein and the OmpF Porin of Yersinia pseudotuberculosis Incorporated into the TI-Complex

Tick-borne encephalitis (TBE) is a widespread, dangerous infection. Unfortunately, all attempts to create safe anti-TBE subunit vaccines are still unsuccessful due to their low immunogenicity. The goal of the present work was to investigate the immunogenicity of a recombinant chimeric protein created by the fusion of the EIII protein, comprising domain III and a stem region of the tick-borne encephalitis virus (TBEV) E protein, and the OmpF porin of Yersinia pseudotuberculosis (OmpF-EIII). Adjuvanted antigen delivery systems, the tubular immunostimulating complexes (TI-complexes) based on the monogalactosyldiacylglycerol from different marine macrophytes, were used to enhance the immunogenicity of OmpF-EIII. Also, the chimeric protein incorporated into the most effective TI-complex was used to study its protective activity. The content of anti-OmpF-EIII antibodies was estimated in mice blood serum by enzyme-linked immunosorbent assay (ELISA). To study protective activity, previously immunized mice were infected with TBEV strain Dal’negorsk (GenBank ID: FJ402886). The animal survival was monitored daily for 21 days. OmpF-EIII incorporated into the TI-complexes induced about a 30–60- and 5–10-fold increase in the production of anti-OmpF-EIII and anti-EIII antibodies, respectively, in comparison with the effect of an individual OmpF-EIII. The most effective vaccine construction provided 60% protection. Despite the dramatic effect on the specific antibody titer, the studied TI-complex did not provide a statistically significant increase in the protection of OmpF-EIII protein. However, our results provide the basis of the future search for approaches to design and optimize the anti-TBEV vaccine based on the OmpF-EIII protein.

Recombinant Fusion Protein Joining E Protein Domain III of Tick-Borne Encephalitis Virus and HSP70 of Yersinia pseudotuberculosis as an Antigen for the TI-Complexes

Domain III (DIII) of the tick-borne encephalitis virus (TBEV) protein E contains epitopes, which induce antibodies capable of neutralizing the virus. To enhance the immunogenicity of this protein, which has a low molecular weight, the aim of the present work was to express, isolate, and characterize a chimeric protein based on the fusion of the bacterial chaperone HSP70 of Yersinia pseudotuberculosis and EIII (DIII + stem) as a prospective antigen for an adjuvanted delivery system, the tubular immunostimulating complex (TI-complex). The chimeric construction was obtained using pET-40b(+) vector by ligating the respective genes. The resulting plasmid was transformed into DE3 cells for the heterologous expression of the chimeric protein, which was purified by immobilized metal affinity chromatography (IMAC). ELISA, differential scanning calorimetry, intrinsic fluorescence, and computational analysis were applied for the characterization of the immunogenicity and conformation of the chimeric protein. Mice immunization showed that the chimeric protein induced twice the number of anti-EIII antibodies in comparison with EIII alone. In turn, the incorporation of the HSP70/EIII chimeric protein in the TI-complex resulted in a twofold increase in its immunogenicity. The formation of this vaccine construction was accompanied by significant conformational changes in the chimeric protein. Using HSP70 in the content of the chimeric protein represents an efficient means for presenting the main antigenic domain of the TBEV envelope protein to the immune system, whereas the incorporation of this chimeric protein into the TI-complex further contributes to the development of a stronger immune response against the TBEV infection.

Zika virus vaccines: immune response, current status, and future challenges

Zika virus (ZIKV) is the most recent mosquito-transmitted virus to cause a global health crisis following its entrance into a naïve population in the Western Hemisphere. Once the ZIKV outbreak began investigators rapidly established small and large animal models of pathogenesis, developed a number candidate vaccines using different platforms, and defined mechanisms of protection. In this review, we characterize the adaptive immune response elicited by ZIKV infections and vaccines, the status of ongoing clinical trials in humans, and discuss future challenges within the field.

Second five-year follow-up after a booster vaccination against tick-borne encephalitis following different primary vaccination schedules demonstrates at least 10 years antibody persistence

BACKGROUND

Tick borne encephalitis (TBE) endemic zones are expanding. We previously evaluated long term persistence of antibody 5 years after the first booster immunization following different primary immunization schedules with the polygeline-free inactivated TBE vaccine (TBEvac) in adults and adolescents. Here, we report anti-TBE virus (TBEV) antibody persistence from 6 to 10 years post-booster administration.

METHODS

This was a phase IV, open-label, single-center, second extension study (NCT01562444), conducted in Czechia. Healthy adults and adolescents ≥12 years who had received 3 different primary vaccination schedules (rapid, conventional and accelerated conventional) in the parent study and a booster dose before (12-18 months post-primary series completion) or at the beginning (3 years post-primary series completion) of the first extension study were screened and enrolled in this study. Blood samples were collected yearly and anti-TBEV antibody response was evaluated by neutralizing test (NT) antibody assays. Analysis was performed overall and per age strata: 15-49 years, ≥50 years, and ≥60 years.

RESULTS

Of 206 screened individuals, 191 completed the study. Overall, 90-100% of participants in the all-screened set and ≥97% in the per-protocol set had the clinically meaningful threshold of protection (NT titers ≥10) across all timepoints, regardless of the primary vaccination schedule. Overall, antibody geometric mean titers (GMTs) varied from 134 to 343 in the all-screened set. Older age groups showed overall lower GMTs, although GMTs remained higher than NT titers ≥10 up to year 10 in all groups.

CONCLUSION

This study showed long-term persistence of anti-TBEV NT antibodies for up to 10 years after the first booster dose of TBEvac in all age groups, regardless of the primary vaccination schedule.

Are we prepared for emerging flaviviruses in Europe? Challenges for vaccination

Tick-borne encephalitis and West Nile fever are endemic flavivirus diseases in Europe. Climate change, virus evolution, and social factors may increase the risk of these flavivirus infections and may lead to the emergence of other flaviviruses in Europe that are endemic in (sub)tropical regions of the world. Control of the spread of flaviviruses is very difficult considering the cycling of flaviviruses between arthropod vectors and animal reservoir hosts. The increasing threat of flavivirus infections emphasizes the necessity of a sustainable vector surveillance system, an active animal health surveillance system and an adequate human surveillance system for early detection of flavivirus infections. Vaccination is the most important approach to prevent flavivirus infections. Effective inactivated whole virus vaccines against tick-borne encephalitis (TBE) infection are available. Implementation of TBE vaccination based on favorable cost-effectiveness estimates per region and per target group can reduce the disease burden of TBE infection. At present, several West Nile virus (WNV) vaccine candidates are in various stages of clinical development. A major challenge for WNV vaccine candidates is to demonstrate efficacy, because of the sporadic nature of unpredictable WNV outbreaks. Universal WNV vaccination is unlikely to be cost-effective, vaccination of high-risk groups will be most appropriate to protect against WNV infections.

Tick-borne encephalitis in patients vaccinated against this disease

BACKGROUND

Information on tick-borne encephalitis (TBE) in patients already vaccinated against the disease is limited.

OBJECTIVES

To compare the course and outcome in patients with vaccination breakthrough TBE with findings in patients who developed TBE without previous vaccination.

METHODS

All adult patients diagnosed with TBE at a single medical centre during a 16-year period and who had received at least two doses of TBE vaccine before the onset of illness qualified for the study. For each patient with breakthrough TBE, two unvaccinated sex- and age-matched patients, diagnosed with TBE in the same year, were included for comparison.

RESULTS

Amongst 2332 patients diagnosed with TBE in the period 2000-2015, 39 (1.7%) had been vaccinated against the disease. Their median age was 59 (20-83) years; 22 of 39 (56.4%) were male. In comparison with unvaccinated patients with TBE, those with breakthrough disease more often experienced a monophasic course of illness (P = 0.006), had a higher CSF leucocyte count (P = 0.005), more often had urine retention (P = 0.012), more often needed ICU treatment (P = 0.009), were hospitalized for longer (P = 0.002) and had more severe acute illness (P = 0.004 for simple clinical assessment, P = 0.001 for severity score).

CONCLUSION

In addition to several findings corroborating previous results in patients with vaccination breakthrough TBE, such as older age and the presence of a particular specific serum antibody pattern indicating anamnestic response, findings in this study indicate that the acute illness in patients with breakthrough TBE is more severe than in unvaccinated sex- and age-matched patients who develop the disease.

Progress and Works in Progress: Update on Flavivirus Vaccine Development

Most areas of the globe are endemic for at least one flavivirus, putting billions at risk for infection. This diverse group of viral pathogens causes a range of manifestations in humans from asymptomatic infection to hemorrhagic fever to encephalitis to birth defects and even death. Many flaviviruses are transmitted by mosquitos and have expanded in geographic distribution in recent years, with dengue virus being the most prevalent, infecting approximately 400 million people each year. The explosive emergence of Zika virus in Latin America in 2014 refocused international attention on this medically important group of viruses. Meanwhile, yellow fever has caused major outbreaks in Africa and South America since 2015 despite a reliable vaccine. There is no vaccine for Zika yet, and the only licensed dengue vaccine performs suboptimally in certain contexts. Further lessons are found when considering the experience with Japanese encephalitis virus, West Nile virus, and tickborne encephalitis virus, all of which now have protective vaccination in human or veterinary populations. Thus, vaccination is a mainstay of public health strategy for combating flavivirus infections; however, numerous challenges exist along the path from development to delivery of a tolerable and effective vaccine. Nevertheless, intensification of investment and effort in this area holds great promise for significantly reducing the global burden of disease attributable to flavivirus infection.

Structural Basis for CD4+ T Cell Epitope Dominance in Arbo-Flavivirus Envelope Proteins: A Meta-Analysis

A meta-analysis of CD4+ T cell epitope maps reveals clusters and gaps in envelope-protein (E protein) immunogenicity that can be explained by the likelihood of epitope processing, as determined by E protein three-dimensional structures. Differential processing may be at least partially responsible for variations in disease severity among arbo-flaviruses and points to structural features that modulate protection from disease.

Cross-neutralisation of viruses of the tick-borne encephalitis complex following tick-borne encephalitis vaccination and/or infection

The tick-borne encephalitis complex contains a number of flaviviruses that share close genetic homology, and are responsible for significant human morbidity and mortality with widespread geographical range. Although many members of this complex have been recognised for decades, licenced human vaccines with broad availability are only available for tick-borne encephalitis virus. While tick-borne encephalitis virus vaccines have been demonstrated to induce significant protective immunity, as determined by virus-neutralisation titres, vaccine breakthrough (clinical infection following complete vaccination), has been described. The aim of this study was to confirm the cross-neutralisation of tick-borne flaviviruses using mouse immune ascitic fluids, and to determine the magnitude of cross-neutralising antibody titres in sera from donors following tick-borne encephalitis vaccination, infection, and vaccine breakthrough. The results demonstrate that there is significant cross-neutralisation of representative members of the tick-borne encephalitis complex following vaccination and/or infection, and that the magnitude of immune responses varies based upon the exposure type. Donor sera successfully neutralised most of the viruses tested, with 85% of vaccinees neutralising Kyasanur forest disease virus and 73% of vaccinees neutralising Alkhumra virus. By contrast, only 63% of vaccinees neutralised Powassan virus, with none of these neutralisation titres exceeding 1:60. Taken together, the data suggest that tick-borne encephalitis virus vaccination may protect against most of the members of the tick-borne encephalitis complex including Kyasanur forest disease virus and Alkhumra virus, but that the neutralisation of Powassan virus following tick-borne encephalitis vaccination is minimal.

Tick-borne encephalitis in China: A review of epidemiology and vaccines

Tick-borne encephalitis (TBE) has been shown to be endemic in northern and western China, including the three mountain areas in Heilongjiang, Jilin, Inner Mongolia, and Xinjiang. In addition, serology evidence shows that there is human infection in south-west provinces of China, including Xizang (Tibet) and Yunnan. TBE in China is caused by the Far Eastern TBE virus subtype and there is no biphasic course for disease presentation. The majority of TBE cases in China have occurred in people who were living or working in forests. TBE vaccines became available in China soon after the virus was identified in the country and they have been used for more than 60years to date, with different vaccine types used in different periods. Currently, an inactivated and purified whole-virus vaccine produced in a primary hamster kidney (PHK) cell line is used. Clinical trials have shown this vaccine to have higher immunogenicity and fewer adverse reactions than previous TBE vaccines. This paper provides a review on the epidemiology of TBE and the history of TBE vaccination in China.

Prediction of promiscuous T-cell epitopes in the Zika virus polyprotein: An in silico approach

OBJECTIVE

To predict immunogenic promiscuous T cell epitopes from the polyprotein of the Zika virus using a range of bioinformatics tools. To date, no epitope data are available for the Zika virus in the IEDB database.

METHODS

We retrieved nearly 54 full length polyprotein sequences of the Zika virus from the NCBI database belonging to different outbreaks. A consensus sequence was then used to predict the promiscuous T cell epitopes that bind MHC 1 and MHC II alleles using PorPred1 and ProPred immunoinformatic algorithms respectively. The antigenicity predicted score was also calculated for each predicted epitope using the VaxiJen 2.0 tool.

RESULTS

By using ProPred1, 23 antigenic epitopes for HLA class I and 48 antigenic epitopes for HLA class II were predicted from the consensus polyprotein sequence of Zika virus. The greatest number of MHC class I binding epitopes were projected within the NS5 (21%), followed by Envelope (17%). For MHC class II, greatest number of predicted epitopes were in NS5 (19%) followed by the Envelope, NS1 and NS2 (17% each). A variety of epitopes with good binding affinity, promiscuity and antigenicity were predicted for both the HLA classes.

CONCLUSION

The predicted conserved promiscuous T-cell epitopes examined in this study were reported for the first time and will contribute to the imminent design of Zika virus vaccine candidates, which will be able to induce a broad range of immune responses in a heterogeneous HLA population. However, our results can be verified and employed in future efficacious vaccine formulations only after successful experimental studies.

Changes in the Proteome of Langat-Infected Ixodes scapularis ISE6 Cells: Metabolic Pathways Associated with Flavivirus Infection

Background

Ticks (Family Ixodidae) transmit a variety of disease causing agents to humans and animals. The tick-borne flaviviruses (TBFs; family Flaviviridae) are a complex of viruses, many of which cause encephalitis and hemorrhagic fever, and represent global threats to human health and biosecurity. Pathogenesis has been well studied in human and animal disease models. Equivalent analyses of tick-flavivirus interactions are limited and represent an area of study that could reveal novel approaches for TBF control.

Methodology/Principal Findings

High resolution LC-MS/MS was used to analyze the proteome of Ixodes scapularis (Lyme disease tick) embryonic ISE6 cells following infection with Langat virus (LGTV) and identify proteins associated with viral infection and replication. Maximal LGTV infection of cells and determination of peak release of infectious virus, was observed at 36 hours post infection (hpi). Proteins were extracted from ISE6 cells treated with LGTV and non-infectious (UV inactivated) LGTV at 36 hpi and analyzed by mass spectrometry. The Omics Discovery Pipeline (ODP) identified thousands of MS peaks. Protein homology searches against the I. scapularis IscaW1 genome assembly identified a total of 486 proteins that were subsequently assigned to putative functional pathways using searches against the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. 266 proteins were differentially expressed following LGTV infection relative to non-infected (mock) cells. Of these, 68 proteins exhibited increased expression and 198 proteins had decreased expression. The majority of the former were classified in the KEGG pathways: “translation”, “amino acid metabolism”, and “protein folding/sorting/degradation”. Finally, Trichostatin A and Oligomycin A increased and decreased LGTV replication in vitro in ISE6 cells, respectively.

Conclusions/Significance

Proteomic analyses revealed ISE6 proteins that were differentially expressed at the peak of LGTV replication. Proteins with increased expression following infection were associated with cellular metabolic pathways and glutaminolysis. In vitro assays using small molecules implicate malate dehydrogenase (MDH2), the citrate cycle, cellular acetylation, and electron transport chain processes in viral replication. Proteins were identified that may be required for TBF infection of ISE6 cells. These proteins are candidates for functional studies and targets for the development of transmission-blocking vaccines and drugs.

High-throughput proteomics offers an approach to evaluate changes in cell protein levels following arboviral infection. Research to understand the molecular basis of human-flavivirus interactions has advanced significantly over the past decade, but comparatively little is known regarding interactions between ticks and tick-borne flaviviruses (TBFs). Here, we employed a proteomics approach using an I. scapularis ISE6 cell line infected with the TBF Langat virus (LGTV) to identify proteins and biochemical pathways affected by viral infection. An LC-MS/MS approach was used to identify proteins that were subsequently assigned to putative cellular pathways based on orthology to proteins in the KEGG database. Biochemical pathways common among arthropods in response to infection with flavivirus and possibly unique to tick-flavivirus interactions, were identified. In vitro cellular assays using small molecules suggest the involvement of the ISE6 proteins, malate dehydrogenase (MDH2), and mitochondria in viral replication. These analyses provide a basis for further studies to identify tick proteins associated with viral replication that could be targeted to disrupt TBF transmission.

Immunogenicity against Far Eastern and Siberian subtypes of tick-borne encephalitis (TBE) virus elicited by the currently available vaccines based on the European subtype: systematic review and meta-analysis

Tick-borne encephalitis (TBE) virus, which is usually divided into European, Far Eastern and Siberian subtypes, is a serious public health problem in several European and Asian countries. Vaccination is the most effective measure to prevent TBE; cross-subtype protection elicited by the TBE vaccines is biologically plausible since all TBE virus subtypes are closely related. This manuscript systematically explores available data on the cross-subtype immunogenicity elicited by the currently available Western vaccines based on the European subtype. Completed immunization course of 3 doses of both Western vaccines determined very high seroconversion/seropositivity rates against both Far Eastern and Siberian subtypes among previously flavivirus-naïve subjects. All but one study found no statistically significant difference in titers of neutralizing antibodies against strains belonging to homologous and heterologous subtypes. Pooled analysis of randomized controlled trials on head-to-head comparison of immunogenicity of Western and Russian TBE vaccines did not reveal differences in seroconversion rates against Far Eastern isolates in either hemagglutination inhibition (risk ratio = 0.98, p = 0.83) or enzyme-linked immunosorbent (risk ratio = 0.95, p = 0.44) assays after 2 vaccine doses. This suggests that, in regions where a heterogeneous TBE virus population circulates, vaccines based on the European subtype may be used alongside vaccines based on the Far Eastern subtype. Studies on the field effectiveness of TBE vaccines and investigation of vaccination failures, especially in countries where different subtypes co-circulate, will further elucidate TBE vaccination-induced cross-subtype protection.