Tick-borne encephalitis virus (TBEV) is a serious viral infection that affects the central nervous system. It was estimated that between 1990 and 2009 a total of 169,937 cases of TBE were recorded in Europe. TBEV belongs to genus Flavivirus that comprises over 70 viruses, many of them are important human pathogens. Most members are either transmitted by mosquitoes e.g. West Nile virus (WNV), Dengue virus (DENV) or ticks e.g. TBEV. Due to the extensive antigenic cross-reactivity among flaviviruses serological diagnosis of TBE infections is commonly difficult in areas where more than one virus type circulates. Particularly, a situation now exists in Europe, where TBEV and WNV are endemic in many countries Thus, this thesis focused on the one hand on optimization of serological test systems using recombinant envelope protein domain III (rED3). It represents domain 3 of the major antigen, the surface protein E, which additionally has been shown to induce flavivirus specific neutralizing antibodies. Therefore rED3 was expressed and purified and its application as antigen in ELISA for TBEV diagnosis was verified. On the other hand a memory B-cell assay was established to analyse antiviral immunity after TBEV-vaccination. Here rED3 was used as antigen to determine the frequency of rED3 specific antibody-secreting cells (ASCs). Vaccination is the most effective method of preventing TBE disease and is currently recommended for all those who live and work or travel to areas of TBE endemicity. An essential requirement of any vaccine is the induction of long-term protective immunity. Several vaccines have defined levels of serum antibody (as measured by ELISA, haemagglutination inhibition test, or neutralisation test) that serve as correlates or surrogates of protective immunity. But this does not take account of vaccine induced memory B cells. Although, not providing direct protection against infection, they represent an important second line of immune defence that is initiated only if pre existing antibody levels are too low to prevent infection or if the invading pathogen is able to circumvent the pre-existing antibody response. A thorough understanding of the frequencies of antigen-specific memory B cells and their relationship with the antibodies in serum serological memory is likely to be critical to give information about the long-term efficacy of vaccine as well as its correlates of protection. This thesis focuses on the establishment of a recombinant protein based ELISA and of a memory B cell assay for analysis of specific antiviral immunity after vaccination with the following two objectives: (1) Expression and purification of recombinant envelope protein domain 3 (rED3) and verification of its application as antigen in ELISA for TBEV diagnosis; (2) Establishment of a memory B cells assay using rED3 for determination of frequency of rED3 specific antibody-secreting cells (ASCs) in individuals vaccinated against TBE. In this study, TBEV- and WNV-specific antigen ED3 was expressed in E. coli as MBP fusion proteins with C-terminal histidine tag using pMAL-c2x vector. By purification with amylose affinity chromatography followed by nickel affinity chromatography, highly purified TBEV rED3 and WNV-rED3 were obtained. Nevertheless, using TBEV-rED3 protein in Western Blot unspecific reaction with serum antibodies of negative serum was detected and a differentiation between WNV infection and TBEV was impossible, probably due to the MBP moiety. However, using the purified rED3 protein as antigen in ELISA, TBE virus-specific antibodies were detected specifically. Twenty-three serum samples predefined as TBEV positive were tested positive by rED3-based ELISA and commercial IgG ELISA. Five predefined negative serum samples were tested negative by rED3-based IgG ELISA as well as commercial IgG ELISA. But cross reactivity of WNV and DENV positive sera was detected in 15 of 18 sera by commercial ELISA. On the other hand, these samples were found negative in TBEV rED3-based ELISA. Thus, TBEV-rED3-based ELISA allows a differentiation of infections caused by TBE serogroup and mosquito-borne flaviviruses but not the inactivated virus based commercial ELISA. Interestingly, compared to neutralisation test the specificity of rED3-based ELISA obtained 100% with a sensitivity of 91.6%. In contrast, the commercial ELISA obtained 100 % sensitivity but a low specificity with only 42.8%. In order to determine frequency of antigen-specific antibody secreting cells (ASCs) produced by individuals who received the vaccination against TBE, peripheral blood mononuclear cells (PBMCs) were isolated from blood samples. Subsequently, memory B cells were activated with R848 (Resiquimod) and human recombinant IL-2 (hrIL-2) for 72 hours in 37°C, 5% CO2, 90% humidity. After 72 hours of incubation, Enzyme-Linked Immunospot (ELISPOT) detected antigen-specific memory B cells. In order to evaluate specificity of TBEV-rED3 in ELISPOT, other antigens including WNV-rED3, Maltose binding protein (MBP) and Influenza Nucleoprotein (NP) were included. Study subjects could be separated into two groups: last vaccination before 5 years or longer than 10 years. TBEV-rED3 specific ASCs could be detected in 11 of 12 TBE vaccinated individuals with different vaccination history and even low serum anti-TBE antibodies levels. TBEV-rED3 specific ASCs were found with frequency of ranging 0.016-0.188 % per total IgG ASCs and lower than frequency of Influenza-NP specific ASCs (between 0.012-0.51%). But TBE-specific memory B cells could be maintained for more than 20 years of post-vaccination. There was a significant difference in number of ASCs between vaccinated and non-vaccinated group (p<0.05). Interestingly, there was no significant difference between TBE vaccinated groups between 1-5 years (mean of 2.5 years) and >10 years (mean of 16.5 years) since vaccination (p>0.05). These finding proved that memory B cells have been stable for years and are maintained up to 25 years since last vaccination. A statistic analysis showed that there was no significant correlation between serum levels of anti-TBEV antibodies and the frequency of rED3 specific IgG ASCs (p>0.05, Spearman’s coefficient r = 0.36). A similar result was also indicated for influenza-vaccinated individuals (p>0.05, Spearman’s coefficient r = 0.27). These findings revealed that memory B cells and plasma cells maybe play an independently role in maintaining of immunological memory. Anyway, neutralizing antibodies have been found in all vaccines (a Geometric mean titre (GMT) of 96.04, 95% confident interval (CI): 52.76-174.8) and thus were maintained for a long time since last vaccination. Interestingly, the quantitative determination of specific IgG in TBE post-vaccination sera by rED3-based ELISA exhibits a good correlation with neutralizing antibody titres. The presence of specific antibodies in rED3-based ELISA is therefore highly predictive for the presence of neutralizing antibodies, and this correlation can probably be used in the future to establish guidelines for recommendations of booster vaccinations. Additionally, it became apparent that the number of previous booster vaccinations correlated strongly with the frequency of circulating memory B cells. As expected, individuals who received a booster increased both the specific antibody titre and frequency of antigen specific memory B cells. This suggests that immunological long-term memory induced by booster immunizations is better reflected by the circulating memory B cells than the amount of the antibody titre. Thus, memory B cells seem to be a more reliable parameter for the assessment of long-term immunity. Taken together, a highly antigenic rED3 using the bacterial expression system was produced and it is a promising alternative to whole inactivated virus in ELISA. Notably, rED3 was a reliable antigen for detecting antigen-specific memory B cells in individuals who have been previously TBEV vaccinated. This study provides data on immunological memory for TBE vaccination and might be useful for reconsideration of recommendations for booster dose. In conclusion, boosters of vaccination should be recommended for all individuals who live and work or travel to areas of TBE endemicity. As consequently, vaccine-induced protection is enhanced by both strong humoral and cell-mediated immune responses. If pace of pathogenesis is rapidly growing, pre-existing virus-specific antibodies represent the first line of defence against infection before the memory response is fully activated and implemented. They clearly function best together to efficiently protect against disease.

Det finns olika sätt att förstå innebörden av fenomenet ’risk för TBE’ och hur den kan presenteras. Denna uppsats problematiserar den befintliga förståelsen och tolkning av fenomenet inom vårdinstanser och forskning. Metoden och empirin som den nuvarande kunskapsbild bygger på, analyseras metodiskt genom en synergi mellan två tolkningsmetoder. Tillvägagångssättets mål är att visa att en annan metodansats behövs för att nå en vidareutveckling av förståelsen inom ämnet. Grundad teori används för att nå slutsatser om vilken kunskap som ska presenteras som relevant empiri och utifrån empirin, genereras teorin att risk för TBE innefattar mer än incidens och att nuvarande sätt att se på risk för TBE har sina tillkortakommanden. / There are a variety of ways to understand the meaning of the phenomenon 'risk for TBE' and how it can be presented. This paper problematises the existing understanding and interpretation of the phenomena by health services and research. The method and empirical knowledge of the present understanding is analysed methodically by a synergy between two interpretation methods. The aim is to show that another methodological approach is needed to achieve further development of the understanding of the subject. Grounded theory is used to reach conclusions about what knowledge could be presented as relevant empirical material for further studies. The empirical material, in turn, generates the theory that risk for TBE covers more than incidence and that the current way of looking at risk of TBE has its shortcomings.

Tick-borne encephalitis virus (TBEV) is a serious viral infection that affects the central nervous system. It was estimated that between 1990 and 2009 a total of 169,937 cases of TBE were recorded in Europe. TBEV belongs to genus Flavivirus that comprises over 70 viruses, many of them are important human pathogens. Most members are either transmitted by mosquitoes e.g. West Nile virus (WNV), Dengue virus (DENV) or ticks e.g. TBEV. Due to the extensive antigenic cross-reactivity among flaviviruses serological diagnosis of TBE infections is commonly difficult in areas where more than one virus type circulates. Particularly, a situation now exists in Europe, where TBEV and WNV are endemic in many countries Thus, this thesis focused on the one hand on optimization of serological test systems using recombinant envelope protein domain III (rED3). It represents domain 3 of the major antigen, the surface protein E, which additionally has been shown to induce flavivirus specific neutralizing antibodies. Therefore rED3 was expressed and purified and its application as antigen in ELISA for TBEV diagnosis was verified. On the other hand a memory B-cell assay was established to analyse antiviral immunity after TBEV-vaccination. Here rED3 was used as antigen to determine the frequency of rED3 specific antibody-secreting cells (ASCs). Vaccination is the most effective method of preventing TBE disease and is currently recommended for all those who live and work or travel to areas of TBE endemicity. An essential requirement of any vaccine is the induction of long-term protective immunity. Several vaccines have defined levels of serum antibody (as measured by ELISA, haemagglutination inhibition test, or neutralisation test) that serve as correlates or surrogates of protective immunity. But this does not take account of vaccine induced memory B cells. Although, not providing direct protection against infection, they represent an important second line of immune defence that is initiated only if pre existing antibody levels are too low to prevent infection or if the invading pathogen is able to circumvent the pre-existing antibody response. A thorough understanding of the frequencies of antigen-specific memory B cells and their relationship with the antibodies in serum serological memory is likely to be critical to give information about the long-term efficacy of vaccine as well as its correlates of protection. This thesis focuses on the establishment of a recombinant protein based ELISA and of a memory B cell assay for analysis of specific antiviral immunity after vaccination with the following two objectives: (1) Expression and purification of recombinant envelope protein domain 3 (rED3) and verification of its application as antigen in ELISA for TBEV diagnosis; (2) Establishment of a memory B cells assay using rED3 for determination of frequency of rED3 specific antibody-secreting cells (ASCs) in individuals vaccinated against TBE. In this study, TBEV- and WNV-specific antigen ED3 was expressed in E. coli as MBP fusion proteins with C-terminal histidine tag using pMAL-c2x vector. By purification with amylose affinity chromatography followed by nickel affinity chromatography, highly purified TBEV rED3 and WNV-rED3 were obtained. Nevertheless, using TBEV-rED3 protein in Western Blot unspecific reaction with serum antibodies of negative serum was detected and a differentiation between WNV infection and TBEV was impossible, probably due to the MBP moiety. However, using the purified rED3 protein as antigen in ELISA, TBE virus-specific antibodies were detected specifically. Twenty-three serum samples predefined as TBEV positive were tested positive by rED3-based ELISA and commercial IgG ELISA. Five predefined negative serum samples were tested negative by rED3-based IgG ELISA as well as commercial IgG ELISA. But cross reactivity of WNV and DENV positive sera was detected in 15 of 18 sera by commercial ELISA. On the other hand, these samples were found negative in TBEV rED3-based ELISA. Thus, TBEV-rED3-based ELISA allows a differentiation of infections caused by TBE serogroup and mosquito-borne flaviviruses but not the inactivated virus based commercial ELISA. Interestingly, compared to neutralisation test the specificity of rED3-based ELISA obtained 100% with a sensitivity of 91.6%. In contrast, the commercial ELISA obtained 100 % sensitivity but a low specificity with only 42.8%. In order to determine frequency of antigen-specific antibody secreting cells (ASCs) produced by individuals who received the vaccination against TBE, peripheral blood mononuclear cells (PBMCs) were isolated from blood samples. Subsequently, memory B cells were activated with R848 (Resiquimod) and human recombinant IL-2 (hrIL-2) for 72 hours in 37°C, 5% CO2, 90% humidity. After 72 hours of incubation, Enzyme-Linked Immunospot (ELISPOT) detected antigen-specific memory B cells. In order to evaluate specificity of TBEV-rED3 in ELISPOT, other antigens including WNV-rED3, Maltose binding protein (MBP) and Influenza Nucleoprotein (NP) were included. Study subjects could be separated into two groups: last vaccination before 5 years or longer than 10 years. TBEV-rED3 specific ASCs could be detected in 11 of 12 TBE vaccinated individuals with different vaccination history and even low serum anti-TBE antibodies levels. TBEV-rED3 specific ASCs were found with frequency of ranging 0.016-0.188 % per total IgG ASCs and lower than frequency of Influenza-NP specific ASCs (between 0.012-0.51%). But TBE-specific memory B cells could be maintained for more than 20 years of post-vaccination. There was a significant difference in number of ASCs between vaccinated and non-vaccinated group (p<0.05). Interestingly, there was no significant difference between TBE vaccinated groups between 1-5 years (mean of 2.5 years) and >10 years (mean of 16.5 years) since vaccination (p>0.05). These finding proved that memory B cells have been stable for years and are maintained up to 25 years since last vaccination. A statistic analysis showed that there was no significant correlation between serum levels of anti-TBEV antibodies and the frequency of rED3 specific IgG ASCs (p>0.05, Spearman’s coefficient r = 0.36). A similar result was also indicated for influenza-vaccinated individuals (p>0.05, Spearman’s coefficient r = 0.27). These findings revealed that memory B cells and plasma cells maybe play an independently role in maintaining of immunological memory. Anyway, neutralizing antibodies have been found in all vaccines (a Geometric mean titre (GMT) of 96.04, 95% confident interval (CI): 52.76-174.8) and thus were maintained for a long time since last vaccination. Interestingly, the quantitative determination of specific IgG in TBE post-vaccination sera by rED3-based ELISA exhibits a good correlation with neutralizing antibody titres. The presence of specific antibodies in rED3-based ELISA is therefore highly predictive for the presence of neutralizing antibodies, and this correlation can probably be used in the future to establish guidelines for recommendations of booster vaccinations. Additionally, it became apparent that the number of previous booster vaccinations correlated strongly with the frequency of circulating memory B cells. As expected, individuals who received a booster increased both the specific antibody titre and frequency of antigen specific memory B cells. This suggests that immunological long-term memory induced by booster immunizations is better reflected by the circulating memory B cells than the amount of the antibody titre. Thus, memory B cells seem to be a more reliable parameter for the assessment of long-term immunity. Taken together, a highly antigenic rED3 using the bacterial expression system was produced and it is a promising alternative to whole inactivated virus in ELISA. Notably, rED3 was a reliable antigen for detecting antigen-specific memory B cells in individuals who have been previously TBEV vaccinated. This study provides data on immunological memory for TBE vaccination and might be useful for reconsideration of recommendations for booster dose. In conclusion, boosters of vaccination should be recommended for all individuals who live and work or travel to areas of TBE endemicity. As consequently, vaccine-induced protection is enhanced by both strong humoral and cell-mediated immune responses. If pace of pathogenesis is rapidly growing, pre-existing virus-specific antibodies represent the first line of defence against infection before the memory response is fully activated and implemented. They clearly function best together to efficiently protect against disease.

Tick-borne encephalitis (TBE) is one of the most important viral zoonosis caused by a neurotropic arbovirus (TBEV). In Germany, TBE is classified as a notifiable disease with an average of 350 autochthonous human cases annually. The incidence-based risk assessment in Germany came under criticism because every year, a number of autochthonous human TBE cases have been detected outside of the official risk areas. Therefore, it is necessary to find additional parameters to strengthen TBEV surveillance. The aim of this study was to examine red foxes as sentinels for TBE. Thus far, there are no published data about the sensitivity and specificity for serological methods testing fox samples. Hence, we aimed to define a system for the screening of TBEV-specific antibodies in red foxes. A total of 1233 fox sera were collected and examined by ELISA and IIFA and confirmed by micro-NT. The overall seroprevalence of antibodies against TBEV in red foxes from Germany confirmed by micro-NT was 21.1%. The seroprevalence differed significantly between risk (30.5%) and non-risk areas (13.1%), with good correlations to local TBE incidence in humans. In conclusion, serological monitoring of red foxes represents a promising surrogate marker system and may even determine unexpected TBEV foci in regions currently regarded as non-risk areas.

Fästingburet encefalitvirus (TBEV) är ett RNA-virus som tillhör genuset flavivirus. Vid en TBEV-infektion är feber, trötthet, allmänpåverkan samt huvudvärk och muskelvärk vanligt förekommande symtom. Viruset överförs via saliven från fästingar under de första minuterna efter fästingbett. TBEV-IgM och ibland även TBEV-IgG återfinns i serum då symtom i centrala nervsystemet (CNS) yttrar sig i den andra fasen av sjukdomsförloppet. De senaste åren har prevalensen av fästingburen encefalit (TBE) ökat. Sedan 2017 har över 300 fall av TBE rapporterats årligen i Sverige. Laterala flödesanalyser (lateral flow assays, LFA) är billiga, enkla, snabba och baseras på portabla instrument som används bland annat inom biomedicinsk vetenskap. ReaScan® TBE IgM från det finska företaget Reagena är ett snabbtest, baserat på LFA-tekniken, för detektion av TBE-specifika IgM-antikroppar i humant serum och likvor. Syftet med studien var att undersöka om ReaScan® TBE IgM kan användas för att diagnostisera TBE på laboratoriet för Klinisk Mikrobiologi på länssjukhuset i Kalmar. Metodens prestanda undersöktes genom att analysera totalt 23 serumprover, 13 prover från TBE-patienter och 10 prover från icke-TBE-patienter. Sensitiviteten uppskattades genom att analysera 13 serumprover där förekomst av TBE-antikroppar sedan tidigare konfirmerats. Specificiteten uppskattades genom att analysera 10 serumprover från patienter utan känd TBEV-infektion. Den diagnostiska sensitiviteten respektive specificiteten beräknades till 100 %. På grund av den begränsade storleken på undersökningsmaterialet är dock den beräknade sensitiviteten och specificiteten ej helt tillförlitlig. Metodens prestanda ansågs vara tillräckligt god för att den skall kunna användas som en screening-metod för TBEV-IgM-antikroppar på laboratoriet för Klinisk Mikrobiologi på länssjukhuset i Kalmar. / Tick-borne encephalitis virus (TBEV) is an RNA virus that belongs to the genus flavivirus. Symptoms that commonly present during a TBEV infection include headaches, muscle pains, fever and malaise. The virus is transmitted with the saliva from ticks during the first minutes of their blood meal. TBEV-IgM and sometimes TBEV-IgG antibodies can be detected in the patient’s serum when central nervous system (CNS) symptoms present in the second phase of the disease. Over the last couple of years, the prevalence of tick-borne encephalitis (TBE) has increased. Since 2017 over 300 cases of TBE are reported every year in Sweden. Lateral flow assays (LFA) is the technology behind inexpensive, simple, quick and portable instruments that are used within the biomedical science field among others. ReaScan® TBE IgM developed by the Finnish company Reagena is a rapid test, based on the LFA technique, used for the detection of TBEV specific IgM antibodies in human serum and cerebrospinal fluid. The trial aimed to evaluate whether ReaScan® TBE IgM could be used to diagnose TBE at the laboratory of Clinical microbiology at the County hospital in Kalmar. The performance of the test was determined by analysing a total of 23 serum samples, 13 of which consisted of samples from patients with a previously confirmed TBE diagnosis and 10 samples from patients with no known TBEV infection. The diagnostic sensitivity and specificity were both determined to be 100 %. Due to the limited sample size, the calculated sensitivity and specificity are not particularly reliable.  The performance of the test was satisfactory and it could be used as a screening method for the detection of TBEV IgM antibodies at the department of Clinical microbiology at Kalmar County Hospital.

Einleitung Die Frühsommer-Meningoenzephalitis (FSME) zählt europaweit zu den bedeutendsten Zecken-übertragenen Krankheiten und ist verantwortlich für mehrere tausend Tote jedes Jahr. Hauptüberträger in Zentraleuropa ist Ixodes ricinus, der Gemeine Holzbock. In Deutschland konzentrieren sich die humanen Fälle vorrangig auf Süddeutschland mit anteilig 83,8% der Fälle, wobei anhand einer Falldefinition, die sich auf humane Meldedaten stützt, Risikogebiete definiert werden. Dabei wird ein Landkreis dann als Risikogebiet gewertet, wenn in einem Fünf-Jahresintervall die Inzidenz von einem Fall pro 100.000 Einwohnern pro Jahr überschritten wird. In Sachsen erscheint diese Risikoabschätzung erschwert, da hier nur wenige sporadische Fälle gemeldet werden. Jedoch wurde im April 2014 der Vogtlandkreis als erstes sächsisches Risikogebiet ernannt. Ziele der Untersuchungen Eine Risikobewertung, die sich alleine auf humane gemeldete Erkrankungsfälle stützt, erscheint überholt, weshalb schon in der Vergangenheit nach einem optimalen Sentineltier für Seroprävalenzstudien gesucht wurde. Im Rahmen dieser Dissertation wurden zwei Veröffentlichungen angefertigt, in denen mithilfe von Seroprävalenzstudien bei Wildtieren und bei Hunden das Risiko für eine Infektion mit der FSME in Sachsen bewertet werden sollte. Materialien und Methoden In der ersten Veröffentlichung wurden 1.886 Wildtierseren, vorrangig von Wildschweinen, auf das Vorhandensein von Antikörpern gegen das FSMEV untersucht. Die zweite Veröffentlichung befasste sich mit 331 Seren von Hunden, die Sachsen in den letzten fünf Jahren nicht verlassen hatten. Für die Untersuchung wurde zunächst ein ELISA (Enzyme-linked-immunosorbent Assay) und zur Bestätigung der positiven Proben ein SNT (Serumneutralisationstest) durchgeführt. Ergebnisse Bei den Wildtierseren wurde eine Gesamtprävalenz von 10,5% ermittelt. Im aktuell ernannten Risikogebiet Vogtlandkreis wurden 20% seropositive Tiere gefunden, im Kreis Meißen sogar 23% flächendeckend nachgewiesen. Sieben der untersuchten Hundeseren waren positiv, wobei vier Tiere hiervon Hunde von Förstern waren. Die positiven Proben kamen aus den Landkreisen Mittelsachsen (1), Erzgebirgskreis(1), Leipziger Land (2) und Sächsische-Schweiz-Osterzgebirge (3). Schlussfolgerungen In ganz Sachsen konnten Antikörper gegen das FSMEV gefunden werden was auf ein flächendeckendes Vorkommen des Virus in Sachsen hinweist. Die Eignung von Wildtieren und Hunden als Sentinels wurde bestätigt. Die jeweiligen Vor- und Nachteile werden dargestellt. Eine stichprobenhafte Untersuchung auf FSME im Rahmen von Screeningprogrammen könnte auch zukünftig zur besseren Lokalisation von FSMEV-Naturherden in Sachsen beitragen. Weiterhin ungeklärt bleibt die Diskrepanz zwischen der hohen ermittelten Seroprävalenz bei den Wildtieren und den wenigen humanen gemeldeten Fällen. Auch die Hundestudie konnte hierzu keine weiteren Informationen liefern. Eine Impfung ist vor allem für Menschen sinnvoll, die sich im Vogtlandkreis aufhalten.

Tick-borne encephalitis virus is the cause of much morbidity and sometimes a fatal infection. A vaccine based on formaldehyde inactivated virus is currently the only available way of preventing disease. This vaccine gives a high rate of seroconversion but there are reports of vaccination breakthrough, even in people who have demonstrated a neutralizing antibody response. The T cell response to inactivated TBE vaccine is largely unknown, but could be of importance for the effect of the vaccine. This study characterizes aspects of the T cell response by investigating the expression of two transcription factors, T-bet and GATA-3 with RT-PCR. T-bet is expressed in CD4+ T cells of the Th1 type, while GATA-3 is expressed in CD4+ T cells of the Th2 type. Our data show that vaccination with inactivated TBE vaccine leads to increase in expression of the T-bet gene when cells of vaccinated subjects are cultured with TBE virus. In contrast, the expression of GATA-3 remains unaffected by vaccination. Thus, this study suggests that the inactivated TBE vaccine leads to a Th1-like immune response in humans.

The present thesis examines questions related to the temporal origin of the Flavivirus genus and the ecology of tick-borne pathogens. In the first study, we date the origin and divergence time of the Flavivirus genus. It has been argued that the first flaviviruses originated after the last glacial maximum. This has been contradicted by recent analyses estimating that the tick-borne flaviviruses emerged at least before 16,000 years ago. It has also been argued that the Powassan virus was introduced into North America at the time between the opening and splitting of the Beringian land bridge. Supported by tip date and biogeographical calibration, our results suggest that this genus originated circa 120,000 (156,100–322,700) years ago if the Tamana bat virus is included in the genus, or circa 85,000 (63,700–109,600) years ago excluding the Tamana bat virus. In the second study we estimate the prevalence of tick-borne encephalitis virus (TBEV) in host-seeking Ixodes ricinus from 29 localities in Sweden and compare our data with those of neighbouring countries. Nymphs and adult ticks were screened for TBEV using a real-time PCR assay. The mean TBEV prevalence for all tick stages combined was 0.26% for Sweden and 0.28% for all Scandinavian countries, excluding Iceland. The low prevalence of TBEV in nature may partly be explained by the fact that TBEV occurs in spatially small foci and that the inclusion of ticks from non-infected foci will reduce the prevalence estimate. In the third and fourth study, we conducted the first large-scale investigations to estimate the prevalence and geographical distribution of Anaplasma spp. and Rickettsia spp. in host-seeking larvae, nymphs and adults of I. ricinus ticks in Sweden. Ticks were collected from several localities in central and southern Sweden and were subsequently screened for the presence of Anaplasma spp. and Rickettsia spp. using a real-time PCR assay. For all active tick stages combined, the mean prevalence of Anaplasma spp. and Rickettsia spp. in I. ricinus in Sweden was estimated to 1.1% and 4.8%, respectively. It was also shown that A. phagocytophilum and R. helvetica are the main Anaplasma and Rickettsia species occurring in Sweden.

Einleitung Die Frühsommer-Meningoenzephalitis (FSME) zählt europaweit zu den bedeutendsten Zecken-übertragenen Krankheiten und ist verantwortlich für mehrere tausend Tote jedes Jahr. Hauptüberträger in Zentraleuropa ist Ixodes ricinus, der Gemeine Holzbock. In Deutschland konzentrieren sich die humanen Fälle vorrangig auf Süddeutschland mit anteilig 83,8% der Fälle, wobei anhand einer Falldefinition, die sich auf humane Meldedaten stützt, Risikogebiete definiert werden. Dabei wird ein Landkreis dann als Risikogebiet gewertet, wenn in einem Fünf-Jahresintervall die Inzidenz von einem Fall pro 100.000 Einwohnern pro Jahr überschritten wird. In Sachsen erscheint diese Risikoabschätzung erschwert, da hier nur wenige sporadische Fälle gemeldet werden. Jedoch wurde im April 2014 der Vogtlandkreis als erstes sächsisches Risikogebiet ernannt. Ziele der Untersuchungen Eine Risikobewertung, die sich alleine auf humane gemeldete Erkrankungsfälle stützt, erscheint überholt, weshalb schon in der Vergangenheit nach einem optimalen Sentineltier für Seroprävalenzstudien gesucht wurde. Im Rahmen dieser Dissertation wurden zwei Veröffentlichungen angefertigt, in denen mithilfe von Seroprävalenzstudien bei Wildtieren und bei Hunden das Risiko für eine Infektion mit der FSME in Sachsen bewertet werden sollte. Materialien und Methoden In der ersten Veröffentlichung wurden 1.886 Wildtierseren, vorrangig von Wildschweinen, auf das Vorhandensein von Antikörpern gegen das FSMEV untersucht. Die zweite Veröffentlichung befasste sich mit 331 Seren von Hunden, die Sachsen in den letzten fünf Jahren nicht verlassen hatten. Für die Untersuchung wurde zunächst ein ELISA (Enzyme-linked-immunosorbent Assay) und zur Bestätigung der positiven Proben ein SNT (Serumneutralisationstest) durchgeführt. Ergebnisse Bei den Wildtierseren wurde eine Gesamtprävalenz von 10,5% ermittelt. Im aktuell ernannten Risikogebiet Vogtlandkreis wurden 20% seropositive Tiere gefunden, im Kreis Meißen sogar 23% flächendeckend nachgewiesen. Sieben der untersuchten Hundeseren waren positiv, wobei vier Tiere hiervon Hunde von Förstern waren. Die positiven Proben kamen aus den Landkreisen Mittelsachsen (1), Erzgebirgskreis(1), Leipziger Land (2) und Sächsische-Schweiz-Osterzgebirge (3). Schlussfolgerungen In ganz Sachsen konnten Antikörper gegen das FSMEV gefunden werden was auf ein flächendeckendes Vorkommen des Virus in Sachsen hinweist. Die Eignung von Wildtieren und Hunden als Sentinels wurde bestätigt. Die jeweiligen Vor- und Nachteile werden dargestellt. Eine stichprobenhafte Untersuchung auf FSME im Rahmen von Screeningprogrammen könnte auch zukünftig zur besseren Lokalisation von FSMEV-Naturherden in Sachsen beitragen. Weiterhin ungeklärt bleibt die Diskrepanz zwischen der hohen ermittelten Seroprävalenz bei den Wildtieren und den wenigen humanen gemeldeten Fällen. Auch die Hundestudie konnte hierzu keine weiteren Informationen liefern. Eine Impfung ist vor allem für Menschen sinnvoll, die sich im Vogtlandkreis aufhalten.:1 Einleitung 1 2 Literaturübersicht 2 2.1 Klassifikation, Taxonomie und geschichtlicher Hintergrund 2 2.2 Aufbau des FSMEV 4 2.3 Epidemiologie 5 2.4 Übertragungswege 8 2.4.1 Zeckenstich 8 2.4.2 Alimentärer Infektionsweg 10 2.5 Rolle verschiedener Spezies als Wirte der FSME 11 2.6 Pathogenese 13 2.7 Klinik beim Menschen 14 2.8 Klinik bei Tieren 15 2.8.1 Wild 15 2.8.2 Hund 15 2.8.3 Weitere Tierarten 17 Pferd 17 Mufflon 17 Affe 17 Ziege 17 2.9 Diagnose 18 2.10 Prävalenzstudien 20 2.10.1 Wild 20 2.10.2 Hund 21 2.10.3 Weitere Tierarten 22 Pferd 22 Mäuse 22 Zecken 22 Füchse 23 Ziegen 24 Schafe 24 Rinder 24 Vögel 25 2.11 Vorbeugung und Kontrolle 26 2.11.1 Impfung beim Menschen 26 2.11.2 Impfung bei Tieren 27 2.12 Sachsen 29 3 Veröffentlichung 1 30 4 Veröffentlichung 2 42 5 Gemeinsame Diskussion und Schlussfolgerung 55 6 Zusammenfassung 59 7 Summary 61 8 Referenzen 63 Literaturverzeichnis 63 Abbildungsverzeichnis 71 Tabellenverzeichnis 71 9 Danksagung 72

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