Prevalence of antibodies against tick-borne encephalitis virus in wild game from Saxony, Germany

Identification of New Microfoci and Genetic Characterization of Tick-Borne Encephalitis Virus Isolates from Eastern Germany and Western Poland

(1) Background: Tick-borne encephalitis (TBE) is the most important tick-borne viral disease in Eurasia, although effective vaccines are available. Caused by the tick-borne encephalitis virus (TBEV, syn. Orthoflavivirus encephalitidis), in Europe, it is transmitted by ticks like Ixodes ricinus and Dermacentor reticulatus. TBEV circulates in natural foci, making it endemic to specific regions, such as southern Germany and northeastern Poland. Our study aimed to identify new TBEV natural foci and genetically characterize strains in ticks in previously nonendemic areas in Eastern Germany and Western Poland. (2) Methods: Ticks were collected from vegetation in areas reported by TBE patients. After identification, ticks were tested for TBEV in pools of a maximum of 10 specimens using real-time RT-PCR. From the positive TBEV samples, E genes were sequenced. (3) Results: Among 8400 ticks from 19 sites, I. ricinus (n = 4784; 56.9%) was predominant, followed by D. reticulatus (n = 3506; 41.7%), Haemaphysalis concinna (n = 108; 1.3%), and I. frontalis (n = 2; <0.1%). TBEV was detected in 19 pools originating in six sites. The phylogenetic analyses revealed that TBEV strains from Germany and Poland clustered with other German strains, as well as those from Finland and Estonia. (4) Conclusions: Although there are still only a few cases are reported from these areas, people spending much time outdoors should consider TBE vaccination.

Phylogenetic characterisation of tick-borne encephalitis virus from Lithuania

The Baltic states are the region in Europe where tick-borne encephalitis (TBE) is most endemic. The highest notification rate of TBE cases is reported in Lithuania, where the incidence of TBE has significantly increased since 1992. A recent study reported 0.4% prevalence of TBE virus (TBEV) in the two most common tick species distributed in Lithuania, Ixodes ricinus and Dermacentor reticulatus, with the existence of endemic foci confirmed in seven out of Lithuania's ten counties. However, until now, no comprehensive data on molecular characterisation and phylogenetic analysis have been available for the circulating TBEV strains. The aim of this study was to analyse TBEV strains derived from I. ricinus and D. reticulatus ticks collected from Lithuania and provide a genotypic characterisation of viruses based on sequence analysis of partial E protein and NS3 genes. The 54 nucleotide sequences obtained were compared with 81 TBEV strains selected from the NCBI database. Phylogenetic analysis of the partial E and NS3 gene sequences derived from 34 Lithuanian TBEV isolates revealed that these were specific to Lithuania, and all belonged to the European subtype, with a maximum identity to the Neudoerfl reference strain (GenBank accession no. U27495) of 98.7% and 97.4%, respectively. The TBEV strains showed significant regional genetic diversity. The detected TBEV genotypes were not specific to the tick species. However, genetic differences were observed between strains from different locations, while strains from the same location showed a high similarity.

Serological screening for tick-borne encephalitis virus in eight Norwegian herds of semi-domesticated reindeer (Rangifer tarandus tarandus)

Tick-borne encephalitis virus (TBEV) is found in Ixodes ricinus ticks throughout the area where viable tick populations exist. In Norway, TBEV is found in I. ricinus from the south coast until Brønnøy municipality in Nordland County and the range of the vector is expanding due to changes in climate, vegetation, host animals and environmental conditions. TBEV might thus have the potential to establish in new areas when I. ricinus expand its geographical distribution. At present, there is little knowledge on the status of the virus in high-altitude areas of inland regions in Norway. It has previously been indicated that reindeer may be an important sentinel species and indicator of the spread of ticks and TBEV in high-altitude regions. In this study, 408 semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus) from eight herds, from Tana in Troms and Finnmark County in northern Norway to Filefjell in Innlandet and Viken Counties in southern Norway, were screened for TBEV antibodies using a commercial enzyme-linked immunosorbent assay (ELISA). We found 16 TBEV reactive reindeer samples by ELISA; however, these results could not be confirmed by the serum neutralization test (SNT). This could indicate that a flavivirusand not necessarily TBEV, may be circulating among Norwegian semi-domesticated reindeer. The results also indicate that TBEV was not enzootic in Norwegian semi-domesticated reindeer in 2013-2015. This knowledge is important as an information base for future TBEV and flavivirus surveillance in Norway.

Seroprevalence of tick-borne encephalitis virus in wild and domestic animals in northern Germany

Tick-borne encephalitis virus (TBEV) is a tick-transmitted flavivirus, which can infect humans and animals, sometimes even with a fatal outcome. Since many decades, TBEV is endemic in southern Germany, while only sporadic occurrence has been noted in northern parts of the country so far. Nevertheless, autochthonous human clinical cases are increasing in the federal state of Lower Saxony in north-western Germany, and several natural foci of TBEV transmission have recently been detected in this federal state. In order to shed more light on the current distribution of TBEV in Lower Saxony, the present study examined blood samples from wild and domestic animals for antibodies against TBEV. Overall, samples from 4,085 animals were tested by ELISA, including wild boar (N = 1,208), roe deer (N = 149), red deer (N = 61), fallow deer (N = 18), red foxes (N = 9), nutria (N = 9), raccoon dogs (N = 3), raccoons (N = 3), badgers (N = 1), European pine martens (N = 1), horses (N = 574), sheep (N = 266), goats (N = 67), dogs (N = 1,317) and cats (N = 399). Samples with an ELISA result of ≥60 Vienna units (VIEU)/ml were subjected to confirmatory serum neutralization tests (SNT). In total, 343 of 4,085 (8.4%) animals tested positive for anti-TBEV-IgG by ELISA, of which 60 samples were confirmed by SNT. Samples of 89 animals showed a cytotoxic effect in the SNT and were excluded from seroprevalence calculation, resulting in an overall seroprevalence of 1.5% (60/3,996). Seroprevalence was higher among wild animals (wild boar: 2.9% [34/1,190], roe deer: 2.7% [4/149], red deer: 1.7% [1/60], fallow deer: 5.6% [1/18]) than among domestic animals (dogs: 1.1% [15/1,317], horses: 0.8% [4/505], sheep: 0.4% [1/266]). No anti-TBEV-antibodies were detected in the other wild animal species as well as goats and cats. A notable clustering of positive samples was observed in districts where TBEV transmission foci have been described. Further clusters in other districts suggest the existence of so far undetected transmission foci, underlining the fact that both wild and domestic animals are useful sentinels for monitoring the spread of TBEV.

Wild ungulates as sentinels of flaviviruses and tick-borne zoonotic pathogen circulation: an Italian perspective

BACKGROUND

Vector-borne zoonotic diseases are a concerning issue in Europe. Lyme disease and tick-borne encephalitis virus (TBEV) have been reported in several countries with a large impact on public health; other emerging pathogens, such as Rickettsiales, and mosquito-borne flaviviruses have been increasingly reported. All these pathogens are linked to wild ungulates playing roles as tick feeders, spreaders, and sentinels for pathogen circulation. This study evaluated the prevalence of TBEV, Borrelia burgdorferi sensu lato, Rickettsia spp., Ehrlichia spp., and Coxiella spp. by biomolecular screening of blood samples and ticks collected from wild ungulates. Ungulates were also screened by ELISA and virus neutralization tests for flaviviral antibody detection.

RESULTS

A total of 274 blood samples were collected from several wild ungulate species, as well as 406 Ixodes ricinus, which were feeding on them. Blood samples tested positive for B. burgdorferi s.l. (1.1%; 0-2.3%) and Rickettsia spp. (1.1%; 0-2.3%) and showed an overall flaviviral seroprevalence of 30.6% (22.1-39.2%): 26.1% (17.9-34.3%) for TBEV, 3.6% (0.1-7.1%) for Usutu virus and 0.9% (0-2.7%) for West Nile virus. Ticks were pooled when possible and yielded 331 tick samples that tested positive for B. burgdorferi s.l. (8.8%; 5.8-11.8%), Rickettsia spp. (26.6%; 21.8-31.2%) and Neoehrlichia mikurensis (1.2%; 0-2.4%). TBEV and Coxiella spp. were not detected in either blood or tick samples.

CONCLUSIONS

This research highlighted a high prevalence of several tick-borne zoonotic pathogens and high seroprevalence for flaviviruses in both hilly and alpine areas. For the first time, an alpine chamois tested positive for anti-TBEV antibodies. Ungulate species are of particular interest due to their sentinel role in flavivirus circulation and their indirect role in tick-borne diseases and maintenance as Ixodes feeders and spreaders.

Comparison of Serological Methods for Tick-Borne Encephalitis Virus-Specific Antibody Detection in Wild Boar and Sheep: Impact of the Screening Approach on the Estimated Seroprevalence

Tick-borne encephalitis virus (TBEV) is a flavivirus transmitted by ticks. Serological screenings in animals are performed to estimate the prevalence and distribution of TBEV. Most screenings consist of a primary screening by ELISA, followed by confirmation of positive samples by plaque reduction neutralization tests (PRNTs). In this study, 406 wild boar sera were tested with 2 regularly used commercial ELISAs for flavivirus screening in animals (Immunozym FSME (TBEV) IgG All Species (Progen) and ID Screen West Nile Competition (Innovative Diagnostics)) and PRNTs for TBEV and USUTU virus. The results showed that the Immunozym and IDScreen ELISAs had low relative sensitivities of 23% and 20%, respectively, compared to the PRNT results. The relative specificities were 88% and 84% due to cross reactions with USUTU virus-specific antibodies. The minimal TBEV prevalence in our sample set was 8.6% when determined by PRNT. When the screening approach of ELISA testing followed by PRNT confirmation was applied, a TBEV seroprevalence of only 2.0% and 1.7% was found. The suboptimal performance of the ELISAs was confirmed by testing sera collected from experimentally TBEV-infected sheep. While the PRNT detected TBEV specific antibodies in 94% of samples collected between 7 and 18 days post-infection, the ELISAs classified only 50% and 31% of the samples as positive. Both routinely used ELISAs for TBEV antibody screening in animal sera were shown to have a low sensitivity, potentially leading to an underestimation of the true prevalence, and furthermore cross-react with other flavivirus antibodies.

Seroprevalence and Risk Factors for Equine West Nile Virus Infections in Eastern Germany, 2020

West Nile virus (WNV) infections were first detected in Germany in 2018, but information about WNV seroprevalence in horses is limited. The study’s overall goal was to gather information that would help veterinarians, horse owners, and veterinary-, and public health- authorities understand the spread of WNV in Germany and direct protective measures. For this purpose, WNV seroprevalence was determined in counties with and without previously registered WNV infections in horses, and risk factors for seropositivity were estimated. The cohort consisted of privately owned horses from nine counties in Eastern Germany. A total of 940 serum samples was tested by competitive panflavivirus ELISA (cELISA), and reactive samples were further tested by WNV IgM capture ELISA and confirmed by virus neutralization test (VNT). Information about potential risk factors was recorded by questionnaire and analyzed by logistic regression. A total of 106 serum samples showed antibodies against flaviviruses by cELISA, of which six tested positive for WNV IgM. The VNT verified a WNV infection for 54 samples (50.9%), while 35 sera neutralized tick-borne encephalitis virus (33.0%), and eight sera neutralized Usutu virus (7.5%). Hence, seroprevalence for WNV infection was 5.8% on average and was significantly higher in counties with previously registered infections (p = 0.005). The risk factor analysis showed breed type (pony), housing in counties with previously registered infections, housing type (24 h turn-out), and presence of outdoor shelter as the main significant risk factors for seropositivity. In conclusion, we estimated the extent of WNV infection in the resident horse population in Eastern Germany and showed that seroprevalence was higher in counties with previously registered equine WNV infections.

The European bison (Bison bonasus) as an indicatory species for the circulation of tick-borne encephalitis virus (TBEV) in natural foci in Poland

Tick-borne encephalitis (TBE) is one of the most common zoonotic diseases in Europe transmitted by Ixodidae vectors. While small mammals such as bank voles and ticks constitute the main reservoirs for virus transmission, large sylvatic species act as a food source for ticks. Cervids such as roe deer and red deer are considered sentinel species for TBE in natural foci. In addition, an increase of the population size and density of large wild mammals in an area corresponds to an increase in the tick burden and may potentially increase the prevalence of TBE virus (TBEV) in ticks and tick hosts and further exposure risk in humans. Humans are considered accidental hosts. The prevalence of TBE relies on interactions between host, vector and environment. The present study examines the exposure of the largest European herbivore, the European bison (Bison bonasus) to TBEV infection. Assessed using the IMMUNOZYM FSME ELISA (PROGEN), the overall TBEV seroprevalence was 62.7% in the 335 European bison that were studied. ELISA results were confirmed by the gold-standard virus neutralization test (VNT) with 98.7% sensitivity and thus giving a true prevalence of 63.5%. TBEV seroprevalence was significantly correlated to the origin, age group, sex, population type (free living/captive) and sanitary status (healthy/selectively eliminated/found dead/killed in accident) of the European bison in the univariable analysis. The highest seroprevalences were observed in the three largest north-eastern wild populations (Białowieska, Borecka and Knyszyńska forests), which corresponded with the highest incidence of human cases reported in the country. The risk of TBEV seropositivity increased with age and was higher in female and free-ranging European bison. Additionally, to the epidemiological investigation, the continuous detection of TBEV antibodies was studied by repetitive testing of animals over the course of 34 months. Two of six seropositive animals remained seropositive throughout the study. The presence of antibodies was followed throughout the study in seropositive European bison and for at least a year in animals that seroconverted during the observation period.

Fivefold higher abundance of ticks (Acari: Ixodida) on the European roe deer (Capreolus capreolus L.) forest than field ecotypes

The European roe deer (Capreolus capreolus) is the most common deer species in Europe. The species can be a reservoir of some tick-borne diseases but it is primarily recognized for its contribution as an amplifier host. In Central Europe, two roe deer ecotypes are living in adjacent areas: field and forest. We investigated differences in tick load and species composition on these two ecotypes. We collected ticks from 160 (80 the forest ecotype and 80 the field ecotype) roe deer culled in Wielkopolska Region (West-Central Poland). The most common was Ixodes ricinus (n = 1610; 99%) followed by Ixodes hexagonus (n = 22; 1%). The dominant life stage of the ticks was female. Prevalence was higher for forest roe deer. Mean number of ticks found on the forest ecotype was almost fivefold higher than on the field ecotype (3.75 ± 0.83 vs. 0.77 ± 0.20 ticks). The mean probability of tick occurrence was threefold higher in the forest (0.915 ± 0.050) than the field ecotype (0.279 ± 0.125). The most infested body parts of roe deer from both ecotypes were the neck and the head.

Comparison of Three Serological Methods for the Epidemiological Investigation of TBE in Dogs

Tick-borne encephalitis (TBE) virus is an emerging pathogen that causes severe infections in humans. Infection risk areas are mostly defined based on the incidence of human cases, a method which does not work well in areas with sporadic TBE cases. Thus, sentinel animals may help to better estimate the existing risk. Serological tests should be thoroughly evaluated for this purpose. Here, we tested three test formats to assess the use of dogs as sentinel animals. A total of 208 dog sera from a known endemic area in Southern Germany were tested in an All-Species-ELISA and indirect immunofluorescence assays (IIFA), according to the manufacturer’s instructions. Sensitivity and specificity for both were determined in comparison to the micro-neutralization test (NT) results. Of all 208 samples, 22.1% tested positive in the micro-NT. A total of 18.3% of the samples showed characteristic fluorescence in the IIFA and were, thus, judged positive. In comparison to the micro-NT, a sensitivity of 78.3% and a specificity of 98.8% was obtained. In the ELISA, 19.2% of samples tested positive, with a sensitivity of 84.8% and a specificity of 99.4%. The ELISA is a highly specific test for TBE-antibody detection in dogs and should be well suited for acute diagnostics. However, due to deficits in sensitivity, it cannot replace the NT, at least for epidemiological studies. With even lower specificity and sensitivity, the same applies to IIFA.

Cross-Sectional Study on the Prevalence and Factors Influencing Occurrence of Tick-Borne Encephalitis in Horses in Lithuania

Various animal species have been evaluated in depth for their potential as Tick-borne encephalitis virus (TBEV) sentinel species, although evidence for equine capacity is incomplete. Therefore, a comprehensive cross-sectional stratified serosurvey and PCR analysis of selected horses (n = 301) were performed in TBEV endemic localities in Lithuania. Attached and moving ticks (n = 241) have been collected from aforementioned hosts to evaluate natural infectivity of TBEV vectors (Ixodes spp.) in the recreational environments surrounding equestrian centers. All samples were screened for TBEV IgG and positive samples were confirmed by virus neutralization test (VNT). 113 (37.5%) horses from all counties of Lithuania tested positive for TBEV IgG, revealing age and sex indifferent results of equine seroprevalence that were significantly dependent on pedigree: horses of mixed breed were more susceptible to infection possibly due to their management practices. TBEV prevalence in equine species corresponded to TBEV-confirmed human cases in the precedent year. As much as 3.9% of horses were viraemic with TBEV-RNA with subsequent confirmation of TBEV European subtype. 4/38 of tested tick pools were positive for TBEV-RNA (Minimal infectious rate 1.2%). Several unknown microfoci were revealed during the study indicating areas of extreme risk close to popular human entertainment sites. The study provides important evidence in favor of horses’ usage as sentinel species, as equines could provide more detailed epidemiological mapping of TBEV, as well as more efficient collection of ticks for surveillance studies.

The Red Fox (Vulpes vulpes) as Sentinel for Tick-Borne Encephalitis Virus in Endemic and Non-Endemic Areas

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.

Tick burden on European roe deer (Capreolus capreolus) from Saxony, Germany, and detection of tick-borne encephalitis virus in attached ticks

Southern Germany is known as tick-borne encephalitis (TBE) risk area; however, the north of the country is almost free of human TBE cases. Due to its location in the transition zone between TBE risk areas and areas with only sporadic cases, Saxony is of importance in the surveillance of TBE. Roe deer (Capreolus capreolus), showing high seroprevalence of TBE virus (TBEV) antibodies, are considered to be sentinels for TBE risk assessment. Thus, roe deer could be used as indicators helping to better understand the focality of the TBEV in nature and as a possible source to isolate TBEV. Therefore, the aims of this study were to examine roe deer coats for the presence of ticks to establish the tick burden and to detect the TBEV in attached ticks. One hundred thirty-four roe deer coats were provided by hunters from the Hunting Association in Saxony (August 2017-January 2019). The coats were frozen at - 80 °C and after de-freezing examined on both sides-inside and outside. Attached and nonattached ticks were collected, morphologically identified and tested using real-time RT-PCR for the presence of TBEV. In total, 1279 ticks were found on 48 coats. The predominant species was Ixodes ricinus (99.76%; n = 1276). Three remaining specimens were Ixodes spp. (0.16%, 1 female and 1 nymph) and Dermacentor reticulatus (0.08%, 1 male). The average infestation rate was 26.7 (SD = 69.5), with maximum of 439 ticks per animal. Females were the dominant life stage of ticks (n = 536; 42%), followed by nymphs (n = 397; n = 31.1%), males (n = 175; 13.7%), and larvae (n = 168; 13.2%). Only half of collected ticks were attached (n = 662; 51.8%). TBEV was detected only in one tick out of 1279 tested ticks. It was a female infesting a roe deer from Saxon Switzerland-East Ore Mountain. The results show that the method used in this study is not sufficient as a sentinel marker to predict TBEV spreading in nature. Although previous studies demonstrated the usefulness of serological testing of roe deer in order to trace TBE-endemic regions, using ticks attached to them to get virus isolates is not productive.

Cervids as sentinel-species for tick-borne encephalitis virus in Norway - A serological study

Tick-borne encephalitis virus (TBEV) is the causative agent of tick-borne encephalitis (TBE). TBEV is one of the most important neurological pathogens transmitted by tick bites in Europe. The objectives of this study were to investigate the seroprevalence of TBE antibodies in cervids in Norway and the possible emergence of new foci, and furthermore to evaluate if cervids can function as sentinel animals for the distribution of TBEV in the country. Serum samples from 286 moose, 148 roe deer, 140 red deer and 83 reindeer from all over Norway were collected and screened for TBE immunoglobulin G (IgG) antibodies with a modified commercial enzyme-linked immunosorbent assay (ELISA) and confirmed by TBEV serum neutralisation test (SNT). The overall seroprevalence against the TBEV complex in the cervid specimens from Norway was 4.6%. The highest number of seropositive cervids was found in south-eastern Norway, but seropositive cervids were also detected in southern- and central Norway. Antibodies against TBEV detected by SNT were present in 9.4% of the moose samples, 1.4% in red deer, 0.7% in roe deer, and nil in reindeer. The majority of the positive samples in our study originated from areas where human cases of TBE have been reported in Norway. The study is the first comprehensive screening of cervid species in Norway for antibodies to TBEV, and shows that cervids are useful sentinel animals to indicate TBEV occurrence, as supplement to studies in ticks. Furthermore, the results indicate that TBEV might be spreading northwards in Norway. This information may be of relevance for public health considerations and supports previous findings of TBEV in ticks in Norway.

Exposure of Wild Ungulates to the Usutu and Tick-Borne Encephalitis Viruses in France in 2009-2014: Evidence of Undetected Flavivirus Circulation a Decade Ago

Abstract: Flaviviruses have become increasingly important pathogens in Europe over the past few decades. A better understanding of the spatiotemporal distribution of flaviviruses in France is needed to better define risk areas and to gain knowledge of the dynamics of virus transmission cycles. Serum samples from 1014 wild boar and 758 roe deer from 16 departments (administrative units) in France collected from 2009 to 2014 were screened for flavivirus antibodies using a competitive ELISA (cELISA) technique. Serum samples found to be positive or doubtful by cELISA were then tested for antibodies directed against West Nile virus (WNV), Usutu virus (USUV), Bagaza virus (BAGV), and tick-borne encephalitis/Louping ill viruses (TBEV/LIV) by microsphere immunoassays (except BAGV) and micro-neutralization tests. USUV antibodies were detected only in southeastern and southwestern areas. TBEV/LIV antibodies were detected in serum samples from eastern, southwestern and northern departments. The results indicate continuous circulation of USUV in southern France from 2009 to 2014, which was unnoticed by the French monitoring system for bird mortality. The findings also confirm wider distribution of TBEV in the eastern part of the country than of human clinical cases. However, further studies are needed to determine the tick-borne flavivirus responsible for the seroconversion in southwestern and northern France.

Tick-Borne Encephalitis Virus Antibodies in Roe Deer, the Netherlands

To increase knowledge of tick-borne encephalitis virus (TBEV) circulation in the Netherlands, we conducted serosurveillance in roe deer (Capreolus capreolus) during 2017 and compared results with those obtained during 2010. Results corroborate a more widespread occurrence of the virus in 2017. Additional precautionary public health measures have been taken.

Exploring the Reservoir Hosts of Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) is an important arbovirus, which is found across large parts of Eurasia and is considered to be a major health risk for humans. Like any other arbovirus, TBEV relies on complex interactions between vectors, reservoir hosts, and the environment for successful virus circulation. Hard ticks are the vectors for TBEV, transmitting the virus to a variety of animals. The importance of these animals in the lifecycle of TBEV is still up for debate. Large woodland animals seem to have a positive influence on virus circulation by providing a food source for adult ticks; birds are suspected to play a role in virus distribution. Bank voles and yellow-necked mice are often referred to as classical virus reservoirs, but this statement lacks strong evidence supporting their highlighted role. Other small mammals (e.g., insectivores) may also play a crucial role in virus transmission, not to mention the absence of any suspected reservoir host for non-European endemic regions. Theories highlighting the importance of the co-feeding transmission route go as far as naming ticks themselves as the true reservoir for TBEV, and mammalian hosts as a mere bridge for transmission. A deeper insight into the virus reservoir could lead to a better understanding of the development of endemic regions. The spatial distribution of TBEV is constricted to certain areas, forming natural foci that can be restricted to sizes of merely 500 square meters. The limiting factors for their occurrence are largely unknown, but a possible influence of reservoir hosts on the distribution pattern of TBE is discussed. This review aims to give an overview of the multiple factors influencing the TBEV transmission cycle, focusing on the role of virus reservoirs, and highlights the questions that are waiting to be further explored.

First Isolation and Phylogenetic Analyses of Tick-Borne Encephalitis Virus in Lower Saxony, Germany

Tick-borne encephalitis (TBE) is the most important tick-borne arboviral disease in Europe. Presently, the main endemic regions in Germany are located in the southern half of the country. Although recently, sporadic human TBE cases were reported outside of these known endemic regions. The detection and characterization of invading TBE virus (TBEV) strains will considerably facilitate the surveillance and assessment of this important disease. In 2018, ticks were collected by flagging in several locations of the German federal state of Lower Saxony where TBEV-infections in humans (diagnosed clinical TBE disease or detection of TBEV antibodies) were reported previously. Ticks were pooled according to their developmental stage and tested for TBEV-RNA by RT-qPCR. Five of 730 (0.68%) pools from Ixodes spp. ticks collected in the areas of "Rauher Busch" and "Barsinghausen/Mooshuette" were found positive for TBEV-RNA. Phylogenetic analysis of the whole genomes and E gene sequences revealed a close relationship between the two TBEV isolates, which cluster with a TBEV strain from Poland isolated in 1971. This study provides first data on the phylogeny of TBEV in the German federal state of Lower Saxony, outside of the known TBE endemic areas of Germany. Our results support the hypothesis of an east-west invasion of TBEV strains in Western Europe.

Phylogenetics of tick-borne encephalitis virus in endemic foci in the upper Rhine region in France and Germany

Objective

Tick-borne encephalitis (TBE) caused by the tick-borne encephalitis virus (TBEV) is the most important tick-borne arboviral disease in Europe and Asia. The Upper Rhine Valley is thought to be the very western border of TBEV distribution in Europe. The aim of our study was to identify natural foci and isolate TBEV from ticks, to determine the prevalence of TBEV in local tick populations and to study the phylogenetic relatedness of circulating TBEV strains in this region.

Material and methods

Ticks were collected between 2016, 2017 and 2018 by flagging. TBEV was isolated from collected ticks and phylogenetic analyses were performed. Minimal infection rates (MIR) of the collected ticks were calculated.

Results

At 12 sampling sites, a total of 4,064 Ixodes ticks were collected in 2016 and 2017 –(and one single collection 2018). 953 male, 856 female adult ticks and 2,255 nymphs were identified. The MIR rates were 0,17% (1/595) for Schiltach (Germany) and 0,11% (1/944) for Foret de la Robertsau (France), respectively. Overall, the three newly described TBEV strains, isolated in the years 2016 and 2017 from the Upper Rhine Valley have no close phylogenetic relation and show a genetic relationship with strains from eastern Europe. The 2018 TBEV strain from Aubachstrasse (Germany), however, is closely related to the TBEV found in Schiltach (Germany).

Conclusion

In conclusion, we demonstrate, to our knowledge for the first time, the phylogenetic relations of the newly isolated TBEV strains on both sides of the upper Rhine river.

Continued expansion of tick-borne pathogens: Tick-borne encephalitis virus complex and Anaplasma phagocytophilum in Denmark

Tick-borne encephalitis virus (TBEV) is a tick-transmitted flavivirus within the tick-borne encephalitis (TBE) complex. The TBE complex is represented by both TBEV and louping ill virus (LIV) in Denmark. Anaplasma phagocytophilum is also transmitted by ticks and is believed to play an essential role in facilitating and aggravating LIV infection in sheep. This study aimed to describe the distribution of TBE complex viruses in Denmark, to establish the possible emergence of new foci and their association with the distribution of A. phagocytophilum. We performed a nationwide seroprevalence study of TBE complex viruses using roe deer (Capreolus capreolus) as sentinels and determined the prevalence of A. phagocytophilum in roe deer. Danish hunters obtained blood samples from roe deer during the hunting season of 2013-14. The samples were examined for TBEV-specific antibodies by virus neutralization tests (NT). A. phagocytophilum infection was assessed by specific real-time-PCR. The overall seroprevalence of the TBE complex viruses in roe deer was 6.9% (51/736). The positive samples were primarily obtained from a known TBE endemic foci and risk areas identified in previous sentinel studies. However, new TBE complex risk areas were also identified. The overall prevalence of A. phagocytophilum was 94.0% (173 PCR-positive of 184 roe deer), which is twice the rate observed ten years ago. These results point to an expansion of these tick-borne diseases geographically and within reservoir populations and, therefore, rationalize the use of sentinel models to monitor changes in transmission of tick-borne diseases and development of new risk areas. We found no association between TBE complex-positive roe deer and the prevalence of A. phagocytophilum, as almost all roe deer were infected. Based on our findings we encourage health care providers to be attentive to tick-borne illnesses such as TBE when treating patients with compatible symptoms.

Survey of tick-borne zoonotic viruses in wild deer in Hokkaido, Japan

Tick-borne encephalitis (TBE) and severe fever with thrombocytopenia syndrome (SFTS) are both tick-borne zoonotic diseases caused by TBE virus (TBEV) and SFTS phlebovirus (SFTSV). In 2016, a second domestic TBE case was reported in Hokkaido, Japan, after an absence of 23 years. We conducted IgG ELISA for TBEV and SFTSV on 314 deer (Cervus nippon yesoensis) serum samples collected from 3 places in Hokkaido. There were 7 seropositive samples for TBEV but none for SFTSV by ELISA. The specificity of the 7 positive samples was confirmed by neutralization tests against TBEV, and 5 sera showed 320 to 640 of 50% focus reduction endpoint titers. Our results provide information about the infectious status of TBEV in wild deer in Hokkaido, Japan.

Seroprevalence of tick-borne-encephalitis virus in wild game in Mecklenburg-Western Pomerania (north-eastern Germany)

Mecklenburg-Western Pomerania, a federal state in the north east of Germany, has never been a risk area for TBEV infection, but a few autochthonous cases, along with TBEV-RNA detection in ticks, have shown a low level of activity in natural foci of the virus in the past. As wild game and domestic animals have been shown to be useful sentinels for TBEV we examined sera from wild game shot in Mecklenburg-Western Pomerania for the prevalence of TBEV antibodies. A total of 359 sera from wild game were investigated. All animals were shot in Mecklenburg-Western Pomerania in 2012. Thirteen of 359 sera tested positive or borderline for anti-TBEV-IgG with ELISA and four samples tested positive using NT. The four TBEV-positive sera confirmed by NT constitute the first detection of TBEV-antibodies in sera of wild game in Mecklenburg-Western Pomerania since 1986-1989. This underlines that the serological examination of wild game can be a useful tool in defining areas of possible TBEV infection, especially in areas of low TBEV-endemicity.

Serological evidence of tick-borne encephalitis virus infection in moose and deer in Finland: sentinels for virus circulation

Background

The incidence of tick-borne encephalitis (TBE) in humans has increased in Finland, and the disease has emerged in new foci. These foci have been investigated to determine the circulating virus subtype, the tick host species and the ecological parameters, but countrywide epidemiological information on the distribution of TBEV has been limited.

Methods

In this study, we screened sera from hunter-harvested wild cervids for the presence of antibodies against tick-borne encephalitis virus (TBEV) with a hemagglutination inhibition test. The positive results were confirmed by a neutralisation assay.

Results

Nine (0.74 %) of 1213 moose, one (0.74 %) of 135 white-tailed deer, and none of the 17 roe deer were found seropositive for TBEV. A close geographical congruence between seropositive cervids and recently reported human TBE cases was observed: nine of the ten seropositive animals were from known endemic areas.

Conclusions

Our results confirm the local circulation of TBEV in several known endemic areas. One seropositive moose had been shot in an area where human TBE cases have not been reported, suggesting a possible new focus. Moose appear to be a useful sentinel animal for the presence of TBEV in the taiga region.

Serological signature of tick-borne pathogens in Scandinavian brown bears over two decades

BACKGROUND

Anthropogenic disturbances are changing the geographic distribution of ticks and tick-borne diseases. Over the last few decades, the tick Ixodes ricinus has expanded its range and abundance considerably in northern Europe. Concurrently, the incidence of tick-borne diseases, such as Lyme borreliosis and tick-borne encephalitis, has increased in the human populations of the Scandinavian countries.

METHODS

Wildlife populations can serve as sentinels for changes in the distribution of tick-borne diseases. We used serum samples from a long-term study on the Scandinavian brown bear, Ursus arctos, and standard immunological methods to test whether exposure to Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, and tick-borne encephalitis virus (TBEV) had increased over time. Bears had been sampled over a period of 18 years (1995-2012) from a southern area, where Ixodes ricinus ticks are present, and a northern area where ticks are uncommon or absent.

RESULTS

Bears had high levels of IgG antibodies against B. burgdorferi sensu lato but not TBEV. Bears at the southern area had higher values of anti-Borrelia IgG antibodies than bears at the northern area. Over the duration of the study, the value of anti-Borrelia IgG antibodies increased in the southern area but not the northern area. Anti-Borrelia IgG antibodies increased with the age of the bear but declined in the oldest age classes.

CONCLUSIONS

Our study is consistent with the view that ticks and tick-borne pathogens are expanding their abundance and prevalence in Scandinavia. Long-term serological monitoring of large mammals can provide insight into how anthropogenic disturbances are changing the distribution of ticks and tick-borne diseases.

Review: Sentinels of tick-borne encephalitis risk

Tick-borne encephalitis (TBE) is a viral zoonotic disease endemic in many regions of Eurasia. The definition of TBE risk areas is complicated by the focal nature of the TBE virus transmission. Furthermore, vaccination may reduce case numbers and thus mask infection risk to unvaccinated persons. Therefore, additional risk indicators are sought to complement the current risk assessment solely based on human incidence. We reviewed studies published over the past ten years investigating potential new sentinels of TBE risk to understand the advantages and disadvantages of the various sentinel animal surveys and surrogate indicator methods. Virus prevalence in questing ticks is an unsuitable indicator of TBE infection risk as viral RNA is rarely detected even in large sample sizes collected at known TBE endemic areas. Seroprevalence in domestic animals, on the other hand, showed good spatial correlation with TBE incidence in humans and might also uncover presently unknown TBEV foci.