The Emergence and Dynamics of Tick-Borne Encephalitis Virus in a New Endemic Region in Southern 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.

Evidence for a 10-year TBE vaccine booster interval: an evaluation of current data

INTRODUCTION

Tick-borne encephalitis (TBE) is rapidly spreading to new areas in many parts of Europe. While vaccination remains the most effective method of protection against the disease, vaccine uptake is low in many endemic countries.

AREAS COVERED

We conducted a literature search of the MEDLINE database to identify articles published from 2018 to 2023 that evaluated the immunogenicity and effectiveness of TBE vaccines, particularly Encepur, when booster doses were administered up to 10 years apart. We searched PubMed with the MeSH terms 'Encephalitis, Tick-Borne/prevention and control' and 'Vaccination' for articles published in the English language.

EXPERT OPINION

Long-term immunogenicity data for Encepur and real-world data on vaccine effectiveness and breakthrough infections following the two European TBE vaccines, Encepur and FSME-Immun, have shown that extending the booster interval from 3-5 years to 10 years does not negatively impact protection against TBE, regardless of age. Such extension not only streamlines the vaccination schedules but may also increase vaccine uptake and compliance among those living in endemic regions.

High neutralizing antibody mismatch as a possible reason for vaccine failure in two children with severe tick-borne encephalitis

We describe two adolescents (13 and 16 years old) with severe tick-borne encephalitis (TBE) and vaccination breakthrough (VBT). Both suffer from severe persistent neurologic sequelae. Both patients had high TBE-IgG-titers after vaccination at the beginning of the infection and a low or missing TBE-IgM response (Type 2 vaccine failure). Neutralization tests show low titers against the respective infecting TBE virus strain and higher titers against the vaccine strain at the beginning of the infection implying an individual weak or impaired immune response to the respective virus as possible cause of TBE vaccine failure. We do not know of any similar observation or explanation for the phenomenon and at the moment can only speculate of a severe course correlated to highly mismatched IgG. This constellation of high TBE IgGs, the lack of immune response and a severe course strongly resembles the severe TBE courses that occurred in the past after TBE immunoglobulin administration. To our knowledge differentiation between structural and functional antibodies by neutralization tests with a) the affecting TBE virus strain and b) the vaccine virus strain in TBE vaccine failures has never been described before. We conclude (1) to consider a TBE virus infection also in vaccinated children presenting with meningoencephalitis, (2) to perform a broad immunological work-up in severe TBE especially after VBT, (3) to further study if high mismatch IgG's are a possible reason for vaccine failure.

Tick-borne encephalitis

PURPOSE OF REVIEW

Tick-borne encephalitis continues to be one of the most significant causes of viral encephalitis in Europe and Asia. This review will focus on recent developments in the epidemiology, pathogenesis and therapeutic approaches related to infection with tick-borne encephalitis virus.

RECENT FINDINGS

There is a growing consensus that tick-borne encephalitis viruses are increasing in geographical range, with countries previously free of disease reporting detection of both human cases and presence of virus within indigenous tick populations. The drivers for this are multifactorial but underpinned by human-mediated climate change. Recent developments in pathogenesis have focussed on the intracellular response to infection, particularly in different cell types within the central nervous system (CNS) that are revealing the array of cellular networks triggered by infection. This in turn highlights the need for small molecule therapeutics, such as nucleoside analogues, that can enter the CNS, and the intracellular environment, to inhibit virus replication following neuroinvasion.

SUMMARY

Based on continued epidemiological surveillance, tick-borne encephalitis viruses will increasingly affect human populations in Europe and Asia. Much of the research highlighted in this review demonstrates incremental advances in our understanding of these viruses. However, more is required if effective prevention and treatment of this devastating encephalitic viruses are to be realized.

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.