Tick-borne encephalitis: A comprehensive review of the epidemiology, virology, and clinical picture

TBEV NS1 Induces Tissue-Specific Microvascular Endothelial Cell Permeability by Activating the TNF-α Signaling Pathway

Orthoflavivirus encephalitidis (tick-borne encephalitis virus, TBEV) is of high concern due to its ability to cause severe neurological manifestations. Despite the fact that the role of NS1 proteins from various mosquito-borne flaviviruses in pathogenesis and their ability to affect human endothelial permeability have been investigated, TBEV NS1 has thus far been insufficiently studied. In this study, human endothelial permeability was assessed using TEER and transwell permeability assays. Signaling pathways were determined by RNAseq. The ability of the NS1 protein of TBEV to affect human endothelial permeability was investigated for the first time. It was shown that recombinant TBEV NS1 produced in eucaryotic cells directly affected human lung microvascular endothelial cells (HLMVECs) in vitro but not human umbilical vein endothelial cells (HUVECs). It was indicated that TBEV NS1 induced endothelial hyperpermeability of HLMVECs through activating TNF-α and other inflammatory signaling pathways.

Where did the attack come from? The mysterious case of paralysis mimicking Guillain-Barré syndrome: Case report

RATIONALE

Tick-borne encephalitis (TBE) can present with neurological symptoms mimicking Guillain-Barré syndrome (GBS), posing a significant diagnostic challenge. Misidentification may lead to delayed or inappropriate treatment, increasing the risk of complications.

PATIENT CONCERNS

A 49-year-old man presented with flu-like symptoms and progressive paralysis of the left upper limb following a tick bite. His condition rapidly deteriorated despite initial therapy, including facial nerve palsy, further paralysis of the left upper limb, and swallowing difficulties.

DIAGNOSES

The initial clinical picture, cerebrospinal fluid analysis showing elevated protein, and electromyography suggested GBS.

INTERVENTIONS

The patient underwent 6 plasmapheresis sessions for suspected GBS, with no neurological improvement.

OUTCOMES

Due to a lack of improvement and further magnetic resonance imaging findings, a repeated lumbar puncture and serological testing revealed the correct diagnosis of TBE, confirmed by the presence of IgM and IgG antibodies against the TBE virus. After stabilization and intensive care unit discharge, the patient was transferred to a neurology ward and later to a rehabilitation unit. Significant neurological improvement was observed, although partial left upper limb paresis and facial nerve palsy persisted. He was eventually discharged with continued outpatient neurology and cardiology follow-up.

LESSONS

This case highlights the importance of detailed medical history, including tick exposure, and maintaining a broad differential diagnosis in acute flaccid paralysis. Early consideration of infectious etiologies, particularly in endemic regions, is essential to prevent unnecessary interventions and improve patient outcomes.

Mitochondrial fission regulates midgut muscle assembly and tick feeding capacity

Ticks ingest over 100 times their body weight in blood. As the primary tissue for blood storage and digestion, the tick midgut's regulation in response to this substantial blood volume remains unclear. Here, we show that blood intake triggers stem cell proliferation and mitochondrial fission in the midgut of Haemaphysalis longicornis. While inhibiting stem cell proliferation does not impact feeding behavior, disruption of mitochondrial fission impairs tick feeding capacity. Mitochondrial fission mediated by dynamin 2 (DNM2) regulates ATP generation, which in turn influences the expression of the tropomyosin-anchoring subunit troponin T (TNT). Knockdown of TNT disrupts muscle fiber assembly, hindering midgut enlargement and contraction, thereby preventing blood ingestion. These findings underscore the indispensable role of musculature in facilitating midgut expansion during feeding in ticks.

Persistence of Tick-Borne Encephalitis Virus in Goat and Cow Milks Under Different Storage Conditions and Following Thermal Inactivation

Tick-borne encephalitis virus (TBEV) is a neuroinvasive arbovirus that is primarily transmitted to humans through the bites of Ixodes ricinus ticks. Consumption of unpasteurised milk and dairy products from infected ruminants can also cause infection in humans. In the majority of food-borne TBE (FB-TBE) cases, goat milk and/or cheese has been identified as the source of infection. The aim of the present study was to analyse the persistence of the infectious strain TBEV_Ain_2020 virus in spiked goat and cow raw milks under different storage conditions, and following pasteurisations performed at 63 °C/30 min or 72 °C/15 s. The total genome of TBEV was stable up to 48 h in goat and cow's milks at 4 °C and 21 °C. In contrast, the viral titre was significantly lower in goat milk from T + 2 h post-contamination up to 17 h compared to culture cell medium and cow milk at 4 °C. At 21 °C, viral titres were lower than in DMEM in both milks up to T + 12 h. Thermal inactivations were effective in goat milk, but were not sufficient to eliminate all infective virus particles in cow milk. These unexpected findings highlighted that pasteurisation processes should be adapted to the species of origin of the milk and to the initial viral load to ensure food safety.

Tick-Borne Encephalitis Presenting as Brachial Plexus Injury: A Case Report

Tick-borne encephalitis (TBE) is a viral infection with variable clinical presentations, including neurological complications. We report a case of TBE in a 34-year-old farmer from an endemic region in Poland. The patient initially presented with paresis of the right brachial plexus. The diagnosis was challenging due to the absence of previous flu-like symptoms, often related to TBE infection. Neurological evaluations revealed paresis and muscle atrophy in the right upper limb, and serological tests confirmed TBE infection. Despite treatment efforts, neurological deficits persisted. This case highlights the need to consider TBE in the differential diagnosis of sudden-onset neurological disorders, especially in TBE-endemic regions, to ensure prompt intervention and prevent long-term complications.

The Factors Associated with the Blood-Brain Barrier Dysfunction in Tick-Borne Encephalitis

The pathogenesis of the central nervous system (CNS) pathology in tick-borne encephalitis (TBE) remains unclear. We attempted to identify mediators of the blood-brain barrier (BBB) disruption in human TBE in paired serum and cerebrospinal fluid (CSF) samples from 100 TBE patients. CSF albumin quotient (Qalb) was calculated as a measure of BBB impairment. Concentrations of cytokines, cytokine antagonists, adhesion molecules, selectins and matrix metalloproteinases (MMP) were measured with a multiplex bead assay. Single nucleotide polymorphisms (SNP) in genes MIF, TNF, TNFRSF1A, TNFRSF1B, IL-10, TLR3 and TLR4 were studied in patient blood DNA extracts and analyzed for associations with Qalb and/or cytokine concentrations. The multivariate regression models of Qalb were built with the soluble mediators as independent variables. The best models obtained included L-selectin, P-selectin, sVCAM, MMP7, MMP8 (or MMP9) and IL-28A as positive and IL-12p70, IL-15, IL-6Rα/IL-6 ratio and TNF-RII/TNFα ratio as negative correlates of Qalb. The genotype did not associate with Qalb, but polymorphism rs4149570 (in TNFRSF1A) associated with TNFα and rs1800629 (TNF) with MIF concentration. We confirm the association of the TNFα-dependent response, L-selectin and MMP8/MMP9 with BBB disruption and identify its novel correlates (IL-12, IL-15, IL-28A, MMP7). We detect no genotype associations with BBB function in TBE.

Clinical Characteristics of Tick-Borne Encephalitis in Adult Patients: A 10-year Retrospective Study in Stockholm, Sweden

BACKGROUND

The incidence of tick-borne encephalitis (TBE) has increased during the last decades in Europe. Our aim was to assess the clinical characteristics and outcome of patients with TBE in Region Stockholm, as a high-risk area in Sweden.

METHODS

The notification database at the regional Department of Communicable Disease Control and Prevention was used to identify TBE cases during 2006-2015. Clinical data were retrieved from the included patients' medical records. The associations of specific variables to predefined outcomes of disease severity were evaluated with multivariate logistic regression models.

RESULTS

Of 1004 identified TBE cases, 703 adult patients were included. Sixty-one percent were men, and the median age was 50 years (range, 18-94 years). The majority of patients were nonvaccinated. Comorbidity was present in 34%, and 4% were receiving immunomodulatory therapy. Seventy-five percent were hospitalized, and 11% had severe disease. More than 70% of the 79 patients followed up for >6 months had persisting symptoms. The case fatality rate was 1.4%, 15% in the group with immunomodulatory treatment. In the multivariate analysis, severe disease was associated with underlying comorbid conditions, age ≥50 years, and previous complete TBE vaccination.

CONCLUSIONS

This is the largest cohort of patients with TBE in Scandinavia. Our findings of a more severe course of disease in older patients, those receiving immunomodulatory therapy, those with comorbid conditions, and those with vaccination breakthrough infections must be interpreted in the context of hospitalized patients. Optimized prevention is needed for patients receiving immunomodulatory therapy, given the considerable case fatality rate. Follow-up visits and rehabilitation should be better standardized.

Viruses and the Brain-A Relationship Prone to Trouble

Neurological disorders, some of which are associated with viral infections, are growing due to the aging and expanding population. Despite strong defenses of the central nervous system, some viruses have evolved ways to breach them, which often result in dire consequences. In this review, we recount the various ways by which different viruses can enter the CNS, and we describe the consequences of such invasions. Consequences may manifest as acute disease, such as encephalitis, meningitis, or result in long-term effects, such as neuromuscular dysfunction, as occurs in poliomyelitis. We discuss evidence for viral involvement in the causation of well-known chronic neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, as well as vascular dementia in the elderly. We also describe the approaches currently available to control a few of the neural viral infections. These include antivirals that are effective against human immunodeficiency virus and herpes simplex virus, as well as vaccines valuable for controlling rabies virus, poliomyelitis virus, and some flavivirus infections. There is an urgent need to better understand, at a molecular level, how viruses contribute to acute and, especially, chronic neurological diseases and to develop more precise and effective vaccines and therapies.

Genotype-driven sensitivity of mice to tick-borne encephalitis virus correlates with differential host responses in peripheral macrophages and brain

BACKGROUND

Tick-borne encephalitis (TBE) is the most common tick-borne viral infection in Eurasia. Outcomes range from asymptomatic infection to fatal encephalitis, with host genetics likely playing a role. BALB/c mice have intermediate susceptibility to TBE virus (TBEV) and STS mice are highly resistant, whereas the recombinant congenic strain CcS-11, which carries 12.5% of the STS genome on the BALB/c background, is more susceptible than BALB/c mice. In the present study, we employed these genetically distinct mouse models to investigate the host response to TBEV infection in both peripheral macrophages, one of the initial target cell populations, and the brain, the terminal target organ of the virus.

METHODS

TBEV growth and the production of key cytokines and chemokines were measured and compared in macrophages derived from BALB/c, CcS-11, and STS mice. In addition, brains from these TBEV-infected mouse strains underwent in-depth transcriptomic analysis.

RESULTS

Virus production in BALB/c and CcS-11 macrophages exhibited similar kinetics 24 and 48 h post-infection (hpi), but CcS-11 macrophages yielded significantly higher titers 72 hpi. Macrophages from both sensitive strains demonstrated elevated chemokine and proinflammatory cytokine production upon infection, whereas the resistant strain, STS, showed no cytokine/chemokine activation. Transcriptomic analysis of brain tissue demonstrated that the genetic background of the mouse strains dictated their transcriptional response to infection. The resistant strain exhibited a more robust cell-mediated immune response, whereas both sensitive strains showed a less effective cell-mediated response but increased cytokine signaling and signs of demyelination, with loss of oligodendrocytes.

CONCLUSIONS

Our findings suggest that variations in susceptibility linked to host genetic background correspond with distinct host responses, both in the periphery upon virus entry into the organism and in the brain, the target organ of the virus. These results provide insights into the influence of host genetics on the clinical trajectory of TBE.

Anti-Tick-Bourne Encephalitis IgM Intrathecal Synthesis as a Prediction Marker in Tick-Borne Encephalitis Patients

The aim of this study was to evaluate the usefulness of IgM anti-Tick-Borne Encephalitis (anti-TBE) intrathecal synthesis in the diagnosis and prediction of the clinical course of the disease. Thirty-six patients were included in the study (patients reported symptoms such as fever, headache, fatigue, and nausea/vomiting). CRP, White Blood Cells (WBC), pleocytosis, Cerebrospinal Fluid (CSF) protein concentration, CSF albumin concentration, serum IgM, serum IgG, CSF IgM, CSF IgG, IgM Index, IgG Index, and IgG Index/IgM Index ratio were the parameters which were examined in the individuals. An analysis of correlation presented statistical significance between IgM Index and pleocytosis and protein concentration in CSF in the whole group of individuals. IgM Index and IgG Index/IgM Index ratio may be used in the prediction of severity of TBE. The most probable link between the IgM intrathecal production and severity of TBE may be a result of delayed seroconversion to IgG, and therefore not an adequate response to the virus presence.

Neurotropic Tick-Borne Flavivirus in Alpine Chamois (Rupicapra rupicapra rupicapra), Austria, 2017, Italy, 2023

The European subtype of tick-borne encephalitis virus (TBEV-Eur; species Orthoflavivirus encephalitidis, family Flaviviridae) was the only tick-borne flavivirus present in central Europe known to cause neurologic disease in humans and several animal species. Here, we report a tick-borne flavivirus isolated from Alpine chamois (Rupicapra rupicapra rupicapra) with encephalitis and attached ticks, present over a wide area in the Alps. Cases were detected in 2017 in Salzburg, Austria, and 2023 in Lombardy and Piedmont, Italy. The virus strains exhibit 94.8-97.3% nucleotide identities to each other and are more closely related to Louping ill viruses (LIV; Orthoflavivirus loupingi; 90-92% identities) than to TBEV-Eur (less than 88%). The chamois-derived virus strains, tentatively termed "Alpine chamois encephalitis virus", form a well-supported independent genetic clade with Spanish goat encephalitis virus, clearly separated from other LIV. This supports its designation as a new virus subtype with the proposed shared taxonomic name "Spanish goat and Alpine chamois encephalitis virus subtype" within the species Orthoflavivirus loupingi. The zoonotic potential of this newly identified virus subtype as well as its host range in other animal species including farm animals needs to be further investigated.

Clinical Characteristics, Laboratory Parameters, and Molecular Epidemiology of Neuroinvasive Flavivirus Infections in a Hotspot Region of Eastern Croatia

Neuroinvasive flaviviruses such as tick-borne encephalitis virus (TBEV) and West Nile virus (WNV) are widely distributed in continental Croatian regions. We analyzed clinical characteristics, laboratory parameters, and molecular epidemiology of neuroinvasive flavivirus infections in eastern Croatia. A total of 43 patients with confirmed flavivirus infection hospitalized from 2017 to 2023 were included in the study. Reverse-transcription polymerase chain reaction (RT-qPCR) was used to detect flavivirus RNA in clinical samples (cerebrospinal fluid; CSF, urine). ELISA was used for IgM and IgG antibody detection in serum and CSF with confirmation of cross-reactive samples by virus neutralization test. WNV was detected more frequently (74.4%) than TBEV (25.6%). A statistically significant age difference was found between WNV patients (median 65 years) and TBEV patients (median 36 years). Comorbidities were more frequently detected in WNV patients (hypertension 56.3 vs. 18.2%; diabetes 31.3 vs. 0%). Meningitis was the most common clinical presentation in both TBE and WNV neuroinvasive disease (WNND; 63.6 and 59.4%, respectively). In addition, some rare clinical presentations of WNND were also detected (cerebellitis, polyradiculoneuritis). No significant differences in the frequency of clinical symptoms were observed between WNV and TBEV-infected patients (fever 93.7 vs. 100%; malaise 78.1 vs. 100%; headache 75.0 vs. 100%; nausea 50.0 vs. 63.6%; vomiting 34.4 vs. 54.6%). Comparative analysis of total and differential leukocyte blood count showed similar results. However, CSF pleocytosis was higher in TBE patients, with a significant difference in the neutrophil and lymphocyte count (WNND median 48.5% and 51.5%; TBE median 10.0 and 90.0%, respectively). The length of hospital stay was 12 days for WNND and 9 days for TBE. Phylogenetic analysis of detected WNV strains revealed the presence of WNV lineage 2 in eastern Croatia.

The assessment of usefulness of cytokines and other soluble mediators as the predictors of sequalae development in various forms of tick-borne encephalitis (TBE)

AIM

The aim of the study was to assess the usefulness of cytokines and other soluble mediators in differentiation between severe and mild course of tick-borne encephalitis (TBE) as well as the predictor of sequalae development.

MATERIAL AND METHODS

122 patients (mean age 47.66 ± 14.77 years, 43 females, 79 males) with TBE were included in the study. Concentrations of 82 cytokines, growth factors, selectins, matrix metalloproteinases and other soluble mediators were measured in serum and CSF samples according to the manufacturer's instruction on a Bio-Plex 200 System using the custom made Luminex assays. Enzyme-linked immunosorbent assays for the quantitative detection of human IL-26, IL-29 IL-22, CXCL12 were performed.

RESULTS

No significant differences between serum concentrations of examined factors between group with sequelae and group with complete recovery were observed. In the CSF the concentrations of GM-CSF, Il-1α, Il-2, Il-4, Il-6, Il-12p70, Il-17A, CXCL1, CXCL6, Il-8, CCL4, CCL20, TRAIL, CD40L, MMP8 were significantly higher in patients who developed sequelae than in patients with complete recovery. For TRAIL concentration over 26.65 pg/ml in CSF the probability of sequalae development was 10.5 higher. In case of CCL20 - the concentration over 21.38 pg/ml in CSF the odds ratio was 6.429 times. For MMP-8 over 4210.54 pg/ml, the odds ratio was 11.222 times.

CONCLUSIONS

TRAIL, CCL-20 and MMP-8 are promising biomarkers of prediction of the sequalae development of TBE. Pro-inflammatory cytokines IL-8, IL-1, IL-2, IL-12, IL-17A also associate well with the risk of sequelae and could be further evaluated as prognostic markers in TBE, individually or as elements of a larger model.

The Known and Unknown of Global Tick-Borne Viruses

Ticks are crucial vectors for various pathogens associated with human and animal diseases, including viruses. Nevertheless, significant knowledge gaps prevail in our understanding of tick-borne viruses (TBVs). We here examined existing studies on TBVs, uncovering 870 documented virus species across 28 orders, 55 families, and 66 genera. The discovery history, vector ticks, and hosts of TBVs, as well as the clinical characteristics of TBV-induced diseases, are summarized. In total, 176 tick species from nine tick genera were confirmed as vectors for TBVs. Overall, 105 TBVs were associated with infection or exposure to humans and animals. Of them, at least 40 were identified to cause human or animal diseases. This review addresses the current challenges associated with TBV research, including the lack of knowledge about the identification of novel and emerging TBVs, the spillover potentials from ticks to hosts, and the pathogenicity and infection mechanisms of TBVs. It is expected to provide crucial insights and references for future studies in this field, while specifically focusing on expanding surveys, improving TBV identification and isolation, and enhancing the understanding of TBV-vector-host interactions. All of these findings will facilitate the preparation for preventing and treating diseases caused by emerging and novel TBVs.

Tick-Borne Diseases and Pregnancy: A Narrative Review Evaluating Pregnancy Complications Caused by Tick-Borne Diseases

Ticks are vectors of public health concern because the pathogens they transmit can cause detrimental diseases in humans. Lyme disease, tick-borne relapsing fever, human granulocytic anaplasmosis, Rocky Mountain spotted fever, tick-borne encephalitis, Crimean-Congo hemorrhagic fever, and babesiosis are some of the most common diseases caused by the pathogens transmitted by ticks. The overlap between human activities and tick habitats is growing, contributing to an increase in tick-borne disease cases. Unfortunately, pregnancy as a risk factor for tick-borne diseases is largely ignored. In this narrative review we use case reports, epidemiological studies, and animal studies to evaluate the maternal, pregnancy, and fetal outcomes caused by Lyme disease, tick-borne relapsing fever, human granulocytic anaplasmosis, Rocky Mountain spotted fever, tick-borne encephalitis, Crimean-Congo hemorrhagic fever, and babesiosis during pregnancy.

Clinical Evaluation of the VirClia IgM/IgG Chemiluminescence Tests for the Diagnosis of Tick-Borne Encephalitis in an Endemic Part of Norway

The aim of this study was to evaluate the clinical usefulness of VirClia IgM/IgG single-assay chemiluminescence tests for the diagnosis of tick-borne encephalitis (TBE) in an endemic part of Norway. Patients hospitalized at Vestfold or Telemark Hospitals with suspected infection in the central nervous system (CNS) in the period between May 2021 and December 2023 were included, with 85 TBE cases identified. The VirClia IgM assay was positive in the initial serum sample in 75/85 cases, giving a sensitivity of 88.2% (95% CI, 79.4-94.2). The ReaScan TBE IgM rapid test was positive in 80/85 cases, with an estimated sensitivity of 94.1% (95% CI, 86.8-98.1). Vaccine breakthrough infections were the predominant cause of non-reactive IgM cases. The calculated specificity for the VirClia IgM was 95.8% (95% CI, 92.5-98.0). In conclusion, the sensitivity of the VirClia IgM was non-inferior to the ReaScan TBE IgM rapid test. However, isolated IgM reactive results must be interpreted with caution, since false-reactive results occur.

TaqMan qPCR and IgM Detection in Samples of Patients with Tick-Borne Encephalitis Virus Infection in Northeast China

Purpose

Tick-borne encephalitis virus (TBEV) infections result in severe central nervous system diseases in humans across Asia and Europe. In China, cases of tick-borne encephalitis are primarily caused by the Far East subtype of TBEV, which exhibits a distinct disease course compared to other extensively studied subtypes. However, there is limited knowledge regarding the nucleic acid and serological diagnostic characteristics of patients infected with the TBEV in China, which is the focus of investigation in the present study.

Methods

This study established a TaqMan qPCR approach to detect TBEV RNA in the serum with optimal specificity, sensitivity, and precision. Using TaqMan qPCR and ELISA assay for TBEV IgM detection, serum samples from 63 hospitalized patients bitten by ticks in Northeast China were investigated for diagnostic characteristics.

Results

Twenty-five patients were positive for viral RNA; nineteen patients were positive for IgM, and nine were positive for both viral RNA and IgM. Through comparative analysis, TBEV RNA copies were negatively correlated with the virus incubation period. IgM levels were positively correlated with the clinical symptom scores of patients. The severity of clinical symptoms and the length after the tick bite could be used to predict the IgM occurrence. Furthermore, IgM levels and viral RNA copies were not correlated in double-positive patients.

Conclusion

Both nucleic acid and serological detection methods exhibited distinct windows for detecting TBEV infection, with some overlap, and were associated with specific correlated factors. This study provided novel insights into the diagnosis and course of TBEV-induced tick-borne encephalitis in China.

Tick-Borne Encephalitis, Lombardy, Italy

Tick-borne encephalitis was limited to northeast portions of Italy. We report in Lombardy, a populous region in the northwest, a chamois displaying clinical signs of tickborne encephalitis virus that had multiple virus-positive ticks attached, as well as a symptomatic man. Further, we show serologic evidence of viral circulation in the area.

Defining the "Correlate(s) of Protection" to tick-borne encephalitis vaccination and infection - key points and outstanding questions

Tick-borne Encephalitis (TBE) is a severe disease of the Central Nervous System (CNS) caused by the tick-borne encephalitis virus (TBEV). The generation of protective immunity after TBEV infection or TBE vaccination relies on the integrated responses of many distinct cell types at distinct physical locations. While long-lasting memory immune responses, in particular, form the basis for the correlates of protection against many diseases, these correlates of protection have not yet been clearly defined for TBE. This review addresses the immune control of TBEV infection and responses to TBE vaccination. Potential correlates of protection and the durability of protection against disease are discussed, along with outstanding questions in the field and possible areas for future research.

Results of Tick-Borne Encephalitis Virus (TBEV) Diagnostics in an Endemic Area in Southern Germany, 2007 to 2022

Tick-borne encephalitis virus (TBEV) is the most important tick-transmitted neurotropic flavivirus in Europe and Asia. Our analysis aimed to investigate the contribution of TBEV-specific antibody detection by serological assays and TBEV RNA detection by real-time PCR to the diagnosis of tick-borne encephalitis (TBE). We analyzed data from 3713 patients from 16 years of laboratory TBEV diagnostics in an endemic area in Southern Germany. During this period, 126 cases of TBE were diagnosed. TBEV-specific IgM ELISA tests showed a high clinical sensitivity (96.8%) and a very high clinical specificity (99.7%). In immunocompetent patients, TBE was reliably diagnosed by detection of TBEV IgM antibodies in serum. Intrathecal TBEV IgG antibody synthesis was detected in 46 of 84 (55%) cases by analysis of paired serum and cerebrospinal fluid (CSF) samples. None of the 87 immunocompetent TBE patients tested had detectable TBEV RNA in serum or CSF. In contrast, in two TBE patients without TBEV-specific antibodies, diagnosis could only be made by the detection of TBEV RNA in CSF. Both patients had previously been treated with the B cell-depleting antibody rituximab. Therefore, in patients with CNS infection and humoral immunodeficiency, it is necessary to include TBEV PCR in the diagnostic approach.

Tick-Borne Encephalitis Virus Vaccination among Tourists in a High-Prevalence Area (Italy, 2023): A Cross-Sectional Study

Tick-borne encephalitis (TBE) represents a potential health threat for tourists in high-risk areas, including the Dolomite Mountains in northeastern Italy. The present questionnaire-based survey was, therefore, designed in order to assess knowledge, attitudes, and preventive practices (KAP) in a convenience sample of Italian tourists visiting the Dolomite Mountains, who were recruited through online discussion groups. A total of 942 participants (39.2% males, with 60.2% aged under 50) filled in the anonymous survey from 28 March 2023 to 20 June 2023. Overall, 24.1% of participants were vaccinated against TBE; 13.8% claimed to have previously had tick bites, but no cases of TBE were reported. The general understanding of TBE was relatively low; while 79.9% of participants acknowledged TBE as a potentially severe disease, its occurrence was acknowledged as high/rather high or very high in the Dolomites area by only 51.6% of respondents. Factors associated with the TBE vaccine were assessed by the calculation of adjusted odds ratios (aOR) and 95% confidence intervals through a logistic regression analysis model. Living in areas considered at high risk for TBE (aOR 3.010, 95%CI 2.062-4.394), better knowledge on tick-borne disorders (aOR 1.515, 95%CI 1.071-2.142), high risk perception regarding tick-borne infections (aOR 2.566, 95%CI 1.806-3.646), a favorable attitude toward vaccinations (aOR 3.824, 95%CI 1.774-8.224), and a tick bite(s) in a previous season (aOR 5.479, 95%CI 3.582-8.382) were characterized as being positively associated with TBE vaccination uptake. Conversely, being <50 years old (aOR 0.646, 95%CI, 0.458-0.913) and with a higher risk perception regarding the TBE vaccine (aOR 0.541, 95%CI 0.379-0.772) were identified as the main barriers to vaccination. In summary, tourists to the high-risk area of the Dolomites largely underestimate the potential occurrence of TBE. Even though the uptake of the TBE vaccine in this research was in line with European data, public health communication on TBE is required in order to improve acceptance of this effective preventive option.

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.

Severe Neurologic Disease in a Horse Caused by Tick-Borne Encephalitis Virus, Austria, 2021

As evidenced by sero-epidemiological studies, infections of horses with the tick-borne encephalitis virus (TBEV) occur frequently in TBEV-endemic areas. However, there are only very few reports of clinical cases. A possible underreporting may be due to a variety of diagnostic challenges. In this study, ELISA and neutralization tests were applied to serum samples. Brain tissue samples were investigated for the presence of nucleic acids of TBEV, Equid alphaherpesvirus 1, Borna disease virus 1, West Nile and Usutu viruses, rustrela virus, as well as Eastern, Western, and Venezuelan equine encephalitis viruses with RT-qPCR, RT-PCR, and qPCR, respectively. TBEV-specific amplification products were subjected to Sanger sequencing. In addition, a direct fluorescent antibody test for rabies was performed. Clinical and patho-histological findings are reported. Using specific RT-qPCR and RT-PCR assays, TBEV nucleic acids were demonstrated in brain tissue samples. Sequencing revealed the Western (formerly Central) European subtype of TBEV as the etiological agent. A high titer of TBEV-specific neutralizing antibodies was found in the serum. RNAscope in situ hybridization revealed TBEV RNA confined to neuronal cell bodies and processes. No other pathogens or nucleic acids thereof could be detected. Diagnostic procedures need to be carried out early after the onset of neurological signs to allow for a final etiological diagnosis of acute TBEV infections in horses.

A combination of two resistance mechanisms is critical for tick-borne encephalitis virus escape from a broadly neutralizing human antibody

Tick-borne encephalitis virus (TBEV) is a flavivirus that causes human neuroinfections and represents a growing health problem. The human monoclonal antibody T025 targets envelope protein domain III (EDIII) of TBEV and related tick-borne flaviviruses, potently neutralizing TBEV in vitro and in preclinical models, representing a promising candidate for clinical development. We demonstrate that TBEV escape in the presence of T025 or T028 (another EDIII-targeting human monoclonal antibody) results in virus variants of reduced pathogenicity, characterized by distinct sets of amino acid changes in EDII and EDIII that are jointly needed to confer resistance. EDIII substitution K311N impairs formation of a salt bridge critical for T025-epitope interaction. EDII substitution E230K is not on the T025 epitope but likely induces quaternary rearrangements of the virus surface because of repulsion of positively charged residues on the adjacent EDI. A combination of T025 and T028 prevents virus escape and improves neutralization.

Emergency Department Syndromic Surveillance to Monitor Tick-Borne Diseases: A 6-Year Small-Area Analysis in Northeastern Italy

Tick-borne diseases (TBD) are endemic in Europe. However, surveillance is currently incomplete. Alternative strategies need to be considered. The aim of this study was to test an Emergency Department Syndromic Surveillance (EDSyS) system as a complementary data source to describe the impact of tick bites and TBD using a small-area analysis approach and to monitor the risk of TBD to target prevention. ED databases in the Local Health Authority 8 District (Veneto, Italy) were queried for tick-bite and TBD-related visits between January 2017 and December 2022. Hospitalisations were also collected. Events involving the resident population were used to calculate incidence rates. A total of 4187 ED visits for tick-bite and 143 for TBD were recorded; in addition, 62 TBD-related hospitalisations (of which 72.6% in over 50 s and 22.6% in over 65 s). ED visits peaked in spring and in autumn, followed by a 4-week lag in the increase in hospital admissions. The small-area analysis identified two areas at higher risk of bites and TBD. The use of a EDSyS system allowed two natural foci to be identified. This approach proved useful in predicting temporal and geographic risk of TBD and in identifying local endemic areas, thus enabling an effective multidisciplinary prevention strategy.