Tick-borne encephalitis: A review of epidemiology, clinical characteristics, and management

The Role of Chemotactic Cytokines in Tick-Borne Encephalitis

In tick-borne encephalitis (TBE), the central nervous system (CNS) is infiltrated by a mixed leukocyte population contributing both to the infection control and the immune-mediated pathology. To elucidate the roles of chemotactic cytokines in this process, we measured concentrations of 25 cytokines in serum and cerebrospinal fluid (CSF) simultaneously with total CSF leukocyte count (pleocytosis) and leukocyte subpopulation counts in 103 TBE patients. We created models describing the dependence of pleocytosis and clinical severity on cytokine concentrations. Ten polymorphisms in genes for cytokines or their receptors were studied with rtPCR in patients' DNA samples. The strongest chemotactic gradients towards CSF were created by CXCL1, IL-8, CXCL10, CCL2, CCL3, CCL4, CCL7, CCL8, CCL19 and CCL20. Neutrophil counts in CSF correlated with concentrations of CXCL1 and IL-8 and lymphocyte counts with IL-16, CCL19, CCL20, CCL4, CXCL12, and CXCL13. The milder disease is associated with CCL11, CCL19, CXCL10 and CXCL13,-while the more severe with CXCL1 and CCL20. The polymorphisms in the genes CCR2, CCL5, CXCR3 and CX3CR1 are associated with the cytokine concentrations and pleocytosis, but not with clinical severity. Multiple chemotactic cytokines contribute to pleocytosis in TBE, with no straightforward relationship between their effects on pleocytosis and the clinical presentation.

Tick-borne encephalitis virus seroprevalence and infection incidence in Switzerland, 2020-2021

Tick-borne encephalitis virus (TBEV) infection can manifest as disease of variable severity, ranging from subclinical infection to severe disease with neurological involvement and potentially fatal outcome. Although TBE is recognized as a major public health problem in Europe, the true burden of disease is potentially underestimated. Here, we investigated TBEV-specific antibody prevalence, infection incidence, and seroreversion and antibody decline rates in a prospective Swiss healthcare worker (HCW) cohort. We screened serum samples from 1444 HCWs between June and October 2020, and from a subset again between August and September 2021, using a TBEV envelope (E) protein IgG ELISA. Positive samples underwent further analysis with a TBEV non-structural protein 1 (NS1) IgG ELISA, and seroconversions in unvaccinated individuals were confirmed by seroneutralization testing. Questionnaire data were used to determine vaccination status and risk factors. TBEV E protein-specific IgG prevalence was 72.1% (95% CI 68.2-75.7%) in TBEV-vaccinated and 6% (95% CI 4.4-7.8%) in unvaccinated individuals. The estimated annual incidence of infection was 735/100,000. Age was the only factor significantly associated with seroprevalence. The seroreversion rate in unvaccinated individuals was 30.3% within one year, which is almost ten times higher than in vaccinated individuals (3.4%, annual decline rate 8.0%). NS1-specific IgG antibodies were six times more common in vaccinated than unvaccinated HCWs. In conclusion, undetected TBEV infections are common, and infection incidence is much higher than reported clinical cases. Individuals with abortive infections have high antibody decline and seroreversion rates. Whether lifelong protection is conferred and by which immune subsets remain unclear.

Tick-borne encephalitis in adults in Denmark: a nationwide prospective cohort study from 2015 to 2023

BACKGROUND

Our aim was to characterize the clinical presentation and outcome in adults with tick-borne encephalitis (TBE) and to determine the incidence and test activity of TBE in Denmark.

METHODS

A nationwide prospective cohort study of all adults hospitalized with TBE at departments of infectious diseases in Denmark from 2015 to 2023. An age- and sex-matched cohort of herpes simplex virus type 1 (HSV-1) encephalitis patients was included to compare outcome.

RESULTS

Fifty-two patients with TBE were included. Median age was 50 years, 32/52 (62%) were men, 1/52 (2%) was fully vaccinated against TBE at the time of infection, 29/52 (56%) were infected in Denmark. Upon admission 25/52 (48%) had meningitis, 27/52 (52%) encephalitis, three of the latter 3/52 (6%) with additional myelitis or radiculitis. Admission to the intensive care unit 6/52 (12%) and death 2/52 (4%) were associated with pre-existing comorbidities and older age. At 3-month follow-up, 16/50 (32%) had an unfavorable outcome (Glasgow Outcome Scale score 1-4) compared to 39/52 (75%) in the HSV-1 cohort. The most common residual symptoms at 6-month follow-up or later were headache, cognitive impairment, and fatigue. The TBE incidence increased from 0.03/100,000 in 2015 to 0.48/100,000 in 2023, and the test rate from 5.5/100,000 in 2015 to 14.4/100,000 in 2023, with a positivity rate of 0.6% in 2015 and 3.3% in 2023.

CONCLUSION

The incidence of TBE in Denmark increased in the study period, with clinical characteristics and outcome of adult patients comparable to reports from other European countries.

Viruses and psychiatric disorders: We have not crossed the borderline from hypothesis to proof yet (Review)

Most psychiatric disorders are heterogeneous and are attributed to the synergistic action of a multitude of factors. It is generally accepted that psychiatric disorders are the outcome of interactions between genetic predisposition and environmental perturbations, which involve psychosocial stress, or alterations in the physiological state of the organism. A number of hypotheses have been presented on such environmental influences that may include direct insults such as injury, malnutrition and hostile living conditions, or indirect sequelae following infection from viruses such as influenza, arboviruses, enteroviruses and several herpesviruses, or the differential expression of human endogenous retroviruses. It is known that the concept of viruses is far more extensive than their perception as mere agents of acute infections, or chronic debilitating diseases, such as AIDS or some forms of cancer. Notably, an apparent causal connection between viruses and the pathophysiology of diseases has been suggested; however, it remains unclear as to how to establish this causal connection. There are inherent difficulties in answering this question with certainty, which may be due to the multitude of genetic and environmental influences that can lead to psychopathology; the latent state of chronic infection exhibited by a number of neurotropic viruses; the late onset of psychiatric disorders with respect to the acute phase of viral infection at which detection tests would be successful; the complexity of the virome; and the existence of thousands of viral species. The present review aims to provide an outline of the conclusions that have thus far been reached regarding a possible association between viral infection and psychiatric disease, and the obstacles confronted during the quest for the truth behind the role of viruses.

Tick-borne encephalitis vaccination in persons with a recent history of Lyme borreliosis: Insights from a Knowledge, Attitudes and Behaviour survey in Bavaria, Germany

Tick-borne encephalitis (TBE) frequently causes severe disease or even long-term sequelae, especially in adults. In Germany, TBE risk areas are defined based on historical TBE incidences at the district level and are updated yearly. Meanwhile, almost all Bavarian districts are designated risk areas. TBE vaccination is recommended for residents or visitors of these risk areas. However, recent evidence indicates that only around one fifth of adults and one third of children and adolescents are vaccinated against TBE. Most persons notified with TBE (>97 %) are found to be not or insufficiently vaccinated. Our study aimed to identify the reasons for and against TBE vaccination among persons at high risk for tick-borne diseases (TBD) based on recent diagnosis of Lyme borreliosis (LB) to inform future preventive measures. We invited persons with a recent course of LB notified between June and August 2019 to complete a self-reported questionnaire about their knowledge, attitudes and behaviours regarding TBD-related themes. We examined self-reported TBE vaccination status using different categories based on the number of doses received. Information on their TBE vaccination status was provided by 366 of 376 eligible participants, of whom 249 (68 %) reported to have been vaccinated. Of 228 participants who provided further details, 142 (62 %) reported to have received a regular booster vaccination. Apart from age category and TBD-specific knowledge level, vaccination status was not associated with any other sociodemographic or residence-specific factors, outdoor behaviours, occupational exposure, or prior experiences with ticks or TBDs. Main reasons for vaccination were living in a TBE risk area, spending time in tick-prone environments and recommendation by a physician. Main barriers were vaccine scepticism, fear of side effects, not having given TBE vaccination any thought and low risk perception. These results suggest that in order to achieve a higher vaccination coverage to prevent TBE cases, awareness about TBE risk areas and the recommended vaccination need to be raised. Addressing misconceptions and increasing trust in vaccine safety appears crucial to address perceived barriers. Engaging trusted sources, such as medical professionals, and both implementing broad public campaigns and focusing on high-risk groups are key strategies for increasing vaccination uptake.

A Retrospective Sero-Surveillance Study for Antibodies Against Tick-Borne Encephalitis Virus in Norway

Tick-borne encephalitis virus (TBEV) is an emerging pathogen that initially causes flu-like symptoms and can progress to central nervous system (CNS) infections. Tick-borne encephalitis (TBE) is an endemic disease in southern coastal counties with regular human cases, while the causative agent, TBEV, is prevalent in ticks in most of the coastal regions of Norway. This study was aimed to understand TBEV infection status across Norway including both TBE endemic and non-endemic areas. For this, we analyzed a total of 1940 residual serum samples from 19 counties of Norway (as of 2016). The samples were initially screened by ELISA, followed by virus neutralization tests for TBEV confirmation. We found a similar TBEV seroprevalence of 1.7% in TBE endemic and 1.6% in non-endemic areas. Since TBE cases are only reported from endemic regions, our findings suggest a potential subclinical or asymptomatic infection and underdiagnosis in non-endemic areas. Notably, only 43% of the ELISA-positive samples were confirmed by virus neutralization tests indicating that not all ELISA positives are true TBEV infections. Additionally, 137 samples of patients presenting with symptoms of CNS infections from a non-endemic area were included. Of these samples, 11 ELISA-positive samples were analyzed for cross-reactivity among flaviviruses. Cross-reactivity was detected with Dengue virus, West Nile Virus, and non-specific reactions. This underscores the importance of using multiple diagnostic tests to confirm TBEV infections. None of the patients with CNS infection was found to be TBE positive, and in the whole cohort, we found a low TBEV seroprevalence of 0.7%.

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.

A Multiplex Polymerase Chain Reaction Assay for the Detection of Herpes Simplex Virus, Cytomegalovirus, and Varicella-Zoster Virus in Cerebrospinal Fluid

Viral meningitis poses a significant clinical challenge due to its rapid onset and potential progression to life-threatening encephalitis. Early detection of treatable viral pathogens such as Herpes simplex virus (HSV), Cytomegalovirus (CMV), and Varicella-zoster virus (VZV) is essential for initiating appropriate therapies. However, multiplex PCRs for the rapid and simultaneous detection of these pathogens are scarce due to the complex PCR design and the elaborate validation process using cerebrospinal fluid samples. In this study, we established and validated a novel multiplex PCR assay for detecting HSV, CMV, and VZV in cerebrospinal fluid samples and implemented the assay on a fully automated platform.

Flaviviruses-Induced Neurological Sequelae

Flaviviruses, a group of single-stranded RNA viruses spread by mosquitoes or ticks, include several significant neurotropic viruses, such as West Nile virus (WNV), Japanese encephalitis virus (JEV), tick-borne encephalitis virus (TBEV), and Zika virus (ZIKV). These viruses can cause a range of neurological diseases during acute infection, from mild, flu-like symptoms to severe and fatal encephalitis. A total of 20-50% of patients who recovered from acute flavivirus infections experienced long-term cognitive issues. Here, we discuss these major neurotropic flaviviruses-induced clinical diseases in humans and the recent findings in animal models and provide insights into the underlying disease mechanisms.

Severe Cases of Tick-Borne Encephalitis in Northeastern Poland

Tick-borne encephalitis (TBE) is the most prevalent viral infection of the central nervous system (CNS) in Poland. The disease is characterized by the presence of two stages. The first phase, called the viremic stage, presents with flu-like symptoms, while the second stage of TBE is characterized by damage to the nervous system and may follow a severe and dramatic course. The aim of this paper is to increase the awareness of the potential sequelae after TBE. In this study, we report cases of severe TBE in 36-year-old and 57-year-old female patients. The outcome of TBE varies from patient to patient, but there are some factors that can help to predict the severity of TBE infection. The risk factors presented in these patients were as follows: the monophasic course of TBE, high pleocytosis in cerebrospinal fluid (CSF) and older age. Both of our patients were not vaccinated despite the World Health Organization's (WHO's) recommendations. Both patients had no history of travel outside their region of residence prior to the onset of illness. The few risk factors shown in our patients and the serious sequelae of the disease may indicate the need to test patients for possible gene mutations.

An Overview of Zika Virus and Zika Virus Induced Neuropathies

Flaviviruses pose a major public health concern across the globe. Among them, Zika virus (ZIKV) is an emerging and reemerging arthropod-borne flavivirus that has become a major international public health problem following multiple large outbreaks over the past two decades. The majority of infections caused by ZIKV exhibit mild symptoms. However, the virus has been found to be associated with a variety of congenital neural abnormalities, including microcephaly in children and Guillain-Barre syndrome in adults. The exact prediction of the potential of ZIKV transmission is still enigmatic and underlines the significance of routine detection of the virus in suspected areas. ZIKV transmission from mother to fetus (including fetal abnormalities), viral presence in immune-privileged areas, and sexual transmission demonstrate the challenges in understanding the factors governing viral persistence and pathogenesis. This review illustrates the transmission patterns, epidemiology, control strategies (through vaccines, antivirals, and vectors), oncolytic aspects, molecular insights into neuro-immunopathogenesis, and other neuropathies caused by ZIKV. Additionally, we summarize in vivo and in vitro models that could provide an important platform to study ZIKV pathogenesis and the underlying governing cellular and molecular mechanisms.

The Role of Chitinase 3-Like-1 (YKL-40) and Proinflammatory Biomarkers in the Pathogenesis of Pediatric Tick-Borne Encephalitis in a Polish Cohort

Background

Chitinase 3-like-1 (CHI3L1), also known as YKL-40, is a potential biomarker for neuroinflammatory conditions. It is upregulated in Alzheimer's disease, multiple sclerosis, and traumatic brain injury. However, its involvement in pediatric tick-borne encephalitis (TBE) has not been addressed yet. This study aimed to evaluate CHI3L1 and its relationship with other inflammatory cytokines, blood-brain barrier (BBB) integrity, immune response, and disease severity in pediatric patients with TBE.

Patients and Methods

A total of 22 pediatric TBE patients hospitalized in Bialystok, Poland were included in this study. Participants were categorized as having meningoencephalitis (n=6) or meningitis (n=16). The integrity of the brain-blood barrier (BBB) was assessed using the albumin quotient (albQ). Biomarker indices were calculated to account for variations in BBB permeability. The concentrations of CHI3L1, CCL2, chemerin, CXCL2, IFN-γ, IL-1-β, IL-4, IL-6, IL-13, and TNF-α in both serum and CSF, were measured using the Luminex Multiplex Assay od admission and two weeks later when symptoms resolved.

Results

CSF and serum concentrations of CHI3L1 did not differ between the encephalitis and meningitis cases. After adjusting for BBB permeability, the CHI3L1 index was 2.4-fold lower in patients with encephalitis than in those with meningitis (P=0.008). There was a post-treatment reduction of CHI3L1, IL-6, and TNF-α CSF concentrations. We also found and improvement in BBB permeability in younger children but in older albQ remained abnormal. Correlation analysis revealed associations between CHI3L1 levels and pro-inflammatory markers, notably chemerin, IL-6, and TNF-α, across both clinical groups.

Conclusion

Our findings suggest that CHI3L1 CSF levels reflect the inflammatory activity in pediatric TBE and may help to differentiate between meningoencephalitis and meningitis. The observed interactions between CHI3L1 and other cytokines underscore its potential involvement in inflammatory response to the virus. The prolonged disruption in BBB integrity in older children might reflect age-dependent differences in the severity of TBE. These insights advance our understanding of TBE pathogenesis in children and support further investigation of CHI3L1 as a biomarker for TBE diagnosis and management.

The Prevalence of Tick-Borne Encephalitis Virus Infection Among Humans in Heilongjiang Province of China in 2020-2023

BACKGROUND AND AIMS

Tick-borne encephalitis (TBE) is a serious and acute central nervous system infection caused by the tick-borne encephalitis virus (TBEV). In recent years, TBE has emerged as a growing public health threat, with cases reported across Europe, the Russian Far East, Japan and China. This study aims to assess the prevalence of TBEV infection and examine behaviours associated with an increased risk of infection among individuals who visited the Heilongjiang Red Cross Sengong General Hospital due to tick bites from 2020 to 2023.

METHODS AND RESULTS

We collected blood samples and administered survey questionnaires from tick-bitten people. A total of 457 samples were screened using Nested PCR, and the detected TBEV prevalence rate was 29.54% (135/457). The symptoms of redness and swelling at the site of tick bite (42.57%), fever (28.71%) and headache (10.89%) were identified in the TBEV-positive individuals when they visited the hospital by the physician. Phylogenetic analysis of the partial E gene of TBEV revealed that the predominant strains in the region are highly virulent Far Eastern subtype. However, they do not cluster with the three established evolutionary clades of the Far Eastern type. Questionnaires data analysis identified age and first tick bite as important factors associated with TBEV infection.

CONCLUSIONS

This study provides basic information on the epidemiology of TBEV in Heilongjiang Province in recent years and identifies that the most related risk factor of infecting TBEV is tick exposure. Further research is needed to develop effective prevention and control measures.

Tick-Borne Encephalitis Virus Infection in a Two-Year-Old Child Returning from Switzerland (July-August 2023): Is It Time for TBE Immunization of Serbian Travelers?

Tick-borne encephalitis (TBE) is a vaccine-preventable viral infection that poses significant public health challenges, particularly in regions where tick-borne diseases are endemic. This case report describes a 2-year-old boy with confirmed abortive TBEV infection following a tick bite during travel to Switzerland. The patient developed fever and mild symptoms but did not exhibit central nervous system involvement. The case underscores the importance of raising awareness among healthcare providers and travelers from non-endemic areas, such as Serbia, about TBE risk and the potential benefits of preventive vaccination. Strategic immunization campaigns could mitigate the public health impact of travel-related TBE.

Limited evidence of infection with other tick-borne pathogens in patients tested for Lyme neuroborreliosis in the Netherlands

Ixodes ricinus is the main vector of the causative agents of Lyme neuroborreliosis. This tick species can also transmit tick-borne encephalitis virus (TBEV), spotted fever group (SFG) Rickettsia and Borrelia miyamotoi to humans. These tick-borne pathogens are present in Dutch ticks and have also been associated with human neurological infections, but well characterized disease cases are seldom reported. We therefore assessed the evidence for TBEV, SFG Rickettsia or B. miyamotoi infection in clinically well-described patients suspected of Lyme neuroborreliosis. We retrospectively included patients with specific predefined clinical criteria from patients that were tested for Lyme neuroborreliosis between 2010 and 2014 at an academic Lyme borreliosis Center. Serology was performed on available serum samples, and cerebrospinal fluid (CSF) was tested by molecular methods. Out of 514 potentially eligible patients, 176 individual patients were included. None of CSF samples was positive for the tested tick-borne pathogens, except for one previously described patient with Borrelia miyamotoi disease (BMD). Serology revealed 27, 14 and three patients with antibodies against SFG Rickettsia, B. miyamotoi and TBEV, respectively. No distinctive clinical symptoms or signs could be associated with seropositivity against any of these tick-borne pathogens. Apart from the previously published BMD case, we were unable to find convincing evidence of new cases of tick-borne encephalitis, spotted fever rickettsiosis or BMD in a cohort of patients suspected of Lyme neuroborreliosis. While antibodies against these tick-borne pathogens were detected, we could not associate these findings to clinical symptoms or signs. Therefore, prospective studies on humans with tick exposure are necessary to describe the prevalence, etiology and clinical symptoms of these tick-borne diseases other than Lyme borreliosis and tick-borne encephalitis.

Clinical Relevance of Oxidative Stress Biomarkers in Human Flavivirus Infections as Predictors of Disease Progression and Severity

Several Flaviviridae constitute an emerging threat to global health because of their continuing spread and the expansion of vector habitats, largely driven by climate change and intensified global travel. Infections can result in severe neurological or visceral pathologies. The relationship between oxidative stress (OS), an imbalance between generated reactive oxygen species and the antioxidant defences of the host, and flavivirus infection has been repeatedly demonstrated in in vitro and animal studies, but measuring biomarkers of oxidative stress in vivo could prove useful in clinical patient management. We summarise the knowledge and prospects of measuring peripheral OS biomarker levels for clinical case management and correlation with disease severity in six important human flavivirus infections (dengue virus (DENV), Japanese encephalitis virus, West Nile virus (WNV), tick-borne encephalitis virus (TBEV), yellow fever virus and zika virus). We searched the Medline and Web of Science databases for 'Oxidative Stress' AND 'Biomarkers' AND 'Flavivirus', combined with 'clinical', 'in vivo/in vivo', 'patient' and/or 'disease' and included 43 peer-reviewed publications. Correlation between OS and infection has been studied in all six Flaviviridae, but most clinically relevant data are available for DENV, TBEV and WNV. Plasma protein carbonyls, glutathione peroxidase activity and nitrogen monoxide are promising prognostic markers, but their measurement would benefit from methodological harmonisation. Future studies should investigate a broad range of OS biomarkers as predictors of clinically relevant outcomes. We advocate the validation and use of universal or disease-specific oxidative stress indexes that incorporate the most significant outcomes into one, easy-to-use clinical determinant.

Environmental and host factors underlying tick-borne virus infection in wild animals: Investigation of the emerging Yezo virus in Hokkaido, Japan

Yezo virus (YEZV) is an emerging tick-borne virus that causes acute febrile illness. It has been continuously reported in patients and ticks in Japan and China since its first identification in Hokkaido, Japan. While serological tests have demonstrated that YEZV infections are prevalent in wild animals, such as raccoons (Procyon lotor), the determinants of infection in wild animals remain largely unknown. We examined the prevalence of YEZV in invasive raccoons, native tanukis (raccoon dogs, Nyctereutes procyonoides albus), and ticks in six study areas in Hokkaido between 2018 and 2023 to identify ecological factors underlying YEZV infection in wild animals. YEZV RNA fragments were detected in 0.22% of the 1,857 questing ticks. Anti-YEZV antibodies were detected in 32 of the 514 (6.2%) raccoon serum samples and in 5 of the 40 (12.5%) tanuki serum samples. Notably, the seroprevalence in raccoons varied significantly in one of the study areas over the years, that is, 0.0%, 60.0%, and 28.6% in 2021, 2022, and 2023, respectively, implying the temporary emergence of YEZV microfoci. By analyzing the tick load and YEZV seropositivity in raccoons in a field-based setting, we found a positive correlation between adult Ixodes ovatus load and YEZV-antibody positivity, highlighting the importance of I. ovatus in YEZV infection in wild animals. We also explored the environmental and host factors influencing YEZV seropositivity in raccoons and tanukis and found that landscape factors, such as the size of forest area around the trap site, were crucial for YEZV seropositivity in these animals. The significant variables for YEZV seropositivity in raccoons were partially different from those affecting tick infestation intensity in raccoons. The present results extend our understanding of tick-borne virus circulation in the field, emphasizing the unique ecology of the emerging YEZV.

Clinical manifestations and outcomes of Tick-borne encephalitis: A systematic literature review

Tick-borne encephalitis (TBE) is caused by a viral infection and can lead to acute and persistent damage to the central and peripheral nervous systems. Recently, the incidence of TBE in Europe has risen, and epidemiological patterns of disease have changed, emphasising the need for improved understanding of this vaccine-preventable disease. Although TBE is endemic in many countries, the disease spectrum of TBE is not well described. We sought to characterise the clinical manifestations and outcomes of TBE by estimating the proportions of TBE patients with each type of manifestation and the risk of adverse outcomes for children and adults separately. A systematic literature review was conducted on 2 August 2022 for articles published in any language since 1 January 2007. Additional relevant studies were found in reference lists of identified articles. The review was limited to countries where only the European subtype of TBEV circulates. Of the 1,632 unique titles and abstracts identified and reviewed, 21 were retained for data analysis. The 21 studies were split into a main analysis (15 studies reporting patients hospitalised with laboratory-confirmed TBE) and a secondary analysis (6 studies reporting hospitalised and non-hospitalised patients who sought medical treatment for laboratory-confirmed TBE). The main analysis included 5,012 adults and 640 children. The predominant clinical manifestation in adults was encephalitis (61 %), followed by meningitis (33 %), radiculitis (14 %), and myelitis (6 %) (the manifestations were evaluated independently, so they will not sum to 100 %). With outliers removed, similar proportions of adults had encephalitis (48 %) and meningitis (44 %). Among cases in children, meningitis (77 %) was the most common manifestation, whereas encephalitis (23 %) and myelitis (1.3 %) were less frequent. Among hospitalised patients with TBE, the proportion of intensive care unit (ICU) admissions and deaths were similar for adults (15.5 % and 0.9 %, respectively) and children (16.4 % and 0 %, respectively.) The percentage of patients with sequelae when examined >12 months from acute TBE was 39.5 % for adults and 16.2 % for children. The evidence was challenging to aggregate due to study heterogeneity, variability in categorising clinical manifestations of central nervous system disease, variability of denominator populations, and differences in healthcare systems and diagnostic practices across countries. Our study disclosed distinct patterns of clinical manifestation among hospitalised adult and child patients with TBE and a high proportion of ICU admissions and long-term neurological sequelae across both age groups. These findings reinforce the continued need for preventive measures in the populations at risk. Moreover, variability of study admission criteria, including difficulty with clinical manifestation categorisation, calls for a more standardised approach to summarising TBE manifestations and outcomes across Europe.

Pathogens transmitted by Ixodes ricinus

Ixodes ricinus is the most important tick vector in central and western Europe and one of the most researched parasites. However, in the published literature on the tick and the pathogens it transmits, conjecture about specific transmission cycles and the clinical significance of certain microbes is not always clearly separated from confirmed facts. This article aims to present up-to-date, evidence-based information about the well-researched human pathogens tick-borne encephalitis virus, louping-ill virus, Anaplasma phagocytophilum, Borrelia burgdorferi sensu lato and several Babesia species, with a focus on their development in the tick, transmission dynamics and the reservoir hosts that support their circulation in the environment. Borrelia miyamotoi, Neoehrlichia mikurensis, Rickettsia helvetica and Rickettsia monacensis, which are much less common causes of disease but may affect immunocompromised patients, are also briefly discussed. Finally, the possible role of I. ricinus in the transmission of Coxiella burnetii, Francisella tularensis, Bartonella spp. and Spiroplasma ixodetis is reviewed.

Five accelerated schedules for the tick-borne encephalitis vaccine FSME-Immun® in last-minute travellers: an open-label, single-centre, randomized controlled pilot trial

BACKGROUND

The purpose of this exploratory study was to evaluate different accelerated tick-borne encephalitis (TBE) vaccine schedules for last-minute travellers.

METHODS

In a single-centre, open-label pilot study, 77 TBE-naïve Belgian soldiers were randomized to one of the following five schedules with FSME-Immun®: group 1 ('classical accelerated' schedule) received one intramuscular (IM) dose at Day 0 and Day 14, group 2 two IM doses at Day 0, group 3 two intradermal (ID) doses at Day 0, group 4 two ID doses at Day 0 and Day 7 and group 5 two ID doses at Day 0 and Day 14. The last dose(s) of the primary vaccination scheme were given after 1 year: IM (1 dose) or ID (2 doses). TBE virus neutralizing antibodies were measured in a plaque reduction neutralization test (PRNT90 and 50) at Days 0, 14, 21, 28, Months 3, 6, 12 and 12+21 days. Seropositivity was defined as neutralizing antibody titres ≥10.

RESULTS

The median age was 19-19.5 years in each group.Median time to seropositivity up to Day 28 was shortest for PRNT90 in ID-group 4 and for PRNT50 in all ID groups. Seroconversion until Day 28 peaked highest for PRNT90 in ID-group 4 (79%) and for PRNT50 in ID-groups 4 and 5 (both 100%). Seropositivity after the last vaccination after 12 months was high in all groups. Previous yellow fever vaccination was reported in 16% and associated with lower geometric mean titres of TBE-specific antibodies at all-time points.The vaccine was generally well tolerated. However, mild to moderate local reactions occurred in 73-100% of ID compared with 0-38% of IM vaccinations, and persistent discolouration was observed in nine ID vaccinated individuals.

CONCLUSION

The accelerated two-visit ID schedules might offer a better immunological alternative to the recommended classical accelerated IM schedule, but an aluminium-free vaccine would be preferable.

Does the Vaccination against Tick-Borne Encephalitis Offer Good Value for Money for Incidence Rates below the WHO Threshold for Endemicity? A Case Study for Germany

Tick-borne encephalitis (TBE) is a viral infection affecting the central nervous system (CNS) with potential long-term consequences including neurological sequelae. Vaccination is critical to reduce TBE morbidity and mortality, as no antiviral treatment is available. The World Health Organization (WHO) defines areas with an incidence of ≥5 cases/100,000 PPY as highly endemic and recommends that vaccination is offered to all individuals in these areas. However, access to TBE vaccination depends on recommendations and funding by national or subnational decision-makers. We assessed if TBE vaccination could offer good value for money at incidences below this threshold.

METHODS

A closed-cohort Markov model was developed to estimate the cost-effectiveness of TBE vaccination. We compared primary vaccination applied to the whole population (aged above 1 year) and to a subpopulation aged between 60 and 85 years to a scenario without vaccination. Since TBE incidence is often underestimated, we included under-ascertained TBE cases and non-CNS TBE infections. Germany was used as a case study due to the availability of detailed incidence data.

RESULTS

Our incidence threshold analysis showed that TBE vaccination offers good value for money well below the WHO threshold in most of the analyzed scenarios.

CONCLUSIONS

Our results support a recommendation for TBE vaccination even in settings with low numbers of reported cases, especially for older patients. Furthermore, this analysis identified major research gaps regarding the costs, utilities, and clinical progression of TBE.

Autoantibodies neutralizing type I IFNs underlie severe tick-borne encephalitis in ∼10% of patients

Tick-borne encephalitis (TBE) virus (TBEV) is transmitted to humans via tick bites. Infection is benign in >90% of the cases but can cause mild (<5%), moderate (<4%), or severe (<1%) encephalitis. We show here that ∼10% of patients hospitalized for severe TBE in cohorts from Austria, Czech Republic, and France carry auto-Abs neutralizing IFN-α2, -β, and/or -ω at the onset of disease, contrasting with only ∼1% of patients with moderate and mild TBE. These auto-Abs were found in two of eight patients who died and none of 13 with silent infection. The odds ratios (OR) for severe TBE in individuals with these auto-Abs relative to those without them in the general population were 4.9 (95% CI: 1.5-15.9, P < 0.0001) for the neutralization of only 100 pg/ml IFN-α2 and/or -ω, and 20.8 (95% CI: 4.5-97.4, P < 0.0001) for the neutralization of 10 ng/ml IFN-α2 and -ω. Auto-Abs neutralizing type I IFNs accounted for ∼10% of severe TBE cases in these three European cohorts.

Tick-borne encephalitis seroprevalence in northern Italy: a cross-sectional study on a randomly selected population

Objectives

Ixodes ricinus is under-recognized in Europe. This study aimed to determine the seroprevalence and spatial distribution of tick-borne encephalitis (TBE) virus (TBEV) in areas close to endemic regions in Northern Italy.

Methods

A multicenter study was conducted on a random sample of the general population afferent to hospitals in Veneto, Lombardy, and Piedmont with a pre-determined sample size of 1500 participants. The presence of TBEV-neutralizing antibodies was determined for sera positive to the TBE-specific immunoglobulin G test in a centralized laboratory.

Results

Out of 1537 samples analyzed (790 from Lombardy, 394 from Veneto, 353 from Piedmont), 39 (2.5%) were immunoglobulin G TBEV-positive. The frequency of positive cases was similar amid the regions (24-3.0% Lombardy, 10-2.5% Veneto, and 5-1.4% Piedmont; P = 0.27). The seropositivity rates were 3.6% in subjects aged over 50 years, 2.0% in those aged 30-50 years, and 1.5% in subjects aged under 30 years (P = 0.10). Two of them (one from Veneto and one from Lombardy) were confirmed by TBEV neutralization test (prevalence 130 per 100,000). One lived close to an endemic area (Treviso); the other spent time in an endemic region (Friuli) and did not remember experiencing tick bites.

Conclusions

The results from this study highlight the need for raising awareness among the population and health care workers to limit the risk of TBE infection.

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.

Age-dependent Powassan virus lethality is linked to glial cell activation and divergent neuroinflammatory cytokine responses in a murine model

Powassan virus (POWV) is an emergent tick-borne flavivirus that causes fatal encephalitis in the elderly and long-term neurologic sequelae in survivors. How age contributes to severe POWV encephalitis remains an enigma, and no animal models have assessed age-dependent POWV neuropathology. Inoculating C57BL/6 mice with a POWV strain (LI9) currently circulating in Ixodes ticks resulted in age-dependent POWV lethality 10-20 dpi. POWV infection of 50-week-old mice was 82% fatal with lethality sequentially reduced by age to 7.1% in 10-week-old mice. POWV LI9 was neuroinvasive in mice of all ages, causing acute spongiform CNS pathology and reactive gliosis 5-15 dpi that persisted in survivors 30 dpi. High CNS viral loads were found in all mice 10 dpi. However, by 15 dpi, viral loads decreased by 2-4 logs in 10- to 40-week-old mice, while remaining at high levels in 50-week-old mice. Age-dependent differences in CNS viral loads 15 dpi occurred concomitantly with striking changes in CNS cytokine responses. In the CNS of 50-week-old mice, POWV induced Th1-type cytokines (IFNγ, IL-2, IL-12, IL-4, TNFα, IL-6), suggesting a neurodegenerative pro-inflammatory M1 microglial program. By contrast, in 10-week-old mice, POWV-induced Th2-type cytokines (IL-10, TGFβ, IL-4) were consistent with a neuroprotective M2 microglial phenotype. These findings correlate age-dependent CNS cytokine responses and viral loads with POWV lethality and suggest potential neuroinflammatory therapeutic targets. Our results establish the age-dependent lethality of POWV in a murine model that mirrors human POWV severity and long-term CNS pathology in the elderly.

IMPORTANCE

Powassan virus is an emerging tick-borne flavivirus causing lethal encephalitis in aged individuals. We reveal an age-dependent POWV murine model that mirrors human POWV encephalitis and long-term CNS damage in the elderly. We found that POWV is neuroinvasive and directs reactive gliosis in all age mice, but at acute stages selectively induces pro-inflammatory Th1 cytokine responses in 50-week-old mice and neuroprotective Th2 cytokine responses in 10-week-old mice. Our findings associate CNS viral loads and divergent cytokine responses with age-dependent POWV lethality and survival outcomes. Responses of young mice suggest potential therapeutic targets and approaches for preventing severe POWV encephalitis that may be broadly applicable to other neurodegenerative diseases. Our age-dependent murine POWV model permits analysis of vaccines that prevent POWV lethality, and therapeutics that resolve severe POWV encephalitis.

The Specificity of Epizootic and Epidemiological Processes in Natural Foci of Hemorrhagic Fever with Renal Syndrome and Tick-Borne Encephalitis in Russia, as the Basis for the Prospects of Creating a Combined Vaccine for the Prevention of These Infections

Hemorrhagic fever with renal syndrome (HFRS) and tick-borne encephalitis (TBE) are the most common viral diseases in Russia. HFRS is caused by six different types of hantaviruses: Hantaan, Amur, Seoul, Puumala, Kurkino, and Sochi, which are transmitted to humans through small mammals of the Muridae and Cricetidae families. TBE is caused by viruses belonging to five different phylogenetic subtypes. The similarities in the ecology of HFRS and TBE pathogens is presented here. Hantavirus-infected small mammals can transmit the virus to uninfected animals, and ticks can also transmit hantavirus to other ticks and mammals. Hantavirus transmission from ticks to humans is possible only hypothetically based on indirect data. Over the past 23 years, 164,582 cases of HFRS (4.9 per 105 people) and 71,579 cases of TBE (2.5 per 105 people) were registered in Russia. The mortality rate was 0.4% (668 cases) in HFRS and 1.6% deaths (1136 cases) in TBE. There were 4030 HFRS (2.5%) and 9414 TBE (13%) cases in children under 14 years old. HFRS and TBE cases were registered in 42 out of 85 Russian regions; in 18-only HFRS, in 13-only TBE, and 12 had no reported cases. The prospects of applying a combined vaccine for HFRS and TBE prevention are shown in this paper.

Tick-borne encephalitis vaccine breakthrough infections induce aberrant T cell and antibody responses to non-structural proteins

Tick-borne encephalitis virus (TBEV) vaccine breakthrough (VBT) infections are not uncommon in endemic areas. The clinical and immunological outcomes have been poorly investigated. We assessed the magnitude and specificity of virus-specific antibody and T cell responses after TBE in previously vaccinated subjects and compared the results with those of unvaccinated TBE patients and study subjects that received vaccination without VBT infection. Symptomatic TBEV infection of unvaccinated study subjects induced virus-specific antibody responses to the E protein and non-structural protein 1 (NS1) as well as T cell responses to structural and other non-structural (NS) proteins. After VBT infections, significantly impaired NS1-specific antibody responses were observed, while the virus-specific T cell responses to the NS proteins were relatively strong. VBT infection caused predominantly moderate to severe disease during hospitalization. The level of TBEV EDIII- and NS1-specific antibodies in unvaccinated convalescent patients inversely correlated with TBE severity and neurological symptoms early after infection.

LC-MS metabolomics and lipidomics in cerebrospinal fluid from viral and bacterial CNS infections: a review

There is compelling evidence that a dysregulated immune inflammatory response in neuroinfectious diseases results in modifications in metabolic processes and altered metabolites, directly or indirectly influencing lipid metabolism within the central nervous system (CNS). The challenges in differential diagnosis and the provision of effective treatment in many neuroinfectious diseases are, in part, due to limited understanding of the pathophysiology underlying the disease. Although there are numerous metabolomics studies, there remains a deficit in neurolipidomics research to provide a comprehensive understanding of the connection between altered metabolites and changes in lipid metabolism. The brain is an inherently high-lipid organ; hence, understanding neurolipidomics is the key to future breakthroughs. This review aims to provide an integrative summary of altered cerebrospinal fluid (CSF) metabolites associated with neurolipid metabolism in bacterial and viral CNS infections, with a particular focus on studies that used liquid chromatography-mass spectrometry (LC-MS). Lipid components (phospholipids) and metabolites (carnitine and tryptophan) appear to be the most significant indicators in both bacterial and viral infections. On the basis of our analysis of the literature, we recommend employing neurolipidomics in conjunction with existing neurometabolomics data as a prospective method to enhance our understanding of the cross link between dysregulated metabolites and lipid metabolism in neuroinfectious diseases.

The Flavivirus Non-Structural Protein 5 (NS5): Structure, Functions, and Targeting for Development of Vaccines and Therapeutics

Flaviviruses, including dengue (DENV), Zika (ZIKV), West Nile (WNV), Japanese encephalitis (JEV), yellow fever (YFV), and tick-borne encephalitis (TBEV) viruses, pose a significant global emerging threat. With their potential to cause widespread outbreaks and severe health complications, the development of effective vaccines and antiviral therapeutics is imperative. The flaviviral non-structural protein 5 (NS5) is a highly conserved and multifunctional protein that is crucial for viral replication, and the NS5 protein of many flaviviruses has been shown to be a potent inhibitor of interferon (IFN) signalling. In this review, we discuss the functions of NS5, diverse NS5-mediated strategies adopted by flaviviruses to evade the host antiviral response, and how NS5 can be a target for the development of vaccines and antiviral therapeutics.

Global Seroprevalence of Tick-Borne Encephalitis Antibodies in Humans, 1956-2022: A Literature Review and Meta-Analysis

Despite the availability of tick-borne encephalitis (TBE) vaccines, the incidence of TBE is increasing. To understand the historical patterns of infection, we conducted a global meta-analysis of studies before December 2023 reporting human antibody prevalence against TBEV (TBE virus) among general or high-risk population groups stratified by country, collection year, serological method, and vaccination status. Pooled data were compared within groups over time by random-effects modeling. In total, 2403 articles were retrieved; 130 articles published since 1959 were included. Data were extracted from 96 general populations (117,620 participants) and 71 high-risk populations (53,986 participants) across 33 countries. Germany had the most population groups (21), and Poland had the most participants (44,688). Seven serological methods were used; conventional IgG/IgM ELISAs were the most common (44%). Four studies (1.7%) used NS1-ELISA serology. Between 1956-1991 and 1992-2022, anti-TBEV seroprevalence remained at ~2.75% across all population groups from "high-risk" areas (p = 0.458) but decreased within general populations (1.7% to 1%; p = 0.001) and high-risk populations (5.1% to 1.3%; p < 0.001), possibly due to differences in the study methodologies between periods. This global summary explores how serological methods can be used to assess TBE vaccination coverage and potential exposure to TBEV or measure TBE burden and highlights the need for standardized methodology when conducting TBE seroprevalence studies to compare across populations.

Robust CXCL10/IP-10 and CCL5/RANTES Production Induced by Tick-Borne Encephalitis Virus in Human Brain Pericytes Despite Weak Infection

Tick-borne encephalitis virus (TBEV) targets the central nervous system (CNS), leading to potentially severe neurological complications. The neurovascular unit plays a fundamental role in the CNS and in the neuroinvasion of TBEV. However, the role of human brain pericytes, a key component of the neurovascular unit, during TBEV infection has not yet been elucidated. In this study, TBEV infection of the primary human brain perivascular pericytes was investigated with highly virulent Hypr strain and mildly virulent Neudoerfl strain. We used Luminex assay to measure cytokines/chemokines and growth factors. Both viral strains showed comparable replication kinetics, peaking at 3 days post infection (dpi). Intracellular viral RNA copies peaked at 6 dpi for Hypr and 3 dpi for Neudoerfl cultures. According to immunofluorescence staining, only small proportion of pericytes were infected (3% for Hypr and 2% for Neudoerfl), and no cytopathic effect was observed in the infected cells. In cell culture supernatants, IL-6 production was detected at 3 dpi, together with slight increases in IL-15 and IL-4, but IP-10, RANTES and MCP-1 were the main chemokines released after TBEV infection. These chemokines play key roles in both immune defense and immunopathology during TBE. This study suggests that pericytes are an important source of these signaling molecules during TBEV infection in the brain.

The structure of immature tick-borne encephalitis virus supports the collapse model of flavivirus maturation

We present structures of three immature tick-borne encephalitis virus (TBEV) isolates. Our atomic models of the major viral components, the E and prM proteins, indicate that the pr domains of prM have a critical role in holding the heterohexameric prM3E3 spikes in a metastable conformation. Destabilization of the prM furin-sensitive loop at acidic pH facilitates its processing. The prM topology and domain assignment in TBEV is similar to the mosquito-borne Binjari virus, but is in contrast to other immature flavivirus models. These results support that prM cleavage, the collapse of E protein ectodomains onto the virion surface, the large movement of the membrane domains of both E and M, and the release of the pr fragment from the particle render the virus mature and infectious. Our work favors the collapse model of flavivirus maturation warranting further studies of immature flaviviruses to determine the sequence of events and mechanistic details driving flavivirus maturation.

Basophil Activation Test Predicts Cetuximab Anaphylaxis Severity in Alpha-Gal IgE-Positive Patients

Upon first exposure to cetuximab, hypersensitivity reactions can occur. We aimed to assess the utility of the basophil activation test (BAT) to alpha-gal and cetuximab for predicting severe reactions. We prospectively recruited 38 patients and evaluated sIgE to alpha-gal in all patients before the first application of cetuximab. In all alpha-gal-sensitized patients, we evaluated skin tests to meat extracts, gelatine, and cetuximab and performed BAT with alpha-gal and cetuximab. In 24% (9/38) of patients, sIgE to alpha-gal was >0.10 kUA/L, and 8/9 reacted to the cetuximab. Basophil activation tests with alpha-gal were positive in all sensitized patients and were higher in those with severe reactions (18.3% in grade 4 [n = 4] vs. 1.8% in grade 2 [n = 3] or no reaction [n = 1] at 3.3 ng/mL of alpha-gal; p = 0.03). All patients with severe grade 4 reactions had a positive CD63 BAT response to cetuximab compared to patients with moderate or no reaction, who all had negative BAT (57.7% vs. 0.9% at 500 µg/mL, 63.2% vs. 4.1% at 100 µg/mL, 58.2% vs. 2.7% at 10 µg/mL, and 32.1% vs. 3.3% at 1 µg/mL of cetuximab, respectively; p ≤ 0.001). In summary, before initiating cetuximab treatment, sIgE to alpha-gal should be assessed in all patients. To predict the severity of the reaction and to assess the risk of cetuximab-induced anaphylaxis, we should perform BATs with alpha-gal or more discriminative BATs with cetuximab.

Clinical characteristics and factors affecting disease severity in hospitalized tick-borne encephalitis patients in Norway from 2018 to 2022

PURPOSE

To describe the clinical characteristics and factors associated with disease severity in a Norwegian cohort of hospitalized patients with tick-borne encephalitis (TBE).

METHODS

This observational multicenter study included hospitalized patients with TBE in the endemic area in the southeastern region of Norway from 2018 to 2022. Clinical signs and findings from laboratory tests, EEG, CT and MRI scans were recorded. Patient characteristics were compared among those with mild, moderate, and severe TBE, and factors associated with disease severity were identified.

RESULTS

Nearly all eligible patients were included in the final cohort (153/189 participants, 81%). The median age was 56 years, 63% were men, and 7% were vaccinated against TBE; no participants were fully vaccinated. TBE presented as mild (meningeal) disease in 31% of patients and as moderate or severe (encephalitic) disease in 54% and 14% of patients, respectively. We found that 46% of the patients had a monophasic course, 64% had hyponatremia, and 7% presented with central nervous system (CNS) symptoms without pleocytosis in cerebrospinal fluid (CSF). Dysesthesia, a symptom previously not described, was reported in 10% of the patients. Most objective findings were related to the CNS. Preexisting comorbidities, CRP and CSF protein levels were predictors of more severe disease.

CONCLUSION

This novel presentation of a large Norwegian cohort supports TBE as a serious disease in the southeastern region of Norway. The majority of hospitalized patients presented with encephalitis, and fewer presented with meningitis. Comorbidities, CRP and CSF protein levels were associated with more severe disease.

TRIAL REGISTRATION

Prosjekt #2,296,959 - The Norwegian Tick-borne Encephalitis Study - NOTES. Acute phase characteristics and long-term outcomes. - Cristin.

First detection of tick-borne encephalitis virus (TBEV) in raw milk samples in North-Western Iran

Tick-borne encephalitis virus (TBEV) is a significant cause of flaviviral infections affecting the human central nervous system, primarily transmitted through tick bites and the consumption of unpasteurized milk. This study aimed to assess the prevalence of TBEV and identify new natural foci of TBEV in livestock milk. In this cross-sectional study, unpasteurized milk samples were collected from livestock reared on farms and analysed for the presence and subtyping of TBEV using nested reverse transcription-polymerase chain reaction , alongside the detection of anti-TBEV total IgG antibodies using ELISA. The findings revealed that the highest prevalence of TBEV was observed in goat and sheep milk combined, whereas no TBEV was detected in cow milk samples. All identified strains were of the Siberian subtype. Moreover, the highest prevalence of anti-TBEV antibodies was detected in sheep milk. These results uncover new foci of TBEV in Iran, underscoring the importance of thermal processing (pasteurization) of milk prior to consumption to mitigate the risk of TBEV infection.

Minocycline Inhibits Tick-Borne Encephalitis Virus and Protects Infected Cells via Multiple Pathways

Tick-borne Encephalitis (TBE) is a zoonotic disease caused by the Tick-borne Encephalitis virus (TBEV), which affects the central nervous system of both humans and animals. Currently, there is no specific therapy for patients with TBE, with symptomatic treatment being the primary approach. In this study, the effects of minocycline (MIN), which is a kind of tetracycline antibiotic, on TBEV propagation and cellular protection in TBEV-infected cell lines were evaluated. Indirect immunofluorescence, virus titers, and RT-qPCR results showed that 48 h post-treatment with MIN, TBEV replication was significantly inhibited in a dose-dependent manner. In addition, the inhibitory effect of MIN on different TBEV multiplicities of infection (MOIs) in Vero cells was studied. Furthermore, the transcriptomic analysis and RT-qPCR results indicate that after incubation with MIN, the levels of TBEV and CALML4 were decreased, whereas the levels of calcium channel receptors, such as RYR2 and SNAP25, were significantly increased. MIN also regulated MAPK-ERK-related factors, including FGF2, PDGFRA, PLCB2, and p-ERK, and inhibited inflammatory responses. These data indicate that administering MIN to TBEV-infected cells can reduce the TBEV level, regulate calcium signaling pathway-associated proteins, and inhibit the MAPK-ERK signaling pathway and inflammatory responses. This research offers innovative strategies for the advancement of anti-TBEV therapy.

No detection of tick-borne encephalitis virus RNA in blood, urine or saliva of hospitalised immunocompetent tick-borne encephalitis patients

Tick-borne encephalitis (TBE) is usually diagnosed based on the presence of TBE virus (TBEV)-specific IgM and IgG antibodies in serum. However, antibodies induced by vaccination or cross-reactivity to previous flavivirus infections may result in false positive TBEV serology. Detection of TBEV RNA may be an alternative diagnostic approach to detect viral presence and circumvent the diagnostic difficulties present when using serology. Viral RNA in blood is commonly detectable only in the first viremic phase usually lasting up to two weeks, and not in the second neurologic phase, when the patients contact the health care system and undergo diagnostic work-up. TBEV RNA has previously been detected in urine in a few retrospective TBE cases in the neurologic phase, and furthermore RNA of other flaviviruses has been detected in patient saliva. In this study, blood, saliva and urine were collected from 31 hospitalised immunocompetent patients with pleocytosis and symptoms of aseptic meningitis and/or encephalitis, suspected to have TBE. We wanted to pursue if molecular testing of TBEV RNA in these patient materials may be useful in the diagnostics. Eleven of the 31 study patients were diagnosed with TBE based on ELISA detection of TBEV specific IgG and IgM antibodies. None of the study patients had TBEV RNA detectable in any of the collected patient material.

Phase 3 immunogenicity and safety study of a tick-borne encephalitis vaccine in healthy Japanese participants 1 year of age and older

BACKGROUND

Tick-borne encephalitis (TBE) virus infects the central nervous system and may lead to severe neurological complications or death. This study assessed immunogenicity, safety, and tolerability of TBE vaccine in Japanese participants 1 year of age and older.

METHODS

This phase 3, multicenter, single-arm, open-label study was conducted in Japanese adult (≥ 16 years) and pediatric (1-< 16 years) populations. Participants received a single 0.5-mL (adult) or 0.25-mL (pediatric) dose of TBE vaccine at each of 3 visits. The primary endpoint was the proportion of participants who were seropositive (neutralization test [NT] titer ≥ 1:10) 4 weeks after Dose 3. Secondary and exploratory endpoints included NT seropositivity rates 4 weeks after Dose 2, immunoglobulin G (IgG) seropositivity 4 weeks after Doses 2 and 3, NT geometric mean titers (GMTs), IgG geometric mean concentrations (GMCs), and geometric mean fold rises. Primary safety endpoints were frequencies of local reactions, systemic events, adverse events (AEs), and serious AEs.

RESULTS

Among 100 adult and 65 pediatric participants, 99.0 % and 100.0 % completed the study, respectively. NT seropositivity was achieved in 98.0 % adult and 100.0 % pediatric participants after Dose 3; seropositivity after Dose 2 was 93.0 % and 92.3 %, respectively. In both age groups, IgG seropositivity was ≥ 90.0 % and ≥ 96.0 % after Doses 2 and 3, respectively; GMTs and GMCs were highest 4 weeks after Dose 3. Reactogenicity events were generally mild to moderate in severity and short-lived. AEs were reported by 15.0 % (adult) and 43.1 % (pediatric) of participants. No life-threatening AEs, AEs leading to discontinuation, immediate AEs, related AEs, or deaths were reported. No serious AEs were considered related to TBE vaccine.

CONCLUSIONS

TBE vaccine elicited robust immune responses in Japanese participants 1 year of age and older. The 3-dose regimen was safe and well tolerated, and findings were consistent with the known safety profile of this TBE vaccine.

CLINICALTRIALS

gov: NCT04648241.

Seroprevalence of West Nile Virus among Equids in Bulgaria in 2022 and Assessment of Some Risk Factors

The aim of this study was to analyze the seroprevalence of West Nile virus (WNV) among equids in Bulgaria, confirm the results of a competitive ELISA versus the virus neutralization test (VNT) and investigate some predisposing factors for WNV seropositivity. A total of 378 serum samples from 15 provinces in northern and southern Bulgaria were tested. The samples originated from 314 horses and 64 donkeys, 135 males and 243 females, aged from 1 to 30 years. IgG and IgM antibodies against WNV protein E were detected by ELISA. ELISA-positive samples were additionally tested via VNT for WNV and Usutu virus. Thirty-five samples were WNV-positive by ELISA (9.26% [CI = 6.45-12.88]), of which 15 were confirmed by VNT; hence, the seroprevalence was 3.97% (CI = 2.22-6.55). No virus-neutralizing antibodies to Usutu virus were detected among the 35 WNV-ELISA-positive equids in Bulgaria. When compared with VNT, ELISA showed 100.0% sensitivity and 94.5% specificity. A statistical analysis showed that the risk factors associated with WNV seropositivity were the region (p < 0.0001), altitude of the locality (p < 0.0001), type of housing (p < 0.0001) and breed (p = 0.0365). The results of the study demonstrate, albeit indirectly, that WNV circulates among equids in northern and southern Bulgaria, indicating that they could be suitable sentinel animals for predicting human cases and determining the risk in these areas or regions of the country.

Neuroinvasion of emerging and re-emerging arboviruses: A scoping review

BACKGROUND

Arboviruses are RNA viruses and some have the potential to cause neuroinvasive disease and are a growing threat to global health.

OBJECTIVES

Our objective is to identify and map all aspects of arbovirus neuroinvasive disease, clarify key concepts, and identify gaps within our knowledge with appropriate future directions related to the improvement of global health.

METHODS

Sources of Evidence: A scoping review of the literature was conducted using PubMed, Scopus, ScienceDirect, and Hinari. Eligibility Criteria: Original data including epidemiology, risk factors, neurological manifestations, neuro-diagnostics, management, and preventive measures related to neuroinvasive arbovirus infections was obtained. Sources of evidence not reporting on original data, non-English, and not in peer-reviewed journals were removed. Charting Methods: An initial pilot sample of 30 abstracts were reviewed by all authors and a Cohen's kappa of κ = 0.81 (near-perfect agreement) was obtained. Records were manually reviewed by two authors using the Rayyan QCRI software.

RESULTS

A total of 171 records were included. A wide array of neurological manifestations can occur most frequently, including parkinsonism, encephalitis/encephalopathy, meningitis, flaccid myelitis, and Guillain-Barré syndrome. Magnetic resonance imaging of the brain often reveals subcortical lesions, sometimes with diffusion restriction consistent with acute ischemia. Vertical transmission of arbovirus is most often secondary to the Zika virus. Neurological manifestations of congenital Zika syndrome, include microcephaly, failure to thrive, intellectual disability, and seizures. Cerebrospinal fluid analysis often shows lymphocytic pleocytosis, elevated albumin, and protein consistent with blood-brain barrier dysfunction.

CONCLUSIONS

Arbovirus infection with neurological manifestations leads to increased morbidity and mortality. Risk factors for disease include living and traveling in an arbovirus endemic zone, age, pregnancy, and immunosuppressed status. The management of neuroinvasive arbovirus disease is largely supportive and focuses on specific neurological complications. There is a need for therapeutics and currently, management is based on disease prevention and limiting zoonosis.

Molecular Mechanisms Associated with Neurodegeneration of Neurotropic Viral Infection

Viral infections of the central nervous system (CNS) cause variable outcomes from acute to severe neurological sequelae with increased morbidity and mortality. Viral neuroinvasion directly or indirectly induces encephalitis via dysregulation of the immune response and contributes to the alteration of neuronal function and the degeneration of neuronal cells. This review provides an overview of the cellular and molecular mechanisms of virus-induced neurodegeneration. Neurotropic viral infections influence many aspects of neuronal dysfunction, including promoting chronic inflammation, inducing cellular oxidative stress, impairing mitophagy, encountering mitochondrial dynamics, enhancing metabolic rewiring, altering neurotransmitter systems, and inducing misfolded and aggregated pathological proteins associated with neurodegenerative diseases. These pathogenetic mechanisms create a multidimensional injury of the brain that leads to specific neuronal and brain dysfunction. The understanding of the molecular mechanisms underlying the neurophathogenesis associated with neurodegeneration of viral infection may emphasize the strategies for prevention, protection, and treatment of virus infection of the CNS.

High-Throughput Sequencing Reveals Three Rhabdoviruses Persisting in the IRE/CTVM19 Cell Line

Cell cultures derived from ticks have become a commonly used tool for the isolation and study of tick-borne pathogens and tick biology. The IRE/CTVM19 cell line, originating from embryos of Ixodes ricinus, is one such line. Previously, reovirus-like particles, as well as sequences with similarity to rhabdoviruses and iflaviruses, were detected in the IRE/CTVM19 cell line, suggesting the presence of multiple persisting viruses. Subsequently, the full genome of an IRE/CTVM19-associated rhabdovirus was recovered from a cell culture during the isolation of the Alongshan virus. In the current work, we used high-throughput sequencing to describe a virome of the IRE/CTVM19 cell line. In addition to the previously detected IRE/CTVM19-associated rhabdovirus, two rhabdoviruses were detected: Chimay rhabdovirus and Norway mononegavirus 1. In the follow-up experiments, we were able to detect both positive and negative RNA strands of the IRE/CTVM19-associated rhabdovirus and Norway mononegavirus 1 in the IRE/CTVM19 cells, suggesting their active replication in the cell line. Passaging attempts in cell lines of mammalian origin failed for all three discovered rhabdoviruses.

Proinflammatory Chemokine Levels in Cerebrospinal Fluid of Patients with Neuroinvasive Flavivirus Infections

Tick-borne encephalitis virus (TBEV) and West Nile virus (WNV) are the most important neuroinvasive arboviruses detected in Europe. In this study, we analyzed cerebrospinal fluid (CSF) concentrations of 12 proinflammatory chemokines (CCL2, CCL3, CCL4, CCL11, CCL17, CCL20, CXCL1, CXCL5, CXCL8, CXCL9, CXCL10, and CXCL11) in 77 patients with neuroinvasive diseases (NIDs). Flavivirus infection was confirmed in 62 patients (TBEV and WNV in 31 patients each), while in 15 patients the etiology of NID was not determined (NDE). Similar patterns of high-level expression of chemokines regulating monocyte/macrophage responses (CCL2), neutrophil recruitment (CXCL1 and CXCL8), and interferon-inducible chemoattractants for leukocytes (CXCL10 and CXCL11) have been observed in WNV and TBEV groups. None of the tested chemokines significantly differed between patients with TBEV or WNV. Concentrations of CCL17, CCL20, CXCL5, CXCL10, and CXCL11 were significantly lower in both WNV and TBEV groups compared to NID NDE patients. The logistic regression model showed that CSF concentrations of CXCL11, CXCL5, and CXCL10 could potentially be used for the classification of patients into the WNV or TBEV group versus groups with other NIDs. This study identified, for the first time, similar patterns of CSF chemokine expression in WNV and TBEV infections, suggesting common immunopathogenic mechanisms in neuroinvasive flavivirus infections that should be further evaluated.

Multiplex Serology for Sensitive and Specific Flavivirus IgG Detection: Addition of Envelope Protein Domain III to NS1 Increases Sensitivity for Tick-Borne Encephalitis Virus IgG Detection

Tick-borne encephalitis is a vaccine-preventable disease of concern for public health in large parts of Europe, with EU notification rates increasing since 2018. It is caused by the orthoflavivirus tick-borne encephalitis virus (TBEV) and a diagnosis of infection is mainly based on serology due to its short viremic phase, often before symptom onset. The interpretation of TBEV serology is hampered by a history of orthoflavivirus vaccination and by previous infections with related orthoflaviviruses. Here, we sought to improve TBEV sero-diagnostics using an antigen combination of in-house expressed NS1 and EDIII in a multiplex, low-specimen-volume set-up for the detection of immune responses to TBEV and other clinically important orthoflaviviruses (i.e., West Nile virus, dengue virus, Japanese encephalitis virus, Usutu virus and Zika virus). We show that the combined use of NS1 and EDIII results in both a specific and sensitive test for the detection of TBEV IgG for patient diagnostics, vaccination responses and in seroprevalence studies. This novel approach potentially allows for a low volume-based, simultaneous analysis of IgG responses to a range of orthoflaviviruses with overlapping geographic circulations and clinical manifestations.

An Overview of Tick-Borne Encephalitis Epidemiology in Endemic Regions of Continental Croatia, 2017-2023

Tick-borne encephalitis (TBE) represents an important public health problem in Europe. We analyzed the epidemiology of TBE based on data from humans, animals, and Ixodes ricinus ticks in endemic regions of continental Croatia. In the period from 2017 to 2023, cerebrospinal fluid (CSF) and serum samples of 684 patients with neuroinvasive diseases, 2240 horse serum samples, and 300 sheep serum samples were tested for TBEV. In addition, 8751 I. ricinus ticks were collected. CSF samples were tested using RT-PCR. Serological tests (serum, CSF) were performed using commercial ELISA, with confirmation of cross-reactive samples by a virus neutralization test. Eighty-four autochthonous human TBEV cases were confirmed. The majority of patients were in the age group of 40-69 years (58.3%) with a male predominance (70.2%). TBE showed a bimodal seasonality with a large peak in April-August and a small one in October-November. In addition to humans, TBEV IgG antibodies were found in 12.2% of horses and 9.7% of sheep. Seasonal tick abundance corresponds to the reported number of human infections. Continental Croatia is still an active natural focus of TBE. Continuous monitoring of infections in humans, sentinel animals, and ticks is needed for the implementation of preventive measures.