Geo-Spatial Characteristics of 567 Places of Tick-Borne Encephalitis Infection in Southern Germany, 2018-2020

Different environmental factors predict the occurrence of tick-borne encephalitis virus (TBEV) and reveal new potential risk areas across Europe via geospatial models

BACKGROUND

Tick-borne encephalitis (TBE) is the most serious tick-borne viral disease in Europe. Identifying TBE risk areas can be difficult due to hyper focal circulation of the TBE virus (TBEV) between mammals and ticks. To better define TBE hazard risks and elucidate regional-specific environmental factors that drive TBEV circulation, we developed two machine-learning (ML) algorithms to predict the habitat suitability (maximum entropy), and occurrence of TBEV (extreme gradient boosting) within distinct European regions (Central Europe, Nordics, and Baltics) using local variables of climate, habitat, topography, and animal hosts and reservoirs.

METHODS

Geocoordinates that reported the detection of TBEV in ticks or rodents and anti-TBEV antibodies in rodent reservoirs in 2000 or later were extracted from published and grey literature. Region-specific ML models were defined via K-means clustering and trained according to the distribution of extracted geocoordinates relative to explanatory variables in each region. Final models excluded colinear variables and were evaluated for performance.

RESULTS

521 coordinates (455 ticks; 66 rodent reservoirs) of TBEV occurrence (2000-2022) from 100 records were extracted for model development. The models had high performance across regions (AUC: 0.72-0.92). The strongest predictors of habitat suitability and TBEV occurrence in each region were associated with different variable categories: climate variables were the strongest predictors of habitat suitability in Central Europe; rodent reservoirs and elevation were strongest in the Nordics; and animal hosts and land cover contributed most to the Baltics. The models predicted several areas with few or zero reported TBE incidence as highly suitable (≥ 60%) TBEV habitats or increased probability (≥ 25%) of TBEV occurrence including western Norway coastlines, northern Denmark, northeastern Croatia, eastern France, and northern Italy, suggesting potential capacity for locally-acquired autochthonous TBEV infections or possible underreporting of TBE cases based on reported human surveillance data.

CONCLUSIONS

This study shows how varying environmental factors drive the occurrence of TBEV within different European regions and identifies potential new risk areas for TBE. Importantly, we demonstrate the utility of ML models to generate reliable insights into TBE hazard risks when trained with sufficient explanatory variables and to provide high resolution and harmonized risk maps for public use.

Poor virus-specific T-cell responses early after tick-borne encephalitis virus infection correlate with disease severity

Tick-borne encephalitis virus (TBEV) infection may cause acute central nervous system inflammation varying in clinical manifestations and severity. A possible correlation of TBEV-specific antibody and cell-mediated immune responses, shortly after infection, with clinical manifestations, severity and long-term outcome has been poorly investigated. In a cohort of thirty early tick-borne encephalitis (TBE) patients, we assessed the magnitude, specificity and functional properties of TBEV-specific T-cell and antibody responses. These responses early during disease were assessed in view of clinical manifestations, severity and long-term outcome. TBEV-specific T-cell responses to C, E, NS1, and NS5 proteins were significantly lower in patients with severe acute illness than in patients with mild TBE. Lower T-cell responses to E, NS1, and NS5 proteins also correlated with the development of meningoencephalomyelitis. Virus-specific antibody titres early after infection did not correlate with disease severity, clinical manifestations, or long-term outcome in this study, possibly due to the small number of patients of which matching serum and peripheral blood mononuclear cells were available. The findings suggest that virus-specific T cells afford a certain degree of protection against the development of severe TBEV-induced disease.

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.

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.

Recovery and sequelae in 523 adults and children with tick-borne encephalitis in Germany

PURPOSE

Despite being vaccine-preventable, tick-borne encephalitis (TBE) continues to cause considerable morbidity in Germany. Limited insight into potentially debilitating consequences of TBE may partially underly low (~ 20%) TBE vaccine uptake. We aimed to systematically assess TBE sequelae and other consequences.

METHODS

Routinely notified TBE patients from 2018 to 2020 from Southern Germany were invited to telephone interviews acutely and again after 18 months. Duration of acute symptoms was prospectively assessed. Recovery was defined as score 0 on the modified RANKIN scale. Determinants of time to recovery were analysed with cox regression, adjusted for covariates identified using directed acyclic graphs, yielding hazard ratios (HR) and 95% confidence intervals (CI).

RESULTS

Of 558 cases, 523 (93.7%) completed follow-up. Full recovery was reported by 67.3% (children: 94.9%, adults: 63.8%). Sequelae included fatigue (17.0%), weakness (13.4%), concentration deficit (13.0%), and impaired balance (12.0%). Compared with 18-39-year-olds, recovery rates were 44% lower in ≥ 50-year-olds (HR: 0.56, 95%CI 0.42-0.75) and 79% higher in children (HR: 1.79, 95%CI 1.25-2.56). The recovery rate was 64% lower after severe TBE (compared to mild; HR: 0.36, 95%CI 0.25-0.52) and 22% lower with comorbidities (HR: 0.78, 95%CI 0.62-0.99). Substantial health-care use was reported (90.1% hospitalisation, 39.8% rehabilitation). Of employed cases, 88.4% required sick leave; 10.3% planned/reported premature retirement due to sequelae.

CONCLUSION

Half the adult and 5% of paediatric patients reported persisting sequelae after 18 months. Improved prevention could alleviate both individual (morbidity) and societal TBE burden (health-care costs, productivity losses). Insights into sequelae can help guide at-risk populations towards tick-avoidant strategies and encourage TBE vaccination.

Severe meningoencephalitis: epidemiology and outcomes

PURPOSE OF REVIEW

This article aims to provide an updated review on the epidemiology and outcomes of severe meningoencephalitis.

RECENT FINDINGS

Meningoencephalitis is a critical medical condition characterized by inflammation in both the meninges and brain parenchyma. Bacterial, viral, or fungal infections are common causes, although noninfectious factors, such as autoimmune causes, can also contribute. In patients requiring intensive care, meningoencephalitis is associated with a severe prognosis, including mortality rates ranging from 11 to 25% and functional disability in 15-25% of survivors. Recent multicenter studies have identified several parameters linked to poor outcomes, including older age, immunocompromised status, focal neurologic signs, abnormal brain imaging, and delayed administration of antimicrobials. The use of new multiplex PCR techniques for diagnosis has generated debate based on recent data. Investigation is still needed to determine the effectiveness of adjunctive therapies, including seizure prophylaxis, and adjunctive steroids for nonbacterial causes.

SUMMARY

Recent multicenter studies have enhanced our understanding of the current epidemiology and outcomes of severe meningoencephalitis in adult patients.

Impact of climate change on vector- and rodent-borne infectious diseases

Background

Endemic and imported vector- and rodent-borne infectious agents can be linked to high morbidity and mortality. Therefore, vector- and rodent-borne human diseases and the effects of climate change are important public health issues.

Methods

For this review, the relevant literature was identified and evaluated according to the thematic aspects and supplemented with an analysis of surveillance data for Germany.

Results

Factors such as increasing temperatures, changing precipitation patterns, and human behaviour may influence the epidemiology of vector- and rodent-borne infectious diseases in Germany.

Conclusions

The effects of climatic changes on the spread of vector- and rodent-borne infectious diseases need to be further studied in detail and considered in the context of climate adaptation measures.

Spatiotemporal spread of tick-borne encephalitis in the EU/EEA, 2012 to 2020

BackgroundTick-borne encephalitis (TBE) is a vaccine-preventable disease involving the central nervous system. TBE became a notifiable disease on the EU/EEA level in 2012.AimWe aimed to provide an updated epidemiological assessment of TBE in the EU/EEA, focusing on spatiotemporal changes.MethodsWe performed a descriptive analysis of case characteristics, time and location using data of human TBE cases reported by EU/EEA countries to the European Centre for Disease Prevention and Control with disease onset in 2012-2020. We analysed data at EU/EEA, national, and subnational levels and calculated notification rates using Eurostat population data. Regression models were used for temporal analysis.ResultsFrom 2012 to 2020, 19 countries reported 29,974 TBE cases, of which 24,629 (98.6%) were autochthonous. Czechia, Germany and Lithuania reported 52.9% of all cases. The highest notification rates were recorded in Lithuania, Latvia, and Estonia (16.2, 9.5 and 7.5 cases/100,000 population, respectively). Fifty regions from 10 countries, had a notification rate ≥ 5/100,000. There was an increasing trend in number of cases during the study period with an estimated 0.053 additional TBE cases every week. In 2020, 11.5% more TBE cases were reported than predicted based on data from 2016 to 2019. A geographical spread of cases was observed, particularly in regions situated north-west of known endemic regions.ConclusionA close monitoring of ongoing changes to the TBE epidemiological situation in Europe can support the timely adaption of vaccination recommendations. Further analyses to identify populations and geographical areas where vaccination programmes can be of benefit are needed.

Determinants of public interest in emerging and re-emerging arboviral diseases in Europe: A spatio-temporal analysis of cross-sectional time series data

Introduction

Climate change, the resulting geographical expansion of arthropod disease vectors, and increasing international mobility are contributing to the emergence of arboviral diseases in Europe. Public interest in vector-borne diseases and a subsequent gain of awareness and knowledge are essential to control outbreaks but had not yet been systematically assessed prior to this analysis.

Methods

Trends, patterns, and determinants of public interest in six emerging and re-emerging arboviral diseases were assessed in a spatio-temporal analysis of Google Trends data from 30 European countries between 2008 and 2020 while controlling for potential confounders.

Results

Only public interest in endemic arboviral diseases in Europe displays seasonal patterns and has been increasing since 2008, while no significant patterns or trends could be determined for public interest in non-endemic diseases. The main drivers for public interest in all six analysed arboviral diseases are reported case rates, and public interest drops rapidly as soon as cases decline. For Germany, the correlation of public interest and the geographical distribution of locally-acquired reported cases of endemic arboviral infections could be shown on a sub-country level.

Conclusions

The results of the analysis indicate that public interest in arboviral diseases in Europe is heavily impacted by perceived susceptibility on a temporal as well as on a spatial level. This result may be crucial for the design of future public health interventions to alert the public to the increasing risk of infection with arboviral diseases.

Decoding the Geography of Natural TBEV Microfoci in Germany: A Geostatistical Approach Based on Land-Use Patterns and Climatological Conditions

Background: Tickborne-encephalitis (TBE) is a potentially life-threating neurological disease that is mainly transmitted by ticks. The goal of the present study is to analyze the potential uniform environmental patterns of the identified TBEV microfoci in Germany. The results are used to calculate probabilities for the present distribution of TBEV microfoci in Germany based on a geostatistical model. Methods: We aim to consider the specification of environmental characteristics of locations of TBEV microfoci detected in Germany using open access epidemiological, geographical and climatological data sources. We use a two-step geostatistical approach, where in a first step, the characteristics of a broad set of environmental variables between the 56 TBEV microfoci and a control or comparator set of 3575 sampling points covering Germany are compared using Fisher's Exact Test. In the second step, we select the most important variables, which are then used in a MaxEnt distribution model to calculate a high resolution (400 × 400 m) probability map for the presence of TBEV covering the entire area of Germany. Results: The findings from the MaxEnt prediction model indicate that multi annual actual evapotranspiration (27.0%) and multi annual hot days (22.5%) have the highest contribution to our model. These two variables are followed by four additional variables with a lower, but still important, explanatory influence: Land cover classes (19.6%), multi annual minimum air temperature (14.9%), multi annual sunshine duration (9.0%), and distance to coniferous and mixed forest border (7.0%). Conclusions: Our findings are based on defined TBEV microfoci with known histories of infection and the repeated confirmation of the virus in the last years, resulting in an in-depth high-resolution model/map of TBEV microfoci in Germany. Multi annual actual evapotranspiration (27%) and multi annual hot days (22.5%) have the most explanatory power in our model. The results may be used to tailor specific regional preventive measures and investigations.