Tick-borne encephalitis virus (TBEV), a member of the Flaviviridae family, can cause serious infection of the central nervous system in humans, resulting in potential neurological complications and fatal outcomes. TBEV is primarily transmitted to humans through infected tick bites, and the viral agent circulates between ticks and animals, such as deer and small mammals. The occurrence of the infection aligns with the seasonal activity of ticks. As no specific antiviral therapy exists for TBEV infection, treatment approaches primarily focus on symptomatic relief and support. Active immunization is highly effective, especially for individuals in endemic areas. The burden of TBEV infections is increasing, posing a growing health concern. Reported incidence rates rose from 0.4 to 0.9 cases per 100,000 people between 2015 and 2020. The Baltic and Central European countries have the highest incidence, but TBE is endemic across a wide geographic area. Various factors, including social and environmental aspects, improved medical awareness, and advanced diagnostics, have contributed to the observed increase. Diagnosing TBEV infection can be challenging due to the non-specific nature of the initial symptoms and potential co-infections. Accurate diagnosis is crucial for appropriate management, prevention of complications, and effective control measures. In this comprehensive review, we summarize the molecular structure of TBEV, its transmission and circulation in natural environments, the pathogenesis of TBEV infection, the epidemiology and global distribution of the virus, associated risk factors, clinical manifestations, and diagnostic approaches. By improving understanding of these aspects, we aim to enhance knowledge and promote strategies for timely and accurate diagnosis, appropriate management, and the implementation of effective control measures against TBEV infections.

Background: Tick-borne encephalitis virus (TBEV) is one of the most significant arboviruses affecting the human central nervous system (CNS) in Europe. Data on cytokine response in TBEV infection are limited. Methods: We analyzed the cytokine response in serum, cerebrospinal fluid (CSF) and urine samples of patients with TBE. The control group consisted of patients with ‘febrile headache’ who had normal CSF cytology. The panel included 12 cytokines: TNF-α, IL-6, Th1 (IL-2, IFN-γ), Th2 (IL-4, IL-5, IL-13), Th9 (IL-9), Th17 (IL-17A, IL-17F), Th22 (IL-22) cytokines and IL-10. Results: TBE patients were more likely to have increased levels of IL-6 and IFN-γ in CSF compared to controls (85.7% vs. 58.8% and 85.7% vs. 47.1%, respectively). However, concentrations of IL-6 (the most abundant cytokine in the CSF of both groups), IL-10 and IL-9 were lower in TBEV patients compared with controls, but the difference was statistically significant for IL-9 only (p = 0.001). By analyzing the cytokine levels in different clinical samples, all measured cytokines were detected in the serum, with the highest concentrations found for IFN-γ, TNF-α, IL-10, IL-17F and IL-22. Higher concentrations of cytokines in the CSF compared with serum were observed for IL-5, IL-6 and IL-22. All cytokines except IL-13 were detectable in urine but in a small proportion of patients, except for IL-22, which was detectable in 95.8% of patients. Conclusions: Cytokine composition in different clinical samples of TBE patients reveals a different network of early innate immune response cytokines, Th1, Th2, Th9, Th22, Th17 and anti-inflammatory cytokines.

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

Cilj: Istraživanju je glavni cilj ispitati kliničke karakteristike u odnosu na dob i komplikacije te pronaći prediktore koji utječu na vjerojatnost pojave komplikacija i negativnog ishoda u hospitaliziranih bolesnika s influencom. Ispitanici i metode: Istraživanjem su obuhvaćeni svi hospitalizirani bolesnici s klinički i/ili laboratorijski dokazanom gripom u Klinici za infektologiju Kliničkog bolničkog centra Osijek u razdoblju od prosinca 2018. do travnja 2019. godine. Istraživanje je provedeno nad 128 ispitanika. Iz povijesti bolesti prikupljeni su i analizirani klinički, demografski, mikrobiološki, radiološki, biokemijski i hematološki podatci. Rezultati: Istraživanjem koje je provedeno, pokazano je kako je starija životna dob povezana s težim oblikom kliničke slike gripe i kompliciranim tijekom bolesti. Kao prediktor negativnog ishoda korisnom se pokazala urea s vrijednosti većom od 9,2 mmol/L te dob veća od 78 godina, a kao prediktori prisutnosti pneumonije ženski spol i CRP uz točku razlučivanja veću od 128,9 mg/L. Komplikacije su općenito češće u bolesnika s duljim kliničkim tijekom bolesti i višim vrijednostima upalnih pokazatelja pri prijamu na bolničko liječenje. Zaključak: Rezultati provedenog istraživanja upućuju na nedvojbenu težinu kliničke slike, razinu laboratorijskih poremećaja, pojavu komplikacija te utjecaj dobi i komorbiditeta u bolesnika s gripom. Za konačno definiranje specifičnih ranih prediktora težine kliničke slike, u svrhu pravovremenog i učinkovitog liječenja te povoljnijeg ishoda bolesti, potrebno je daljnje sustavno praćenje bolesnika i prospektivne studije.