Tick-borne encephalitis (TBE) in childhood

Vaccine uptake in 20 countries in Europe 2020: Focus on tick-borne encephalitis (TBE)

Vaccination as a highly effective measure to protect against tick-borne encephalitis (TBE) comes into new focus as known risk areas are expanding across Europe and Asia. Here we present an online household survey conducted in 20 European countries spanning endemic and non-endemic regions of TBE in 2020. With a comprehensive and standardized list of questions, this survey provided a unique opportunity to compare TBE/TBE vaccine awareness, TBE severity perception, vaccine uptake, vaccination completeness/compliance and motivators/barriers for vaccination across Europe. Among the 51,478 participants, tetanus- (72-92%), influenza- (83-98%), and measles-awareness (79-96%) were highest, but awareness was low for Lyme borreliosis, bacterial meningitis and pneumococcal pneumonia. Awareness towards TBE and a TBE vaccine was 74% and 56% in endemic countries, respectively, compared to 30% and 12% in non-endemic countries. Vaccine uptake defined as at least one TBE vaccination was found to be highly heterogenous across both endemic (range 7-81%) and non-endemic countries (range 1-8%). Compliance with the recommended vaccination schedule was 21% for the primary vaccination series and dropped to 7% for the first booster vaccination in endemic countries. The percentage of participants protected against TBE by vaccination at the time of the survey ranged from 21% in Slovakia to 69% in Lithuania. The perception of personal risk or lack thereof was found to be the most influencing factor for and against TBE vaccination. Overall, these data indicate highly heterogenous responses in different European countries regarding not only awareness towards a TBE vaccine, but also regarding TBE vaccine uptake and compliance. Regionally focused strategies to increase diagnostic completeness as well as TBE vaccination are needed across Europe.

Effect of the combination of DEET and flupyradifurone on the tick Ixodes ricinus: Repellency bioassay and pharmacological characterization using microtransplantation of synganglion membranes

Ticks are vectors of many human and animal pathogens, and represent a major threat to public health. In recent years, an increase in tick-borne diseases has been observed, and new strategies are therefore needed in order to control tick numbers and reduce human tick bites. In the present study, we adapted the previous tick repellency bioassay based on the exploration behavior of the tick, using the ToxTrac software and video-tracking, to compare the repellent effect of two compounds on the tick Ixodes ricinus: N,N-diethyl-methyl-m-toluamide (DEET), and butenolide, flupyradifurone (FLU). We found that when applied alone, 10% DEET or FLU have no/or low repellency effect. But, the combination of both 10% DEET and FLU demonstrated a significant repellency effect against I. ricinus, similar to the repellency of 20% DEET. Using membrane microtransplantation, we evaluated the effect of DEET and FLU on native acetylcholine receptors expressed on the tick synganglion. We found that DEET has no effect on acetylcholine-evoked currents, but significantly reduced nicotine-induced current amplitudes. FLU induced an ionic current but was not able to reduce acetylcholine or nicotine evoked currents. The combination of both DEET and FLU strongly reduced nicotine-evoked currents. Finally, we demonstrated that our recording device for repellency, as well as the use of membrane microtransplantation, could be used as methods to study the mode of action of active compounds on ticks.

Nicotinic acetylcholine receptors in the synganglion of the tick Ixodes ricinus: Functional characterization using membrane microtransplantation

Nicotinic acetylcholine receptors are an important class of excitatory receptors in the central nervous system of arthropods. In the ticks Ixodes ricinus, the functional and pharmacological properties of nicotinic receptors located in their neurons are still unknown. The objective of this study was to characterize the pharmacological properties of tick nicotinic receptors using membrane microtransplantation in Xenopus laevis oocytes and two-electrodes voltage clamp method. The membranes microtransplanted were extracted from the tick synganglion. We found that oocytes microtransplanted with tick synganglion membranes expressed nicotinic acetylcholine receptor subtypes which were activated by acetylcholine (1 mM) and nicotine (1 mM). Currents induced by pressure application of acetylcholine and nicotine were diminished by 10 nM α-bungarotoxin and methyllycaconitine, suggesting that they expressed two subtypes of nicotinic receptors, α-bungarotoxin-sensitive and -insensitive, respectively. In addition, we found that nicotine receptors expressed in the synganglion membranes were poorly sensitive to the neonicotinoid insecticides clothianidin (CLT), imidacloprid (IMI), acetamiprid (ACE) and thiamethoxam (TMX), in agreement with their lack of activity as acaricides. Interestingly, current amplitudes were strongly potentialized in the presence of 1 μM PNU-120596. CLT was more active as an agonist than IMI, TMX and ACE. Finally, we demonstrated that microtransplantation of purified membrane from the tick synganglion can be a valuable tool for the development and screening of compounds targeting tick nicotinic acetylcholine receptor subtypes.

Polymorphisms in chemokine receptor 5 and Toll-like receptor 3 genes are risk factors for clinical tick-borne encephalitis in the Lithuanian population

Background

Tick-borne encephalitis virus (TBEV) infections can be asymptomatic or cause moderate to severe injuries of the nervous system. We previously reported that a nonfunctional chemokine receptor 5 (CCR5) and a functional Toll-like receptor 3 (TLR3) predispose adults to clinical tick-borne encephalitis (TBE). This study expands our previous findings and further examines polymorphisms in CCR5 and TLR3 genes in different age and disease severity groups.

Methods

117 children and 129 adults, stratified into mild, moderate and severe forms of TBE, and 103 adults with severe TBE were analyzed. 135 healthy individuals and 79 patients with aseptic meningoencephalitis served as controls. CCR5 delta 32 and rs3775291 TLR3 genotypes were established by pyrosequencing, and their frequencies were analyzed using recessive genetic, genotype and allelic models.

Findings

The prevalence of CCR5Δ32 homozygotes was higher in children (2.5%), in adults with severe TBE (1.9%), and in the combined cohort of TBE patients (2.3%) than in controls (0%) (p<0.05). The nonfunctional homozygous TLR3 genotype was less prevalent among the combined TBE cohort (11.5%) than among controls (19.9%) (p = 0.025), but did not differ between children TBE and controls. The genotype and allele prevalence of CCR5 and TLR3 did not differ in children nor adult TBE cohorts stratified by disease severity. However, in the severe adult TBE cohort, homozygous functional TLR3 genotype and wt allele were less prevalent compared to the adult cohort with the whole disease severity spectrum (44.4% vs 59.8% p = 0.022 and 65.2% vs 76.4% p = 0.009; respectively).

Conclusions

Independently of age, nonfunctional CCR5Δ32 mutation is a significant risk factor for development of clinical TBE, but not for disease severity. The polymorphism of TLR3 gene predisposes to clinical TBE in adults only and may be associated with disease severity. Further studies are needed to clarify the role of these polymorphisms in susceptibility to TBEV infection.

Distribution of tick-borne diseases in China

As an important contributor to vector-borne diseases in China, in recent years, tick-borne diseases have attracted much attention because of their increasing incidence and consequent significant harm to livestock and human health. The most commonly observed human tick-borne diseases in China include Lyme borreliosis (known as Lyme disease in China), tick-borne encephalitis (known as Forest encephalitis in China), Crimean-Congo hemorrhagic fever (known as Xinjiang hemorrhagic fever in China), Q-fever, tularemia and North-Asia tick-borne spotted fever. In recent years, some emerging tick-borne diseases, such as human monocytic ehrlichiosis, human granulocytic anaplasmosis, and a novel bunyavirus infection, have been reported frequently in China. Other tick-borne diseases that are not as frequently reported in China include Colorado fever, oriental spotted fever and piroplasmosis. Detailed information regarding the history, characteristics, and current epidemic status of these human tick-borne diseases in China will be reviewed in this paper. It is clear that greater efforts in government management and research are required for the prevention, control, diagnosis, and treatment of tick-borne diseases, as well as for the control of ticks, in order to decrease the tick-borne disease burden in China.

Development of simple and rapid assay to detect viral RNA of tick-borne encephalitis virus by reverse transcription-loop-mediated isothermal amplification

Background

Tick-borne encephalitis virus (TBEV) is a causative agent of acute central nervous system disease in humans. It has three subtypes, far eastern (FE), Siberian (Sib) and European (Eu) subtypes, which are distributed over a wide area of Europe and Asia. The objective of this study was to develop a simple and rapid assay for the detection of TBEV RNA by using reverse-transcriptase loop-mediated isothermal amplification (RT-LAMP) method that can differentiate the three subtypes of TBEV and can be used for clinical diagnosis and epidemiological study.

Methods

Primers for TBEV-specific and subtype-specific RT-LAMP assay were designed to target the consensus sequence in NS1 of all subtypes and the consensus sequence in the E gene of each subtype, respectiveluy. In vitro transcribed RNA of Oshima strain that belongs to FE subtype was serially diluted and used to examine the sensitivity of the assay. Cross-reactivity of subtype-specific RT-LAMP assay was tested by using the RNA of Oshima and Sofjin (FE), IR-99 (Sib) and Hochosterwitz (Eu) strains. RNA extracted from the mixtures of TBEV and ticks, and of TBEV and human blood, and the mouse tissues infected with TBEV, were evaluated in the assay. Positive amplification was observed by real-time monitoring of turbidity and by visual detection of color change.

Results

The sensitivity of TBEV-specific RT-LAMP assay was 10² copies of target RNA per reaction volume. FE-specific RT-LAMP assay amplified viral genes of Oshima and Sofjin strains but not of IR-99 and Hochosterwitz strains, and of Japanese encephalitis virus. RT-LAMP assay for Sib and for Eu specifically amplified viral genes of IR-99 and Hochosterwitz strains, respectively. We also showed that tick or human blood extract did not inhibit the amplification of viral gene during the assay. Furthermore, we confirmed that the TBEV RT-LAMP could detect virus RNA from peripheral and central nervous system tissues of laboratory mice infected with TBEV.

Conclusion

TBEV RT-LAMP assay offers a sensitive, specific, rapid and easy-to-handle method for the detection of TBEV RNA in tick samples and this may be applied in the clinical samples collected from TBE-suspected patients.

Pediatric tick-borne infections of the central nervous system in an endemic region of Sweden: a prospective evaluation of clinical manifestations

Tick-borne encephalitis (TBE) and neuroborreliosis (NB) are well-known central nervous system (CNS) infections in children. Childhood tick-borne CNS infections are generally described as mild conditions. However, this view has recently been challenged, and the natural course, including potential sequelae, has been debated. If the diseases present with nonspecific symptoms and signs, some children may elude diagnosis. This study estimates the incidence of symptomatic tick-borne CNS infections in children under medical care and describes the spectrum of manifestations. One hundred twenty-four children with neurologic symptoms attending the Pediatric Emergency Department were included prospectively. Anti-TBE virus and anti-Borrelia serology results were analyzed together with inflammatory parameters in the blood and cerebrospinal fluid. Nearly one fourth of the children with neurologic symptoms were diagnosed with a tick-borne CNS infection (TBE, n = 10 [8%] and NB, n = 21 [16.8%]). In general, these children displayed an indistinct medical history and presented with nonspecific signs such as malaise/fatigue and headache. Diagnosis was based on analysis of acute and convalescent sera. Blood inflammatory parameters were nonspecific and did not contribute to the diagnostics.

CONCLUSION

Pediatric tick-borne CNS infections are unexpectedly common and should be considered in children with unspecific and unexplained acute CNS-related symptoms.

High burden of tick-borne encephalitis in Slovenia--challenge for vaccination policy

Slovenia is one of the countries with the highest reported incidence rates of tick-borne encephalitis (TBE). Vaccination uptake is low, estimated to be 12.4%. TBE surveillance data for the last 20 years were analysed. Though nearly all of Slovenia is endemic for TBE with national yearly incidence rates up to 26.7/100,000, we showed that two regions (Gorenjska and Koroška) were much more affected than other seven regions, with annual incidence rates up to 57.2/100,000 and 76.9/100,000 population, respectively. In the last decade, there was a shift in the age distribution of reported TBE cases to the older age groups, which resulted in the highest age-specific incidence rates nationally in 55-64 age group (up to 33.4/100,000 in 2006). To reduce this high burden of TBE, ideally the whole population of Slovenia should be offered free of charge vaccination against TBE. Alternatively, in view of limited resources available, sensible approach would be increasing vaccination coverage of the general population using social marketing and increasing TBE awareness, and in addition, offering free of charge vaccination to the most affected groups. The following priority target groups should be considered to be prospectively covered with free of charge vaccination: (1) 45-69 years old individuals in the two most affected regions (Gorenjska, Koroška), (2) the remaining age groups in the two most affected regions, (3) 45-69 years old individuals in the region with the next highest TBE incidence rates (Ljubljana), and (4) individuals 45-69 years old in all remaining Slovenian regions.

Clinical evaluation to determine the appropriate paediatric formulation of a tick-borne encephalitis vaccine

Two dose-finding studies and one open label safety study with a paediatric FSME-IMMUN formulation were conducted in children and adolescents aged 1-15 years (N=3697). The 1.2 microg antigen dose was identified as the optimal dose, inducing high seroconversion rates following the primary vaccination series. Adolescents (aged 12-15 years) vaccinated with the optimal paediatric dose (1.2 microg) attained similarly high seroprotective rates to adults (aged 16-35 years) vaccinated with the 2.4 microg formulation of FSME-IMMUN. We concluded that the FSME-IMMUN paediatric vaccine formulation is safe and highly immunogenic, not only for children <12 years, but also for adolescents <16 years.