A one health approach to investigating an outbreak of alimentary tick-borne encephalitis in a non-endemic area in France (Ain, Eastern France): a longitudinal serological study in livestock, detection in ticks, and the first TBE virus isolation and molecular characterization

Tick borne encephalitis virus geographic range and human incidence is increasing throughout Europe, putting a number of non-endemic regions and countries at risk of outbreaks. In spring 2020, there was an outbreak of TBE in Ain, Eastern France, where the virus had never been detected before. All patients but one had consumed traditional unpasteurized raw goat cheese from a local producer. We conducted an investigation in the suspected farm using an integrative One Health approach. Our methodology included (i) the detection of virus in cheese and milk products, (ii) serological testing of all animals in the suspected farm and surrounding farms, (iii) an analysis of the landscape and localisation of wooded area, (iv) the capture of questing ticks and small mammals for virus detection and estimating enzootic hazard, and (v) virus isolation and genome sequencing. This approach allowed us to confirm the alimentary origin of the TBE outbreak and to witness in real time the seroconversion of recently exposed individuals and the excretion of virus in goat milk. In addition, we identified a wooded focus area where and around which there is a risk of TBEV exposure. We provide the first TBEV isolate responsible for as a source of dietary contamination in France, obtained its full-length genome sequence, and found that it does not cluster very closely neither with the isolate circulating in Alsace nor with any other isolate within the European lineage. TBEV is now a notifiable human disease in France, which should facilitate surveillance of TBEV incidence and distribution throughout France.

Tick Borne Encephalitis

Tick-borne encephalitis (TBE) is the medically most common tick-borne viral disease in Europe and Asia. The TBE virus (TBEV) is a member of the family Flaviviridae. Transmission mainly to humans occurs by ticks of the Family Ixodidae, mainly the castor bean tick (Ixodes ricinus) in Europe and the taiga tick (Ixodes persulcatus) in Asia. Rarely TBEV is also transmitted by contaminated milk of infected ungulates (goat, sheep, cow). The clinical course of TBE is variable and may range from subclinical to fatal encephalomyelitis. Probably host and viral factors are involved in the pathogenesis of disease. So far, no specific treatment of the disease is available. The only effective prevention of TBE is vaccination. A number of different vaccines are available worldwide. In Europe two vaccines are licensed which contain inactivated European subtype TBEV. Probably the European vaccines protect also against infections with other subtypes of TBEV.

The regional decline and rise of tick-borne encephalitis incidence do not correlate with Lyme borreliosis, Austria, 2005 to 2018

Background Tick-borne encephalitis (TBE) virus is a human pathogen that is expanding its endemic zones in Europe, emerging in previously unaffected regions. In Austria, increasing incidence in alpine regions in the west has been countered by a decline in traditional endemic areas to the east of the country. Aim To shed light on the cause of this disparity, we compared the temporal changes of human TBE incidences in all federal provinces of Austria with those of Lyme borreliosis (LB), which has the same tick vector and rodent reservoir. Methods This comparative analysis was based on the surveillance of hospitalised TBE cases by the National Reference Center for TBE and on the analysis of hospitalised LB cases from hospital discharge records across all of Austria from 2005 to 2018. Results The incidences of the two diseases and their annual fluctuations were not geographically concordant. Neither the decline in TBE in the eastern lowlands nor the increase in western alpine regions is paralleled by similar changes in the incidence of LB. Conclusion The discrepancy between changes in incidence of TBE and LB support the contributions of virus-specific factors beyond the mere availability of tick vectors and/or human outdoor activity, which are a prerequisite for the transmission of both diseases. A better understanding of parameters controlling human pathogenicity and the maintenance of TBE virus in its natural vector−host cycle will generate further insights into the focal nature of TBE and can potentially improve forecasts of TBE risk on smaller regional scales.

Tick-borne encephalitis related uveitis: a case report

Background Tick-borne encephalitis (TBE) is an infectious disease of the central nervous system caused by the TBE virus (TBEV), which is usually transmitted by a tick-bite, with increasing incidence in northeastern Europe and eastern Asia during the past decade. Ocular involvement has not been described in the literature to date. Case presentation A 58-year-old patient presented to the emergency department with occipital headaches and poor balance for 5 days. He reported a tick-bite 6 weeks before without erythema migrans followed by a flu-like syndrome. Serological testing was negative for Borreliosis and TBEV. At presentation, he was febrile with neck stiffness and signs of ataxia. Three days later, he presented unilateral visual loss in his right eye. Examination revealed non granulomatous anterior uveitis, vitreous inflammation, and retinal haemorrhages at the posterior pole without macular oedema or papillitis. Polymerase chain reaction (PCR) of the cerebrospinal fluid returned negative for all Herpes family viruses. No clinical evidence of other infection nor malignancy was identified. A seroconversion of the TBEV- immunoglobulin titres was observed 2 weeks later while the serum antibodies for Borrelia were still not detected. Magnetic resonance imaging was unremarkable. We concluded to the diagnosis of TBE-related uveitis. Under supportive treatment, there was complete resolution of the neurological symptoms and the intraocular inflammation without sequelae within the following weeks. Conclusions We describe a new association of TBEV with uveitis. In view of the growing number of TBE cases and the potential severity of the disease we aim at heightening awareness to achieve prompt recognition, prevention, and treatment.

Clinical Characteristics of Patients with Tick-Borne Encephalitis (TBE): A European Multicentre Study from 2010 to 2017

Tick-borne encephalitis (TBE) virus is a major cause of central nervous system infections in endemic countries. Here, we present clinical and laboratory characteristics of a large international cohort of patients with confirmed TBE using a uniform clinical protocol. Patients were recruited in eight centers from six European countries between 2010 and 2017. A detailed description of clinical signs and symptoms was recorded. The obtained information enabled a reliable classification in 553 of 555 patients: 207 (37.3%) had meningitis, 273 (49.2%) meningoencephalitis, 15 (2.7%) meningomyelitis, and 58 (10.5%) meningoencephalomyelitis; 41 (7.4%) patients had a peripheral paresis of extremities, 13 (2.3%) a central paresis of extremities, and 25 (4.5%) had single or multiple cranial nerve palsies. Five (0.9%) patients died during acute illness. Outcome at discharge was recorded in 298 patients. Of 176 (59.1%) patients with incomplete recovery, 80 (27%) displayed persisting symptoms or signs without recovery expectation. This study provides further evidence that TBE is a severe disease with a large proportion of patients with incomplete recovery. We suggest monitoring TBE in endemic European countries using a uniform protocol to record the full clinical spectrum of the disease.

Experimental Assessment of Possible Factors Associated with Tick-Borne Encephalitis Vaccine Failure

Currently the only effective measure against tick-borne encephalitis (TBE) is vaccination. Despite the high efficacy of approved vaccines against TBE, rare cases of vaccine failures are well documented. Both host- and virus-related factors can account for such failures. In this work, we studied the influence of mouse strain and sex and the effects of cyclophosphamide-induced immunosuppression on the efficacy of an inactivated TBE vaccine. We also investigated how an increased proportion of non-infectious particles in the challenge TBE virus would affect the protectivity of the vaccine. The vaccine efficacy was assessed by mortality, morbidity, levels of viral RNA in the brain of surviving mice, and neutralizing antibody (NAb) titers against the vaccine strain and the challenge virus. Two-dose vaccination protected most animals against TBE symptoms and death, and protectivity depended on strain and sex of mice. Immunosuppression decreased the vaccine efficacy in a dose-dependent manner and changed the vaccine-induced NAb spectrum. The vaccination protected mice against TBE virus neuroinvasion and persistence. However, viral RNA was detected in the brain of some asymptomatic animals at 21 and 42 dpi. Challenge with TBE virus enriched with non-infectious particles led to lower NAb titers in vaccinated mice after the challenge but did not affect the protective efficacy.

Chapter 2a: Virology

TBEV is the most medically important member of the tick-borne serocomplex group within the genus Flavivirus, family Flaviviridae. Three antigenic subtypes of TBEV correspond to the 3 recognized genotypes: European (TBEV-EU), also known as Western, Far Eastern (TBEV-FE), and Siberian (TBEV-SIB). An additional 2 genotypes have been identified in the Irkutsk region of Russia, currently named TBE virus Baikalian subtype (TBEV-BKL) and TBE virus Himalayan subtype (Himalayan and “178-79” group; TBEV-HIM). TBEV virions are small enveloped spherical particles about 50 nm in diameter. The TBEV genome consists of a single-stranded positive sense RNA molecule. The genome encodes one open reading frame (ORF), which is flanked by untranslated (non-coding) regions (UTRs). The 5′-UTR end has a methylated nucleotide cap for canonical cellular translation. The 3′-UTR is not polyadenylated and is characterized by extensive length and sequence heterogeneity. The ORF encodes one large polyprotein, which is co- and post-translationally cleaved into 3 structural proteins (C, prM, and E) and 7 non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). TBEV replicates in the cytoplasm of the host cell in close association with virus-induced intracellular membrane structures. Virus assembly occurs in the endoplasmic reticulum. The immature virions are transported to the Golgi complex, and mature virions pass through the host secretory pathway and are finally released from the host cell by fusion of the transport vesicle membrane with the plasma membrane.

TBE in Bosnia and Herzegovina

Very limited information is available for Bosnia showing the occurrence of TBE Even though there have been some elder case reports in the northern parts of the country, including alimentary infections, details have not been published. In early 1996 United States military forces were deployed to Bosnia as part of Operation Joint Endeavor. Only 4 (0.42%) unvaccinated individuals, all males, demonstrated a 4-fold seroconversion. All 4 seemingly were infected with TBE virus (or a closely-related variant) during their 6–9-month deployment period in Bosnia, but did not report with symptoms to any health care provider.

TBE in Moldova

Although there are no reliable data on the number of tick-borne encephalitis (TBE) cases or the percentage of infected ticks, based on the geography and the presence of TBE virus (TBEV) in all neighboring countries, it must be assumed that TBEV is present somewhere in Moldova.

TBE in Croatia

Even though tick-borne encephalitis (TBE) has been a notifiable disease in Croatia since 2007, there are no or only limited data available on the occurring tick species in the endemic areas, on the prevalence of TBE virus (TBEV) in ticks, its distribution in Croatia, and its genetic characteristics. Reporting of human cases also is very scarce. The Central European subtype of virus (TBEV-EU) appears to be present in Croatia.