Conference report
Tick-borne encephalitis (TBE): An underestimated risk…still: Report of the 14th Annual Meeting of the International Scientific Working Group on Tick-Borne Encephalitis (ISW-TBE)

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Abstract

Today, the risk of getting tick-borne encephalitis (TBE) is still underestimated in many parts of Europe and worldwide. Therefore, the 14th meeting of the International Scientific Working Group on Tick-Borne Encephalitis (ISW-TBE) – a group of neurologists, general practitioners, clinicians, travel physicians, virologists, pediatricians, and epidemiologists – was held under the title “Tick-borne encephalitis: an underestimated risk…still”. Among the discussed issues were: TBE, an underestimated risk in children, a case report in two Dutch travelers, the very emotional report of a tick victim, an overview of the epidemiological situation, investigations to detect new TBE cases in Italy, TBE virus (TBEV) strains circulation in Northern Europe, TBE Program of the European Centre for Disease Prevention and Control (ECDC), efforts to increase the TBE vaccination rate in the Czech Republic, positioning statement of the World Health Organization (WHO), and TBE in dogs.

To answer the question raised above: Yes, the risk of getting TBE is underestimated in children and adults, because awareness is still too low. It is still underestimated in several areas of Europe, where, for a lack of human cases, TBEV is thought to be absent. It is underestimated in travelers, because they still do not know enough about the risk, and diagnostic awareness in non-endemic countries is still low.

Introduction

It has now been 14 years since the International Scientific Working Group on Tick-Borne Encephalitis (ISW-TBE) kicked off its first official meeting in 1998. Since then, no fewer than 760 expert scientists – including neurologists, general practitioners, clinicians, travel physicians, virologists, pediatricians, and epidemiologists – from 30 different European countries have convened to take the opportunity of exchanging late-breaking research, identifying obstacles to increasing vaccination rates, and shaping feasible strategies to overcome them. By publishing annual conference reports, the ISW-TBE wants to keep the scientific community updated about the latest developments (Kunze et al., 2004, Kunze et al., 2005, Kunze et al., 2006, Kunze et al., 2007, Kunze et al., 2008, Kunze et al., 2009, Kunze et al., 2010, Kunze et al., 2011).

The risk of getting TBE is still underestimated in many parts of Europe, and worldwide.

Therefore this year's conference was held under the title “tick-borne encephalitis (TBE): an underestimated risk…still”. The agenda was divided into the following parts: (i) underestimated risk, (ii) look more – find more, (iii) poster session: epidemiological update in Europe, (iv) TBE as a notifiable disease – status quo and the way forward, and (v) increased efforts in prevention.

Within this schedule, the working group discussed various themes, e.g. TBE – an underestimated risk in children, a case report in 2 Dutch travelers, the very emotional report of a tick victim, an overview of the epidemiological situation, investigations to detect new TBE cases in Italy, TBE virus (TBEV) strains circulation in Northern Europe, TBE Program of the European Centre for Disease Prevention and Control (ECDC), efforts to increase the vaccination rate in the Czech Republic, positioning statement of the World Health Organization (WHO), TBE in dogs. This meeting report presents some of the topics in detail.

In all these years, the main aims of the ISW-TBE have been promoting national and international scientific, medical, and regulatory collaboration on TBE, stimulating and co-ordinating applied and basic research, contributing to training and educational programs in the field, providing high-quality information and promoting appropriate distribution, promoting and aligning international standards on epidemiological surveillance, and defining and promoting proposals to harmonize national and international policies on prevention. Through these activities, the working group has gained recognition for the past years as an independent advisory committee to national and international health authorities as well as to scientific and medical professions. Table 1 shows an overview of ISW-TBE key activities.

Together with dengue virus, Japanese encephalitis virus, and yellow fever virus, the TBEV belongs to the genus Flavivirus in the Flaviviridae family. Due to the close antigenic relationship between TBEV and other flaviviruses, TBEV-binding antibodies may cross-react with antibodies induced by other flaviviruses, posing a diagnostic challenge in travelers either vaccinated against diseases (such as yellow fever, dengue fever, or West Nile encephalitis) or having acquired one of these infections. In patients with previous exposure to other flaviviruses, therefore, ELISA does not suffice to establish a diagnosis of TBE, and a neutralization test, the most specific serologic test measuring virus-neutralizing antibodies, has to be performed (presentation by F.X. Heinz).

The three TBEV subtypes have a similarity of about 95%, a relationship strong enough to not only cause cross-reactivity, but also cross-protection. Cross-neutralization between the European, the Siberian, and the Far Eastern TBEV isolates has been known to occur, but this was difficult to quantify (Hayasaka et al., 1999, Holzmann et al., 1992). Recent studies demonstrate that the TBE vaccine based on the European subtype strain Neudörfl induces equally potent protection against TBEV strains of the European, Far Eastern, and Siberian subtypes (Orlinger et al., 2010, Orlinger et al., 2011, Fritz et al., 2012).

Austria is a high-risk country for getting TBE, although the low incidence of 0.88 per 100,000 inhabitants may suggest otherwise. This seeming contradiction has been the result of a mass vaccination campaign initiated in 1981 and a vaccination rate that has meanwhile increased to 86% of the population, assuming that this percentage of people has received at least one shot (Heinz et al., 2007, Kollaritsch et al., 2011). Thus, whereas TBE case numbers in Austria in the prevaccination era were among the highest in central Europe (several hundred every year), case numbers have stayed at below 100 since 1997, with the single exception of 2011, when 113 cases were reported. There have also been significant changes in the locations of infection in the course of years, especially in valley regions of the Alps, new foci were detected. The western states of Austria (Tyrol and Vorarlberg) are now among those with the highest incidences. Attention must be paid to the fact that – despite fluctuating numbers of TBE cases and a high vaccination rate – the risk of getting a TBE infection for an unvaccinated person stays the same.

Section snippets

Evaluation of clinical manifestations in children

Recent findings from Sweden indicate that the incidence in children may be higher than previously thought. With symptoms mainly unspecific, TBE is unlikely to be found unless specifically sought. Accurate diagnoses are a precondition for elucidating the long-term effects of TBE in the very young.

In a study with 124 children (<18 years old) seeking medical attention for neurological complaints, anti-TBEV and anti-Borrelia serologies were performed (presentation by M. Sundin). All these children

Epidemiological situation in Europe

In the 20 years from 1991 to 2010, no fewer than 169,292 TBE cases were reported for Europe and Russia, 35% (n = 58,451) of these in Europe alone, reflecting an average of 2923 cases per year (presentation by J. Süss). The dynamics of TBE have differed greatly between countries and from year to year. Extensive fluctuations of TBE cases are a well-known phenomenon, which still lacks sufficient explanation.

When comparing the number of cases of 1991–2000 with those of 2001–2010, significant

TBE Program of the European Centre for Disease Prevention and Control

ECDC's mission is to identify, assess, and communicate current and emerging threats to human health posed by infectious diseases. An ECDC representative presented the ECDC TBE Program (presentation by H. Hrabcik). It is estimated that Europe-wide only 30–40% of TBE cases are reported. The objectives of ECDC are to strengthen the capacity of the EU Member States for surveillance and prevention of tick-borne diseases and to harmonize case definitions of TBE and Lyme borreliosis in order to draft

TBE as a travel-associated disease and TBE Travel Advisory Board

When it comes to travelers and travel medicine specialists, awareness of TBE at both the giving and the receiving ends is low. There are many different specialists involved in the field of TBE (mainly working on infectious diseases, virology, and epidemiology), however, the majority of travel medicine experts lack specific knowledge – therefore TBE in association with travelling is frequently neglected (presentation by M. Haditsch). The aim must be to bridge the gaps between these experts to

Conclusion

Sometimes, facing the true burden of a given illness requires a very close look, a keen awareness of the disease, tight surveillance, and international cooperation to look beyond natural foci and national borders. TBE is a good example. Reflecting the question “Is TBE still an underestimated risk?” the following answers can be given:

It is underestimated in children, in whom symptoms are often unspecific and unlikely to be correctly diagnosed unless serology is routinely performed in those with

Acknowledgements

We thank Ms. Gabriele Berghammer for assistance in writing and translation.

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