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Chapter 12a: Epidemiology by country – overview

2) A high local vaccine uptake may result in a clearly, at least some parts of The Netherlands
low disease incidence, whereas the and Japan are now TBEV-endemic areas.
incidence in the unvaccinated (e.g., a
Following the ECDC definition, in this
traveler) may be much higher than the publication we name all areas with
reported risk in the local population.
documentation of TBEV presence by either
3) TBEV exists in microfoci, i.e. the virus often confirmed human TBE case(s) or by any viral
is detectable in small areas only, whereas detection as ‘TBEV-risk areas’ (Figure 3).
the surrounding areas are TBEV-free. Physicians, travelers, or the public in general
may refer to the respective country in Chapter
A high local vaccine uptake may result in a low 12b of this publication to see the number of
disease incidence, whereas the incidence in
reported cases by year, the local vaccine
the unvaccinated (e.g., a traveler) may be
uptake (as available), and other key
much higher than the reported risk in the local
information for to judge on possible risks –
population.
bearing in mind the limitations on surveillance
TBEV exists in microfoci, i.e. the virus often is and reporting mentioned herein. It is the task
detectable in small areas only, whereas the of local authorities then to define “TBE-
surrounding areas are TBEV-free. endemic areas”, i.e. areas, where vaccination
may be considered.”
Considering these points, the prevalence of
TBEV in ticks obviously can vary considerably,
even within 1 country or 1 area within an See Chapter 12b for evidence of TBEV/TBE in
endemic region. For instance, in some highly individual countries.
endemic areas, TBEV prevalence in ticks
reaches 20– 40%, but in other areas it can be See Chapter 12c: Risk map for TBE virus.
3
as low as 0.1–0.5% (see Chapter 11).

To date there is no commonly accepted
definition to characterize ‘TBE risk’ areas. The Areas without confirmed TBE
country surveys listed in this publication
therefore follow a proposal by ECDC: The key risk
10
point from this is that “… any area where the
chances of transmission of an arthropod- No presence of TBEV has been confirmed for
borne disease to humans are higher than nil is Spain, Portugal, United Kingdom, Republic of
a risk area.” This definition is compelling as it Ireland, Luxembourg, Georgia, Albania,
refrains from requiring any incidence data, Kosovo, Macedonia, Montenegro, Greece,
which may vary from year to year even for the Turkey, …
same region. We also acknowledge that the
ECDC definition has relevant limitations. In First reports of TBEV seropositivity for TBEV in
South Korea, TBEV has been detected in ticks, Spain were published in animals in
but no single human case has been identified Extremadura in 2003 and in Andalusia in 2014,
and neutralizing antibodies against TBEV were
to date. In Japan, only 1 case had been
confirmed by 1993, and 4 other cases were recently detected in a horse on the island of
13,14
Mallorca (off the eastern coast of Spain).
identified between 2016 and 2018. In The
Netherlands, 3 autochthonous TBE cases were Nonetheless these data are difficult to inter-
identified in 2017. 11,12 It remains unknown if pret as they could be due to cross-reactivity
travelers to Korea have any risk for TBE when with IgG directed against closely related
exposed to ticks in this country, whereas viruses of the same serogroup. Indeed, the
louping ill virus, a member of the TBEV

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