Emergence of tick-borne encephalitis (TBE) in the Netherlands

Recently, tick-borne encephalitis virus (TBEV) was detected in the Netherlands for the first time, in ticks collected in 2015 in the National Park Sallandse heuvelrug in response to the detection of anti-TBEV antibodies in roe deer. Hereafter, two human cases of autochthonous TBE have been reported, occurring in 2016. One case was geographically linked to the area of the previously reported ticks, which harbored a genetically divergent TBEV-Eu strain variant (TBEV-NL). So far these are the few reported events that point to endemic transmission of TBEV in the Netherlands and the true prevalence of TBEV and TBE disease in the Netherlands and its impact on the human population remains to be determined. We describe the third human case, identified in 2017, which geographically clusters with the aforementioned case and TBEV-positive ticks. We also describe the identification of another TBEV-NL-positive tick in the Netherlands, collected 2 years after the initial find in that same region (in 2017). These observations support the concept of continued circulation of TBEV-NL and the presence of a possible TBEV hot spot in the Sallandse Heuvelrug region.