First detection of tick-borne encephalitis virus in Ixodes ricinus ticks in Belgium, May 2024.

Tick-borne encephalitis (TBE) is the most frequent tick-borne viral disease transmitted by ticks in Europe and Asia. In Belgium, autochthonous cases of TBE have been reported, but even though some tick collection was carried out in the past, no TBEV-positive ticks have been found thus far. In this study, questing ticks were collected by flagging at the precise location where a patient was reported to have been bitten by a tick before developing TBE in Belgium in 2020. In total, 350 ticks were pooled by life stage (nymphs, adult females, adult males) and collection date, lysed, and RNA extracted. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was performed to detect tick-borne encephalitis virus (TBEV) and Ixodes 18S rRNA, followed by Oxford nanopore amplicon sequencing. TBEV was detected in all three types of pools. Out of 69 nymph pools, 2 were positive, in adult female pools, 2 out of 16 were positive, and 1 of the 14 adult male pools was positive. A complete sequence was retrieved through sequencing. This sequence shares greater similarity with a strain found in Finland than the neighboring Salland strain (the Netherlands) and the Neudoerfl reference strain. These findings confirm that TBE can be acquired from tick bites within the country. It is therefore necessary to increase awareness of the disease among healthcare professionals.