Boogarts et al.
A household cluster of tick-borne encephalitis in Belgium in 2025: is the epidemiology evolving? Viruses. 2026;18:491. doi:10.3390/v18050491
In Belgium, no autochthonous human tick-borne encephalitis (TBE) case had been reported before 2018, when the first two possibly or probably locally acquired cases were notified. The first confirmed autochthonous cases were subsequently reported in 2020. Direct detection of TBE virus RNA in ticks in 2024 further supported the circulation of TBE virus in Belgium.
In 2025, three TBE cases were reported in Belgium, including two cases occurring within the same household. Case 1 was a 58-year-old woman. Case 2 was her 55-year-old husband, who presented with fever, malaise, anorexia, and weight loss. Given the overlap in clinical symptoms, he underwent extensive diagnostic investigations. However, TBE is not routinely included in the diagnostic workup in Belgium, reflecting limited clinical awareness and likely contributing to underdiagnosis.
Both patients tested positive for TBE virus IgM and IgG antibodies by ELISA, and infection was confirmed by plaque-reduction neutralization testing. Both patients reported purchasing and consuming unpasteurized milk and goat cheese from a local farm. However, no field investigation of the suspected farm was conducted.
The increase in reported TBE cases in Belgium in recent years may partly reflect enhanced clinical and public health awareness associated with new surveillance initiatives, including the launch of the NeuroSur network in January 2024. Increased awareness was illustrated by Case 2, who likely would not have been tested for TBE virus infection in the absence of the index diagnosis in Case 1.
The currently limited number of confirmed TBE cases in Belgium may represent only the tip of the iceberg. These findings underscore the need to improve clinical awareness and strengthen diagnostic testing among patients presenting with non-specific febrile illness or neurological syndromes.