European subtype tick-borne encephalitis virus (TBEV), transmitted by Ixodes ricinus ticks and occasionally by unpasteurised ruminant milk, is currently the most important arthropod-borne viral infection in humans in Europe. About one third of humans infected with TBEV develop neuro-invasive disease, characterised by fever and neurological signs, ranging from meningitis to severe encephalitis with or without myelitis. These patients need hospitalisation and approximately 35-58% develop permanent sequels (“post-encephalitic syndrome”). Despite low mortality rates of 0-3.9%, Western subtype TBEV represents a risk for public health and food safety. TBE is of growing concern in several European countries and about 3,000 people are hospitalised yearly. Recently, human incidence has increased in several endemic countries and TBE seems to emerge in Northern/Western Europe. The virus has already been identified in two of Belgium’s neighbouring countries: Germany and France (Alsace). In July 2016, the first autochthonous case of tick-born encephalitis was diagnosed in the Netherlands (Sallandse Heuvelrug). No cases have been reported yet in humans in Belgium, but we found indirect evidence that the virus is also circulating in the wild in Belgium.
The main animal reservoirs of TBEV are small rodents. Different species of wild and domestic mammals (especially hares, deer, wild boar, sheep, cattle, goats) play a role in supporting virus circulation indirectly by enabling tick multiplication. Humans are incidental and dead-end hosts. Therefore, veterinary sentinel screening remains a valuable tool in identifying and characterizing endemic foci. Several seroprevalence studies on sentinel animals (bovine, roe deers and wild boars) have been conducted in Belgium by Sciensano between 2014 and 2016. TBEV-seroprevalence in the targeted area was estimated between 2.61 and 4.29% for bovine, 5.1% in roe deers and 2.9% in wild boar. In order to detect TBEV in Belgium, we led a prevalence study of TBEV in rodents in Wallonie in 2014 and 2015. In total, 258 Myodes Glareolus and 47 Apodemus Sylvaticus were captured. All of them tested negative for TBEV by qPCR.
The aim of this project is to conduct serological surveillance in animals, both in Flanders and Wallonia. In area’s with seropositive sentinel animals, targeted follow-up surveys are performed in rodents to detect and analyse the circulating TBEV strain(s) in the wild.
In parallel, we are also examining the infection characteristics of TBEV in local wild rodents in order to better understand the virulence and transmission dynamics of this virus in our region.