Tick-Borne Encephalitis Virus Prevalence in Sheep, Wild Boar and Ticks in Belgium

Abstract

Tick-borne encephalitis virus (TBEV) is the most important tick-borne zoonotic virus in Europe. In Belgium, antibodies to TBEV have already been detected in wildlife and domestic animals, but up-to-date prevalence data for TBEV are lacking, and no studies have assessed its seroprevalence in sheep. Serum samples of 480 sheep from all over Belgium and 831 wild boar hunted in Flanders (northern Belgium) were therefore screened for TBEV antibodies by ELISA and plaque reduction neutralization test (PRNT), respectively. The specificity of positive samples was assessed by PRNTs for TBEV and the Louping Ill, West Nile, and Usutu viruses. TBEV seroprevalence was 0.42% (2/480, CI 95%: 0.11–1.51) in sheep and 9.27% (77/831, CI 95%: 7.48–11.43) in wild boar. TBEV seroprevalence in wild boar from the province of Flemish Brabant was significantly higher (22.38%, 15/67) compared to Limburg (7.74%, 34/439) and Antwerp (8.61%, 28/325). Oud-Heverlee was the hunting area harboring the highest TBEV seroprevalence (33.33%, 11/33). In an attempt to obtain a Belgian TBEV isolate, 1983 ticks collected in areas showing the highest TBEV seroprevalence in wild boars were tested by real-time qPCR. No TBEV-RNA-positive tick was detected. The results of this study suggest an increase in TBEV prevalence over the last decade and highlight the need for One-Health surveillance in Belgium.

Comparison of Serological Methods for Tick-Borne Encephalitis Virus-Specific Antibody Detection in Wild Boar and Sheep: Impact of the Screening Approach on the Estimated Seroprevalence

“…Wild boar sera (n = 406) were selected from a set of 886 serum samples that had previously been used to determine the TBEV seroprevalence in Flanders, Belgium [ 15 ]. All samples for which sufficient serum remained to perform all serological tests were used.…”

“…In Belgium, the TBEV seroprevalence was examined in different animal species. TBEV-specific antibodies have been detected in wild boar, roe deer, domestic dogs, cattle and sheep [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Depending on the species, the detected seroprevalence varied between 0.35% (dogs [ 12 ]) and 12.4% (roe deer [ 14 ]).…”

“…Depending on the species, the detected seroprevalence varied between 0.35% (dogs [ 12 ]) and 12.4% (roe deer [ 14 ]). Recently, our laboratory reported a TBEV seroprevalence of 0.42% in sheep and 9.27% in wild boar [ 15 ]. In 2020, for the first time, three autochthonous cases were identified in humans [ 17 ].…”

“…In 2020, for the first time, three autochthonous cases were identified in humans [ 17 ]. Ticks have also been screened, but so far, TBEV has not been detected [ 15 ]. This is probably due to the fact that TBEV is only present in ticks in very small focus areas [ 10 ].…”

“…Afterwards, the positive samples are subjected to a virus neutralization test, which is considered as the golden standard test for flavivirus antibody detection, to eliminate potential false positive results. From 38 identified screening studies of flavivirus antibodies in animals, 19 used the Immunozym FSME IgG All Species ELISA (Progen, Heidelberg, Germany) [ 12 , 14 , 15 , 19 , 20 , 21 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ], 10 used the ID Screen WNV Competition ELISA Kit (Innovative diagnostics, Montpellier, France) [ 13 , 33 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ] and 9 used other ELISA kits [ 9 , 22 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ] as a first screening. Based on this literature study, it was decided to evaluate the performance of the Immunozym ELISA and the IDScreen ELISA in more details.…”