Emergence of Bluetongue Serotypes in Europe, Part 2: The Occurrence of a BTV-11 Strain in Belgium

Abstract

An EDTA-blood sample from a cow without clinical signs, which gave early birth to a newborn calf that died soon after delivery, was shown to be positive for bluetongue virus (BTV)-RNA using a group-specific real-time RT-PCR (RT-qPCR). In-house serotype-specific RT-qPCR assays for bluetongue virus serotype 1 (BTV-1), -6 and -8 all gave negative results. Subsequent assays were carried out using conventional (gel-based) RT-PCR primers for all 25 BTV serotypes and only two primer sets, both specific for BTV-11, gave bands of the expected size. The cDNAs generated were sequenced and comparisons of the genome segment 2 sequence with that of the modified 'live' vaccine strain of BTV-11 from South Africa showed 100% identity. A survey of all ruminants in a 1-km area around the first positive farm using a BTV-11 serotype-specific RT-qPCR revealed five other holdings with in total nine BTV-11 positive animals. A cross-sectional monitoring of dairy cattle in Belgium showed an overall prevalence of 3.8% on herd level and 0.2% on animal level. A BTV-11 has been introduced into the Belgian cattle herd during the 2008 vector season. The source of the infection and the way by which the virus was introduced are unknown.

Bluetongue vaccination in Europe

“…Inactivated products were then developed and commercialized for BTV-9, BTV-1 and BTV-8. All of the most recent European BTV vaccination campaigns have exclusively used inactivated vaccines [10,17], in part owing to fears that some field viruses may be related to MLV vaccines [11,12].…”

“…In 2008, two other BTV serotypes were detected in Northern Europe: BTV-6 in the Netherlands and BTV-11 in Belgium [11,12].…”

Current and next-generation bluetongue vaccines: Requirements, strategies, and prospects for different field situations

“…Abortions and stillbirths have also been reported as well as lower milk production after vaccination with MLVs. Officially, MLVs for other serotypes were never used in Europe but have been detected, and are likely introduced via unknown introduction routes (De Clercq et al, 2009;van Rijn et al, 2012). In several parts of the world, such as the USA, Turkey, Africa, and India, MLVs are still used to protect the ruminant population against BT (Bhanuprakash et al, 2009;McVey & MacLachlan, 2015).…”

Retrospective Analysis of the Bluetongue Outbreak in Serbia

“…However, after nearly 20 years of absence BTV was recorded again on four Greek islands, where BTV-9 was isolated and that was the first report of this serotype on the European continent (15,16 (14,17,19). There have been indications that serotypes BTV-6 (detected in Germany and Holland) and BTV-11 (detected in Belgium) could have been introduced by illegal import of live attenuated vaccines (20,21), as no virus has been isolated and no clinical signs of bluetongue disease have been observed (22).…”