Abstract
Since 1998, Bluetongue virus (BTV)-serotypes 1, 2, 4, 9, and 16 have invaded European countries around the Mediterranean Basin. In 2006, a huge BT outbreak started after incursion of BTV serotype 8 (BTV8) in North-Western Europe. IN 2008, BTV6 and BTV11 were reported in the Netherlands and Germany, and in Belgium, respectively. In addition, Toggenburg orbivirus (TOV) was detected in 2008 in Swiss goats, which was recognized as a new serotype of BTV (BTV25). The (re-)emergency of BTV serotypes needs a rapid response to supply effective vaccines. Reverse genetics has been developed for BTV1 and more recently also for BTV6. This latter strain, BTV6/net08, is closely related to live-attenuated vaccine for serotype 6 as determined by full genome sequencing. Here, we used this strain as backbone and exchanged segment 2 and 6, respectively Seg-2 (VP2) and Seg-6 (VP5), for those of BTV serotype 1 and 8 using reverse genetics. These so-called ‘serotyped’ vaccine viruses, as mono-serotype and multi-serotype vaccine, were compared for their protective capacity in sheep. In general, all vaccinated animals developed a neutralizing antibody response against their respective serotype. After challenge at three weeks post vaccination with cell-passaged, virulent BTV8/net07 (BTV8/net07/e1/bhkp3) the vaccinated animals showed nearly no clinical reaction. Even more, challenge virus could not be detected, and seroconversion or boostering after challenge was negligible. These data demonstrate that all sheep were protected from a challenge with BTV8/net07, since sheep of the control group showed viremia, seroconversion and clinical signs that are specific for Bluetongue. The high level of cross-protection is discussed.
Highlights
Bluetongue virus (BTV) belongs to the family Reoviridae, genus Orbivirus [1]
Reassortants with the outer shell of different serotypes Since rgBTV6 was proven to be avirulent [14], we studied the possibilities of using this avirulent BTVac-6 as virus backbone to generate ‘synthetic’ reassortants with the outer shell originating from BTV1 or BTV serotype 8 (BTV8)/net07
After virus stocks were prepared on BSR cells, viruses were characterized by S2-genotyping for serotype 1, 6 and 8 and by PCR with primers specific for the respective Seg6 of BTV1, 26 or 28
Summary
Bluetongue virus (BTV) belongs to the family Reoviridae, genus Orbivirus [1]. BTV transmission between ruminants, including cattle, sheep, and goats, occurs in majority by bites of species of Culicoides. The genome of BTV consists of ten linear double-stranded RNA genome segments Seg-1 to Seg-10 encoding structural proteins VP1 to VP7, nonstructural proteins, NS1, NS2 and NS3/ NS3a, for reviews see [5,6], and the recently discovered nonstructural protein NS4 [7,8]. The virus particle composes three shells of proteins, the inner shell consists of VP3 encoded by Seg-3, the middle shell consists of VP7 encoded by Seg-7, and the outer shell is formed by VP2 (Seg-2) and VP5 (Seg-6). The BTV particle further contains three enzymatic proteins, VP1 (Seg-1), VP4 (Seg-4) and VP6 (Seg-9), and one copy of each of the ten genome segments Seg-1 to Seg-10 in the inner shell. The nonstructural proteins NS1 (Seg-5), NS2 (Seg-8), NS3/NS3a (Seg-10), and NS4 (Seg-9) are not part of the BTV particle
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