Nielsen Henriette S, Oleksiewicz Martin B, Forsberg Roald, Stadejek Tomasz, Bøtner Anette, Storgaard Torben
Danish Veterinary Institute for Virus Research, Lindholm, DK-4771 Kalvehave, Denmark1.
Institute of Biological Science, University of Aarhus, Aarhus, Denmark2.
J Gen Virol. 2001 Jun;82(Pt 6):1263-1272. doi: 10.1099/0022-1317-82-6-1263.
A live attenuated porcine reproductive and respiratory syndrome (PRRS) vaccine virus has been shown to revert to virulence under field conditions. In order to identify genetic virulence determinants, ORF1 from the attenuated vaccine virus and three Danish vaccine-derived field isolates was sequenced and compared with the parental strain of the vaccine virus (VR2332). This revealed five mutations that had occurred independently in all three vaccine-derived field isolates, indicating strong parallel selective pressure on these positions in the vaccine virus when used in swine herds. Two of these parallel mutations were direct reversions to the parental VR2332 sequence and were situated in a papain-like cysteine protease domain and in the helicase domain. The remaining parallel mutations might be seen as second-site compensatory mutations for one or more of the mutations that accumulated in the vaccine virus sequence during cell-culture adaptation. Evaluation of the remaining mutations in the ORF1 sequence revealed stronger selective pressure for amino acid conservation during spread in pigs than during vaccine production. Furthermore, it was found that the selective pressure did not change during the time period studied. The implications of these findings for PRRS vaccine attenuation and reversion are discussed.
一种减毒活猪繁殖与呼吸综合征（PRRS）疫苗病毒已被证明在田间条件下会恢复毒力。为了确定基因毒力决定因素，对减毒疫苗病毒和三株丹麦疫苗衍生的田间分离株的ORF1进行了测序，并与疫苗病毒的亲本菌株（VR2332）进行了比较。这揭示了在所有三株疫苗衍生的田间分离株中独立发生的五个突变，表明在猪群中使用疫苗病毒时，这些位置受到强大的平行选择压力。其中两个平行突变直接恢复为亲本VR2332序列，位于木瓜样半胱氨酸蛋白酶结构域和螺旋酶结构域。其余的平行突变可能被视为对疫苗病毒在细胞培养适应过程中积累的一个或多个突变的第二位点补偿突变。对ORF1序列中其余突变的评估表明，在猪体内传播期间，氨基酸保守性的选择压力比疫苗生产期间更强。此外，还发现在所研究的时间段内选择压力没有变化。讨论了这些发现对PRRS疫苗减毒和恢复的影响。
