Claine François, Coupeau Damien, Wiggers Laetitia, Muylkens Benoît, Kirschvink Nathalie
Department of Veterinary Medicine, Pole of Infectiology, University of Namur, Rue de Bruxelles 61, 5000, Namur, Belgium.
Department of Veterinary Medicine, Pole of Infectiology, University of Namur, Rue de Bruxelles 61, 5000, Namur, Belgium.
Prev Vet Med. 2018 Jun 1;154:132-138. doi: 10.1016/j.prevetmed.2018.03.024. Epub 2018 Mar 31.
Modelling the long-term seroprevalence evolution against Schmallenberg virus (SBV) is of first interest to plan vaccination strategies and to predict viral resurgence. The objectives of this study were first to estimate the duration of colostral immunity and the persistence of active immunity in a sheep flock that encountered two episodes of natural SBV infection and then to model the evolution of SBV seroprevalence by considering immune status as well as zootechnical variables. The entire sheep flock of the University of Namur composed by around 400 ewes producing 600 lambs a year and characterized by an annual 24.0% renewal rate was used for this study from January 2012 until December 2016. Antibody titers were estimated by performing Virus Neutralization Test (VNT) from blood and colostrum samples collected in lambs and adult sheep. Colostral antibodies against SBV of lambs born to seropositive ewes were detectable during four months. A significant increase of anti-SBV antibody titers was observed in lambs' serum as well as in ewes' colostrum between the time of first viral episode (2011) and the time of SBV reemergence (2012) suggesting a booster effect of viral resurgence on immune status. In naturally SBV infected adult sheep, the active immunity was estimated to last at least four years. These results combined with flock management data allowed to develop a mathematical model to predict the evolution of SBV seroprevalence at a herd scale. The accuracy of this model was assessed by VNT experiment performed at the end of the study. By applying this model to the sheep flock of the University of Namur, it was estimated that an annual 24.0% renewal rate led to total seronegativity, and so high susceptibility to viral resurgence, in 50 months after time of last natural infection. The third SBV episode detected in this research sheep flock within the expected time demonstrated huge within-flock susceptibility.
模拟针对施马伦贝格病毒（SBV）的长期血清阳性率演变对于规划疫苗接种策略和预测病毒复发至关重要。本研究的目的首先是估计在经历了两起自然SBV感染事件的羊群中初乳免疫的持续时间和主动免疫的持久性，然后通过考虑免疫状态以及畜牧学变量来模拟SBV血清阳性率的演变。从2012年1月至2016年12月，本研究使用了那慕尔大学的整个羊群，该羊群由约400只母羊组成，每年产600只羔羊，年更新率为24.0%。通过对从羔羊和成年羊采集的血液和初乳样本进行病毒中和试验（VNT）来估计抗体滴度。血清阳性母羊所生羔羊的抗SBV初乳抗体在四个月内均可检测到。在第一次病毒感染事件（2011年）到SBV再次出现（2012年）期间，羔羊血清和母羊初乳中的抗SBV抗体滴度均显著增加，这表明病毒复发对免疫状态有增强作用。在自然感染SBV的成年羊中，主动免疫估计至少持续四年。这些结果与畜群管理数据相结合，得以建立一个数学模型来预测畜群规模上SBV血清阳性率的演变。本研究结束时通过VNT实验评估了该模型的准确性。将该模型应用于那慕尔大学的羊群后估计，年更新率为24.0%会导致在最后一次自然感染后50个月出现完全血清阴性，从而对病毒复发高度易感。在本研究的羊群中在预期时间内检测到的第三次SBV感染事件表明畜群内部存在巨大的易感性。
