VISAVET Health Surveillance Centre, Complutense University of Madrid, Madrid, Spain.
Zoetis Manufacturing & Research Spain, S.L., Olot, Girona, Spain.
Transbound Emerg Dis. 2016 Apr;63(2):e220-8. doi: 10.1111/tbed.12256. Epub 2014 Aug 6.
Since the first reports of the Schmallenberg disease (SBD) outbreaks in late 2011, the disease has spread across Europe, affecting cattle and sheep farms. While Schmallenberg virus (SBV) causes a mild clinical disease in adults, infection of pregnant females may lead to the production of typical congenital malformations (CMFs) in their offspring. It is speculated that the immunity acquired after a SBV infection is effective in preventing further infections. However, this has not been proven in naturally infected sheep, especially if they are pregnant when reinfected. The aim of this study was to monitor the natural immunity in SBV-infected sheep. Twenty-four ewes from the only Spanish farm with a SBV OIE-notified outbreak were sampled. Subsequently, nine pregnant ewes were inoculated with SBV infectious plasma under controlled conditions. Six of them were euthanized before delivery, and their fetuses were inspected for lesions indicative for the SBV infection. The three remaining ewes were allowed to deliver one lamb each. Inoculation of the lambs was scheduled at approx. 3 months after birth. All samples were analyzed for viral RNA by RT-PCR, and for antibodies by an indirect ELISA and a virus neutralization test (VNT). The majority of the 24 ewes showed a serological reaction against SBV. The three ewes that were allowed to lamb down demonstrated variable degrees of seroconversion which corresponded to the levels of immune reaction observed in their lambs. Moreover, no viral RNA was detected, no lesions were observed in the fetuses, and no clinical signs were detected in the inoculated animals. These findings suggest that the immunity acquired by sheep following a natural SBV infection could be sufficient to stop SBV reinfection. However, vaccination could be a valuable tool to control SBV infections and associated economic losses as it affords a more uniform and predictable protection at the flock/herd level.
自 2011 年末首次报告沙尔门贝格病（SBD）疫情以来，该病已在欧洲蔓延，影响了牛和羊养殖场。虽然沙尔门贝格病毒（SBV）在成年动物中引起轻度临床疾病，但感染怀孕母羊可能导致其后代产生典型的先天性畸形（CMF）。据推测，感染 SBV 后获得的免疫力可有效预防进一步感染。然而，这在自然感染的绵羊中尚未得到证实，尤其是如果它们在再次感染时怀孕。本研究旨在监测 SBV 感染绵羊的自然免疫力。从唯一一家西班牙农场采集了 24 只感染 SBV 的母羊进行采样。随后，在受控条件下，将 9 只怀孕母羊接种 SBV 感染性血浆。其中 6 只在分娩前被安乐死，并检查其胎儿是否存在表明 SBV 感染的病变。其余 3 只母羊被允许各产一只羔羊。羔羊的接种定于出生后约 3 个月进行。所有样本均通过 RT-PCR 分析病毒 RNA，并通过间接 ELISA 和病毒中和试验（VNT）分析抗体。24 只母羊中的大多数对 SBV 表现出血清学反应。允许产羔的 3 只母羊显示出不同程度的血清转化，与在其羔羊中观察到的免疫反应水平相对应。此外，未检测到病毒 RNA，未在胎儿中观察到病变，也未在接种动物中观察到临床症状。这些发现表明，绵羊在自然感染 SBV 后获得的免疫力足以阻止 SBV 的再次感染。然而，疫苗接种可能是控制 SBV 感染和相关经济损失的有价值工具，因为它在群体/畜群水平上提供了更均匀和可预测的保护。
