Norwegian Veterinary Institute, Elizabeth Stephansens vei 1, Ås, 1433, Norway.
Norwegian Food Safety Authority, Stensberggata 25/27, Oslo, 0170, Norway.
Acta Vet Scand. 2024 Jul 4;66(1):28. doi: 10.1186/s13028-024-00749-7.
Visna-maedi is a notifiable disease in Norway, and eliminating the disease is a national goal. The import of sheep into Norway is very limited, and strict regulations apply to the movement of small ruminants between flocks and within defined geographical regions. Several outbreaks have occurred in the last 50 years, and the most recent before 2019 occurred in Trøndelag county in Central Norway in 2002. A national surveillance programme for small ruminant lentivirus infection exists since 2003.
In 2019, the national surveillance programme detected seropositive animals for small ruminant lentivirus in a sheep flock in Trøndelag. Based on the result of polymerase chain reaction analysis and histopathological findings, the Norwegian Food Safety Authority concluded the diagnosis of maedi. Further investigations detected maedi in eight additional sheep flocks in the same county. The flocks were placed under restrictions, and the authorities also imposed restrictions on 82 contact flocks. Sequencing of partial gag genes indicated that the virus in the current outbreak was related to the small ruminant lentivirus detected in the same area between 2002 and 2005.
The outbreak investigation shows the need for sensitive and specific diagnostic methods, and an improved and more targeted surveillance strategy. It also demonstrates the risk of disease spreading between flocks through animal movements, and highlights the importance of biosecurity and structured livestock trade. In addition to allowing livestock trade only from flocks documented free from maedi, it may be necessary to monitor sheep flocks over many years, when aiming to eliminate maedi from the Norwegian sheep population.
维斯纳-梅迪病在挪威是一种须通报的疾病，消灭该病是挪威的一个国家目标。挪威对绵羊的进口非常有限，对小反刍动物在畜群之间以及在特定地理区域内的移动有严格的规定。在过去的 50 年中，已经发生了几起疫情，最近一次在 2019 年之前发生在挪威中部特隆德拉格县，时间是 2002 年。自 2003 年以来，挪威一直存在针对小反刍动物慢病毒感染的国家监测计划。
2019 年，国家监测计划在特隆德拉格的一个绵羊群中检测到小反刍动物慢病毒血清阳性动物。根据聚合酶链反应分析和组织病理学发现的结果，挪威食品管理局得出了梅迪病的诊断。进一步的调查在该县的另外 8 个绵羊群中发现了梅迪病。这些羊群被限制活动，当局还对 82 个接触羊群实施了限制。部分 gag 基因测序表明，当前疫情中的病毒与 2002 年至 2005 年在同一地区检测到的小反刍动物慢病毒有关。
疫情调查表明需要敏感和特异的诊断方法，以及改进和更有针对性的监测策略。它还表明了疾病通过动物运动在畜群之间传播的风险，突出了生物安全和结构化牲畜贸易的重要性。除了允许仅从无梅迪病记录的畜群进行牲畜贸易外，在试图从挪威绵羊种群中消除梅迪病时，可能需要多年监测绵羊群。
