Qviller Lars, Kristoffersen Anja B, Lyngstad Trude M, Lillehaug Atle
Norwegian Veterinary Institute, Oslo, Norway.
Front Vet Sci. 2020 Jan 15;6:481. doi: 10.3389/fvets.2019.00481. eCollection 2019.
Infectious salmon anemia (ISA) is an infectious disease, and outbreaks must be handled to avoid spread between salmon sea farms. Intensive culling at infected farms is an important biosecurity measure to avoid further spread but is also a costly intervention that farmers try to avoid. A lack of action, however, may lead to new outbreaks in nearby salmon sea farms, with severe impacts on both economy and animal welfare. Here, we aim to explore how a time delay between a detected outbreak and the culling of both infected cages and entire farms affects the further spread of the disease. We use a previously published model to calculate how many salmon sea farms were directly infected in each outbreak. To investigate the effect of culling on the further spread of disease, we use the number of months elapsed from the detected outbreak to (a) the first cage being depopulated, and (b) to the entire salmon sea farm being depopulated as predictors of how many new farms the virus was transmitted to, after controlling for contact between the farms. We show that the lapse in time before the first cage is depopulated correlates positively with how many new salmon sea farms are infected, indicating that infected cages should be culled with as little time delay as possible. The model does not have sufficient power to separate between culling of only cages assumed to be infected and the entire farm, and, consequently, provides no direct empirical evidence for the latter. Lack of evidence is not evidence, however, and we argue that a high probability of spread between cages in infected salmon sea farms still supports the depopulation of entire farms as the safest option.
传染性鲑鱼贫血症（ISA）是一种传染病，必须对疫情爆发进行处理，以避免在鲑鱼养殖场之间传播。在受感染的养殖场进行密集扑杀是一项重要的生物安全措施，可避免疫情进一步扩散，但这也是一项成本高昂的干预措施，养殖户试图避免。然而，不采取行动可能会导致附近的鲑鱼养殖场出现新的疫情，对经济和动物福利都产生严重影响。在此，我们旨在探讨从检测到疫情爆发到扑杀受感染网箱和整个养殖场之间的时间延迟如何影响疾病的进一步传播。我们使用先前发表的模型来计算每次疫情爆发中直接受感染的鲑鱼养殖场数量。为了研究扑杀对疾病进一步传播的影响，我们将从检测到疫情爆发到（a）第一个网箱清空，以及（b）整个鲑鱼养殖场清空所经过的月数作为预测指标，来预测在控制养殖场之间的接触后，病毒传播到了多少新的养殖场。我们表明，第一个网箱清空之前的时间间隔与新感染的鲑鱼养殖场数量呈正相关，这表明应尽可能少地延迟对受感染网箱进行扑杀。该模型没有足够的能力区分仅对假定受感染的网箱进行扑杀和对整个养殖场进行扑杀，因此，没有为后者提供直接的实证证据。然而，缺乏证据并不等同于没有证据，我们认为，受感染的鲑鱼养殖场中网箱之间传播的高可能性仍然支持将整个养殖场清空作为最安全的选择。
