Hopp Petter, Webb Cerian R, Jarp Jorun
Section of Epidemiology, National Veterinary Institute, PO Box 8156 Dep, NO-0033 Oslo, Norway.
Prev Vet Med. 2003 Oct 15;61(2):103-25. doi: 10.1016/s0167-5877(03)00192-2.
Our aim was to compare the efficiency of different surveillance strategies for detecting scrapie-infected sheep flocks in the Norwegian population using simulation modelling. The dynamic Monte Carlo simulation model has the flock as the unit. The input parameters include properties of the sheep population (number of flocks, flock size, age distribution, reasons for culling, breeds, prion protein-allele distribution); properties of scrapie (genotype-dependent infection rate and incubation periods, and age- and genotype-dependent prevalence of scrapie); properties of the surveillance strategy (selection of sheep for examination, period in which infected sheep are detectable, and properties of the diagnostic tests). For simplification, the prion protein-alleles were grouped into three allele groups: VRQ, ARR, and ARQ' (ARQ' represents ARQ, ARH and AHQ). Through either abattoir surveillance or surveillance of fallen stock, <or=9% of scrapie flocks were detected. The necessary sample size for detecting any particular number of scrapie flocks was considerably lower using surveillance of fallen stock than abattoir surveillance. After increasing the diagnostic method's sensitivity, only the efficiency of abattoir surveillance increased. The prion protein-genotypes ARQ'/ARQ', VRQ/ARQ' and VRQ/VRQ were overrepresented both in the sampled infected sheep and in the detected sheep. Sheep with ARQ'/ARQ' constituted >70% of the detected sheep (compared to 33% in the underlying population). The model output was sensitive to the susceptibility of infection for the genotype ARQ'/ARQ'. The effect was large for abattoir surveillance (increased susceptibility increased the efficiency of abattoir surveillance).
我们的目标是通过模拟建模比较不同监测策略在挪威绵羊群体中检测痒病感染羊群的效率。动态蒙特卡洛模拟模型以羊群为单位。输入参数包括绵羊群体的属性（羊群数量、羊群规模、年龄分布、淘汰原因、品种、朊病毒蛋白等位基因分布）；痒病的属性（基因型依赖性感染率和潜伏期，以及年龄和基因型依赖性痒病患病率）；监测策略的属性（用于检查的绵羊选择、可检测到感染绵羊的时间段以及诊断测试的属性）。为简化起见，朊病毒蛋白等位基因被分为三个等位基因组：VRQ、ARR和ARQ'（ARQ'代表ARQ、ARH和AHQ）。通过屠宰场监测或死亡牲畜监测，检测到的痒病感染羊群占比≤9%。使用死亡牲畜监测检测任何特定数量痒病感染羊群所需的样本量比屠宰场监测要低得多。提高诊断方法的灵敏度后，只有屠宰场监测的效率提高了。朊病毒蛋白基因型ARQ'/ARQ'、VRQ/ARQ'和VRQ/VRQ在采样的感染绵羊和检测到的绵羊中均占比过高。ARQ'/ARQ'基因型的绵羊占检测到绵羊的70%以上（相比之下，在基础群体中占33%）。模型输出对ARQ'/ARQ'基因型的感染易感性敏感。对屠宰场监测影响较大（感染易感性增加会提高屠宰场监测的效率）。
