Ausvet, Bruce, 2617, Australia.
UCD School of Veterinary Medicine, University College Dublin, Belfield, Dublin, D04 W6F6, Ireland.
J Dairy Sci. 2019 Mar;102(3):2427-2442. doi: 10.3168/jds.2018-14883. Epub 2019 Jan 11.
In light of the various adverse effects of Johne's disease on animal productivity and the debate on the role of its causative organism, Mycobacterium avium ssp. paratuberculosis, in the etiology of Crohn's disease, major dairy-producing countries around the world have implemented national control programs aimed at reducing the prevalence of this infection in cattle. A pilot control program was initiated in Ireland in 2013, with a key objective to provide farmers with test-negative dairy herds with tools and knowledge to increase their confidence of freedom over time. The aim of this study was to estimate the confidence of freedom obtained in test-negative Irish dairy herds over time with various sampling scenarios and to evaluate the cost-effectiveness of alternative scenarios for achieving an acceptable level of confidence of freedom in herds with no evidence of infection. A stochastic model was developed to simulate repeated annual testing of individual animals using ELISA and confirmatory assays over a period of 20 yr. Two scenarios modeled the current herd-screening options, whereas 14 alternative scenarios explored the effect of varying parameters from the current testing strategies, such as the frequency of testing, the eligibility criteria for selecting animals, the type of assay, the probability of introduction, and the assay sensitivity. Results showed that the current testing strategy with milk twice a year or serum once a year in all animals over 2 yr old provided the highest annual herd sensitivity, with a median value of 55%. Although the median confidence of freedom increased over time for all scenarios, the time required to reach 90 and 95% confidence of freedom was highly variable between scenarios. Under the testing scenario where serum tests were used once a year, the confidence of freedom reached 90% after 4 yr and 95% after 7 yr of testing. Some of the alternative scenarios achieved an acceptable level of confidence of freedom in a reasonable timeframe and at lesser cost than the current testing strategies. The results of this work are used to provide recommendations for the next phases of the program.
鉴于约翰氏病对动物生产力的各种不利影响，以及其病原体分枝杆菌副结核亚种在克罗恩病病因学中的作用存在争议，世界上主要的奶牛生产国已实施国家控制计划，旨在降低牛群中这种感染的流行率。爱尔兰于 2013 年启动了一项试点控制计划，其主要目标是为农民提供无感染奶牛群的阴性检测工具和知识，以随着时间的推移增加他们对无感染的信心。本研究旨在估计随着时间的推移，不同抽样方案下爱尔兰阴性检测奶牛群获得的信心，并评估实现无感染牛群可接受信心水平的替代方案的成本效益。开发了一个随机模型，以在 20 年内使用 ELISA 和确认试验对个体动物进行年度重复测试。两个方案模拟了当前的群体筛选方案，而 14 个替代方案则探讨了改变当前测试策略的各种参数的效果，例如测试频率、选择动物的资格标准、检测类型、引入概率和检测灵敏度。结果表明，目前的检测策略是每年两次对所有 2 岁以上的奶牛进行牛奶检测，每年一次对所有动物进行血清检测，可提供最高的年度群体敏感性，中位数为 55%。尽管所有方案的信心中位数随着时间的推移而增加，但达到 90%和 95%信心所需的时间在方案之间差异很大。在每年一次进行血清检测的检测方案中，经过 4 年和 7 年的检测，信心中位数分别达到 90%和 95%。一些替代方案在合理的时间内以较低的成本实现了可接受的信心水平。该研究的结果用于为该计划的下一阶段提供建议。
