Sergeant E S G, Nielsen S S, Toft N
International EpiLab, The National Veterinary Institute, Danish Technical University, Bülowsvej 27, 1790 Copenhagen V, Denmark.
Prev Vet Med. 2008 Jun 15;85(1-2):92-106. doi: 10.1016/j.prevetmed.2008.01.005. Epub 2008 Mar 11.
Paratuberculosis is a chronic infection affecting cattle and other ruminants. In the dairy industry, losses due to paratuberculosis can be substantial in infected herds and several countries have implemented national programmes based on herd-classification to manage the disease. The aim of this study was to develop a method to estimate the probability of low within-herd prevalence of paratuberculosis for Danish dairy herds. A stochastic simulation model was developed using the R programming environment. Features of this model included: use of age-specific estimates of test-sensitivity and specificity; use of a distribution of observed values (rather than a fixed, low value) for design prevalence; and estimates of the probability of low prevalence (PrLow) based on a specific number of test-positive animals, rather than for a result less than or equal to a specified cut-point number of reactors. Using this model, five herd-testing strategies were evaluated: (1) milk-ELISA on all lactating cows; (2) milk-ELISA on lactating cows<or=4 years old; (3) milk-ELISA on lactating cows>4 years old; (4) faecal culture on all lactating cows; and (5) milk-ELISA plus faecal culture in series on all lactating cows. The five testing strategies were evaluated using observed milk-ELISA results from 19 Danish dairy herds as well as for simulated results from the same herds assuming that they were uninfected. Whole-herd milk-ELISA was the preferred strategy, and considered the most cost-effective strategy of the five alternatives. The five strategies were all efficient in detecting infection, i.e. estimating a low PrLow in infected herds, however, PrLow estimates for milk-ELISA on age-cohorts were too low in simulated uninfected herds and the strategies involving faecal culture were too expensive to be of practical interest. For simulated uninfected herds, whole-herd milk-ELISA resulted in median PrLow values>0.9 for most herds, depending on herd size and age-structure. None of the strategies provided enough power to establish a high PrLow in smaller herds, or herds with a younger age-structure. Despite this, it appears as if the method is a useful approach for herd-classification for most herds in the Danish dairy industry.
副结核病是一种影响牛和其他反刍动物的慢性感染病。在乳制品行业，受副结核病影响的牛群会遭受巨大损失，一些国家已实施基于牛群分类的国家计划来管理该疾病。本研究的目的是开发一种方法，用于估计丹麦奶牛群中副结核病群体内低流行率的概率。使用R编程环境开发了一个随机模拟模型。该模型的特点包括：使用特定年龄的检测灵敏度和特异性估计值；使用观察值的分布（而非固定的低值）作为设计流行率；基于特定数量的检测呈阳性动物估计低流行率的概率（PrLow），而非针对小于或等于指定临界值数量的反应动物的结果。使用该模型，评估了五种牛群检测策略：（1）对所有泌乳奶牛进行牛奶ELISA检测；（2）对年龄≤4岁的泌乳奶牛进行牛奶ELISA检测；（3）对年龄>4岁的泌乳奶牛进行牛奶ELISA检测；（4）对所有泌乳奶牛进行粪便培养；（5）对所有泌乳奶牛依次进行牛奶ELISA检测和粪便培养。使用来自19个丹麦奶牛群的观察到的牛奶ELISA结果以及假设这些牛群未感染时相同牛群的模拟结果，对这五种检测策略进行了评估。全群牛奶ELISA检测是首选策略，并且被认为是这五种方案中最具成本效益的策略。这五种策略在检测感染方面都很有效，即在感染牛群中估计低PrLow，但在模拟的未感染牛群中，按年龄队列进行牛奶ELISA检测的PrLow估计值过低，且涉及粪便培养的策略成本过高，不具有实际意义。对于模拟的未感染牛群，全群牛奶ELISA检测在大多数牛群中导致的PrLow中值>0.9，这取决于牛群规模和年龄结构。没有一种策略有足够的能力在较小的牛群或年龄结构较年轻的牛群中建立高PrLow。尽管如此，对于丹麦乳制品行业的大多数牛群来说，该方法似乎是一种用于牛群分类的有用方法。
