IFM Theory and Modelling, Linköping University, 581 83 Linköping, Sweden.
Prev Vet Med. 2011 Mar 1;98(4):230-42. doi: 10.1016/j.prevetmed.2010.11.005. Epub 2010 Dec 21.
A method to assess the influence of between herd distances, production types and herd sizes on patterns of between herd contacts is presented. It was applied on pig movement data from a central database of the Swedish Board of Agriculture. To determine the influence of these factors on the contact between holdings we used a Bayesian model and Markov chain Monte Carlo (MCMC) methods to estimate the posterior distribution of model parameters. The analysis showed that the contact pattern via animal movements is highly heterogeneous and influenced by all three factors, production type, herd size, and distance between holdings. Most production types showed a positive relationship between maximum capacity and the probability of both incoming and outgoing movements. In agreement with previous studies, holdings also differed in both the number of contacts as well as with what holding types contact occurred with. Also, the scale and shape of distance dependence in contact probability was shown to differ depending on the production types of holdings.To demonstrate how the methodology may be used for risk assessment, disease transmissions via animal movements were simulated with the model used for analysis of contacts, and parameterized by the analyzed posterior distribution. A Generalized Linear Model showed that herds with production types Sow pool center, Multiplying herd and Nucleus herd have higher risk of generating a large number of new infections. Multiplying herds are also expected to generate many long distance transmissions, while transmissions generated by Sow pool centers are confined to more local areas. We argue that the methodology presented may be a useful tool for improvement of risk assessment based on data found in central databases.
提出了一种评估畜群间距离、生产类型和畜群规模对畜群间接触模式影响的方法。该方法应用于瑞典农业委员会中央数据库中的猪运动数据。为了确定这些因素对养殖场之间接触的影响，我们使用了贝叶斯模型和马尔可夫链蒙特卡罗（MCMC）方法来估计模型参数的后验分布。分析表明，通过动物运动进行的接触模式高度异质，并受到生产类型、畜群规模和畜群间距离这三个因素的影响。大多数生产类型的最大容量与传入和传出运动的概率之间呈正相关关系。与之前的研究一致，养殖场在接触次数以及与哪些养殖场接触方面也存在差异。此外，接触概率的距离依赖性的规模和形状也被证明取决于养殖场的生产类型。为了展示该方法如何用于风险评估，使用用于分析接触的模型模拟了通过动物运动传播的疾病，并通过分析的后验分布进行参数化。广义线性模型表明，具有母猪集中饲养场、繁殖群和核心群生产类型的畜群产生大量新感染的风险更高。繁殖群也有望产生许多长距离传播，而母猪集中饲养场产生的传播则局限于更局部的区域。我们认为，所提出的方法可以成为基于中央数据库中发现的数据进行风险评估改进的有用工具。
