Kao Rowland R, Green Darren M, Johnson Jethro, Kiss Istvan Z
Department of Zoology, University of Oxford, Oxford OX1 3PS, UK.
J R Soc Interface. 2007 Oct 22;4(16):907-16. doi: 10.1098/rsif.2007.1129.
We analyse the relationship between the network of livestock movements in the UK and the dynamics of two diseases: foot-and-mouth disease (FMD), which has an incubation period of days, and scrapie, which incubates over years. For FMD, the time-scale of expected epidemics is similar to the time-scale of the evolution of the network. We argue that, under appropriate conditions, a static network analysis can be an appropriate tool for gaining insights into disease dynamics even when the relevant time-scales are similar, as with FMD. We show that a subclass of 'linkage moves' maintains the network structure, and so removing these links has a dramatic effect on the number of potentially infected farms, an effect corroborated by simulations. In contrast, because scrapie has a low probability of transmission per contact and a long incubation period, a static network representation is probably appropriate; however, the signature of the network in the pattern of transmission is likely to be faint. Scrapie-notifying farms were more likely to be associated with each other via trading at markets than were control farms; however, network community structure proves to be less representative of prevalence patterns than geographical region. These contradictory indicators emphasize that appropriate observation time frames and good discrimination among types of potentially infectious contacts are vital in order for network analysis to be a valuable epidemiological tool.
口蹄疫（FMD），其潜伏期为几天；以及羊瘙痒症，其潜伏期长达数年。对于口蹄疫而言，预期疫情的时间尺度与网络演化的时间尺度相似。我们认为，在适当条件下，即使相关时间尺度相似，如口蹄疫的情况，静态网络分析也可以成为洞察疾病动态的合适工具。我们表明，“连锁移动”的一个子类维持了网络结构，因此去除这些链接会对潜在感染农场的数量产生巨大影响，模拟结果证实了这一效果。相比之下，由于羊瘙痒症每次接触的传播概率较低且潜伏期较长，静态网络表示可能是合适的；然而，网络在传播模式中的特征可能很微弱。与对照农场相比，报告羊瘙痒症的农场通过在市场上交易而相互关联的可能性更大；然而，网络社区结构在反映流行模式方面不如地理区域具有代表性。这些相互矛盾的指标强调，为了使网络分析成为有价值的流行病学工具，合适的观察时间框架以及对潜在传染性接触类型的良好区分至关重要。
