Division of Environmental Health Sciences, College of Public Health, The Ohio State University, Columbus, OH, USA.
Department of Anthropology, The Ohio State University, Columbus, OH, USA.
Epidemics. 2019 Sep;28:100334. doi: 10.1016/j.epidem.2019.02.005. Epub 2019 Apr 25.
Foot-and-mouth disease (FMD) affects cloven-hoofed livestock and agricultural economies worldwide. Analyses of the 2001 FMD outbreak in the United Kingdom informed how livestock movement contributed to disease spread. However, livestock reared in other locations use different production systems that might also influence disease dynamics. Here, we investigate a livestock production system known as transhumance, which is the practice of moving livestock between seasonal grazing areas. We built mechanistic models using livestock movement data from the Far North Region of Cameroon. We represented these data as a dynamic network over which we simulated disease transmission and examined three questions. First, we asked what were characteristics of simulated FMDV transmission across a transhumant pastoralist system. Second, we asked how simulated FMDV transmission across a transhumant pastoralist system differed from transmission across this same population held artificially stationary, thereby revealing the effect of movement on disease dynamics. Third, we asked if disease simulations on well-studied theoretical networks are similar to disease simulations on this empirical dynamic network. The results show that the empirical dynamic network was sparsely connected except for an eight-week period in September and October when pastoralists move from rainy season to dry season grazing areas. The mean epidemic size across all 3,744 simulations was 99.9% and the mean epidemic duration was 1.45 years. Disease simulations across the static network showed a smaller mean epidemic size (27.6%) and a similar epidemic duration (1.5 years). Epidemics simulated on theoretical networks showed similar final epidemic sizes (100%) and different mean durations. Our simulations indicate that transhumant livestock systems have the potential to host FMDV outbreaks that affect almost all livestock and last longer than a year. Furthermore, our comparison of empirical and theoretical networks underscores the importance of using empirical data to understand the role of mobility in the transmission of infectious diseases.
口蹄疫（FMD）影响全球有蹄类牲畜和农业经济。对 2001 年英国口蹄疫爆发的分析表明，牲畜流动促进了疾病的传播。然而，在其他地方饲养的牲畜采用不同的生产系统，这些系统也可能影响疾病动态。在这里，我们研究了一种被称为游牧的牲畜生产系统，即牲畜在季节性放牧区之间移动的做法。我们使用喀麦隆北部地区的牲畜流动数据构建了机械模型。我们将这些数据表示为一个动态网络，并在该网络上模拟疾病传播，以回答三个问题。首先，我们询问在游牧牧民系统中模拟 FMDV 传播的特征是什么。其次，我们询问在游牧牧民系统中模拟 FMDV 传播与将同一人群人为固定在同一地点的传播有何不同，从而揭示了运动对疾病动态的影响。第三，我们询问在研究良好的理论网络上进行疾病模拟是否与在这个经验动态网络上进行疾病模拟相似。结果表明，除了 9 月和 10 月牧民从雨季向旱季放牧区转移的 8 周外，经验动态网络的连接稀疏。在所有 3744 次模拟中，平均疫情规模为 99.9%，平均疫情持续时间为 1.45 年。在静态网络上进行的疾病模拟显示出较小的平均疫情规模（27.6%）和相似的疫情持续时间（1.5 年）。在理论网络上进行的疾病模拟显示出相似的最终疫情规模（100%）和不同的平均持续时间。我们的模拟表明，游牧牲畜系统有可能爆发口蹄疫，影响几乎所有牲畜，持续时间超过一年。此外，我们对经验和理论网络的比较强调了使用经验数据来理解流动性在传染病传播中的作用的重要性。
