Palisson Aurore, Courcoul Aurélie, Durand Benoit
University Paris Sud, Orsay, France.
University Paris Est, Anses, Laboratory for Animal Health, Epidemiology Unit, Maisons-Alfort, France.
PLoS One. 2017 Jan 6;12(1):e0169881. doi: 10.1371/journal.pone.0169881. eCollection 2017.
The use of pastures is part of common herd management practices for livestock animals, but contagion between animals located on neighbouring pastures is one of the major modes of infectious disease transmission between herds. At the population level, this transmission is strongly constrained by the spatial organization of pastures. The aim of this study was to answer two questions: (i) is the spatial configuration of pastures favourable to the spread of infectious diseases in France? (ii) would biosecurity measures allow decreasing this vulnerability? Based on GIS data, the spatial organization of pastures was represented using networks. Nodes were the 3,159,787 pastures reported in 2010 by the French breeders to claim the Common Agricultural Policy subsidies. Links connected pastures when the distance between them was below a predefined threshold. Premises networks were obtained by aggregating into a single node all the pastures under the same ownership. Although the pastures network was very fragmented when the distance threshold was short (1.5 meters, relevant for a directly-transmitted disease), it was not the case when the distance threshold was larger (500 m, relevant for a vector-borne disease: 97% of the nodes in the largest connected component). The premises network was highly connected as the largest connected component always included more than 83% of the nodes, whatever the distance threshold. Percolation analyses were performed to model the population-level efficacy of biosecurity measures. Percolation thresholds varied according to the modelled biosecurity measures and to the distance threshold. They were globally high (e.g. >17% of nodes had to be removed, mimicking the confinement of animals inside farm buildings, to obtain the disappearance of the large connected component). The network of pastures thus appeared vulnerable to the spread of diseases in France. Only a large acceptance of biosecurity measures by breeders would allow reducing this structural risk.
牧场的使用是家畜常见畜群管理实践的一部分，但相邻牧场的动物之间的传染是畜群间传染病传播的主要方式之一。在种群层面，这种传播受到牧场空间组织的强烈限制。本研究的目的是回答两个问题：（i）法国牧场的空间配置是否有利于传染病的传播？（ii）生物安全措施能否降低这种脆弱性？基于地理信息系统（GIS）数据，利用网络来表示牧场的空间组织。节点是2010年法国饲养者为申领共同农业政策补贴而上报的3159787个牧场。当两个牧场之间的距离低于预定义阈值时，它们之间就会建立连接。通过将同一所有者名下的所有牧场聚合为一个节点来获得场地网络。当距离阈值较短（1.5米，适用于直接传播的疾病）时，牧场网络非常分散，但当距离阈值较大（500米，适用于媒介传播的疾病：最大连通分量中的97%的节点）时，情况并非如此。无论距离阈值如何，场地网络的连通性都很高，因为最大连通分量始终包含超过83%的节点。进行渗流分析以模拟生物安全措施在种群层面的效果。渗流阈值根据模拟的生物安全措施和距离阈值而变化。它们总体上较高（例如，必须移除超过17%的节点，模拟将动物限制在农场建筑物内，才能使最大连通分量消失）。因此，法国的牧场网络似乎容易受到疾病传播的影响。只有饲养者广泛接受生物安全措施，才有可能降低这种结构风险。
