Data from: Spatial analyses of wildlife contact networks

Datasets from which wildlife contact networks of epidemiological importance can be inferred are becoming increasingly common. A largely unexplored facet of these data is finding evidence of spatial constraints on who has contact with whom, despite theoretical epidemiologists having long realized spatial constraints can play a critical role in infectious disease dynamics. A graph dissimilarity measure is proposed to quantify how close an observed contact network is to being purely spatial whereby its edges are completely determined by the spatial arrangement of its nodes. Statistical techniques are also used to fit a series of mechanistic models for contact rates between individuals to the binary edge data representing presence or absence of observed contact. These are the basis for a second measure that quantifies the extent to which contacts are being mediated by distance. We apply these methods to a set of 128 contact networks of field voles (Microtus agrestis) inferred from mark–recapture data collected over 7 years and from four sites. Large fluctuations in vole abundance allow us to demonstrate that the networks become increasingly similar to spatial proximity graphs as vole density increases. The average number of contacts, Embedded Image, was (i) positively correlated with vole density across the range of observed densities and (ii) for two of the four sites a saturating function of density. The implications for pathogen persistence in wildlife may be that persistence is relatively unaffected by fluctuations in host density because at low density Embedded Image is low but hosts move more freely, and at high density Embedded Image is high but transmission is hampered by local build-up of infected or recovered animals.

可用于推断具有流行病学重要性的野生动物接触网络的数据集正日益常见。尽管理论流行病学家早已意识到空间约束在传染病传播动态中可发挥关键作用，但此类数据中一个尚未被充分探索的方向，是探寻个体间接触存在空间约束的相关证据。本研究提出一种图相似度度量方法，用以量化某一观测接触网络与纯空间接触网络的接近程度——后者的边完全由其节点的空间排布所决定。同时，研究人员采用统计技术，针对个体间接触率构建系列机制模型，并将其拟合至代表观测接触存在与否的二元边数据。基于这些模型，我们可构建第二种度量指标，用以量化接触关系在多大程度上受距离介导。我们将上述方法应用于128组田鼠（Microtus agrestis）接触网络数据集，这些网络均基于7年间采集的4个研究位点的标记重捕数据推断得到。田鼠种群丰度的大幅波动，使得我们得以证明：随着田鼠种群密度升高，接触网络与空间邻近图的相似度也随之提升。平均接触次数（嵌入式图像）呈现出两项特征：(i) 在所有观测密度范围内均与田鼠种群密度呈正相关；(ii) 在4个研究位点中的2个位点上，其与种群密度的关系符合饱和函数形式。该研究结果对于野生动物体内病原体的持续存在具有如下启示：病原体的持续存活相对不受宿主种群密度波动的影响——因为在低密度条件下，平均接触次数较低，但宿主活动更为自由；而在高密度条件下，平均接触次数较高，但受感染或已康复个体的局部聚集会阻碍病原体传播。