Manlove Kezia R, Cassirer E Frances, Plowright Raina K, Cross Paul C, Hudson Peter J
Department of Biology, Center for Infectious Disease Dynamics, Pennsylvania State University, 208 Mueller Labs, University Park, PA, 16802, USA.
Idaho Department of Fish and Game, 3316 16th St., Lewiston, ID, 83501, USA.
J Anim Ecol. 2017 Jul;86(4):908-920. doi: 10.1111/1365-2656.12664. Epub 2017 May 2.
Understanding both contact and probability of transmission given contact are key to managing wildlife disease. However, wildlife disease research tends to focus on contact heterogeneity, in part because the probability of transmission given contact is notoriously difficult to measure. Here, we present a first step towards empirically investigating the probability of transmission given contact in free-ranging wildlife. We used measured contact networks to test whether bighorn sheep demographic states vary systematically in infectiousness or susceptibility to Mycoplasma ovipneumoniae, an agent responsible for bighorn sheep pneumonia. We built covariates using contact network metrics, demographic information and infection status, and used logistic regression to relate those covariates to lamb survival. The covariate set contained degree, a classic network metric describing node centrality, but also included covariates breaking the network metrics into subsets that differentiated between contacts with yearlings, ewes with lambs, and ewes without lambs, and animals with and without active infections. Yearlings, ewes with lambs, and ewes without lambs showed similar group membership patterns, but direct interactions involving touch occurred at a rate two orders of magnitude higher between lambs and reproductive ewes than between any classes of adults or yearlings, and one order of magnitude higher than direct interactions between multiple lambs. Although yearlings and non-reproductive bighorn ewes regularly carried M. ovipneumoniae, our models suggest that a contact with an infected reproductive ewe had approximately five times the odds of producing a lamb mortality event of an identical contact with an infected dry ewe or yearling. Consequently, management actions targeting infected animals might lead to unnecessary removal of young animals that carry pathogens but rarely transmit. This analysis demonstrates a simple logistic regression approach for testing a priori hypotheses about variation in the odds of transmission given contact for free-ranging hosts, and may be broadly applicable for investigations in wildlife disease ecology.
了解接触情况以及接触后的传播概率是管理野生动物疾病的关键。然而，野生动物疾病研究往往侧重于接触的异质性，部分原因是接触后的传播概率极难测量。在此，我们朝着实证研究自由放养野生动物接触后的传播概率迈出了第一步。我们利用实测的接触网络来测试大角羊的种群状态在感染传染性肺炎支原体（一种导致大角羊肺炎的病原体）方面是否存在系统性差异，或者对其易感性是否存在系统性差异。我们使用接触网络指标、种群信息和感染状况构建协变量，并使用逻辑回归将这些协变量与羔羊存活情况相关联。协变量集包含度（一种描述节点中心性的经典网络指标），但也包括将网络指标分解为不同子集的协变量，这些子集区分了与一岁羊、带羔羊的母羊、不带羔羊的母羊以及有和没有活跃感染的动物之间的接触。一岁羊、带羔羊的母羊和不带羔羊的母羊表现出相似的群体成员模式，但涉及触摸的直接互动在羔羊与繁殖期母羊之间发生的频率比任何成年羊或一岁羊类别之间高两个数量级，比多只羔羊之间的直接互动高一个数量级。尽管一岁羊和非繁殖期大角羊母羊经常携带肺炎支原体，但我们的模型表明，与感染的繁殖期母羊接触导致羔羊死亡事件的几率大约是与感染的空怀母羊或一岁羊进行相同接触的五倍。因此，针对感染动物的管理行动可能会导致不必要地移除携带病原体但很少传播的幼畜。该分析展示了一种简单的逻辑回归方法，用于检验关于自由放养宿主接触后传播几率变化的先验假设，并且可能广泛适用于野生动物疾病生态学的研究。
