McLaughlin Centre for Population Health Risk Assessment, University of Ottawa, Ottawa, Ontario, Canada.
J Theor Biol. 2014 Jan 7;340:50-9. doi: 10.1016/j.jtbi.2013.09.003. Epub 2013 Sep 10.
Behavior and habitat of wildlife animals change seasonally according to environmental conditions. Mathematical models need to represent this seasonality to be able to make realistic predictions about the future of a population and the effectiveness of human interventions. Managing and modeling disease in wild animal populations requires particular care in that disease transmission dynamics is a critical consideration in the etiology of both human and animal diseases, with different transmission paradigms requiring different disease risk management strategies. Since transmission of infectious diseases among wildlife depends strongly on social behavior, mechanisms of disease transmission could also change seasonally. A specific consideration in this regard confronted by modellers is whether the contact rate between individuals is density-dependent or frequency-dependent. We argue that seasonal behavior changes could lead to a seasonal shift between density and frequency dependence. This hypothesis is explored in the case of chronic wasting disease (CWD), a fatal disease that affects deer, elk and moose in many areas of North America. Specifically, we introduce a strategic CWD risk model based on direct disease transmission that accounts for the seasonal change in the transmission dynamics and habitats occupied, guided by information derived from cervid ecology. The model is composed of summer and winter susceptible-infected (SI) equations, with frequency-dependent and density-dependent transmission dynamics, respectively. The model includes impulsive birth events with density-dependent birth rate. We determine the basic reproduction number as a weighted average of two seasonal reproduction numbers. We parameterize the model from data derived from the scientific literature on CWD and deer ecology, and conduct global and local sensitivity analyses of the basic reproduction number. We explore the effectiveness of different culling strategies for the management of CWD: although summer culling seems to be an effective disease eradication strategy, the total culling rate is limited by the requirement to preserve the herd.
野生动物的行为和栖息地会根据环境条件季节性变化。数学模型需要能够代表这种季节性，以便能够对种群的未来和人类干预的效果做出现实的预测。在管理和建模野生动物种群疾病时，需要特别注意，因为疾病传播动力学是人类和动物疾病病因学的关键考虑因素，不同的传播范式需要不同的疾病风险管理策略。由于传染病在野生动物中的传播强烈依赖于社会行为，因此疾病传播机制也可能季节性变化。建模者在这方面特别需要考虑的是，个体之间的接触率是密度依赖的还是频率依赖的。我们认为，季节性行为变化可能导致密度和频率依赖性之间的季节性转变。在慢性消耗性疾病（CWD）的情况下，探讨了这种假设，CWD 是一种致命疾病，影响北美许多地区的鹿、麋鹿和驼鹿。具体来说，我们引入了一种基于直接疾病传播的战略性 CWD 风险模型，该模型考虑了传播动力学和栖息地占用的季节性变化，这些变化是根据鹿生态学获得的信息得出的。该模型由夏季和冬季易感感染（SI）方程组成，分别具有频率依赖性和密度依赖性的传播动力学。该模型包括具有密度依赖性出生率的脉冲出生事件。我们将基本繁殖数确定为两个季节性繁殖数的加权平均值。我们从 CWD 和鹿生态学的科学文献中获取的数据对模型进行参数化，并对基本繁殖数进行全局和局部敏感性分析。我们探讨了不同的扑杀策略在 CWD 管理中的有效性：尽管夏季扑杀似乎是一种有效的疾病根除策略，但总扑杀率受到保护畜群的要求的限制。
