Prentice Jamie C, Marion Glenn, White Piran C L, Davidson Ross S, Hutchings Michael R
Disease Systems Team, SRUC, Edinburgh, United Kingdom; Biomathematics and Statistics Scotland, Edinburgh, United Kingdom; Environment Department, University of York, York, United Kingdom.
Biomathematics and Statistics Scotland, Edinburgh, United Kingdom.
PLoS One. 2014 May 2;9(5):e86563. doi: 10.1371/journal.pone.0086563. eCollection 2014.
Population reduction is often used as a control strategy when managing infectious diseases in wildlife populations in order to reduce host density below a critical threshold. However, population reduction can disrupt existing social and demographic structures leading to changes in observed host behaviour that may result in enhanced disease transmission. Such effects have been observed in several disease systems, notably badgers and bovine tuberculosis. Here we characterise the fundamental properties of disease systems for which such effects undermine the disease control benefits of population reduction. By quantifying the size of response to population reduction in terms of enhanced transmission within a generic non-spatial model, the properties of disease systems in which such effects reduce or even reverse the disease control benefits of population reduction are identified. If population reduction is not sufficiently severe, then enhanced transmission can lead to the counter intuitive perturbation effect, whereby disease levels increase or persist where they would otherwise die out. Perturbation effects are largest for systems with low levels of disease, e.g. low levels of endemicity or emerging disease. Analysis of a stochastic spatial meta-population model of demography and disease dynamics leads to qualitatively similar conclusions. Moreover, enhanced transmission itself is found to arise as an emergent property of density dependent dispersal in such systems. This spatial analysis also shows that, below some threshold, population reduction can rapidly increase the area affected by disease, potentially expanding risks to sympatric species. Our results suggest that the impact of population reduction on social and demographic structures is likely to undermine disease control in many systems, and in severe cases leads to the perturbation effect. Social and demographic mechanisms that enhance transmission following population reduction should therefore be routinely considered when designing control programmes.
在管理野生动物种群中的传染病时，种群减少常被用作一种控制策略，目的是将宿主密度降低到临界阈值以下。然而，种群减少可能会扰乱现有的社会和人口结构，导致观察到的宿主行为发生变化，进而可能增加疾病传播。这种影响在一些疾病系统中已被观察到，尤其是獾和牛结核病。在此，我们描述了这类影响会削弱种群减少对疾病控制益处的疾病系统的基本特性。通过在一个通用的非空间模型中，根据增强的传播来量化对种群减少的反应大小，确定了这类影响会降低甚至逆转种群减少对疾病控制益处的疾病系统的特性。如果种群减少不够严重，那么增强的传播可能会导致违反直觉的扰动效应，即疾病水平在原本会灭绝的情况下反而增加或持续存在。对于疾病水平较低的系统，如低流行程度或新出现疾病的系统，扰动效应最大。对一个人口统计学和疾病动态的随机空间集合种群模型的分析得出了定性相似的结论。此外，增强的传播本身被发现是这类系统中密度依赖性扩散的一种涌现特性。这种空间分析还表明，在某个阈值以下，种群减少会迅速增加受疾病影响的面积，可能扩大对同域物种的风险。我们的结果表明，种群减少对社会和人口结构的影响可能会在许多系统中破坏疾病控制，在严重情况下会导致扰动效应。因此，在设计控制方案时，应常规考虑种群减少后会增强传播的社会和人口机制。
