Hall Richard J, Altizer Sonia, Bartel Rebecca A
Odum School of Ecology, University of Georgia, Athens, GA, 30602, USA.
Department of Infectious Diseases, University of Georgia, Athens, GA, 30602, USA.
J Anim Ecol. 2014 Sep;83(5):1068-77. doi: 10.1111/1365-2656.12204. Epub 2014 Mar 6.
Animal migrations are spectacular and migratory species have been shown to transmit pathogens that pose risks to human health. Although migration is commonly assumed to enhance pathogen dispersal, empirical work indicates that migration can often have the opposite effect of lowering disease risk. Key to assessing disease threats to migratory species is the ability to predict how migratory behaviour influences pathogen invasion success and impacts on migratory hosts, thus motivating a mechanistic understanding of migratory host-pathogen interactions. Here, we develop a quantitative framework to examine pathogen transmission in animals that undergo two-way directed migrations between wintering and breeding grounds annually. Using the case of a pathogen transmitted during the host's breeding season, we show that a more extreme migratory strategy (defined by the time spent away from the breeding site and the total distance migrated) lowers the probability of pathogen invasion. Moreover, if migration substantially lowers the survival probability of infected animals, then populations that spend comparatively less time at the breeding site or that migrate longer distances are less vulnerable to pathogen-induced population declines. These findings provide theoretical support for two non-exclusive mechanisms proposed to explain how seasonal migration can lower infection risk: (i) escape from habitats where parasite transmission stages have accumulated and (ii) selective removal of infected hosts during strenuous journeys. Our work further suggests that barriers to long-distance movement could increase pathogen prevalence for vulnerable species, an effect already seen in some animal species undergoing anthropogenically induced migratory shifts.
动物迁徙蔚为壮观，且已证明迁徙物种会传播对人类健康构成风险的病原体。尽管人们通常认为迁徙会促进病原体传播，但实证研究表明，迁徙往往会产生降低疾病风险的相反效果。评估对迁徙物种的疾病威胁的关键在于能够预测迁徙行为如何影响病原体入侵成功以及对迁徙宿主的影响，从而激发对迁徙宿主与病原体相互作用的机制性理解。在此，我们建立了一个定量框架，以研究每年在越冬地和繁殖地之间进行双向定向迁徙的动物中的病原体传播。以宿主繁殖季节传播的一种病原体为例，我们表明，一种更为极端的迁徙策略（由离开繁殖地的时间和迁徙的总距离定义）会降低病原体入侵的概率。此外，如果迁徙大幅降低了受感染动物的生存概率，那么在繁殖地停留时间相对较短或迁徙距离较长的种群就不太容易受到病原体导致的种群数量下降的影响。这些发现为提出的两种非排他性机制提供了理论支持，这两种机制用以解释季节性迁徙如何降低感染风险：（i）逃离寄生虫传播阶段已经积累的栖息地；（ii）在艰苦旅程中选择性清除受感染宿主。我们的研究还表明，长途迁徙障碍可能会增加脆弱物种的病原体流行率，这种影响在一些经历人为诱导迁徙变化的动物物种中已经有所体现。
