Department of Forestry & Environmental Resources, North Carolina State University, Raleigh, North Carolina, 27695, USA.
Center for Geospatial Analytics, North Carolina State University, Raleigh, North Carolina, 27695, USA.
Ecology. 2019 May;100(5):e02686. doi: 10.1002/ecy.2686.
Disease dynamics are governed by variation of individuals, species, and environmental conditions across space and time. In some cases, an alternate reservoir host amplifies pathogen loads and drives disease transmission to less competent hosts in a process called pathogen spillover. Spillover is frequently associated with multi-host disease systems where a single species is more tolerant of infection and more competent in pathogen transmission compared to other hosts. Pathogen spillover must be driven by biotic factors, including host and community characteristics, yet biotic factors interact with the abiotic environment (e.g., temperature) to create disease. Despite its fundamental role in disease dynamics, the influence of the abiotic environment on pathogen spillover has seldom been examined. Improving our understanding of disease processes such as pathogen spillover hinges on disentangling the effects of interrelated biotic and abiotic factors over space and time. We applied 10 yr of fine-scale microclimate, disease, and tree community data in a path analysis to investigate the relative influence of biotic and abiotic factors on pathogen spillover for the emerging infectious forest disease sudden oak death (SOD). Disease transmission in SOD is primarily driven by the reservoir host California bay laurel, which supports high foliar pathogen loads that spillover onto neighboring oak trees and create lethal canker infections. The foliar pathogen load and susceptibility of oaks is expected to be sensitive to forest microclimate conditions. We found that biotic factors of pathogen load and tree diversity had relatively stronger effects on pathogen spillover compared to abiotic microclimate factors, with pathogen load increasing oak infection and tree diversity reducing oak infection. Abiotic factors still had significant effects, with greater heat exposure during summer months reducing pathogen loads and optimal pathogen conditions during the wet season increasing oak infection. Our results offer clues to possible disease dynamics under future climate change where hotter and drier or warmer and wetter conditions could have opposing effects on pathogen spillover in the SOD system. Disentangling direct and indirect effects of biotic and abiotic factors affecting disease processes can provide key insights into disease dynamics including potential avenues for reducing disease spread and predicting future epidemics.
疾病动态受个体、物种和环境条件在空间和时间上的变化所支配。在某些情况下，替代储主会放大病原体负荷，并将疾病传播给能力较弱的宿主，这一过程称为病原体溢出。病原体溢出通常与多宿主疾病系统有关，在这种系统中，与其他宿主相比，单一物种对感染的容忍度更高，在病原体传播方面的能力更强。病原体溢出必须由生物因素驱动，包括宿主和群落特征，但生物因素与非生物环境（例如温度）相互作用，从而引发疾病。尽管它在疾病动态中起着根本性的作用，但非生物环境对病原体溢出的影响很少受到关注。要提高我们对病原体溢出等疾病过程的理解，关键在于要理清相关生物和非生物因素在空间和时间上的影响。我们应用了 10 年的微观气候、疾病和树木群落数据，通过路径分析来研究生物和非生物因素对新兴传染病森林疾病突发橡树死亡（SOD）病原体溢出的相对影响。SOD 中的疾病传播主要由储主加利福尼亚湾月桂树驱动，该树支持高叶片病原体负荷，这些病原体溢出到邻近的橡树并产生致命的溃疡感染。叶片病原体负荷和橡树的易感性预计对森林小气候条件敏感。我们发现，与非生物小气候因素相比，病原体负荷和树木多样性等生物因素对病原体溢出的影响相对更强，病原体负荷增加了橡树的感染，而树木多样性降低了橡树的感染。非生物因素仍有显著影响，夏季暴露在更多热量下会降低病原体负荷，而雨季的最佳病原体条件会增加橡树的感染。我们的研究结果为未来气候变化下可能的疾病动态提供了线索，在未来气候变化下，更热更干燥或更温暖更湿润的条件可能会对 SOD 系统中的病原体溢出产生相反的影响。厘清影响疾病过程的生物和非生物因素的直接和间接影响，可以为疾病动态提供关键见解，包括减少疾病传播和预测未来流行的潜在途径。
