Bar-David Shirli, Lloyd-Smith James O, Getz Wayne M
Department of Environmental Science, Policy and Management, University of California, Berkeley 94720-3112, USA.
Ecology. 2006 May;87(5):1215-24. doi: 10.1890/0012-9658(2006)87[1215:damoid]2.0.co;2.
The introduction of chronic, infectious diseases by colonizing populations (invasive or reintroduced) is a serious hazard in conservation biology, threatening the original host and other spillover species. Most research on spatial invasion of diseases has pertained to established host populations, either at steady state or fluctuating through time. Within a colonizing population, however, the spread of disease may be influenced by the expansion process of the population itself. Here we explore the simultaneous expansion of a colonizing population and a chronic, nonlethal disease introduced with it, describing basic patterns in homogeneous and structured landscapes and discussing implications for disease management. We describe expected outcomes of such introductions for three qualitatively distinct cases, depending on the relative velocities at which the population and epidemic expand. (1) If transmissibility is low the disease cannot be sustained, although it may first expand its range somewhat around the point of introduction. (2) If transmissibility is moderate but the wave-front velocity for the population, vp, is higher than that for the disease, vd, the disease wave front lags behind that of the population. (3) A highly transmissible disease, with vd > vp, will invade sufficiently rapidly to track the spread of the host. To test these elementary theoretical predictions, we simulated disease outbreaks in a spatially structured host population occupying a real landscape. We used a spatially explicit, individual-based model of Persian fallow deer (Dama mesopotamica) reintroduced in northern Israel, considering a hypothetical introduction of bovine tuberculosis. Basic patterns of disease expansion in this realistic setting were similar to our conceptual predictions for homogeneous landscapes. Landscape heterogeneity, however, induced the establishment of population activity centers and disease foci within them, leading to jagged wave fronts and causing local variation in the relative velocities at which the population and epidemic expanded. Based on predictions from simple theory and simulations of managed outbreaks, we suggest that the relative velocities at which the population and epidemic expand have important implications for the impact of different management strategies. Recognizing which of our three general cases best describes a particular outbreak will aid in planning an efficient strategy to contain the disease.
殖民种群（入侵或重新引入）带来的慢性传染病对保护生物学而言是严重危害，会威胁到原始宿主及其他溢出物种。大多数关于疾病空间入侵的研究都针对已建立的宿主种群，这些种群要么处于稳定状态，要么随时间波动。然而，在殖民种群中，疾病传播可能受种群自身扩张过程的影响。在此，我们探讨殖民种群及其引入的慢性非致命疾病的同步扩张，描述同质和结构化景观中的基本模式，并讨论对疾病管理的影响。我们针对三种性质不同的情况描述了此类引入的预期结果，这取决于种群和疫情扩张的相对速度。（1）如果传播率较低，疾病无法持续存在，尽管它可能首先在引入点周围有所扩展其范围。（2）如果传播率适中，但种群的波前速度vp高于疾病的波前速度vd，疾病波前会落后于种群波前。（3）一种高传播性疾病，vd > vp，将足够迅速地入侵以追踪宿主的传播。为了检验这些基本理论预测，我们在占据真实景观的空间结构化宿主种群中模拟了疾病爆发。我们使用了一个空间明确的、基于个体的以色列北部重新引入的波斯黇鹿（美索不达米亚黇鹿）模型，考虑了牛结核病的假设引入。在这种现实环境中疾病扩张的基本模式与我们对同质景观的概念预测相似。然而，景观异质性导致了种群活动中心及其内部疾病病灶的形成，导致波前参差不齐，并使种群和疫情扩张的相对速度产生局部变化。基于简单理论的预测和受控爆发的模拟，我们认为种群和疫情扩张的相对速度对不同管理策略的影响具有重要意义。识别我们的三种一般情况中哪一种最能描述特定爆发将有助于规划控制疾病的有效策略。
