Department of Environmental Health, Rollins School of Public Health, Emory University, 1518 Clifton Rd. NE, Atlanta, GA 30322, USA.
Epidemics. 2009 Dec;1(4):213-20. doi: 10.1016/j.epidem.2009.10.001.
The environmental determinants of vector- and host-borne diseases include time-varying components that modify key transmission parameters, resulting in transient couplings between environmental phenomena and transmission processes. While some time-varying drivers are periodic in nature, some are aperiodic, such as those that involve episodic events or complex patterns of human behavior. Understanding these couplings can allow for prediction of periods of peak infection risk, and ultimately presents opportunities for optimizing intervention selection and timing. Schistosome macroparasites of humans exhibit multiple free-living stages as well as intermediate hosts, and are thus model organisms for illustrating the influence of environmental forcing on transmission. Time-varying environmental factors, termed gating functions, for schistosomes include larval response to temperature and rainfall, seasonal water contact patterns and snail population dynamics driven by weather variables. The biological bases for these modifiers are reviewed, and their values are estimated and incorporated into a transmission model that simulates a multi-year period in two schistosomiasis endemic regions. Modeling results combined with a scale dependent correlation analysis indicate the end effect of these site-specific gating functions is to strongly govern worm burden in these communities, in a manner particularly sensitive to the hydrological differences between sites. Two classes of gating functions were identified, those that act in concert to modify human infection (and determine worm acquisition late in the season), and those that act on snail infection (and determine early season worm acquisition). The importance of these factors for control programs and surveillance is discussed.
媒介传播和宿主传播疾病的环境决定因素包括随时间变化的成分，这些成分改变了关键的传播参数，导致环境现象和传播过程之间存在瞬时耦合。虽然有些随时间变化的驱动因素是周期性的，但有些是无周期性的，例如涉及偶发事件或人类行为复杂模式的驱动因素。了解这些耦合关系可以预测感染风险的高峰期，并为优化干预措施的选择和时机提供机会。人类的血吸虫大型寄生虫具有多个自由生活阶段和中间宿主，因此是说明环境胁迫对传播影响的模型生物。血吸虫的随时间变化的环境因素，称为门控函数，包括幼虫对温度和降雨的反应、季节性的水接触模式以及受天气变量驱动的蜗牛种群动态。本文回顾了这些调节剂的生物学基础，并对其值进行了估计，并将其纳入一个传输模型中，该模型模拟了两个血吸虫病流行地区的多年期。模型结果与基于尺度的相关分析相结合表明，这些特定于地点的门控函数的最终效应是以一种对地点之间的水文差异特别敏感的方式强烈控制这些社区中的蠕虫负担。确定了两类门控函数，一类是协同作用以改变人类感染（并确定季节后期的蠕虫获取）的函数，另一类是作用于蜗牛感染（并确定季节早期的蠕虫获取）的函数。讨论了这些因素对控制计划和监测的重要性。
