Temperature impacts on parasite epidemiology - case study of a contact-transmitted insect parasite

流行病学研究的是疾病发生频率如何随时间变化，以及这种变化的驱动因素。对于传染病（在个体之间传播的疾病），疾病在群体中的传播与个体之间的接触率密切相关。对于人类疾病，人口密度和流动是决定有多少人患病的一个重要因素。事实上，人类历史上的城市化进程一直伴随着新疾病的出现和持续存在。对于人类和温血动物来说，日常活动水平几乎不受气候变化的影响。然而，对于冷血动物来说，运动的模式和速度与天气密切相关。在寒冷多云的日子里，与温暖的晴天相比，几乎没有什么活动。在这项研究中，我们将研究热环境对疾病流行病学的影响：本质上，疾病在冷血动物种群中传播的程度受到气候的影响。假设是温暖的天气会增加活动水平，从而增加宿主之间的接触率。因此，气候将是冷血动物疾病流行的重要驱动因素。除了日常活动之外，气候还影响着每年繁殖、出生和死亡周期的时间——物候学。对于像英国这样的国家的昆虫来说，成虫通常会从冬眠中出来，在春天变得活跃并开始繁殖。许多亲代会在它们的后代成熟和在夏天出生之前死去，这样几代之间就很少有“重叠”。重叠的程度因地而异（一般来说，南方地区重叠较多），并且在影响疾病传播方面可能非常重要——疾病必须在几代人之间传递才能持续存在。假设是更长、更温暖的春季气候可能会加速下一代的发育，增加与亲代的重叠，并增加疾病传播给下一代。进行这类研究的问题之一是如何定义使动物暴露于疾病的“接触”。我们将通过检查一种性传播感染来解决这个问题，一种生活在瓢虫翅膀下的螨虫，在性行为中在伴侣之间传播。因为交配是持久的，这可以很容易地测量，并评估温度敏感性。这种寄生虫也具有非常简单的流行病学特征——性接触是迄今为止最常见的接触方式，可以很容易地对个体进行无创感染和传染性评分，并且感染后无法恢复。每年都有与春季宿主繁殖活动有关的年度流行病。虽然我们将研究一个特定的系统，但期望结果将对气候如何影响温带地区昆虫的疾病模式提供总体见解。它应该预测当前的疾病模式将如何随空间变化，以及气候变化后英国昆虫的疾病模式将如何变化。

Epidemiology is the study of how the frequency of disease changes over time, and the drivers of this change. For infectious disease (diseases that pass from individual to individual), the passage of disease through a community is intimately related to the rate of contact between individuals. For human diseases, the density and movement of people is an important element in determining how many people get the disease. Indeed, urbanization through human history has been followed by the emergence and persistence of new diseases. For humans, and warm-blooded animals, day-to-day activity levels are little affected by variation in the climate. However, for cold-blooded creatures, the pattern and rate of movement are intimately tied into the weather. On a cold, cloudy day, there will be little activity compared to a warm sunny day. In this study, we will examine the effect that thermal environment has on disease epidemiology: in essence, the degree to which the rate of disease spread through a population of cold blooded animals is affected by climate. The hypothesis is that warm weather will raise activity levels, which will increase contact rate between hosts. Thus, climate will be an important driver of disease epidemics in cold blooded animals. Beyond daily activity, climate also affects the timing of the yearly cycle of reproduction, birth and death - phenology. For insects in countries like the UK, adults commonly emerge from overwinter stasis, become active and start to reproduce in spring. Many of the parental generation will die before their progeny reach maturity and emerge in summer, such that there is little 'overlap' between the generations. The level of overlap varies geographically (generally, more overlap in Southern areas), and may be very important in affecting disease transmission- the disease has to pass between generations to persist. The hypothesis is that longer, warmer spring climates may speed the development of the next generation, increasing overlap with the parental generation, and increasing disease transmission to it. One of the problems in conducting research of this kind is in defining a 'contact' that exposes an animal to disease. We will circumvent this by examining a sexually transmitted infection, a mite that lives under the wing cases of ladybirds, and passes between partners during sex. Because mating is durable, this can be measured easily, and temperature-sensitivity assessed. This parasite also has a very simple epidemiology-sexual contact is by far the most common means of exposure, individuals can be easily and non-invasively scored for infection and infectivity, and there is no recovery from infection. There are annual epidemics each year associated with reproductive activity of the host in spring. Whilst we will study one particular system, the expectation is that the results will give a general insight into how climate affects the pattern of disease in insects from temperate regions. It should predict how current disease patterns will vary over space, and also how disease patterns of insects may change in the UK following climate change.