The smell of infection - detecting infectious disease and determining mechanisms underlying the spread of disease in social networks

社会组织促进了个体之间的接触，改变了寄生虫传播的可能性（Perkins et al., 2009）。因此，群居动物进化出了减轻感染风险的机制。寄生虫改变接触模式的一种机制可能是根据“气味”的变化，使未感染者避开受感染的个体。非传染性和传染性疾病都可导致许多物种（包括牲畜、野生动物和人类）体内挥发性有机化合物（VOCs）的变化（Penn和Potts， 1998年；Balseiro和Correia， 2006年）。对雌性小鼠的研究表明，受感染和未受感染的雄性小鼠对一系列寄生虫，包括流感病毒、原生动物、蠕形艾美耳虫和线虫、多回Heligomosomoides （Kavaliers and Colwell 1995, Penn et al. 1998; Ehman and Scott 2001）具有气味辨别能力。在我们的寄生虫-蟑螂群体系统中的概念证明表明，我们可以在整个动物中检测到与感染相关的独特气味（Perkins， Muller等人，in prep）。然而，寄生虫也可能进化到利用和/或操纵宿主的行为-接触模式-来改善传播（Moore, 2002）。因此，流行病本身可能驱动接触网络模式。全世界的养蜂业都受到传染病的威胁（包括欧洲和美国的臭蜂病、瓦螨和几种病毒），并带来从蜂蜜产量下降到蜂群完全崩溃的影响。利用蜜蜂作为模型系统，我们的目标是研究病原体负荷、毒力、传播方式对接触网络的影响，以及“气味”作为一种改变流行病如何在社会网络中发展的机制的作用。通过将VOC分析与详细的行为观察相结合，我们的目标是确定感染的气味是否是驱动传染病动力学的机制，并梳理受感染个体和未感染个体之间接触的定向效应——未感染个体是否避免感染个体，从而减少寄生虫传播。或者，寄生虫是否会操纵宿主的气味来吸引未感染的个体，从而增加寄生虫的传播？我们将从动物和菌落中原位收集顶空空气样品到热解吸管上，并使用最先进的热解吸结合气相色谱-飞行时间质谱（TD-GC-MS-TOF）对样品进行分析。行为实验将使用“Ethovision”等行为软件分析感染者和未感染者的社交网络回避行为。我们预计该项目的研究结果将阐明疾病传播的关键机制，并提供一种监测养蜂业感染和一般潜在感染的新方法。

Social organization facilitates contacts between individuals altering the probability of parasite transmission (Perkins et al., 2009). Consequently, social animals have evolved mechanisms to mitigate the risks of infection. One mechanism by which parasites may alter contact patterns could be through avoidance of infected individuals by uninfected based on changes in 'smell'. Both non-infectious and infectious diseases can cause a change in volatile organic compounds (VOCs) in many species, including, livestock, wildlife and humans (Penn and Potts, 1998; Balseiro and Correia, 2006). Studies on female mice demonstrate odour-based discrimination between infected and uninfected males for a range of parasites, including, influenza virus, the protozoan, Eimeria vermiformis, and the nematode, Heligomosomoides polygyrus (Kavaliers and Colwell 1995, Penn et al. 1998; Ehman and Scott 2001). Proof of concept in our parasite-cockroach colony system has shown that we can detect distinct scents associated with infection in whole animals (Perkins, Muller et al., in prep) However, parasites may also have evolved to exploit and/or manipulate host behaviour - contact patterns - to improve transmission (Moore, 2002). As such, epidemics may themselves drive contact network patterns.Apiculture worldwide has been threatened by the emergence of infectious diseases (including European and American foulbrood, varroa mite, and several viruses), and associated with effects ranging from reduction in honey productivity to full colony collapse. Using honey bees as a model system we aim to investigate the effect of pathogen load, virulence, mode of transmission on contact networks and the role of 'smell' as a mechanism that alters how epidemics progress in social networks.By combining VOC analysis with detailed behavioural observations, we aim to determine if the odour of infection is a mechanism driving infectious disease dynamics and to tease apart the directional effects of contacts between infected and uninfected individuals - are infected individuals avoided by uninfected individuals thereby reducing parasite transmission. Alternatively, does the parasite manipulate host odour to attract uninfected individuals, so increasing parasite transmission?We will collect headspace air samples in-situ from animals and colonies onto thermal desorption tubes and use state-of-the-art thermal desorption combined with gas chromatography - time-of-flight mass spectrometry (TD-GC-MS-TOF) for analysis of the samples. Behavioural experiments will analyse social network avoidance behaviours of infected and uninfected individuals using behavioural software such as 'Ethovision'.We anticipate that the findings of the project will elucidate key mechanisms in disease transmission and deliver a novel approach to monitoring infections in apiculture and potentially infections in general.