Data from: Endemic infection reduces transmission potential of an epidemic parasite during co-infection

Endemic, low-virulence parasitic infections are common in nature. Such infections may deplete host resources, which in turn could affect the reproduction of other parasites during co-infection. We aimed to determine whether the reproduction, and therefore transmission potential, of an epidemic parasite was limited by energy costs imposed on the host by an endemic infection. Total lipids, triacylglycerols (TAG) and polar lipids were measured in cockroaches (Blattella germanica) that were fed ad libitum, starved or infected with an endemic parasite, Gregarina blattarum. Reproductive output of an epidemic parasite, Steinernema carpocapsae, was then assessed by counting the number of infective stages emerging from these three host groups. We found both starvation and gregarine infection reduced cockroach lipids, mainly through depletion of TAG. Further, both starvation and G. blattarum infection resulted in reduced emergence of nematode transmission stages. This is, to our knowledge, the first study to demonstrate directly that host resource depletion caused by endemic infection could affect epidemic disease transmission. In view of the ubiquity of endemic infections in nature, future studies of epidemic transmission should take greater account of endemic co-infections.在自然界中，低毒力的地方性寄生感染十分普遍。此类感染会消耗宿主资源，进而可能影响共感染状态下其他寄生虫的繁殖。本研究旨在明确：地方性感染对宿主造成的能量消耗，是否会限制流行性寄生虫的繁殖能力，进而影响其传播潜能。研究对自由摄食、饥饿或感染地方性寄生虫布氏簇虫（Gregarina blattarum）的德国小蠊（Blattella germanica）进行了总脂质、三酰甘油（triacylglycerols, TAG）及极性脂质水平的检测。随后通过计数三组宿主释放的感染期虫体数量，评估流行性寄生虫斯氏异小杆线虫（Steinernema carpocapsae）的繁殖产出。结果显示，饥饿与布氏簇虫感染均会降低德国小蠊的脂质水平，且主要通过消耗三酰甘油实现。此外，饥饿与布氏簇虫感染均会导致线虫感染期虫体的释放量下降。据我们所知，本研究首次直接证实：地方性感染引发的宿主资源消耗，可对流行性疾病的传播产生影响。鉴于地方性感染在自然界中普遍存在，未来的流行性疾病传播研究应更加重视共感染状态下的地方性寄生感染因素。