Data from: The consequences of co-infections for parasite transmission in the mosquito Aedes aegypti

1)Co-infections may modify parasite transmission opportunities directly as a consequence of interactions in the within host environment, but also indirectly through changes in host life-history. Furthermore, host and parasite traits are sensitive to the abiotic environment with variable consequences for parasite transmission in co-infections. (2)We investigate how co-infection of the mosquito Aedes aegypti with two microsporidian parasites (Vavraia culicis and Edhazardia aedis) at two levels of larval food availability affects parasite transmission directly, and indirectly through effects on host traits (3)In a laboratory infection experiment we compared how co-infection, at low and high larval food availability, affected the probability of infection, within-host growth and the transmission potential of each parasite, compared to single infections. Horizontal transmission was deemed possible for both parasites when infected hosts died harbouring horizontally-transmitting spores. Vertical transmission was judged possible for E. aedis when infected females emerged as adults. We also compared the total input number of spores used to seed infections with output number, in single and co-infections for each parasite. (4)The effects of co-infection on parasite fitness were complex, especially for V. culicis. In low larval food conditions, co-infection increased the chances of mosquitoes dying as larvae or pupae, thus increasing opportunities for V. culicis’ horizontal transmission. However, co-infection reduced larval longevity and hence time available for V. culicis spore production. Overall there was a negative net effect of co-infection on V. culicis whereby the number of spores produced was less than the number used to seed infection. Co-infections also negatively affected horizontal transmission of the more virulent parasite, E. aedis, through reduced longevity of pre-adult hosts. However, its potential transmission suffered less relative to V. culicis. (5)Our results show that co-infection can negatively affect parasite transmission opportunities, both directly as well as indirectly via effects on host life-history. We also find that transmission is contingent on the combined effect of the abiotic environment.

(1) 共感染（co-infection）可通过宿主内环境（within-host environment）中的相互作用直接改变寄生虫的传播机会，也可通过调控宿主生活史（host life-history）产生间接影响。此外，宿主与寄生虫的性状均对非生物环境（abiotic environment）敏感，而非生物环境会对共感染情境下的寄生虫传播产生多样效应。
(2) 本研究旨在探究：当埃及伊蚊（Aedes aegypti）被两种微孢子虫（microsporidian parasites，即Vavraia culicis与Edhazardia aedis）在两种幼虫食物可获得性（larval food availability）水平下共感染时，共感染如何直接影响寄生虫的传播，以及通过调控宿主性状（host traits）产生间接传播效应的路径。
(3) 本研究通过室内感染实验，对比了单感染与共感染在低、高幼虫食物可获得性条件下，对每种寄生虫的感染概率、宿主内增殖（within-host growth）水平以及传播潜力（transmission potential）的差异。当感染宿主死亡并携带水平传播（horizontal transmission）孢子时，即可判定两种寄生虫均具备水平传播能力；当感染雌蚊羽化至成虫阶段时，即可判定伊氏埃德哈虫（Edhazardia aedis）具备垂直传播（vertical transmission）能力。此外，本研究还对比了单感染与共感染情境下，每种寄生虫用于侵染宿主的孢子输入总量与产出总量的差异。
(4) 共感染对寄生虫适合度（parasite fitness）的影响较为复杂，对V. culicis（库氏瓦粒虫）而言尤为显著。在低幼虫食物可获得性条件下，共感染提升了蚊幼虫或蛹的死亡概率，进而增加了V. culicis的水平传播机会；但与此同时，共感染缩短了幼虫的寿命，从而压缩了V. culicis的孢子生产时长。总体而言，共感染对V. culicis存在净负面效应，其产出的孢子数量低于初始侵染的孢子输入量。共感染还通过缩短成虫前宿主（pre-adult hosts）的寿命，对毒力更强的E. aedis（伊氏埃德哈虫）的水平传播产生了负面影响，但相较于V. culicis，E. aedis的传播潜力受影响程度更低。
(5) 本研究结果表明，共感染可通过直接途径以及通过调控宿主生活史的间接途径，对寄生虫的传播机会产生负面影响。同时本研究还发现，寄生虫的传播能力取决于非生物环境的综合效应。