Data from: Host infection history modifies co-infection success of multiple parasite genotypes

1. Co-infections by multiple parasite genotypes are common and have important implications for host-parasite ecology and evolution through within-host interactions. Typically, these infections take place sequentially and therefore, the outcome of co-infection may be shaped by host immune responses triggered by previous infections. For example, in vertebrates specific immune responses play a central role in protection against disease over the course of life, but co-infection research has mostly focused on previously uninfected individuals. 2. Here, we investigated whether sequential exposure and activation of host resistance in rainbow trout Oncorhynchus mykiss affects infection success and interactions between co-infecting parasite genotypes of the trematode eye-fluke Diplostomum pseudospathaceum. 3. In accordance with earlier results, we show that a simultaneous attack of two parasite genotypes facilitates parasite establishment in previously uninfected hosts. However, we find for the first time that this facilitation in co-infection is lost in hosts with prior infection. 4. We conclude that vertebrate host infection history can affect the direction of within-host parasite interactions. Our results may have significant implications for the evolution of co-infections and parasite transmission strategies.

1. 多种寄生虫基因型的共感染现象十分普遍，其通过宿主体内相互作用对宿主-寄生虫生态学与演化具有重要意义。此类感染多以先后顺序发生，因此共感染的结局可能受既往感染触发的宿主免疫应答调控。例如，脊椎动物的特异性免疫应答在其终生疾病防护中发挥核心作用，但当前共感染研究大多聚焦于未发生过感染的个体。
2. 本研究以虹鳟（Oncorhynchus mykiss）为实验对象，探讨宿主先后暴露于寄生虫并激活抗性的过程，是否会影响复口吸虫（Diplostomum pseudospathaceum，一种眼吸虫）的共感染寄生虫基因型的感染成功率及其相互作用。
3. 与既往研究结果一致，本研究证实，两种寄生虫基因型同时侵袭可提升未感染宿主的寄生虫定植成功率。但本研究首次发现，在具有既往感染史的宿主中，这种共感染促进效应会消失。
4. 综上，脊椎动物宿主的感染史可调控宿主体内寄生虫相互作用的方向。本研究结果或对共感染演化及寄生虫传播策略的研究具有重要参考价值。