McPherson Olivia G, Friesen Olwyn C, Selbach Christian, Poulin Robert
Department of Zoology, University of Otago, PO Box 56, Dunedin, New Zealand.
Parasitol Res. 2018 Jun;117(6):1915-1923. doi: 10.1007/s00436-018-5885-8. Epub 2018 Apr 25.
Inducible defences against parasites that are only activated when needed can mitigate the cost of immune or behavioural evasion of parasites. Priming of the immune system and activation of behavioural defences can follow exposure to cues associated with imminent infection risk. In contrast, prior infection can cause immune depression or leave the host with less energy to defend itself against further infections. We investigate the priming of anti-parasite defences and the effect of prior infections in the amphipod Paracalliope fluviatilis, the second intermediate host of the trematode Coitocaecum parvum. During experimental infections, amphipods that had been primed by exposure to chemical cues (from first intermediate snail hosts infected by C. parvum) of infection risk were not better at avoiding further infection than control amphipods. All amphipods showed the same swimming behaviour, whether or not they had been primed by chemical cues from infected snails, or whether or not they were in the presence of live infective stages. In contrast, regardless of whether or not they had been exposed to control water or chemical cues from infected snails, amphipods harbouring prior infections acquired in nature were significantly more likely to acquire new parasites under controlled conditions. These results suggest that the induction of defences via external cues associated with the threat of infection do not play a role in the amphipod's anti-parasite strategy. However, prior infections may pre-dispose a host to acquire further parasites, with consequences for the distribution of parasites among host individuals and the regulation of the host population.
针对寄生虫的可诱导防御机制仅在需要时才被激活，这可以减轻免疫或行为上逃避寄生虫的成本。免疫系统的预激发和行为防御的激活可以在接触到与即将来临的感染风险相关的线索之后发生。相比之下，先前的感染可能会导致免疫抑制，或者使宿主用于抵御进一步感染的能量减少。我们研究了在双壳类动物Paracalliope fluviatilis（吸虫Coitocaecum parvum的第二中间宿主）中抗寄生虫防御的预激发以及先前感染的影响。在实验性感染期间，通过接触感染风险的化学线索（来自被C. parvum感染的第一中间螺宿主）而被预激发的双壳类动物，在避免进一步感染方面并不比对照双壳类动物更好。所有双壳类动物都表现出相同的游泳行为，无论它们是否通过来自受感染蜗牛的化学线索进行了预激发，也无论它们是否处于活的感染阶段。相比之下，无论它们是否接触过对照水或来自受感染蜗牛的化学线索，在自然环境中曾有过先前感染的双壳类动物在受控条件下感染新寄生虫的可能性显著更高。这些结果表明，通过与感染威胁相关的外部线索诱导防御在双壳类动物的抗寄生虫策略中不起作用。然而，先前的感染可能会使宿主更容易感染更多寄生虫，这会对寄生虫在宿主个体间的分布以及宿主种群的调节产生影响。
