Department of Zoology, P.O. Box 56, Dunedin 9054, New Zealand.
Int J Parasitol. 2012 May 1;42(5):453-61. doi: 10.1016/j.ijpara.2012.02.014.
Trematode parasites are integral components of intertidal ecosystems which experience high levels of ultraviolet radiation. Although these parasites mostly live within hosts, their life cycle involves free-living larval transmission stages such as cercariae which are directly exposed to ambient conditions. UV has previously been shown to considerably reduce the survival of cercariae. Here, we investigated potential mechanisms of protection and damage related to UV in the intertidal trematode Maritrema novaezealandensis. Firstly, the presence of sunscreen compounds (i.e. mycosporine-like amino acids) was quantified in the parasite tissue producing cercariae within a snail host, as well as in the free-swimming cercariae themselves. Secondly, levels of oxidative stress in cercariae after exposure to UV were investigated (i.e.protein carbonyls, catalase and superoxide dismutase). Thirdly, the DNA damage (i.e. cyclobutane–pyrimidine dimers) was compared between cercariae exposed and not exposed to UV. Lastly, functional aspects(survival and infectivity) of cercariae were assessed, comparing cercariae under light conditions versus dark after exposure to UV. We confirmed the presence of my cosporine-like amino acids in cercariae-producing tissue from within snail hosts, but were unable to do so in cercariae directly. Results further suggested that exposure to UV induced high levels of oxidative stress in cercariae which was accompanied by a reduction in the levels of protective antioxidant enzymes present. We also identified higher levels of DNA damage in cercariae exposed to UV, compared with those not exposed. Moreover, no clear effect of light condition was found on survival and infectivity of cercariae after exposure to UV. We concluded that cercariae are highly susceptible to UV damage and that they have very little scope for protection against or repair of UV-induced damage.
吸虫寄生虫是潮间带生态系统的组成部分，这些生态系统经历高水平的紫外线辐射。尽管这些寄生虫大多生活在宿主体内，但它们的生命周期包括自由生活的幼虫传播阶段，如直接暴露于环境条件下的尾蚴。紫外线此前已被证明会大大降低尾蚴的存活率。在这里，我们研究了与潮间带吸虫 Maritrema novaezealandensis 相关的潜在的与 UV 有关的保护和损伤机制。首先，在宿主蜗牛体内产生尾蚴的寄生虫组织以及自由游动的尾蚴本身中，定量了防晒霜化合物（即菌氨酸类似物氨基酸）的存在。其次，研究了暴露于 UV 后尾蚴中的氧化应激水平（即蛋白质羰基、过氧化氢酶和超氧化物歧化酶）。第三，比较了暴露于 UV 和未暴露于 UV 的尾蚴之间的 DNA 损伤（即环丁烷嘧啶二聚体）。最后，通过比较暴露于 UV 后的光条件下和黑暗条件下的尾蚴，评估了尾蚴的功能方面（存活率和感染力）。我们证实了在来自蜗牛宿主内部的产生尾蚴的组织中存在菌氨酸类似物氨基酸，但无法在直接的尾蚴中证实这一点。结果进一步表明，暴露于 UV 会在尾蚴中诱导高水平的氧化应激，同时降低存在的保护性抗氧化酶的水平。我们还发现，与未暴露于 UV 的尾蚴相比，暴露于 UV 的尾蚴中的 DNA 损伤水平更高。此外，在暴露于 UV 后，光条件对尾蚴的存活率和感染力没有明显影响。我们得出的结论是，尾蚴对 UV 损伤非常敏感，而且它们几乎没有保护或修复 UV 诱导损伤的能力。
