Laboratoire EcoSym, UMR5119, Université Montpellier 2, CC 093, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France.
Int J Parasitol. 2013 Dec;43(14):1089-99. doi: 10.1016/j.ijpara.2013.07.008. Epub 2013 Sep 29.
The dynamics of the protozoan parasite Marteilia refringens was studied in Thau lagoon, an important French shellfish site, for 1 year in three potential hosts: the Mediterranean mussel Mytilus galloprovincialis (Mytiliidae), the grooved carpet shell Ruditapes decussatus (Veneriidae) and the copepod Paracartia grani (Acartiidae). Parasite DNA was detected by PCR in R. decussatus. In situ hybridisation showed necrotic cells of M. refringens in the digestive epithelia of some R. decussatus suggesting the non-involvement of this species in the parasite life cycle. In contrast, the detection of M. refringens in mussels using PCR appeared bimodal with two peaks in spring and autumn. Histological observations of PCR-positive mussels revealed the presence of different parasite stages including mature sporangia in spring and autumn. These results suggest that the parasite has two cycles per year in the Thau lagoon and that mussels release parasites into the water column during these two periods. Moreover, PCR detection of the parasite in the copepodid stages of P. grani between June and November supports the hypothesis of the transmission of the parasite from mussels to copepods and conversely. In situ hybridisation performed on copepodites showed labeling in some sections. Unusual M. refringens cells were observed in the digestive tract and the gonad from the third copepodid stage, suggesting that the parasite could infect a copepod by ingestion and be released through the gonad. This hypothesis is supported by the PCR detection of parasite DNA in copepod eggs from PCR-positive females, which suggests that eggs could contribute to the parasite spreading in the water and could allow overwintering of M. refringens. Finally, in order to understand the interactions between mussels and copepods, mussel retention efficiency (number of copepods retained by a mussel) was measured for all P. grani developmental stages. Results showed that all copepod stages could contribute to the transmission of the parasite, especially eggs and nauplii which were retained by up to 90%.
在法国重要的贝类养殖地——索恩河口泻湖，研究人员在三种潜在宿主（贻贝、皱纹盘鲍和帕拉卡塔拟哲水蚤）中研究了旋口虫的动态，为期 1 年。PCR 检测表明栉孔扇贝体内有旋口虫 DNA。原位杂交显示，一些皱纹盘鲍的消化上皮中有旋口虫的坏死细胞，这表明该物种不参与寄生虫的生命周期。相比之下，PCR 检测贻贝中的旋口虫呈现双峰模式，峰值出现在春季和秋季。对 PCR 阳性贻贝的组织学观察显示，存在不同的寄生虫阶段，包括春季和秋季的成熟孢子囊。这些结果表明，寄生虫在索恩河口泻湖每年有两个生命周期，贻贝在这两个时期将寄生虫释放到水柱中。此外，6 月至 11 月期间在桡足幼体阶段检测到寄生虫，支持寄生虫从贻贝传播到桡足类，反之亦然的假设。对桡足幼体进行原位杂交显示，一些部位有标记。在从第三桡足幼体期开始的消化道和性腺中观察到异常的旋口虫细胞，这表明寄生虫可以通过摄入感染桡足类，并通过性腺释放。PCR 检测到 PCR 阳性雌体的桡足类卵中的寄生虫 DNA，这支持了寄生虫在水中传播的假设，并且可以允许旋口虫越冬。最后，为了了解贻贝和桡足类之间的相互作用，测量了所有帕拉卡塔拟哲水蚤发育阶段的贻贝保留效率（贻贝保留的桡足类数量）。结果表明，所有桡足类阶段都可能有助于寄生虫的传播，特别是卵和无节幼体，它们的保留率高达 90%。
