Grabner Daniel S, Mohamed Faten A M M, Nachev Milen, Méabed Eman M H, Sabry Abdel Hameed A, Sures Bernd
Aquatic Ecology and Centre for Water and Environmental Research, University of Duisburg-Essen, Essen, Germany.
Parasitology Department, Faculty of Medicine, Fayoum University, Fayoum, Egypt.
PLoS One. 2014 Feb 11;9(2):e88537. doi: 10.1371/journal.pone.0088537. eCollection 2014.
The liver fluke Fasciola gigantica is a trematode parasite of ruminants and humans that occurs naturally in Africa and Asia. Cases of human fascioliasis, attributable at least in part to F. gigantica, are significantly increasing in the last decades. The introduced snail species Galba truncatula was already identified to be an important intermediate host for this parasite and the efficient invader Pseudosuccinea columella is another suspect in this case. Therefore, we investigated snails collected in irrigation canals in Fayoum governorate in Egypt for prevalence of trematodes with focus on P. columella and its role for the transmission of F. gigantica. Species were identified morphologically and by partial sequencing of the cytochrome oxidase subunit I gene (COI). Among all 689 snails found at the 21 sampling sites, P. columella was the most abundant snail with 296 individuals (42.96%) and it was also the most dominant species at 10 sites. It was not found at 8 sites. Molecular detection by PCR and sequencing of the ITS1-5.8S-ITS2 region of the ribosomal DNA (rDNA) revealed infections with F. gigantica (3.38%), Echinostoma caproni (2.36%) and another echinostome (7.09%) that could not be identified further according to its sequence. No dependency of snail size and trematode infection was found. Both high abundance of P. columella in the Fayoum irrigation system and common infection with F. gigantica might be a case of parasite spill-back (increased prevalence in local final hosts due to highly susceptible introduced intermediate host species) from the introduced P. columella to the human population, explaining at least partly the observed increase of reported fascioliasis-cases in Egypt. Eichhornia crassipes, the invasive water hyacinth, which covers huge areas of the irrigation canals, offers safe refuges for the amphibious P. columella during molluscicide application. As a consequence, this snail dominates snail communities and efficiently transmits F. gigantica.
巨片形吸虫是反刍动物和人类的一种吸虫寄生虫，自然分布于非洲和亚洲。在过去几十年中，至少部分归因于巨片形吸虫的人类片形吸虫病病例显著增加。已确认引入的截口圆扁螺是这种寄生虫的重要中间宿主，而高效入侵种柱形伪琥珀螺也是可疑宿主。因此，我们调查了在埃及法尤姆省灌溉渠中采集的蜗牛体内吸虫的流行情况，重点关注柱形伪琥珀螺及其在巨片形吸虫传播中的作用。通过形态学鉴定和细胞色素氧化酶亚基I基因（COI）的部分测序来识别物种。在21个采样点发现的所有689只蜗牛中，柱形伪琥珀螺是数量最多的蜗牛，有296只（42.96%），也是10个采样点中最占优势的物种。在8个采样点未发现该物种。通过对核糖体DNA（rDNA）的ITS1-5.8S-ITS2区域进行PCR分子检测和测序，发现感染了巨片形吸虫（3.38%）、卡氏棘口吸虫（2.36%）和另一种无法根据序列进一步鉴定的棘口吸虫（7.09%）。未发现蜗牛大小与吸虫感染之间存在相关性。柱形伪琥珀螺在法尤姆灌溉系统中的高丰度以及与巨片形吸虫的常见感染，可能是寄生虫反向传播（由于引入的高度易感中间宿主物种，导致本地终末宿主中的流行率增加）的一个例子，这至少部分解释了埃及报告的片形吸虫病病例增加的现象。入侵性凤眼莲覆盖了灌溉渠的大片区域，在施用杀螺剂期间为两栖的柱形伪琥珀螺提供了安全的避难所。因此，这种蜗牛在蜗牛群落中占主导地位，并有效地传播巨片形吸虫。
