Laboratory of Parasitology, Faculty of Pharmacy, 2 Rue du Docteur Raymond Marcland, 87025 Limoges Cedex, France.
Parasite. 2020;27:17. doi: 10.1051/parasite/2020013. Epub 2020 Mar 18.
Field investigations in 14 wild watercress beds located in the French region of Limousin, a known endemic area for distomatosis, were performed for three years to determine the distance that cercariae of Fasciola hepatica can reach in water before their encystment on the host plant. Each bed was located on the course of an open drainage furrow, while snails (Galba truncatula) lived upstream around the emergence of a source. Five plant species were collected in early April and examined to find metacercariae. Most cysts were noted on Nasturtium officinale (188 on 48.7 kg of dripped plants), followed by Helosciadium nodiflorum (125 on 33.4 kg). On the other plant species, there were few larvae. Most cercariae encysted on the plants growing in the most upstream part of each bed, usually on the first 50 cm in length. When water in the beds was fast running, the distribution of metacercariae was more limited and their number was fewer than those in the beds fed by a slow flow of water. Cercariae were able to swim or were carried away by the current up to a mean of 5 m in slow-flow waters before encysting; this distance was only 4 m in faster waters. Plants growing on the most upstream section of a watercress bed located in a drainage furrow are the most used by cercariae for their encystment, when snails live around the emergence of a source. The speed of the water current affected the number and distribution of metacercariae in the bed.
三年来，在法国利穆赞地区的 14 个野生水田芥菜床进行了实地调查，以确定肝片形吸虫的尾蚴在囊蚴在宿主植物上形成之前在水中可以达到的距离。每个床都位于一个露天排水沟的河道上，而蜗牛（Galba truncatula）则生活在源头附近的上游。在四月初收集了五种植物物种并进行检查以寻找似囊尾蚴。在 Nasturtium officinale 上发现了最多的囊蚴（在 48.7 公斤滴水植物上发现了 188 个），其次是 Helosciadium nodiflorum（在 33.4 公斤上发现了 125 个）。在其他植物物种上，幼虫很少。大多数尾蚴在每个床最上游部分的植物上形成囊蚴，通常在 50 厘米的长度内。当床中的水快速流动时，似囊尾蚴的分布范围更有限，数量也比水流缓慢的床中的数量少。在水流缓慢的情况下，尾蚴可以游泳或被水流冲走，平均可达 5 米，然后形成囊蚴；在水流较快的情况下，这个距离只有 4 米。当蜗牛生活在源头附近时，位于排水沟中的水田芥菜床的最上游部分生长的植物是尾蚴最常用于形成囊蚴的植物。水流速度影响了床中的似囊尾蚴的数量和分布。
