Belfaiza M, Moncef M, Rondelaud D
Laboratoire d'Hydrobiologie, Département de Biologie, Faculté des Sciences, Université Chouaïb Doukkali, BP 20, 24000, El Jadida, Morocco.
Parasitol Res. 2005 Apr;95(6):374-8. doi: 10.1007/s00436-004-1281-7. Epub 2005 Feb 18.
Parent snails, F1, and F2, originating from a Moroccan population of Galba truncatula, were experimentally subjected to sympatric miracidia of Fasciola hepatica at 20 degrees C to determine the mode of adaptation of this parasite to the local intermediate host via the study of redial burdens and by following cercarial shedding. In spite of an increase in the global prevalences of infections, the frequencies recorded for immature or mature infections in dissected snails did not show any significant variations from parents to F2. If the redial burdens in mature infections were mainly composed of first-generation rediae in parent snails, the numbers of rediae belonging to subsequent generations significantly increased in the F1 and F2 generations. In mature infections, the lengths of first-generation rediae and their contents significantly decreased from parent snails to F2. Conversely, in the first redial cohort of the second generation (R2a rediae), only the intraredial contents increased significantly with snail generation. In mature infections, daughter redia production was ensured by all mother rediae of the first generation in parent snails, whereas it was progressively effected by the first mother redia in the F1 and F2 infections. The numbers of cercariae shed by snails increased significantly from parents to F2. If the cercariae produced by first-generation rediae decreased with snail generation, an inverse finding was noted in the case of R2a rediae. We suggest that snails impose a bottleneck on the development of the first mother redia, so that other mother rediae of the first generation react with greater growth (until 3.9 mm in parent snails), an important daughter redia production and a high cercarial production. As the first mother redia remained alive until day 49 post-exposure but without growth after week 2, this mode of development must be considered as a new developmental pattern of redial generations, and it is useful to determine its frequency in snails, as it has never been found in naturally or experimentally infected snails in central France.
来自摩洛哥截口圆扁螺种群的亲代蜗牛、F1代和F2代，在20摄氏度下接受了来自肝片吸虫的同域尾蚴感染实验，以通过研究雷蚴负荷和追踪尾蚴逸出情况，来确定该寄生虫对当地中间宿主的适应模式。尽管感染的总体患病率有所上升，但解剖后的蜗牛中未成熟或成熟感染的记录频率从亲代到F2代并未显示出任何显著变化。在成熟感染中，如果亲代蜗牛中成熟感染的雷蚴负荷主要由第一代雷蚴组成，那么在F1代和F2代中属于后续世代的雷蚴数量显著增加。在成熟感染中，从亲代蜗牛到F2代，第一代雷蚴的长度及其内含物显著减少。相反，在第二代的第一个雷蚴群体（R2a雷蚴）中，只有雷蚴内的内含物随着蜗牛世代显著增加。在成熟感染中，亲代蜗牛中第一代的所有母雷蚴都能产生子雷蚴，而在F1代和F2代感染中，逐渐由第一个母雷蚴来完成。蜗牛逸出的尾蚴数量从亲代到F2代显著增加。如果第一代雷蚴产生的尾蚴随着蜗牛世代减少，那么在R2a雷蚴的情况下则出现相反的情况。我们认为，蜗牛对第一个母雷蚴的发育形成了瓶颈，因此第一代的其他母雷蚴会以更大的生长（亲代蜗牛中可达3.9毫米）、重要的子雷蚴产生和高尾蚴产量做出反应。由于第一个母雷蚴在暴露后第49天仍然存活，但在第2周后不再生长，这种发育模式必须被视为雷蚴世代的一种新的发育模式，确定其在蜗牛中的频率是有用的，因为在法国中部自然感染或实验感染的蜗牛中从未发现过这种模式。
