Lowenberger C A, Rau M E
Institute of Parasitology, McGill University, Ste-Anne-de-Bellevue, Quebec, Canada.
Parasitology. 1994 Jul;109 ( Pt 1):65-72. doi: 10.1017/s0031182000077775.
We investigated changes in the behaviour of Stagnicola elodes associated with the emergence of Plagiorchis elegans cercariae. Within 15 min of the reduction in light intensity, which triggered the onset of cercarial emergence, infected snails moved to the top of the water column and remained there for 2-3 h. Seventy-nine percent of all cercariae that emerged from the snail did so during this period. Uninfected snails showed no such behavioural changes following the change in light intensity. Cercariae were released in a dense cloud around the snail at the water surface and dispersed passively. Within 3-4 h more than 80% of all cercariae had settled in the bottom 5 cm of the water column. The infectivity of cercariae increased from less than 20% upon emergence from the snail to greater than 75% 4-6 h post-emergence, and then declined steadily to below 5% by 24 h post-emergence. Cercarial longevity was greater than 30 h and exceeded the period of infectivity. This may be related to steadily falling endogenous glycogen levels. A delay in attaining maximum infectivity may represent an adaptive mechanism allowing time for cercarial dissemination, thus reducing superinfection, and subsequent parasite-associated mortality, of second intermediate hosts.
我们研究了与秀丽斜睾吸虫尾蚴出现相关的静水椎实螺行为变化。在光照强度降低后的15分钟内，光照强度降低引发了尾蚴的出现，受感染的蜗牛游到水柱顶部并在那里停留2 - 3小时。从蜗牛体内逸出的所有尾蚴中有79%是在此期间逸出的。光照强度变化后，未受感染的蜗牛没有出现这种行为变化。尾蚴在水面蜗牛周围以密集云团的形式释放并被动扩散。在3 - 4小时内，超过80%的尾蚴沉降到水柱底部5厘米处。尾蚴的感染力从刚从蜗牛体内逸出时的不到20%增加到逸出后4 - 6小时的超过75%，然后在逸出后24小时稳步下降到5%以下。尾蚴寿命超过30小时，超过了感染期。这可能与内源性糖原水平稳步下降有关。达到最大感染力的延迟可能代表一种适应性机制，为尾蚴传播留出时间，从而减少第二中间宿主的重复感染以及随后与寄生虫相关的死亡率。
