Abstract

Background

Schistosomiasis is a neglected tropical disease caused by trematodes of the genus Schistosoma. The pathogen is transmitted via freshwater snails. These snails are highly tolerant to agricultural pesticides and indirectly benefit from exposure due to adverse effects on their more sensitive enemy species. Pesticides in surface waters may thus increase the risk of schistosomiasis transmission unless they also affect the pathogen. We tested the tolerance of the free-swimming life stages (miracidia and cercariae) of Schistosoma mansoni to the insecticides diazinon and imidacloprid. We also investigated whether these pesticides decrease the ability of miracidia to infect and further develop as sporocysts within the host snail Biomphalaria pfeifferi.

Results

Exposure to imidacloprid for 6 and 12 h immobilized 50% of miracidia at 150 and 16 µg/L, respectively (nominal EC50); 50% of cercariae were immobilized at 403 and 284 µg/L. Diazinon immobilized 50% of miracidia at 51 and 21 µg/L after 6 and 12 h; 50% of cercariae were immobilized at 25 and 13 µg/L. The observed insecticide tolerance is lower than those of the host snail B. pfeifferi and comparable to those of other commonly tested freshwater invertebrates. Exposure for up to 6 h decreased the infectivity of miracidia at high sublethal concentrations (48.8 µg imidacloprid/L and 10.5 µg diazinon/L, i.e. 20–33% of EC50), but not at lower concentrations commonly observed in the field (4.88 µg imidacloprid/L and 1.05 µg diazinon/L). The development of sporocysts within the snail host was not affected at any of these test concentrations.

Conclusions

Insecticides did not affect the performance of S. mansoni at environmentally relevant concentrations. Particularly within its host snail the pathogen can escape exposure peaks that have been shown to affect other sensitive invertebrates and their biological control of host snails. Our findings suggest that freshwater pollution with agricultural pesticides increases the risk of schistosomiasis; they illustrate the need to integrate an environmental and public health risk assessment and management.

中文翻译：

---

曼氏血吸虫的高农药耐受性：对血吸虫病风险的影响

摘要

背景

血吸虫病是一种被忽视的热带疾病，由血吸虫属吸虫引起。病原体通过淡水蜗牛传播。这些蜗牛对农业杀虫剂具有高度耐受性，并且由于对其更敏感的敌对物种产生不利影响而间接受益于接触杀虫剂。因此，地表水中的农药可能会增加血吸虫病传播的风险，除非它们也影响病原体。我们测试了曼氏血吸虫自由游动生命阶段（毛蚴和尾蚴）对杀虫剂二嗪农和吡虫啉的耐受性。我们还研究了这些农药是否会降低毛蚴感染宿主蜗牛Biomphalaria pfeifferi内并进一步发育为孢子囊的能力。

结果

分别以 150 µg/L 和 16 µg/L 浓度接触吡虫啉 6 小时和 12 小时，固定 50% 的毛蚴（名义 EC50）；50% 的尾蚴在 403 和 284 µg/L 下被固定。6 小时和 12 小时后，二嗪农以 51 和 21 µg/L 的浓度固定了 50% 的毛蚴；50% 的尾蚴在 25 和 13 µg/L 下被固定。观察到的杀虫剂耐受性低于宿主蜗牛B. pfeifferi的耐受性，与其他常见测试的淡水无脊椎动物的耐受性相当。在高亚致死浓度（48.8 µg 吡虫啉/L 和 10.5 µg 二嗪农/L，即 EC50 的 20-33%）下，暴露长达 6 小时可降低毛蚴的感染性，但在现场常见的较低浓度（4.88 µg）下则不会降低毛蚴的感染性。吡虫啉/L 和 1.05 µg 二嗪农/L)。在任何这些测试浓度下，蜗牛宿主内孢子被的发育均不受影响。

结论

杀虫剂在环境相关浓度下不会影响曼氏链霉菌的性能。特别是在其寄主蜗牛内，病原体可以逃避暴露高峰，这已被证明会影响其他敏感无脊椎动物及其对寄主蜗牛的生物控制。我们的研究结果表明，农业杀虫剂造成的淡水污染会增加患血吸虫病的风险；它们说明了整合环境和公共卫生风险评估和管理的必要性。