Mutuku Martin W, Lu Lijun, Otiato Fredrick O, Mwangi Ibrahim N, Kinuthia Joseph M, Maina Geoffrey M, Laidemitt Martina R, Lelo Eric A, Ochanda Horace, Loker Eric S, Mkoji Gerald M
Centre for Biotechnology Research and Development, Kenya Medical Research Institute, P.O. Box 54840-00200, Nairobi, Kenya.
J Parasitol. 2017 Dec;103(6):669-676. doi: 10.1645/17-72. Epub 2017 Jul 14.
In Kenya, schistosomes infect an estimated 6 million people with >30 million people at risk of infection. We compared compatibility with, and ability to support and perpetuate, Schistosoma mansoni of Biomphalaria pfeifferi and Biomphalaria sudanica, 2 prominent freshwater snail species involved in schistosomiasis transmission in Kenya. Field-derived B. pfeifferi (from a stream in Mwea, central Kenya) and B. sudanica (from Nawa, Lake Victoria, in western Kenya) were exposed to S. mansoni miracidia isolated from fecal samples of naturally infected humans from Mwea or Nawa. Juvenile (<6 mm shell diameter), young adult (6-9 mm), and adult snails (>9 mm) were each exposed to a single miracidium. Schistosoma mansoni developed faster and consistently had higher infection rates (39.6-80.7%) in B. pfeifferi than in B. sudanica (2.4-21.5%), regardless of the source of S. mansoni or the size of the snails used. Schistosoma mansoni from Nawa produced higher infection rates in both B. pfeifferi and B. sudanica than did S. mansoni from Mwea. Mean daily cercariae production was greater for B. pfeifferi exposed to sympatric than allopatric S. mansoni (583-1,686 vs. 392-1,232), and mean daily cercariae production among B. sudanica were consistently low (50-590) with no significant differences between sympatric or allopatric combinations. Both non-miracidia-exposed and miracidia-exposed B. pfeifferi had higher mortality rates than for B. sudanica, but mean survival time of shedding snails (9.3-13.7 wk) did not differ significantly between the 2 species. A small proportion (1.5%) of the cercariae shedding B. pfeifferi survived up to 40 wk post-exposure. Biomphalaria pfeifferi was more likely to become infected and to shed more cercariae than B. sudanica, suggesting that the risk per individual snail of perpetuating transmission in Kenyan streams or lacustrine habitats may differ considerably. High infection rates exhibited by the preferential self-fertilizing B. pfeifferi relative to the out-crossing B. sudanica point to the need to investigate further the role of host breeding systems in influencing transmission of schistosomiasis by snail hosts.
在肯尼亚，血吸虫感染了约600万人，另有3000多万人面临感染风险。我们比较了肯尼亚血吸虫病传播中两种主要的淡水蜗牛物种——费氏扁卷螺和苏丹扁卷螺与曼氏血吸虫的兼容性，以及它们支持和维持曼氏血吸虫生存的能力。从野外采集的费氏扁卷螺（来自肯尼亚中部姆韦亚的一条溪流）和苏丹扁卷螺（来自肯尼亚西部维多利亚湖的纳瓦）被暴露于从姆韦亚或纳瓦自然感染人类的粪便样本中分离出的曼氏血吸虫毛蚴。将幼体（壳直径<6毫米）、年轻成体（6 - 9毫米）和成年蜗牛（>9毫米）分别暴露于单个毛蚴。无论曼氏血吸虫的来源或所用蜗牛的大小如何，曼氏血吸虫在费氏扁卷螺中的发育速度更快，感染率始终更高（39.6 - 80.7%），而在苏丹扁卷螺中的感染率为（2.4 - 21.5%）。来自纳瓦的曼氏血吸虫在费氏扁卷螺和苏丹扁卷螺中的感染率均高于来自姆韦亚的曼氏血吸虫。暴露于同域曼氏血吸虫的费氏扁卷螺的平均每日尾蚴产量高于异域曼氏血吸虫（583 - 1686对392 - 1232），而苏丹扁卷螺的平均每日尾蚴产量一直较低（50 - 590），同域或异域组合之间无显著差异。未暴露于毛蚴和暴露于毛蚴的费氏扁卷螺的死亡率均高于苏丹扁卷螺，但两种蜗牛中排尾蚴蜗牛的平均存活时间（9.3 - 13.7周）无显著差异。一小部分（1.5%）排尾蚴的费氏扁卷螺在暴露后存活长达40周。与苏丹扁卷螺相比，费氏扁卷螺更易感染且排出更多尾蚴，这表明在肯尼亚溪流或湖泊栖息地中，单个蜗牛在维持传播方面的风险可能有很大差异。相对于异交的苏丹扁卷螺，优先自体受精的费氏扁卷螺所表现出的高感染率表明，有必要进一步研究宿主繁殖系统在影响蜗牛宿主传播血吸虫病中的作用。
