Cooper L A, Ramani S K, Martin A E, Richards C S, Lewis F A
Biomedical Research Institute, Rockville, Maryland 20852.
J Parasitol. 1992 Jun;78(3):441-6.
In areas endemic for schistosomiasis, the population dynamics of the snail intermediate hosts have a direct effect on parasite transmission. The present study focused on the potential for neonatal Biomphalaria glabrata snails to become infected with Schistosoma mansoni and to produce cercariae under various conditions. It was found that snails as small as 0.74 mm in shell diameter could survive miracidial penetration and could release cercariae when as small as 1.6 mm in diameter. Cercariae produced by small snails were equally infectious for mice when compared with those shed by larger snails. Likewise, histological examination of neonatally exposed snails revealed normally developing parasites at all stages of infection. It was found that in 2 snail populations expressing either high or low susceptibility to the parasite, peak susceptibility occurred at 25 days of age in both groups. Daily cercarial production for neonatally exposed snails was initially low but increased dramatically as the snails grew, eventually reaching values as high as 2,100 cercariae/snail/day. A moderate to high percentage of snails infected as neonates was eventually capable of simultaneously producing both eggs and cercariae. These studies emphasize the potential importance of neonatal and preadult snails in helping to maintain foci of S. mansoni infection in endemic areas.
在血吸虫病流行地区，中间宿主螺类的种群动态对寄生虫传播有直接影响。本研究聚焦于新生光滑双脐螺感染曼氏血吸虫并在不同条件下产生尾蚴的可能性。研究发现，壳径小至0.74毫米的螺能够在毛蚴侵入后存活，且直径小至1.6毫米时就能释放尾蚴。与较大螺释放的尾蚴相比，小螺产生的尾蚴对小鼠的感染性相同。同样，对新生期接触寄生虫的螺进行组织学检查发现，在感染的各个阶段寄生虫均正常发育。研究发现，在对该寄生虫表现出高易感性或低易感性的两个螺种群中，两组的峰值易感性均出现在25日龄时。新生期接触寄生虫的螺每日产生的尾蚴数量最初较低，但随着螺的生长而急剧增加，最终达到高达每只螺每天2100条尾蚴的水平。相当高比例的新生期感染螺最终能够同时产出虫卵和尾蚴。这些研究强调了新生期和未成年期螺类在维持流行地区曼氏血吸虫感染疫源地方面的潜在重要性。
