Basáñez M G, Remme J H, Alley E S, Bain O, Shelley A J, Medley G F, Anderson R M
Department of Biology, Imperial College of Science, Technology and Medicine, London, UK.
Parasitology. 1995 May;110 ( Pt 4):409-27. doi: 10.1017/s0031182000064751.
A previous paper reported that the intake of Onchocerca volvulus microfilariae (mff) by different species of Simulium is essentially proportional to the parasite load in the skin of infected carriers. This paper examines the fate of the ingested mff in susceptible vectors to assess the relationship between parasite intake and infective larval output in blackfly species with and without well-developed cibarial armatures. Analysis is based on data from 3 onchocerciasis endemic areas: Guatemala (S. ochraceum s.l.), West Africa (S. damnosum s.l./S. sirbanum) and the Amazonian focus between South Venezuela and Northern Brazil (S. guianense and S. oyapockense s.l.). The data, which include published and unedited information collected in the field, record experimental studies of parasite uptake by wild flies maintained in captivity until the completion of the extrinsic incubation period. The relationship between L3 output (measured as the mean number of successful larvae/fly or, as the proportion of flies with infective larvae) and average microfilarial intake, was strongly non-linear. This non-linearity was best represented by a sigmoid function in case of armed simuliids (S. ochraceum s.l., S. oyapockense s.l.), or by a hyperbolic expression in that of unarmed flies (S. damnosum s.l., S. guianense). These results are compatible, respectively, with the patterns of 'initial facilitation' and 'limitation' described in culicid vectors of lymphatic filariases. A maximum mean number of 1-3 L3/fly was observed in all 4 vectors. It is concluded that O. volvulus larval development to the infective stage is regulated by density-dependent mechanisms acting at the early phase of microfilarial migration out of the blackfly's bloodmeal. Damage by the bucco-pharyngeal armature may also be density dependent. A hypothesis, based on this density dependence is forwarded to explain initial facilitation, so far only recorded in vectors with well-developed cibarial teeth. Our results provide quantitative support for the conjecture that chemotherapy alone is likely to have a greater impact on reducing onchocerciasis transmission in endemic areas where the main vector has a toothed fore-gut than in foci where the vectors have unarmed cibaria.
此前有一篇论文报道，不同种类的蚋对盘尾丝虫微丝蚴（mff）的摄取量基本上与受感染宿主皮肤中的寄生虫负荷成正比。本文研究了易感媒介中摄入的微丝蚴的命运，以评估在具有和不具有发达下咽骨片的蚋种中，寄生虫摄取与感染性幼虫产出之间的关系。分析基于来自3个盘尾丝虫病流行地区的数据：危地马拉（奥氏蚋复合种）、西非（恶蚋复合种/锡尔巴蚋）以及委内瑞拉南部和巴西北部之间的亚马逊疫区（圭亚那蚋和奥亚波克蚋复合种）。这些数据包括在实地收集的已发表和未编辑的信息，记录了对圈养野生蝇摄取寄生虫的实验研究，直至完成外在潜伏期。L3产出（以成功发育的幼虫平均数量/只蝇来衡量，或以带有感染性幼虫的蝇的比例来衡量）与平均微丝蚴摄取量之间的关系呈强烈的非线性。对于有武装的蚋种（奥氏蚋复合种、奥亚波克蚋复合种），这种非线性最好用S形函数表示；对于无武装的蝇种（恶蚋复合种、圭亚那蚋），则用双曲线表达式表示。这些结果分别与淋巴丝虫病蚊媒中描述的“初始促进”和“限制”模式相符。在所有4种媒介中均观察到最大平均L3数量为1 - 3条/只蝇。得出的结论是，盘尾丝虫幼虫发育到感染阶段受微丝蚴从蚋的血餐中移出早期阶段的密度依赖性机制调控。口咽骨片造成的损伤也可能是密度依赖性的。基于这种密度依赖性提出了一个假说，以解释迄今仅在具有发达下咽齿的媒介中记录到的初始促进现象。我们的结果为以下推测提供了定量支持：在主要媒介具有带齿前肠的流行地区，单纯化疗对减少盘尾丝虫病传播的影响可能比对媒介下咽无武装的疫区更大。
