Wahl G, Ekale D, Schmitz A
Institut für Tropenmedizin, Eberhard Karls Universität, Tübingen, Germany.
Parasitology. 1998 Apr;116 ( Pt 4):327-36. doi: 10.1017/s0031182097002333.
In the savanna areas of tropical Africa, cattle are frequently infected with the filaria Onchocerca ochengi. This parasite is closely related to Onchocerca volvulus, the causative agent of human onchocerciasis (river blindness), and is capable of developing in the same vector, Simulium damnosum s.l. In North Cameroon, where both O. ochengi and O. volvulus are endemic, we carried out a field study (reported in this and 2 following papers) to examine to which extent the transmission of the 2 parasite species overlap and what influence this has on the epidemiology of human onchocerciasis. In this paper we report our experiments to determine which of the S. damnosum species in North Cameroon act as vectors of O. ochengi, how efficiently they do so and whether other Simulium species play a vector role. To this end, infected cattle were exposed near 5 rivers in different geographical areas. Among 14 Simulium species identified as aquatic and/or adult stages at these rivers, only 6 (S. squamosum, S. damnosum s.s., S. sirbanum, S. bovis, S. wellmanni and S. hargreavesi) were found to bite cattle in important numbers in at least 1 of the sites. The 3 species of the S. damnosum complex were all capable of ingesting microfilariae (mf) of O. ochengi and developing a proportion of them to infective larvae (L3). Whereas S. squamosum and S. damnosum s.s., the prevailing vectors in the Guinea and Sudan savanna respectively, showed a high vector competence (17% of ingested mf developed to L3), S. sirbanum, which was much rarer in both areas, appeared to have a much lower susceptibility (2%). Other boophilic Simulium species were only seen in certain sites and seasons, being either incapable of ingesting important numbers of O. ochengi mf from body regions where these mf were abundant (S. bovis, S. hargreavesi); not able to support the development of ingested mf to L3 (S. wellmanni), or bit cattle preferentially in the ears, where O. ochengi mf do not occur (S. hargreavesi). We conclude that in North Cameroon members of the S. damnosum complex are the only important vectors of O. ochengi, with S. squamosum and S. damnosum s.s. being the main vectors.
在热带非洲的稀树草原地区，牛经常感染丝状虫奥氏盘尾丝虫。这种寄生虫与引起人类盘尾丝虫病（河盲症）的旋盘尾丝虫密切相关，并且能够在同一种媒介——恶蚋复合种中发育。在喀麦隆北部，奥氏盘尾丝虫和旋盘尾丝虫都是地方病流行区，我们开展了一项实地研究（本论文及随后两篇论文进行了报道），以调查这两种寄生虫的传播在多大程度上重叠，以及这对人类盘尾丝虫病的流行病学有何影响。在本文中，我们报告了我们的实验，以确定喀麦隆北部的哪些恶蚋种类是奥氏盘尾丝虫的传播媒介，它们的传播效率如何，以及其他蚋属种类是否起到传播媒介的作用。为此，将感染的牛放置在不同地理区域的5条河流附近。在这些河流中鉴定出的14种处于水生和/或成虫阶段的蚋属种类中，只有6种（鳞状蚋、指名亚种恶蚋、锡尔巴蚋、牛蚋、韦尔曼蚋和哈格里夫斯蚋）在至少一个地点被发现大量叮咬牛。恶蚋复合种的3个种类都能够摄取奥氏盘尾丝虫的微丝蚴，并将其中一部分发育为感染性幼虫（L3）。几内亚稀树草原和苏丹稀树草原的主要传播媒介鳞状蚋和指名亚种恶蚋表现出较高的传播能力（摄取的微丝蚴中有17%发育为L3），而在这两个地区都较为罕见的锡尔巴蚋似乎易感性低得多（2%）。其他嗜牛蚋属种类仅在某些地点和季节出现，要么无法从微丝蚴丰富的身体部位摄取大量奥氏盘尾丝虫微丝蚴（牛蚋、哈格里夫斯蚋）；要么无法支持摄取的微丝蚴发育为L3（韦尔曼蚋），或者优先叮咬牛的耳朵，而奥氏盘尾丝虫微丝蚴不在耳朵中出现（哈格里夫斯蚋）。我们得出结论，在喀麦隆北部，恶蚋复合种的成员是奥氏盘尾丝虫唯一重要的传播媒介，鳞状蚋和指名亚种恶蚋是主要传播媒介。
