Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham Maritime ME4 4 TB, Kent, UK.
School of Natural Sciences and Psychology, Liverpool John Moores University, Byrom Street, Liverpool L3 3AH, UK; London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
Acta Trop. 2023 Sep;245:106970. doi: 10.1016/j.actatropica.2023.106970. Epub 2023 Jun 18.
Simulium damnosum s.l., the most important vector of onchocerciasis in Africa, is a complex of sibling species described on the basis of differences in their larval polytene chromosomes. These (cyto) species differ in their geographical distributions, ecologies and epidemiological roles. In Togo and Benin, distributional changes have been recorded as a consequence of vector control and environmental changes (e.g. creation of dams, deforestation), with potential epidemiological consequences. We review the distribution of cytospecies in Togo and Benin and report changes observed from 1975 to 2018. The elimination of the Djodji form of S. sanctipauli in south-western Togo in 1988 seems to have had no long-term effects on the distribution of the other cytospecies, despite an initial surge by S. yahense. Although we report a general tendency for long-term stability in most cytospecies' distributions, we also assess how the cytospecies' geographical distributions have fluctuated and how they vary with the seasons. In addition to seasonal expansions of geographical ranges by all species except S. yahense, there are seasonal variations in the relative abundances of cytospecies within a year. In the lower Mono river, the Beffa form of S. soubrense predominates in the dry season but is replaced as the dominant taxon in the rainy season by S. damnosum s.str. Deforestation was previously implicated in an increase of savanna cytospecies in southern Togo (1975-1997), but our data had little power to support (or refute) suggestions of a continuing increase, partly because of a lack of recent sampling. In contrast, the construction of dams and other environmental changes including climate change seem to be leading to decreases in the populations of S. damnosum s.l. in Togo and Benin. If so, combined with the disappearance of the Djodji form of S. sanctipauli, a potent vector, plus historic vector control actions and community directed treatments with ivermectin, onchocerciasis transmission in Togo and Benin is much reduced compared with the situation in 1975.
斯氏按蚊复合体（Simulium damnosum s.l.）是非洲最重要的盘尾丝虫病传播媒介，是根据幼虫多线染色体差异描述的姊妹种复合物。这些（细胞）种在地理分布、生态和流行病学作用上存在差异。在多哥和贝宁，由于媒介控制和环境变化（例如大坝的建设、森林砍伐），记录到分布发生了变化，可能带来流行病学方面的后果。我们回顾了多哥和贝宁细胞种的分布情况，并报告了 1975 年至 2018 年观察到的变化。1988 年，多哥西南部的 Djodji 型圣塔保罗按蚊（S. sanctipauli）被消灭，这似乎并没有对其他细胞种的分布产生长期影响，尽管 S. yahense 最初有所增加。尽管我们报告说，大多数细胞种的分布长期以来一直保持稳定，但我们也评估了细胞种的地理分布如何波动，以及它们如何随季节变化。除了除 S. yahense 以外的所有种的地理范围季节性扩张外，一年内细胞种的相对丰度也存在季节性变化。在莫诺河下游，Beffa 型 S. soubrense 在旱季占主导地位，但在雨季被 S. damnosum s.str. 取代成为优势分类群。森林砍伐此前被认为是导致多哥南部稀树草原细胞种增加的原因（1975-1997 年），但我们的数据没有足够的能力来支持（或反驳）持续增加的说法，部分原因是缺乏最近的采样。相比之下，水坝的建设和包括气候变化在内的其他环境变化似乎导致多哥和贝宁的斯氏按蚊复合体种群减少。如果是这样，再加上 Djodji 型圣塔保罗按蚊（一种强有力的传播媒介）的消失，加上历史上的媒介控制行动和伊维菌素的社区定向治疗，与 1975 年相比，多哥和贝宁的盘尾丝虫病传播大大减少。
