Indices of onchocerciasis transmission by different members of the Simulium damnosum complex conflict with the paradigm of forest and savanna parasite strains
Indices of onchocerciasis transmission by different members of the Simulium damnosum complex conflict with the paradigm of forest and savanna parasite strains
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DOI：
10.1016/j.actatropica.2012.09.002
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发表时间：
2013-01-01
期刊：
影响因子：
2.7
通讯作者：
Garms, Rolf
中科院分区：
文献类型：
--
作者：
Cheke, Robert A.;Garms, Rolf
盘尾丝虫病在热带稀树草原地区通常比在森林中更严重，病理也因地理而异，差异往往归因于两种或两种以上菌株的存在以及病媒和菌株之间的不相容性。然而，苍蝇在森林中传播更多的感染性幼虫比他们的热带稀树草原同行，即使在同域性，矛盾的期望的基础上的森林和热带稀树草原菌株的范例。我们分析了来自非洲西部塞拉利昂到东部乌干达的48，800多个苍蝇解剖的Simujumdamnosum复合体的10个不同分类类别中发现的不同阶段盘尾丝虫幼虫数量的数据。样品是在伊维菌素广泛分布之前采集的，因此为评价控制措施提供了基线。稀树草原物种包含较少的幼虫每感染或每感染苍蝇比森林物种，即使当咬和parous率占。传播指数最高的是森林栖息的Pra型的圣保Simu（616 L3/1000经产蝇），最低的是草原栖息的物种S。damnosum/S. sirandum（135）和S. kilibrium（65）.在经产的S. damnosum/S. sirabe，S. kliyanshan，S. squamosum、S. yahense，S. sanctipauli，S. leonense和S. soubrense均符合负二项分布，以草原种（S. damnosum/S. sirabe）比主要的森林居住物种具有较少的过度分散分布。即使在森林和稀树草原同域分布并叮咬同一人群时，这些感染模式也得以维持。此外，第一次，失明程度与森林媒介S的感染强度呈正相关。yahense，与以前报告的热带草原区的关系一致。另一个新的结果是，L1-2幼虫转化为L3的转化率是相等的森林和稀树草原载体。我们认为，无论是多种因素都有助于观察到的疾病模式或许多寄生虫菌株存在于一个连续体。(C)2012爱思唯尔有限公司版权所有。
Onchocerciasis in savanna zones is generally more severe than in the forest and pathologies also differ geographically, differences often ascribed to the existence of two or more strains and incompatibilities between vectors and strains. However, flies in the forest transmit more infective larvae than their savanna counterparts, even in sympatry, contradicting expectations based on the forest and savanna strains paradigm. We analysed data on the numbers of Onchocerca volvulus larvae of different stages found in 10 different taxonomic categories of the Simulium damnosum complex derived from more than 48,800 dissections of flies from Sierra Leone in the west of Africa to Uganda in the east. The samples were collected before widespread ivermectin distribution and thus provide a baseline for evaluating control measures. Savanna species contained fewer larvae per infected or per infective fly than the forest species, even when biting and parous rates were accounted for. The highest transmission indices were found in the forest-dwelling Pra form of Simulium sanctipauli (616 L3/1000 parous flies) and the lowest in the savanna-inhabiting species S. damnosum/S. sirbanum (135) and S. kilibanum (65). Frequency distributions of numbers of L1-2 and L3 larvae found in parous S. damnosum/S. sirbanum, S. klibanum, S. squamosum, S. yahense, S. sanctipauli, S. leonense and S. soubrense all conformed to the negative binomial distribution, with the mainly savanna-dwelling species (S. damnosum/S. sirbanum) having less overdispersed distributions than the mainly forest-dwelling species. These infection patterns were maintained even when forest and savanna forms were sympatric and biting the same human population. Furthermore, for the first time, levels of blindness were positively correlated with infection intensities of the forest vector S. yahense, consistent with relations previously reported for savanna zones. Another novel result was that conversion rates of L1-2 larvae to L3s were equivalent for both forest and savanna vectors. We suggest that either a multiplicity of factors are contributing to the observed disease patterns or that many parasite strains exist within a continuum. (C) 2012 Elsevier B.V. All rights reserved.