Feeding habits of mosquitoes (Diptera: Culicidae) in an area of sylvatic transmission of yellow fever in the state of São Paulo, Brazil

AbstractBackground The reintroduction of sylvatic yellow fever in the state of São Paulo after about six decades was confirmed in the Northwestern region in 2000, where in 2008 there also occurred an important epizootic. The purpose of this study was to investigate the feeding habits of culicids potentially involved in the sylvatic transmission of the virus in this region.Methods Specimens were collected in 24 forested localities at ground level with hand nets and mouth aspirators. Collections were made quarterly between October 2006 and July 2008 during daylight hours. Blood-meal identification was carried out in mosquitoes of the tribes Aedini, Mansoniini and Sabethini. The biotin/avidin sandwich ELISA was employed to determine six source types: bird, bovine, equine, rat, human and monkey.Results A total of 24,879 females of the three tribes were obtained, 245 (0.98%) of which were engorged. The presence of three different blood sources per engorged female was the predominant situation, and included 35.10% of the total of samples processed. Samples with two or four different sources were represented by 25.31% and 25.71%, of the specimens, respectively, while just 9.39% had only one type and 1.22%, five different sources. Aedes scapularis, Ae. serratus(Group),Psorophora albigenu and Ps. ferox were the most abundant species and accounted for about 95% of the engorged specimens. Of the principal vector species,Haemagogus janthinomys/capricorniiwas found with bird, bovine and primate blood. These sources were predominant and alternated top ranking as the most frequent source according to the mosquito species and collection site. In general, primate blood was the most prevalent source.Conclusions The human population of the region visits this ecotone frequently, which indicates the need for the periodical assessment of vaccination coverage against yellow fever. The frequency of non-human primate blood source in mosquito species that show minor vector importance in yellow fever virus transmission deserves attention. The eclectic feeding habits and some aspects of the interactions between potential vectors and reservoirs of yellow fever may be associated with the habitat fragmentation characteristic of the region. We recommend that further studies on the capacity and vector competence be performed on secondary vectors in extra-Amazonian region.

摘要 背景
2000年，圣保罗州西北部地区证实时隔约60年后再次出现森林型黄热病（sylvatic yellow fever）；2008年该区域亦暴发大规模兽疫（epizootic）。本研究旨在探究该区域内可能参与病毒森林型传播的蚊类（culicids）的吸血习性。
方法
2006年10月至2008年7月期间，每季度于日间在24处林地的地面层，采用手持捕虫网（hand nets）与口吸式采集器（mouth aspirators）采集标本。对伊蚊族（Aedini）、曼蚊族（Mansoniini）及塞蚊族（Sabethini）的蚊虫开展血餐鉴定（blood-meal identification）。采用生物素-亲和素夹心酶联免疫吸附试验（biotin/avidin sandwich ELISA）检测6类血源：鸟类、牛、马、大鼠、人类及非人灵长类。
结果
共采集到3个族的雌蚊24879只，其中245只（占比0.98%）为吸饱血个体（engorged）。单只吸饱血雌蚊携带3种不同血源的情况最为普遍，占总检测样本的35.10%；携带2种、4种血源的样本占比分别为25.31%与25.71%；仅携带1种血源的样本占9.39%，携带5种血源的仅占1.22%。常见优势物种为鬃伊蚊（Aedes scapularis）、锯缘伊蚊复合组（Ae. serratus(Group)）、白基哈蚊（Psorophora albigenu）及费氏哈蚊（Ps. ferox），其吸饱血个体占总吸饱血样本的约95%。在主要媒介物种中，检测到紫腰哈蚊/卡氏哈蚊（Haemagogus janthinomys/capricornii）携带鸟类、牛及灵长类血源；根据蚊虫物种与采集地点的不同，上述血源的出现频率交替位居前列。整体而言，灵长类血源最为常见。
结论
该区域的人类活动频繁涉足该生态交错带（ecotone），提示需定期评估黄热病疫苗接种覆盖情况。在黄热病病毒传播中媒介作用较弱的蚊类物种中，非人灵长类血源的检出频率值得关注。潜在媒介与黄热病病毒储存宿主间的兼性吸血习性（eclectic feeding habits）及部分相互作用特征，或与该区域特有的生境破碎化（habitat fragmentation）相关。我们建议针对亚马逊以外区域的次要媒介物种，开展媒介能力与媒介效能（vector competence）的相关后续研究。