Nyssorhynchus dunhami: bionomics and natural infection by Plasmodium falciparum and P. vivax in the Peruvian Amazon

BACKGROUND Nyssorhynchus dunhami, a member of the Nuneztovari Complex, has been collected in Brazil, Colombia, and Peru and described as zoophilic. Although to date Ny. dunhami has not been documented to be naturally infected by Plasmodium, it is frequently misidentified as other Oswaldoi subgroup species that are local or regional malaria vectors. OBJECTIVES The current study seeks to verify the morphological identification of Nuneztovari Complex species collected in the peri-Iquitos region of Amazonian Peru, to determine their Plasmodium infection status, and to describe ecological characteristics of their larval habitats. METHODS We collected Ny. nuneztovari s.l. adults in 2011-2012, and Ny. nuneztovari s.l. larvae and adults in 2016-2017. When possible, samples were identified molecularly using cytochrome c oxidase subunit I (COI) barcode sequencing. Adult Ny. nuneztovari s.l. from 2011-2012 were tested for Plasmodium using real-time PCR. Environmental characteristics associated with Ny. nuneztovari s.l. larvae-positive water bodies were evaluated. FINDINGS We collected 590 Ny. nuneztovari s.l. adults and 116 larvae from eight villages in peri-Iquitos. Of these, 191 adults and 111 larvae were identified by COI sequencing; all were Ny. dunhami. Three Ny. dunhami were infected with P. falciparum, and one with P. vivax, all collected from one village on one night. Ny. dunhami larvae were collected from natural and artificial water bodies, and their presence was positively associated with other Anophelinae larvae and amphibians, and negatively associated with people living within 250m. MAIN CONCLUSIONS Of Nuneztovari Complex species, we identified only Ny. dunhami across multiple years in eight peri-Iquitos localities. This study is, to our knowledge, the first report of natural infection of molecularly identified Ny. dunhami with Plasmodium. We advocate the use of molecular identification methods in this region to monitor Ny. dunhami and other putative secondary malaria vectors to more precisely evaluate their importance in malaria transmission.

研究背景：邓氏按蚊（Nyssorhynchus dunhami）属于努涅兹托瓦里复合群（Nuneztovari Complex），目前已在巴西、哥伦比亚及秘鲁被采集记录，其吸血习性被描述为嗜动物源性。截至目前，尚无文献记载邓氏按蚊自然感染疟原虫属（Plasmodium），但该物种常被误鉴定为奥斯瓦尔德氏亚群（Oswaldoi subgroup）的其他物种，而后者多为当地或区域疟疾传播媒介。研究目标：本研究旨在验证秘鲁亚马逊伊基托斯周边区域采集的努涅兹托瓦里复合群物种的形态学鉴定结果，明确其疟原虫感染状况，并描述其幼虫孳生地的生态学特征。研究方法：我们分别于2011-2012年采集了广义努涅兹托瓦里按蚊（Ny. nuneztovari s.l.）成虫，2016-2017年采集了该复合群的幼虫与成虫。若条件允许，通过细胞色素c氧化酶亚基I（cytochrome c oxidase subunit I, COI）条形码测序对样本进行分子鉴定。2011-2012年采集的广义努涅兹托瓦里按蚊成虫采用实时荧光定量PCR（real-time PCR）检测疟原虫感染情况。同时，对邓氏按蚊幼虫阳性水体的环境特征进行评估。研究结果：我们在伊基托斯周边8个村落共采集到590只广义努涅兹托瓦里按蚊成虫及116只幼虫。其中191只成虫与111只幼虫经COI测序完成鉴定，所有样本均为邓氏按蚊。3只邓氏按蚊感染了恶性疟原虫（Plasmodium falciparum），1只感染了间日疟原虫（Plasmodium vivax），所有感染个体均于同一夜间在同一村落采集获得。邓氏按蚊幼虫可孳生于自然及人工水体中，其存在与按蚊亚科（Anophelinae）其他幼虫及两栖动物呈正相关，与250米范围内的居民数量呈负相关。主要结论：在努涅兹托瓦里复合群物种中，我们在伊基托斯周边8个采样点连续多年仅检测到邓氏按蚊。据我们所知，本研究首次报道了经分子鉴定的邓氏按蚊自然感染疟原虫的案例。我们倡议在该区域采用分子鉴定方法，以监测邓氏按蚊及其他疑似次要疟疾媒介，从而更精准地评估它们在疟疾传播中的作用。