River Boats Contribute to the Regional Spread of the Dengue Vector Aedes aegypti in the Peruvian Amazon

Background and ObjectivesThe dramatic range expansion of the dengue vector Aedes aegypti is associated with various anthropogenic transport activities, but little is known about the underlying mechanisms driving this geographic expansion. We longitudinally characterized infestation of different vehicle types (cars, boats, etc.) to estimate the frequency and intensity of mosquito introductions into novel locations (propagule pressure).MethodsExhaustive adult and immature Ae. aegypti collections were performed on six different vehicle types at five ports and two bus/ taxi departure points in the Amazonian city of Iquitos, Peru during 2013. Aquatic vehicles included 32 large and 33 medium-sized barges, 53 water taxis, and 41 speed boats. Terrestrial vehicles sampled included 40 buses and 30 taxis traveling on the only highway in the region. Ae. aegypti adult infestation rates and immature indices were analyzed by vehicle type, location within vehicles, and sampling date.ResultsLarge barges (71.9% infested) and medium barges (39.4% infested) accounted for most of the infestations. Notably, buses had an overall infestation rate of 12.5%. On large barges, the greatest number of Ae. aegypti adults were found in October, whereas most immatures were found in February followed by October. The vast majority of larvae (85.9%) and pupae (76.7%) collected in large barges were produced in puddles formed in cargo holds.ConclusionsBecause larges barges provide suitable mosquito habitats (due to dark, damp cargo storage spaces and ample oviposition sites), we conclude that they likely serve as significant contributors to mosquitoes’ propagule pressure across long distances throughout the Peruvian Amazon. This information can help anticipate vector population mixing and future range expansions of dengue and other viruses transmitted by Ae. aegypti.

背景与研究目的
登革热媒介埃及伊蚊（Aedes aegypti）的分布范围大幅扩张与各类人为运输活动密切相关，但目前对推动其地理扩张的潜在机制仍知之甚少。本研究通过纵向表征不同类型交通工具（汽车、船舶等）的蚊虫侵染情况，以估算蚊虫向新区域扩散的频率与强度（即繁殖体压力）。

研究方法
2013年，研究团队在秘鲁亚马逊城市伊基托斯的5个港口及2个公交/出租车发车点，针对6类不同交通工具开展了埃及伊蚊成蚊与幼体的全面采样工作。其中水上交通工具包括32艘大型驳船、33艘中型驳船、53艘水上出租车以及41艘高速快艇；陆地交通工具则涵盖该区域唯一一条公路上运营的40辆公交与30辆出租车。研究人员按交通工具类型、车内栖息位置及采样日期，对埃及伊蚊的成蚊侵染率与幼体指数进行了统计分析。

研究结果
大型驳船（侵染率71.9%）与中型驳船（侵染率39.4%）是蚊虫侵染的主要载体。值得注意的是，公交车辆的总体侵染率达12.5%。在大型驳船上，埃及伊蚊成蚊的最大检出量出现在10月，而幼体的最大检出量则集中在2月，其次为10月。在大型驳船采集的幼虫（85.9%）与蛹（76.7%）绝大多数滋生在货舱内形成的积水坑中。

研究结论
由于大型驳船具备黑暗潮湿的货舱存储空间与充足的产卵位点，可为蚊虫提供适宜的滋生环境，因此本研究认为，大型驳船极有可能是秘鲁亚马逊地区蚊虫远距离扩散繁殖体压力的重要贡献者。本研究结果可为预测媒介种群混合以及登革热等由埃及伊蚊传播的其他病毒的未来分布扩张提供参考依据。