Department of Vector Disease Control and Prevention, Xi'an Center for Disease Control and Prevention, Xi'an, Shaanxi, China.
Department of Hospital Infection Management, The Affiliated Hospital of Zunyi Medical University, Zun Yi, Guizhou, China.
PeerJ. 2024 Oct 22;12:e18246. doi: 10.7717/peerj.18246. eCollection 2024.
Dengue, a mosquito-borne viral disease, has occurred in many cities in China, and it tends to spread to higher latitudes (Huang et al., 2023). Xi'an, situated in central-west China, has witnessed an increase imported cases in the past few years, raising concerns of local dengue transmission. It is crucial to investigate the population density of and its insecticides resistance to enhance early warning of dengue fever.
Eight sampling sites in eight counties (YT, BL, WY, CH, YL, LN, LT, ZZ) of Xi'an city were surveyed by larval dipping and human-baited double net trap biweekly from June 2021 to September 2022. The Breteau Index (BI, number of positive containers per 100 houses) and Container Index (CI, the percentage of containers containing larvae or pupae) were used to assess larval density, and the human-baited double net trap (HDN, the number of females collected per person per hour) to indicate human bating rate (HBR). Meanwhile, the association between the meteorological factors and mosquito density was analyzed. The adult insecticides resistance was evaluated by the World Health Organization (WHO) standard resistance bioassay. Adult females were exposed to insecticide-impregnated paper for 1 h, then transferred to the recovery tube, and mortality rate was calculated after 24 h. According to the Implementation Plan for National Vector Surveillance (2016), resistance status was classified into three levels based on mortality: <80% mortality as resistant, between 80% and 98% mortality as possibly resistant, and >98% mortality as sensitive.
From June 2021 to September 2022, a total of 1,065 houses were surveyed for water holding containers, and 99 of 430 water holding containers were checked to be positive for larvae and pupae. A total of 1,048 females were collected. The average BI, CI and HBR were 10.39, 21.41, and 11.20 female/man/hour in 2021 and 8.86, 20.86, and 11.63 f/m/h in 2022, respectively. The findings showed that the BI exceeded 5 in most months and reached above 20 in specific months. The CI varied in different months and monitoring sites, with the highest CI in August 2021 and July 2022. The discarded tires had the highest positivity rate, with up to 40.32% testing positive for larvae. The monthly average temperature showed a positive correlation with CI ( = 0.77), and the monthly BI was positively associated with CI ( = 0.93). The BI, CI, and HBR were significantly higher in the rainy season than other seasons. The bioassay results showed that the mortality rate of at the YT monitoring site was 76.92%, indicating resistance to deltamethrin. The mortality rate of at BL, WY, CH, YL, LN, LT, and ZZ sampling sites were varying from 81.25%∼100%, suggesting possibly resistant or still sensitive to beta-cypermethrin, alpha-cypermethrin, malathion, chlorpyrifos, and propoxur.
登革热是一种由蚊子传播的病毒性疾病，已在中国许多城市发生，并倾向于传播到更高的纬度地区（Huang 等人，2023 年）。位于中国中西部的西安市在过去几年中见证了输入性病例的增加，引发了当地登革热传播的担忧。调查蚊虫种群密度及其对杀虫剂的抗药性，对于提高登革热的预警能力至关重要。
2021 年 6 月至 2022 年 9 月，采用幼虫浸渍法和人诱双帐法，在西安市 8 个县（YT、BL、WY、CH、YL、LN、LT、ZZ）的 8 个采样点进行每周两次的调查。布雷特指数（BI，每 100 户阳性容器数）和容器指数（CI，含有幼虫或蛹的容器百分比）用于评估幼虫密度，人诱双帐法（HDN，每小时每人人诱捕的雌蚊数）用于表示人诱捕率（HBR）。同时，分析气象因素与蚊虫密度的关系。采用世界卫生组织（WHO）标准抗性生物测定法评估成蚊对杀虫剂的抗性。将成年雌性昆虫暴露在浸渍有杀虫剂的纸上 1 小时，然后转移到恢复管中，24 小时后计算死亡率。根据《全国病媒生物监测方案（2016 年）》，死亡率<80%为抗性，80%至 98%为可能抗性，>98%为敏感。
2021 年 6 月至 2022 年 9 月，共调查了 1065 户有蓄水容器的房屋，对其中 430 个蓄水容器中的 99 个进行了检查，发现有 幼虫和蛹。共收集了 1048 只成年雌性昆虫。2021 年的平均 BI、CI 和 HBR 分别为 10.39、21.41 和 11.20 雌/人/小时，2022 年分别为 8.86、20.86 和 11.63 f/m/h。结果表明，大多数月份 BI 超过 5，特定月份 BI 超过 20。CI 在不同月份和监测点有所不同，2021 年 8 月和 2022 年 7 月 CI 最高。废弃轮胎的阳性率最高，达 40.32%。月平均温度与 CI 呈正相关（=0.77），月 BI 与 CI 呈正相关（=0.93）。雨季 BI、CI 和 HBR 明显高于其他季节。生物测定结果显示，YT 监测点的死亡率为 76.92%，表明对溴氰菊酯有抗性。BL、WY、CH、YL、LN、LT 和 ZZ 采样点的死亡率在 81.25%∼100%之间，表明对β-氯氰菊酯、α-氯氰菊酯、马拉硫磷、氯菊酯和残杀威可能有抗性或仍敏感。
