Ifakara Health Institute, Biomedical and Environmental Thematic Group, Ifakara, Tanzania.
Malar J. 2011 Apr 9;10:80. doi: 10.1186/1475-2875-10-80.
Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) represent the front-line tools for malaria vector control globally, but are optimally effective where the majority of baseline transmission occurs indoors. In the surveyed area of rural southern Tanzania, bed net use steadily increased over the last decade, reducing malaria transmission intensity by 94%.
Starting before bed nets were introduced (1997), and then after two milestones of net use had been reached-75% community-wide use of untreated nets (2004) and then 47% use of ITNs (2009)-hourly biting rates of malaria vectors from the Anopheles gambiae complex and Anopheles funestus group were surveyed.
In 1997, An. gambiae s.l. and An. funestus mosquitoes exhibited a tendency to bite humans inside houses late at night. For An. gambiae s.l., by 2009, nocturnal activity was less (p = 0.0018). At this time, the sibling species composition of the complex had shifted from predominantly An. gambiae s.s. to predominantly An. arabiensis. For An. funestus, by 2009, nocturnal activity was less (p = 0.0054) as well as the proportion biting indoors (p < 0.0001). At this time, An. funestus s.s. remained the predominant species within this group. As a consequence of these altered feeding patterns, the proportion (mean ± standard error) of human contact with mosquitoes (bites per person per night) occurring indoors dropped from 0.99 ± 0.002 in 1997 to 0.82 ± 0.008 in 2009 for the An. gambiae complex (p = 0.0143) and from 1.00 ± <0.001 to only 0.50 ± 0.048 for the An. funestus complex (p = 0.0004) over the same time period.
High usage of ITNs can dramatically alter African vector populations so that intense, predominantly indoor transmission is replaced by greatly lowered residual transmission, a greater proportion of which occurs outdoors. Regardless of the underlying mechanism, the residual, self-sustaining transmission will respond poorly to further insecticidal measures within houses. Additional vector control tools which target outdoor biting mosquitoes at the adult or immature stages are required to complement ITNs and IRS.
经杀虫剂处理的蚊帐（ITN）和室内滞留喷洒（IRS）是全球疟疾媒介控制的一线工具，但在大多数基线传播发生在室内的地方效果最佳。在坦桑尼亚南部农村地区，过去十年中，蚊帐的使用稳步增加，将疟疾传播强度降低了 94%。
从引入蚊帐之前（1997 年）开始，然后在达到两个蚊帐使用里程碑后——2004 年社区范围内未处理蚊帐使用率达到 75%，2009 年 ITN 使用率达到 47%——对冈比亚按蚊复合体和致倦库蚊组的疟疾病媒按蚊的每小时叮咬率进行了调查。
1997 年，冈比亚按蚊复合体和致倦库蚊组的蚊子有在深夜到室内叮咬人类的趋势。对于冈比亚按蚊复合体，到 2009 年，夜间活动减少（p=0.0018）。此时，该复合体的种系组成已从主要的冈比亚按蚊 s.s.转变为主要的冈比亚按蚊 arabiensis。对于致倦库蚊，到 2009 年，夜间活动减少（p=0.0054），以及室内叮咬的比例（p<0.0001）。此时，致倦库蚊 s.s.仍然是该组中的主要物种。由于这些改变的摄食模式，在室内与人接触的蚊子（每人每晚叮咬数）的比例从 1997 年的 0.99±0.002 下降到 2009 年的冈比亚按蚊复合体的 0.82±0.008（p=0.0143）和从致倦库蚊复合体的 1.00±<0.001 下降到 0.50±0.048（p=0.0004）。
高使用率的 ITN 可以显著改变非洲病媒种群，使强烈的、主要发生在室内的传播被大大降低的残留传播所取代，其中更大比例发生在户外。无论潜在机制如何，残留的、自我维持的传播对室内进一步的杀虫措施反应不佳。需要在成虫或幼虫阶段针对户外叮咬蚊子的额外病媒控制工具来补充 ITN 和 IRS。
