Russell Tanya L, Beebe Nigel W, Bugoro Hugo, Apairamo Allan, Chow Weng K, Cooper Robert D, Collins Frank H, Lobo Neil F, Burkot Thomas R
Australian Institute of Tropical Health and Medicine, James Cook University, Cairns, QLD, 4870, Australia.
School of Biological Sciences, University of Queensland, St. Lucia, Brisbane, QLD, 4068, Australia.
Malar J. 2016 Mar 10;15:156. doi: 10.1186/s12936-016-1195-8.
The effectiveness of vector control on malaria transmission by long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) depends on the vectors entering houses to blood feed and rest when people are inside houses. In the Solomon Islands, significant reductions in malaria have been achieved in the past 20 years with insecticide-treated bed nets, IRS, improved diagnosis and treatment with artemisinin combination therapies; despite the preference of the primary vector, Anopheles farauti, to feed outdoors and early in the evening and thereby avoid potential exposure to insecticides. Rational development of tools to complement LLINs and IRS by attacking vectors outdoor requires detailed knowledge of the biology and behaviours of the target species.
Malaria transmission in Central Province, Solomon Islands was estimated by measuring the components comprising the entomological inoculation rate (EIR) as well as the vectorial capacity of An. farauti. In addition, the daily and seasonal biting behaviour of An. farauti, was examined and the duration of the feeding cycle was estimated with a mark-release-recapture experiment.
Anopheles farauti was highly exophagic with 72% captured by human landing catches (HLC) outside of houses. Three-quarters (76%) of blood feeding on humans was estimated to occur before 21.00 h. When the hourly location of humans was considered, the proportion of exposure to mosquito bites on humans occurring indoors (πi) was only 0.130 ± 0.129. Peak densities of host seeking An. farauti occurred between October and January. The annual EIR was estimated to be 2.5 for 2012 and 33.2 for 2013. The length of the feeding cycle was 2.1 days.
The short duration of the feeding cycle by this species offers an explanation for the substantial control of malaria that has been achieved in the Solomon Islands by LLINs and IRS. Anopheles farauti is primarily exophagic and early biting, with 13% of mosquitoes entering houses to feed late at night during each feeding cycle. The two-day feeding cycle of An. farauti requires females to take 5-6 blood meals before the extrinsic incubation period (EIP) is completed; and this could translate into substantial population-level mortality by LLINs or IRS before females would be infectious to humans with Plasmodium falciparum and Plasmodium vivax. Although An. farauti is primarily exophagic, the indoor vector control tools recommended by the World Health Organization (LLINs and IRS) can still provide an important level of control. Nonetheless, elimination will likely require vector control tools that target other bionomic vulnerabilities to suppress transmission outdoors and that complement the control provided by LLINs and IRS.
长效驱虫蚊帐（LLINs）和室内滞留喷洒（IRS）等病媒控制措施对疟疾传播的有效性取决于病媒在人们身处室内时进入房屋进行吸血和休息。在所罗门群岛，过去20年通过使用杀虫剂处理过的蚊帐、室内滞留喷洒、改进青蒿素联合疗法的诊断和治疗，疟疾已大幅减少；尽管主要病媒法氏按蚊偏好户外吸血且在傍晚早期吸血，从而避免潜在接触杀虫剂。合理开发通过攻击户外病媒来补充长效驱虫蚊帐和室内滞留喷洒的工具，需要详细了解目标物种的生物学特性和行为。
通过测量构成昆虫学接种率（EIR）的各个组成部分以及法氏按蚊的传播能力，估算所罗门群岛中部省份的疟疾传播情况。此外，还研究了法氏按蚊的每日和季节性叮咬行为，并通过标记释放再捕获实验估算了取食周期的时长。
法氏按蚊具有很强的嗜外习性，72%是在房屋外通过人饵诱捕法（HLC）捕获的。估计四分之三（76%）的人血吸食发生在21:00之前。考虑到人类的每小时位置后，人类在室内遭受蚊虫叮咬的暴露比例（πi）仅为0.130±0.129。寻找宿主的法氏按蚊的密度峰值出现在10月至1月之间。2012年的年度昆虫学接种率估计为2.5，2013年为33.2。取食周期时长为2.1天。
该物种取食周期短，这为长效驱虫蚊帐和室内滞留喷洒在所罗门群岛实现疟疾的有效控制提供了解释。法氏按蚊主要嗜外且叮咬较早，在每个取食周期中，有13%的蚊子会在深夜进入房屋吸血。法氏按蚊两天的取食周期要求雌蚊在完成外在潜伏期（EIP）之前吸食5 - 6次血餐；这可能导致长效驱虫蚊帐或室内滞留喷洒在雌蚊能够将恶性疟原虫和间日疟原虫传染给人类之前造成大量种群水平的死亡。尽管法氏按蚊主要嗜外，但世界卫生组织推荐的室内病媒控制工具（长效驱虫蚊帐和室内滞留喷洒）仍可提供重要程度的控制。尽管如此，要实现消除疟疾，可能需要针对其他生物学弱点的病媒控制工具，以抑制户外传播，并补充长效驱虫蚊帐和室内滞留喷洒所提供的控制。
