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A critical assessment of vector control for dengue prevention.

ABSTRACT: Recently, the Vaccines to Vaccinate (v2V) initiative was reconfigured into the Partnership for Dengue Control (PDC), a multi-sponsored and independent initiative. This redirection is consistent with the growing consensus among the dengue-prevention community that no single intervention will be sufficient to control dengue disease. The PDC's expectation is that when an effective dengue virus (DENV) vaccine is commercially available, the public health community will continue to rely on vector control because the two strategies complement and enhance one another. Although the concept of integrated intervention for dengue prevention is gaining increasingly broader acceptance, to date, no consensus has been reached regarding the details of how and what combination of approaches can be most effectively implemented to manage disease. To fill that gap, the PDC proposed a three step process: (1) a critical assessment of current vector control tools and those under development, (2) outlining a research agenda for determining, in a definitive way, what existing tools work best, and (3) determining how to combine the best vector control options, which have systematically been defined in this process, with DENV vaccines. To address the first step, the PDC convened a meeting of international experts during November 2013 in Washington, DC, to critically assess existing vector control interventions and tools under development. This report summarizes those deliberations.

SUBMITTER: Achee NL

PROVIDER: S-EPMC4423954 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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A critical assessment of vector control for dengue prevention.

Achee Nicole L NL Gould Fred F Perkins T Alex TA Reiner Robert C RC Morrison Amy C AC Ritchie Scott A SA Gubler Duane J DJ Teyssou Remy R Scott Thomas W TW

PLoS neglected tropical diseases 20150507 5

Recently, the Vaccines to Vaccinate (v2V) initiative was reconfigured into the Partnership for Dengue Control (PDC), a multi-sponsored and independent initiative. This redirection is consistent with the growing consensus among the dengue-prevention community that no single intervention will be sufficient to control dengue disease. The PDC's expectation is that when an effective dengue virus (DENV) vaccine is commercially available, the public health community will continue to rely on vector cont ...[more]

PMID: 25951103

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Project description:BackgroundAn estimated 2·5 billion people are at risk of dengue. Incidence of dengue is especially high in resource-constrained countries, where control relies mainly on insecticides targeted at larval or adult mosquitoes. We did epidemiological and economic assessments of different vector control strategies.MethodsWe developed a dynamic model of dengue transmission that assesses the evolution of insecticide resistance and immunity in the human population, thus allowing for long-term evolutionary and immunological effects of decreased dengue transmission. We measured the dengue health burden in terms of disability-adjusted life-years (DALYs) lost. We did a cost-effectiveness analysis of 43 insecticide-based vector control strategies, including strategies targeted at adult and larval stages, at varying efficacies (high-efficacy [90% mortality], medium-efficacy [60% mortality], and low-efficacy [30% mortality]) and yearly application frequencies (one to six applications). To assess the effect of parameter uncertainty on the results, we did a probabilistic sensitivity analysis and a threshold analysis.FindingsAll interventions caused the emergence of insecticide resistance, which, with the loss of herd immunity, will increase the magnitude of future dengue epidemics. In our model, one or more applications of high-efficacy larval control reduced dengue burden for up to 2 years, whereas three or more applications of adult vector control reduced dengue burden for up to 4 years. The incremental cost-effectiveness ratios of the strategies for two high-efficacy adult vector control applications per year was US$615 per DALY saved and for six high-efficacy adult vector control applications per year was $1267 per DALY saved. Sensitivity analysis showed that if the cost of adult control was more than 8·2 times the cost of larval control then all strategies based on adult control became dominated.InterpretationSix high-efficacy adult vector control applications per year has a cost-effectiveness ratio that will probably meet WHO's standard for a cost-effective or very cost-effective intervention. Year-round larval control can be counterproductive, exacerbating epidemics in later years because of evolution of insecticide resistance and loss of herd immunity. We suggest the reassessment of vector control policies that are based on larval control only.FundingThe Fulbright Programme, CAPES (Brazilian federal agency for post-graduate education), the Miriam Burnett trust, and the Notsew Orm Sands Foundation.

Project description:BackgroundBecause no dengue vaccine or antiviral therapy is commercially available, controlling the primary mosquito vector, Aedes aegypti, is currently the only means to prevent dengue outbreaks. Traditional models of Ae. aegypti assume that population dynamics are regulated by density-dependent larval competition for food and little affected by oviposition behavior. Due to direct impacts on offspring survival and development, however, mosquito choice in oviposition site can have important consequences for population regulation that should be taken into account when designing vector control programs.Methodology/principal findingsWe examined oviposition patterns by Ae. aegypti among 591 naturally occurring containers and a set of experimental containers in Iquitos, Peru. Using larval starvation bioassays as an indirect measure of container food content, we assessed whether females select containers with the most food for their offspring. Our data indicate that choice of egg-laying site is influenced by conspecific larvae and pupae, container fill method, container size, lid, and sun exposure. Although larval food positively influenced oviposition, our results did not support the hypothesis that females act primarily to maximize food for larvae. Females were most strongly attracted to sites containing immature conspecifics, even when potential competitors for their progeny were present in abundance.Conclusion/significanceDue to strong conspecific attraction, egg-laying behavior may contribute more to regulating Ae. aegypti populations than previously thought. If highly infested containers are targeted for removal or larvicide application, females that would have preferentially oviposited in those sites may instead distribute their eggs among other suitable, previously unoccupied containers. Strategies that kill mosquitoes late in their development (i.e., insect growth regulators that kill pupae rather than larvae) will enhance vector control by creating "egg sinks," treated sites that exploit conspecific attraction of ovipositing females, but reduce emergence of adult mosquitoes via density-dependent larval competition and late acting insecticide.

Project description:BackgroundControl and prevention of dengue relies heavily on the application of insecticides to control dengue vector mosquitoes. In Colombia, application of the larvicide temephos to the aquatic breeding sites of Aedes aegypti is a key part of the dengue control strategy. Resistance to temephos was recently detected in the dengue-endemic city of Cucuta, leading to questions about its efficacy as a control tool. Here, we characterize the underlying mechanisms and estimate the operational impact of this resistance.Methodology/principal findingsLarval bioassays of Ae. aegypti larvae from Cucuta determined the temephos LC50 to be 0.066 ppm (95% CI 0.06-0.074), approximately 15× higher than the value obtained from a susceptible laboratory colony. The efficacy of the field dose of temephos at killing this resistant Cucuta population was greatly reduced, with mortality rates <80% two weeks after application and <50% after 4 weeks. Neither biochemical assays nor partial sequencing of the ace-1 gene implicated target site resistance as the primary resistance mechanism. Synergism assays and microarray analysis suggested that metabolic mechanisms were most likely responsible for the temephos resistance. Interestingly, although the greatest synergism was observed with the carboxylesterase inhibitor, DEF, the primary candidate genes from the microarray analysis, and confirmed by quantitative PCR, were cytochrome P450 oxidases, notably CYP6N12, CYP6F3 and CYP6M11.Conclusions/significanceIn Colombia, resistance to temephos in Ae. aegypti compromises the duration of its effect as a vector control tool. Several candidate genes potentially responsible for metabolic resistance to temephos were identified. Given the limited number of insecticides that are approved for vector control, future chemical-based control strategies should take into account the mechanisms underlying the resistance to discern which insecticides would likely lead to the greatest control efficacy while minimizing further selection of resistant phenotypes.

Project description:The application of the organophosphate larvicide temephos to water storage containers is one of the most commonly employed dengue vector control methods. This systematic literature review is to the knowledge of the authors the first that aims to assess the community-effectiveness of temephos in controlling both vectors and dengue transmission when delivered either as a single intervention or in combination with other interventions. A comprehensive literature search of 6 databases was performed (PubMed, WHOLIS, GIFT, CDSR, EMBASE, Wiley), grey literature and cross references were also screened for relevant studies. Data were extracted and methodological quality of the studies was assessed independently by two reviewers. 27 studies were included in this systematic review (11 single intervention studies and 16 combined intervention studies). All 11 single intervention studies showed consistently that using temephos led to a reduction in entomological indices. Although 11 of the 16 combined intervention studies showed that temephos application together with other chemical vector control methods also reduced entomological indices, this was either not sustained over time or-as in the five remaining studies--failed to reduce the immature stages. The community-effectiveness of temephos was found to be dependent on factors such as quality of delivery, water turnover rate, type of water, and environmental factors such as organic debris, temperature and exposure to sunlight. Timing of temephos deployment and its need for reapplication, along with behavioural factors such as the reluctance of its application to drinking water, and operational aspects such as cost, supplies, time and labour were further limitations identified in this review. In conclusion, when applied as a single intervention, temephos was found to be effective at suppressing entomological indices, however, the same effect has not been observed when temephos was applied in combination with other interventions. There is no evidence to suggest that temephos use is associated with reductions in dengue transmission.

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A critical assessment of vector control for dengue prevention.

Publications

A critical assessment of vector control for dengue prevention.

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