title: Strategies for dengue early warning, surveillance and control
Creators: name: Bowman, Leigh
Publisher: name: University of Liverpool Repository
Year: 2016

description: Dengue is a neglected tropical disease of global importance today. Transmitted by the mosquito vectors Aedes aegypti and Aedes albopictus, dengue afflicts both urban and rural human populations in a cycle of endemic and epidemic transmission. As the global dengue burden continues to grow, there is an urgent need for timely and effective vector control, the only means to prevent transmission of dengue. This thesis addressed these contemporary dengue challenges by investigating three key elements of dengue outbreak alert and response. At present, entomological surveillance protocols are used to quantify vector abundance as a measure of dengue transmission risk, and although routinely undertaken in numerous endemic areas, there has been no evidence-based consideration of their reliability or accuracy. Similarly, vector control tools and approaches are numerous and widely used, especially during outbreaks, despite insufficient evidence of effectiveness and impact on dengue transmission. Finally, effective early warning systems could provide sufficient time to mobilise resources for a timely response to possibly mitigate the impact of dengue outbreaks. A systematic review of the literature explored the evidence for the value of entomological indices and dengue transmission. Of 13 studies investigating associations between vector indices (mainly the Stegomyia indices) and dengue cases, 4 reported positive correlations, 4 found no correlation and 5 reported ambiguous or inconclusive associations. Single values of the Breteau Index (BI), widely used as dengue transmission thresholds, were shown to be unreliable. Hence, there is little evidence that vector indices correlate with dengue transmission, although some methods, such as adult mosquito indices, merit further research. The effectiveness of vector control tools was examined in a systematic review and meta-analysis. Of 41 studies eligible for inclusion, 19 provided sufficient data for meta-analyses. Though evidence was weak, reduced odds of dengue incidence were observed for house screening from 3 trials (Pooled OR: 0.22 (95% CI 0.05, 0.93)). 3 community-based combination interventions significantly impacted mosquito indices: BI Rate Ratio (RR) 0.48 (95% CI 0.26, 0.89); BI RR0.65 (95% CI 0.52, 0.81); BI Mean difference (MD) -4.66 (-5.89, -3.43). Remarkably, impact on dengue cases by fogging, a method widely used during outbreaks, had never been evaluated in randomised trials; only one study demonstrated effectiveness against the vector. Effectiveness of vector control methods were also analysed in a 1-year randomised controlled trial, in particular, indoor/outdoor fogging, indoor residual spraying and handheld spray-cans. Finally, a retrospective study of data from 5 countries in Asia and Latin America was conducted to prospect for alarm signals that potentially could warn of impending dengue outbreaks. The Shewhart method and Endemic Channel identified probable dengue cases and mean temperature as predictors of outbreaks, with sensitivities and positive predictive values of 95% and 48% in Dominican Republic, 86% and 44% in Mexico, indicating that these predictors could be beneficial if utilised in early warning systems. This thesis has highlighted fundamental knowledge gaps in dengue transmission dynamics and vector control that are crucial for effective outbreak warning and response systems. These must be addressed before existing or novel vector control tools can be optimised, with or without an efficacious vaccine, to reduce endemic and epidemic dengue.