Residual Spray for the Control of <i>Aedes</i>Vectors in Dengue Outbreak Residential Areas

The incidence of dengue in Malaysia has shown an increasing trend since the year 2000. Vector control is the primary approach for dengue control in Malaysia. There is an urgent need for new or modified approaches such as the residual spraying on the outer walls that can potentially last long enough to control the Aedes population, particularly in the outbreak-prone areas. In this field study, we conducted outdoor residual spraying (ORS) using a newly formulated polymer-enhanced suspension concentrate (SC-PE) of deltamethrin. The objectives of this study were to evaluate the efficacy of ORS using deltamethrin SC-PE and its effect on wild Aedes populations and to assess its residual bio-efficacy on painted cement walls against the pyrethroid-susceptible strains of laboratory-reared Aedes mosquitoes. Three rounds of spraying in a four-month cycle were conducted between 2014 and 2015 in four residential areas (low-rise and high-rise housing types) in Hulu Langat, Selangor. The bio-efficacy of the insecticide was evaluated by assessing its impact on vector population using ovitrap surveillance. Standard WHO wall deposit bioassay was adapted to determine bio-efficacy of deltamethrin, i.e. post 30 min knockdown and post 24 h mortality after exposure. During the treatment period, we observed significant reductions in the population of Ae. albopictus in the sprayed low-rise housing in both semi-indoor and outdoor environments, while in the high-rise housing, there was also a significant decline in Ae. aegypti population in the semi-indoor environment. The evaluation of the residual bio-efficacy of deltamethrin SC-PE against laboratory-reared Aedes mosquitoes showed that the insecticide lasted longer in the high-rise housing compared to the low-rise housing with >80% mortality achieved continuously for 16 weeks. We provide initial evidence on residual efficacy of deltamethrin SC-PE in reducing Aedes population size in the low-rise and high-rise housing. Our results showed that ORS is a promising tool in the dengue vector control and like IRS in malaria control;it is a powerful and effective method if conducted correctly. However, large scale and well-designed studies with entomological and epidemiological endpoints are still warranted before its routine use in dengue control.

The practicality of Malaysia dengue outbreak forecasting model as an early warning system

Dengue is a harmful tropical disease that causes death to many people.Currently,the dengue vaccine development is still at an early stage,and only intervention methods exist after dengue cases increase.Thus,previously,two scientific experimental field studies were conducted in producing a dengue outbreak forecasting model as an early warning system.Successfully,an Autoregressive Distributed Lag(ADL)Model was developed using three factors:the epidemiological,entomological,and environmental with an accuracy of 85%;but a higher percentage is required in minimizing the error for the model to be useful.Hence,this study aimed to develop a practical and cost-effective dengue outbreak forecasting model with at least 90%accuracy to be embedded in an early warning computer system using the Internet of Things(IoT)approach.Eighty-one weeks of time series data of the three factors were used in six forecasting models,which were Autoregressive Distributed Lag(ADL),Hierarchical Forecasting(Bottom-up and Optimal combination)and three Machine Learning methods:(Artificial Neural Network(ANN),Support Vector Machine(SVM)and Random Forest).Five error measures were used to evaluate the consistency performance of the models in order to ensure model performance.The findings indicated Random Forest outperformed the other models with an accuracy of 95%when including all three factors.But practically,collecting mosquito related data(the entomological factor)was very costly and time consuming.Thus,it was removed from the model,and the accuracy dropped to 92%but still high enough to be of practical use,i.e.,beyond 90%.However,the practical ground operationalization of the early warning system also requires several rain gauges to be located at the dengue hot spots due to localized rainfall.Hence,further analysis was conducted in determining the location of the rain gauges.This has led to the recommendation that the rain gauges should be located about 3e4 km apart at the dengue hot spots to ensure the accuracy of the rainfall data to be included in the dengue outbreak forecasting model so that it can be embedded in the early warning system.Therefore,this early warning system can save lives,and prevention is better than cure.