Abstract
In recent decades, dengue incidence has trended upward worldwide causing urgent needs for new or modified vector control methods. We modified the existing indoor residual spraying (IRS) method by applying insecticide on the outer walls of building structures in an outdoor residual spraying (ORS) study. A semi-field study was conducted to investigate the bio-efficacy of two different deltamethrin formulations: K-Othrine® Polyzone, new polymer-enhanced deltamethrin formulated as a suspension concentrate (SC-PE), and K-Othrine® WG 250, traditional deltamethrin formulated as water dispersible granule (WG). The residual bio-efficacy of deltamethrin SC-PE was compared to deltamethrin WG on finished cement surfaces applied to the outer walls at the Institute for Medical Research (IMR), Malaysia. Standard WHO cone wall bioassays were adapted to evaluate the effective duration of action of these deltamethrin formulations against susceptible laboratory-reared and wild, free-flying Aedes aegypti and Ae. albopictus. Analyses of bioassay results showed that deltamethrin SC-PE 30 mg/m2 has improved longevity in comparison to deltamethrin WG 30 mg/m2. Deltamethrin SC-PE 30 mg/m2 was effective until week 17 (producing > 80% mortality), surpassing deltamethrin WG 30 mg/m2 which only lasted until week 10. This was supported by post-hoc test analyses which demonstrated that deltamethrin SC-PE 30 mg/m2 produced the highest mean of mortality in laboratory-reared Aedes species and the wild Ae. albopictus. However, the effective duration of action of deltamethrin SC-PE (17 weeks) was less than the recommended period by WHO (6 months) but was reasonable given that the spraying was undertaken outdoor. This preliminary data could be of use for the deployment of locally adapted ORS operation in controlling dengue.
Highlights
Dengue is a mosquito-borne viral disease of humans affecting the economy and health of communities worldwide
Mosquitoes were exposed to deltamethrin water dispersible granule (WG) and SC-PE at two dosages: 25 mg/m2 and 30 mg/m2. 30 min knockdown (KD30) was recorded and mortality was assessed 24 h after exposure
It was rather unexpected that delta WG 25 treated wall showed knockdown percentages of more than 80% until week 17 compared to delta SC-PE 25 which caused knockdown > 80% until week 11 (Figure 1a, c)
Summary
Dengue is a mosquito-borne viral disease of humans affecting the economy and health of communities worldwide. Dengue incidence has increased dramatically from 2.2 million in 2010 to 3.2 million globally in 2015 due to rapid and unplanned urbanization, increased human mobility and trade, viral evolution such as vector resistance to insecticides, and climate change (Murray et al, 2013; WHO, 2017). Safe and cost-effective vaccine and specific anti-viral treatment against dengue is presently available, current efforts to reduce dengue transmission have focused primarily on vector control through combinations of biological-, gene-, mechanical-, and insecticide-based tools (Lee et al, 2015). While IRS has proved to be successful in reducing malaria transmission, evidence on the potential robustness of the IRS to reduce dengue burden is gradually emerging (Paredes-Esquivel et al, 2016; Vazquez-Prokopec et al, 2017a, 2017b). In Cairns, Australia, targeted IRS was combined with location-based contact tracing has reduced the probability of dengue transmission by 86–96% in comparison to unsprayed control (Vazquez-Prokopec et al, 2017b)
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