Abstract
House Index, Container Index, and Breteau Index are the most commonly used indices for dengue vector surveillance. However, these larval indices are a poor proxy for measuring the adult population—which is responsible for disease transmission. Information on the adult distribution and density are important for assessing transmission risk as well as for developing effective control strategies. This study introduces a new entomological index, Gravitrap aegypti index (GAI), which estimates the adult female Aedes aegypti population in the community and presents its association with dengue cases. Gravitraps were deployed across 34 treatment sites in Singapore from September 2013 to September 2016. The GAI, derived from the Gravitrap surveillance data, was analysed to investigate the spatio-temporal patterns of the Ae. aegypti population in Singapore. The index was further categorised into low, moderate, and high-risk groups and its association with dengue cases were examined. A Before-After Control Impact analysis was performed to evaluate the epidemiology impact of Gravitrap system on dengue transmission. The Ae. aegypti population exhibits a seasonal pattern, and spatial heterogeneity in Ae. aegypti abundance was observed among treatment sites. The Ae. aegypti population was also found to be unevenly distributed among floors of an apartment block, with low floors (floors 1–4) having a higher abundance of mosquitoes trapped than mid (floors 5–8) and high (floors ≥9) floors. Areas with high GAI were shown to have higher dengue case count. Gravitrap has also demonstrated to be a good dengue control tool. The contribution of cases by treatment sites to the national numbers was lower after Gravitraps deployment. The GAI, which is of better relevance to dengue transmission risk, could be recommended as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adult Aedes population in the country. In addition, findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission.
Highlights
Dengue fever has become the most important mosquito-borne viral disease due to its increasing frequency and magnitude of dengue epidemics as well as its high morbidity and mortality [1,2]
The Gravitrap aegypti index (GAI), which is of better relevance to dengue transmission risk, could be recommended as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adult Aedes population in the country
Findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission
Summary
Dengue fever has become the most important mosquito-borne viral disease due to its increasing frequency and magnitude of dengue epidemics as well as its high morbidity and mortality [1,2]. Dengue fever is caused by infection with one of the four dengue virus serotypes and is transmitted to humans primarily by the mosquito Aedes aegypti and by Ae. albopictus as a secondary vector [5,6]. Both Ae. aegypti and Ae. albopictus are known to be widely distributed in the tropical and subtropical areas of the world [7]. The outbreak on Madeira island was the first dengue epidemic in Europe since the 1920s, and it occurred in a territory where Ae. aegypti was introduced less than a decade before the outbreak [14]
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