A novel entomological index, Aedes aegypti Breeding Percentage, reveals the geographical spread of the dengue vector in Singapore and serves as a spatial risk indicator for dengue

Janet Ong,Grace Yap,Derek Ho,Lee Ching Ng,Jayanthi Rajarethinam,Xu Liu

doi:10.1186/s13071-018-3281-y

Janet Ong, Grace Yap + Show 4 more

Open Access

https://doi.org/10.1186/s13071-018-3281-y

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Abstract

BackgroundAedes aegypti is an efficient primary vector of dengue, and has a heterogeneous distribution in Singapore. Aedes albopictus, a poor vector of dengue, is native and ubiquitous on the island. Though dengue risk follows the dispersal of Ae. aegypti, the spatial distribution of the vector is often poorly characterized. Here, based on the ubiquitous presence of Ae. albopictus, we developed a novel entomological index, Ae. aegypti Breeding Percentage (BP), to demonstrate the expansion of Ae. aegypti into new territories that redefined the dengue burden map in Singapore. We also determined the thresholds of BP that render the specific area higher risk of dengue transmission.MethodsWe performed analysis of dengue fever incidence and Aedes mosquito breeding in Singapore by utilizing island-wide dengue cases and vector surveillance data from 2003 to 2013. The percentage of Ae. aegypti breeding among the total Aedes breeding habitats (BP), and the reported number of dengue fever cases in each year were calculated for each residential grid.ResultsThe BP of grids, for every year over the 11-year study period, had a consistent positive correlation with the annual case counts. Our findings suggest that the geographical expansion of Ae. aegypti to previously “non-dengue” areas have contributed substantially to the recent dengue fever incidence in Singapore. Our analysis further indicated that non-endemic areas in Singapore are likely to be at risk of dengue fever outbreaks beyond an Ae. aegypti BP of 20%.ConclusionsOur analyses indicate areas with increasing Ae. aegypti BP are likely to become more vulnerable to dengue outbreaks. We propose the usage of Ae. aegypti BP as a factor for spatial risk stratification of dengue fever in endemic countries. The Ae. aegypti BP could be recommended as an indicator for decision making in vector control efforts, and also be used to monitor the geographical expansion of Ae. aegypti.

Highlights

Aedes aegypti is an efficient primary vector of dengue, and has a heterogeneous distribution in Singapore
In the present study, we used a novel entomological index, Ae. aegypti Breeding Percentage (BP), which has consistent positive spatial correlation with localized dengue fever burden to demonstrate the geographical expansion of Ae. aegypti in Singapore
Analysis using the BP further revealed that the geographical expansion of Ae. aegypti has contributed to the recent increase and altered corresponding distribution of dengue cases in Singapore

Summary

Introduction

Aedes aegypti is an efficient primary vector of dengue, and has a heterogeneous distribution in Singapore. A poor vector of dengue, is native and ubiquitous on the island. Though dengue risk follows the dispersal of Ae. aegypti, the spatial distribution of the vector is often poorly characterized. Based on the ubiquitous presence of Ae. albopictus, we developed a novel entomological index, Ae. aegypti Breeding Percentage (BP), to demonstrate the expansion of Ae. aegypti into new territories that redefined the dengue burden map in Singapore. Dengue fever has caught global attention due to its increasing frequency of major epidemics in recent years. It is estimated that 2.5 billion individuals, residing in more than 100 countries, are at risk of dengue fever, with an annual case burden of approximately 50–100 million infections [1]. It has been observed previously that there is a cyclical pattern of outbreaks that peaks every five to seven years in Singapore [4, 5]

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