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- Aedes; Aedes aegypti; Aedes albopictus; dengue; transmission; virus
thesis / dissertation description
Dengue is arguably the most important arboviral disease of humans, having increased dramatically in geographic range and prevalence over the last 25 years. Dengue virus has two main vectors, Aedes aegypti and Aedes albopictus. For decades both vectors have also been increasing their geographic range on regional and global scales. This study took place in Singapore, where dengue fever is a major public health threat despite a successful vector control program. Similar to other hyperendemic countries, local dengue transmission dynamics in Singapore are not well understood: where dengue transmission is occurring, the relative contribution of the two dengue vectors, and the ability to correlate traditional vector surveillance methods to transmission risk remains controversial. In collaboration with the Program of Infectious Diseases at Duke-NUS Graduate Medical School, Singapore Ministry of Health, Singapore National Environmental Agency, and Ang Mo Kio Town Council an adult Aedes female fixed position vector surveillance program was established that detailed temporal and spatial Ae. aegypti and Ae. albopictus distribution and abundance in Ang Mo Kio, Central Singapore. This surveillance method yielded similar results to standard surveillance techniques over a range of habitats and time points. Furthermore, sensitivity of the adult surveillance method presented here is uniquely increased by placing traps on the second floor of Housing Development Board (HDB), government subsidized multistory residential buildings, as opposed to ground level; average Ae. aegypti catch rate of the ground floor was 0.09 and average Ae. aegypti catch rate of the second floor was 0.42. Starting on the second floor a very strong inverse relationship between Ae. aegypti catch rate and floor height (Pearson linear correlation r=-0.91, t=-4.47, df=4, p=0.01) was also identified. In addition, intensive entomological investigations, in focal areas with varying levels of Aedes abundance, identified by the fixed position surveillance system, uncovered details about mosquito ecology and "hotspots" at a local scale that can improve our understanding of dengue transmission dynamics. Dengue transmission is believed to primarily occur in residential units but host seeking Ae. aegypti and Ae. albopcitus were collected at similar frequencies in congregation areas on the ground floors of, HDBs and at greater abundance than inside residential units. Improving knowledge on the focal nature of dengue transmission is critical to designing more targeted and cost-effective surveillance and control strategies in the future, both in Singapore and urban areas elsewhere.