Dengue and its vectors in Thailand: calculated transmission risk from total pupal counts of Aedes aegypti and association of wing-length measurements with aspects of the larval habitat

Abstract

Working in a village dengue focus in Chachoengsao Province, Thailand, aedine mosquito larvae and pupae were counted in all containers of 10 houses per month. The wings of female Aedes aegypti (L.) emerging from pupae were measured. Number of pupae and size of emerging females increased in containers with qualities that favored availability of larval food sources (e.g., uncovered containers). The small size of most mosquitoes compared with those raised in the laboratory indicated that the larval population as a whole was under nutritional stress. Applying the number of pupae per house and measurement of air and water temperature with an existing model, the risk of dengue transmission was greatest in May and June. The estimated number of female Ae. aegypti per house was well above the threshold for increasing transmission in all months but December through February. A phased approach to sampling immature aedine mosquitoes in Thailand is proposed, which would consist of routine surveillance of larval index and occasional total counts with measurement of wing size. Such a system would combine the benefits of the simple application of larval surveillance with the valuable data gathered from pupal counts and wing measurements.