Community-based perceptions and behaviour around water source preference, household water storage patterns and water use, and householders' knowledge and behaviour with respect to dengue etiology and transmission, were examined in three communes located in the Mekong Delta area in southern Vietnam. Through focus group discussions, most participants identified poorly screened or uncovered water containers (including household water storage containers and other types of artificial containers) as habitats for mosquitoes that transmit dengue viruses, and thereby demonstrated a clear understanding of the links between household water storage practices and the threat of dengue. Our qualitative analyses also revealed broader community-based concerns about the limited availability of water and strong preferences for storage of rainwater based upon perceptions of cost, quality and security of supply. These perceptions are central to shaping householders' responses to water infrastructure projects. The limited availability of water during the dry season and insufficient numbers of water storage containers are over-riding community concerns which provide an important context to understanding community behaviours and responses to public health interventions against dengue. Such concerns are important precursors to selecting the type of intervention.

We examined changes in the abundance of immature Aedes aegypti at the household and water storage container level during the dry-season (June-July, 2008) in Tri Nguyen village, central Vietnam. We conducted quantitative immature mosquito surveys of 171 containers in the same 41 households, with replacement of samples, every two days during a 29-day period. We developed multi-level mixed effects regression models to investigate container and household variability in pupal abundance. The percentage of houses that were positive for I/II instars, III/IV instars and pupae during any one survey ranged from 19.5–43.9%, 48.8–75.6% and 17.1–53.7%, respectively. The mean numbers of Ae. aegypti pupae per house ranged between 1.9–12.6 over the study period. Estimates of absolute pupal abundance were highly variable over the 29-day period despite relatively stable weather conditions. Most variability in pupal abundance occurred at the container rather than the household level. A key determinant of Ae. aegypti production was the frequent filling of the containers with water, which caused asynchronous hatching of Ae. aegypti eggs and development of cohorts of immatures. We calculated the probability of the water volume of a large container (>500L) increasing or decreasing by ≥20% to be 0.05 and 0.07 per day, respectively, and for small containers (<500L) to be 0.11 and 0.13 per day, respectively. These human water-management behaviors are important determinants of Ae. aegypti production during the dry season. This has implications for choosing a suitable Wolbachia strain for release as it appears that prolonged egg desiccation does not occur in this village.

The study aims to make an update on the distribution and ecology of sand flies in the Quang Ninh province, Northern Vietnam, where Leishmania cases were reported in 2001. Seventeen sites were chosen in three districts of the province: Ha Long, Cam Pha, and Hoanh Bo. Phlebotomine sand flies were collected using 68 CDC light traps from May 30 to 3 June 2016. Captured specimens were transferred individually into Eppendorf tubes with 90% ethanol. The sand fly heads and genitalia were removed and were mounted in Euparal after successive different baths. Specimen identification was determined based on the morphology of the cibarium, pharynx, and/or male genitalia or female spermathecae. A total of 416 sand flies (125 females, 283 males) belonging to four genera were collected and 10 sand fly species were identified: Sergentomyia silvatica, Se. barraudi, Se. hivernus, Se. bailyi, Phlebotomus mascomai, Ph. stantoni, Ph. yunshengensis, Ph. betisi, Chinius junlianensis, Idiophlebotomus longiforceps. The Sergentomyia genus prevailed (79.7% of the collected sand flies), followed by the Phlebotomus genus (13.7%), the Chinius genus (6.1%), and the Idiophlebotomus genus (0.8%). Besides these well-defined taxa, five specimens, named sp1, showed unknown morphological characteristics, requiring further study. The majority of sand flies were collected in rock caves suggesting the cavernicolous character of the species in the Quang Ninh province. However, specimens were also collected in intra and peridomiciliary sites in which Ph. stantoni and Se. hivernus were found as the main species. It is worth noting that two Ph. stantoni were found in the house of a patient affected by Leishmania.

Although quantitative surveillance data for immature stages of Aedes aegypti are often used to prioritize containers or specific types of containers for control, the relationship between immature and emergent adult populations under field conditions is largely unknown. We examined the relationships between abundance of III/IV instars and pupae, and emerging adult population for a series of water storage containers in southern Vietnam. A large proportion of III/IV instars failed to progress to adulthood, and the relationships between III/IV instars and adults were poor. Collected IV instars appeared to be nutritionally deprived, although their size and nutrient levels were not reliable indicators of emergence success. Conversely, pupal abundance was a good indicator of emerging adult populations, especially over the ensuing 48-h period. Although there were clear advantages of pupal surveillance over surveillance of III/IV instars for the estimation of adult mosquito productivity, there were practical limitations associated with the enumeration of pupae, and their comparatively low densities may preclude the identification of potentially productive containers.