RESUMEN
Background: The wMel strain of Wolbachia has been successfully introduced into Aedes aegypti mosquitoes and subsequently shown to reduce transmission of dengue and other pathogens, under both laboratory and field conditions. Here we describe the entomological outcomes of wMel Wolbachia mosquito releases in two small communities in Nha Trang City in central Vietnam. Methods: The wMel strain of Wolbachia was backcrossed into local Aedes aegypti genotype and mosquito releases were undertaken by community members or by staff. Field monitoring was undertaken to track Wolbachia establishment in local Ae. aegypti mosquito populations. Ecological studies were undertaken to assess relationships between environmental factors and the spatial and temporal variability in Wolbachia infection prevalence in mosquitoes. Results: Releases of wMel Wolbachia Ae. aegypti mosquitoes in two small communities in Nha Trang City resulted in the initial establishment of Wolbachia in the local Ae. aegypti mosquito populations, followed by seasonal fluctuations in Wolbachia prevalence. There was significant small-scale spatial heterogeneity in Wolbachia infection prevalence in the Tri Nguyen Village site, resulting in the loss of wMel Wolbachia infection in mosquitoes in north and center areas, despite Wolbachia prevalence remaining high in mosquitoes in the south area. In the second site, Vinh Luong Ward, Wolbachia has persisted at a high level in mosquitoes throughout this site despite similar seasonal fluctuations in wMel Wolbachia prevalence. Conclusion: Seasonal variation in Wolbachia infection prevalence in mosquitoes was associated with elevated temperature conditions, and was possibly due to imperfect maternal transmission of Wolbachia. Heterogeneity in Wolbachia infection prevalence was found throughout one site, and indicates additional factors may influence Wolbachia establishment.
RESUMEN
BACKGROUND: Rotavirus disease causes a significant health and economic burden worldwide. Several rotavirus vaccines may soon be available for use. A country's decision to introduce these vaccines will depend on its rotavirus disease burden, on the cost of the vaccine, and on the results of an economic assessment of the cost and effectiveness of a rotavirus vaccination program. METHODS: Data on medical and nonmedical direct costs and indirect costs were established in Khanh Hoa Province, Vietnam, and extrapolated to national estimates on the basis of the birth cohort in 2004. The main outcome measures were economic burden and cost-effectiveness ratio (United States dollars per disability-adjusted life-year averted and dollars per life saved) of vaccination. RESULTS: The disease burden is equivalent to an economic burden of an estimated 3.1 million US dollars in medical direct costs, 685,000 US dollars in nonmedical direct costs, and 1.5 million US dollars in indirect costs. From a societal perspective, treatment of rotavirus disease costs an estimated 5.3 million US dollars per year. From the health care system perspective, universal vaccination of infants at a cost of < or = 7.26 US dollars/vaccine dose would be a cost-effective public health intervention, according to the World Bank cost-effectiveness standard for low-income countries (140 US dollars/disability-adjusted life-year). CONCLUSIONS: Vaccination can effectively reduce the disease burden and health care costs of rotavirus-specific diarrhea in Vietnam.