Chitti Chansang

Population Genetic Structure of Aedes (Stegomyia) aegypti (L.) at a Micro-Spatial Scale in Thailand: Implications for a Dengue Suppression Strategy

Background The genetic population structure of Aedes (Stegomyia) aegypti (L.), the main vector of dengue virus, is being investigated in areas where a novel dengue suppression program is to be implemented. The aim of the program is to release and establish mosquito populations with impaired virus transmission capabilities. To model effects of the release and devise protocols for its implementation, information about the genetic structure of populations at a range of spatial scales is required. Methodology/Principal Findings This study investigates a potential release site in the Hua Sam Rong Subdistrict of Plaeng Yao District, Chachoengsao Province, in eastern Thailand which comprises a complex of five villages within a 10 km radius. Aedes aegypti resting indoors was sampled at four different times of year from houses within the five villages. Genetic markers were used to screen the mosquitoes: two Exon Primed Intron Crossing (EPIC) markers and five microsatellite markers. The raw allele size was determined using several statistical software packages to analyze the population structure of the mosquito. Estimates of effective population size for each village were low, but there was no evidence of genetic isolation by geographic distance. Conclusions The presence of temporary genetic structure is possibly caused by genetic drift due to large contributions of adults from a few breeding containers. This suggests that the introduction of mosquitoes into an area needs to proceed through multiple releases and targeting of sites where mosquitoes are emerging in large numbers.

Community Participation and Appropriate Technologies for Dengue Vector Control at Transmission Foci in Thailand

ABSTRACT A community-based dengue vector control trial was conducted at transmission foci in Plaeng Yao District, Chachoengsao Province, eastern Thailand. Implementation was done by the local community in collaboration with local administration, public health, and school authorities. Our cost-effective approaches combined a source reduction campaign with appropriate vector control technologies applied within the foci (within 100 m around the foci) and also within schools attended by children from the treated areas. Vector management measures by local government included cleanup campaigns before the rainy season followed by a routine garbage pickup during the rainy season. Locally made screen covers for water jars, a combination of local Bacillus thuringiensis subsp. israelensis and Mesocyclops thermocyclopoides (copepod), and locally made lethal ovitraps were appropriate technologies used by the community in this campaign. The success of our intervention was evidenced by the significant reduction of dengue vectors and dengue hemorrhagic fever cases in treated areas compared with untreated areas.

Predictiveness of disease risk in a global outreach tourist setting in Thailand using meteorological data and vector-borne disease incidences.

Dengue and malaria are vector-borne diseases and major public health problems worldwide. Changes in climatic factors influence incidences of these diseases. The objective of this study was to investigate the relationship between vector-borne disease incidences and meteorological data, and hence to predict disease risk in a global outreach tourist setting. The retrospective data of dengue and malaria incidences together with local meteorological factors (temperature, rainfall, humidity) registered from 2001 to 2011 on Koh Chang, Thailand were used in this study. Seasonal distribution of disease incidences and its correlation with local climatic factors were analyzed. Seasonal patterns in disease transmission differed between dengue and malaria. Monthly meteorological data and reported disease incidences showed good predictive ability of disease transmission patterns. These findings provide a rational basis for identifying the predictive ability of local meteorological factors on disease incidence that may be useful for the implementation of disease prevention and vector control programs on the tourism island, where climatic factors fluctuate.