BackgroundConstruction of the Nam Theun 2 hydroelectric project and flooding of a 450 km2 area of mountain plateau in south-central Lao PDR resulted in the resettlement of 6,300 people to newly built homes. We examined whether new houses would have altered risk of house entry by mosquitoes compared with traditional homes built from poorer construction materials.Methodology/Principal FindingsSurveys were carried out in the Nam Theun 2 resettlement area and a nearby traditional rice farming area in 2010. Mosquitoes were sampled in bedrooms using CDC light traps in 96 resettlement houses and 96 traditional houses and potential risk factors for mosquito house entry were recorded. Risk of mosquito house entry was more than twice as high in traditional bamboo houses compared with those newly constructed from wood (Putative Japanese Encephalitis (JE) vector incidence rate ratio (IRR) = 2.26, 95% CI 1.38–3.70, P = 0.001; Anopheline IRR = 2.35, 95% CI: 1.30–4.23, P = 0.005). Anophelines were more common in homes with cattle compared against those without (IRR = 2.32, 95% CI: 1.29–4.17, P = 0.005).Wood smoke from cooking fires located under the house or indoors was found to be protective against house entry by both groups of mosquito, compared with cooking in a separate room beside the house (Putative JE vector IRR = 0.43, 95% CI: 0.26–0.73, P = 0.002; Anopheline IRR = 0.22, 95% CI: 0.10–0.51, P<0.001).Conclusions/SignificanceConstruction of modern wooden homes should help reduce human-mosquito contact in the Lao PDR. Reduced mosquito contact rates could lead to reduced transmission of diseases such as JE and malaria. Cattle ownership was associated with increased anopheline house entry, so zooprophylaxis for malaria control is not recommended in this area. Whilst wood smoke was protective against putative JE vector and anopheline house entry we do not recommend indoor cooking since smoke inhalation can enhance respiratory disease.

Abstract. We assessed risk factors for vectors of dengue and chikungunya viruses near a new hydroelectric project, Nam Theun 2, in Laos. Immature stages of Aedes aegypti were found only in sites within 40 km of the urban provincial capital, but Aedes albopictus was found throughout. Aedes aegypti pupae were most common in water storage jars (odds ratio [OR] = 4.72) and tires (OR = 2.99), and Ae. albopictus pupae were associated with tires in 2009 (OR = 10.87) and drums, tires, and jars in 2010 (drums OR = 3.05; tires OR = 3.45, jars OR = 6.59). Compared with water storage vessels, containers used for hygiene, cooking, and drinking were 80% less likely to harbor Ae. albopictus pupae in 2010 (OR = 0.20), and discarded waste was associated with a 3.64 increased odds of infestation. Vector control efforts should focus on source reduction of water storage containers, particularly concrete jars and tires.

Hydroelectric projects offer opportunities for infrastructure development and economic growth; yet, if not well designed, implemented and operated, they have the potential to negatively affect the health and well-being of local and distant downstream communities. Remote rural populations are particularly vulnerable to the sudden influx of men, materials and money, and associated population mixing that accompany project construction phases. Two large-scale baseline health surveys, carried out in 2001/2002 in two communities that were affected by the Nam Theun 2 hydroelectric project in central Lao PDR, were analysed. For the population to be resettled on the Nakai plateau it was observed that access to clean water and basic sanitation facilities was lacking. Faecal examinations revealed a high infection prevalence for Ascaris lumbricoides (67.7%), but relatively low prevalences for hookworm (9.7%), Taenia spp. (4.8%), Enterobius vermicularis (4.4%), Trichuris trichiura (3.9%), Strongyloides stercoralis (1.4%) and Opisthorchis viverrini (0.9%). For the population in the Xe Bang Fai downstream area, rapid diagnostic tests for malaria carried out in the rainy season found a prevalence below 1%, which might be explained by the complete coverage of households with insecticide-treated nets (99.8%). Anthropometric measurements in both populations suggest that wasting, stunting and underweight in under 5-year-old children were moderate to high; 15.9-17.5%, 40.4-55.7% and 35.8-55.7%, respectively. One out of six individuals aged above 14 years were malnourished, most likely as a result of early childhood wasting. Moderate anaemia, assessed by age- and sex-specific haemoglobin levels, was present in 43.8% (Nakai) and 54.9% of the individuals examined (Xe Bang Fai). Several indicators were extracted that can be utilised for monitoring changes in health, well-being and equity, as the project is implemented and operated.

A large-scale cross-sectional seroprevalence study of dengue (DEN) and Japanese encephalitis (JE) was conducted in Khammouane province, Lao PDR, as part of the initial baseline health impact assessment of the Nam Theun 2 hydroelectric dam construction project. Health surveys were performed between May 2007 and February 2008 with serum samples collected from healthy individuals involved in the resettlement program of 16 villages (total surveyed population 4,369). Hemagglutination inhibition assay using flavivirus antigens (DENV1, DENV3, and JEV) performed on 1,708 plasma specimens revealed 30.4% (519) cross-reactive positives, and 10% (172) and 1.3% (22) positives to JEV or DENV, respectively. Entomological surveys conducted during the rainy season of 2008 indicated the presence of competent flavivirus vectors (Culex vishnui group and Aedes albopictus), although Aedes aegypti was not found. Continued surveillance and investigation is warranted to assess the clinical disease burden of flaviviruses in this area that is undergoing rapid ecological and demographic change.

Naturally occurring bithyniid snails, Bithynia siamensis goniomphalos (Prosobranchia: Bithyniidae), and their intermediate hosts were sampled from Khammouane Province, the Lao People's Democratic Republic, and the prevalence of the carcinogenic human liver fluke, Opisthorchis viverrini, was examined. The presence of O. viverrini cercariae in snails was examined by cercarial shedding test and then confirmed by specific hybridization probe-based real-time fluorescence resonance energy transfer (FRET) PCR method. The real-time FRET PCR method is based on a fluorescence melting curve analysis of a hybrid between an amplicon produced from the pOV-A6 specific sequence (Genbank accession no. S80278), a 162-bp repeated sequence specific to O. viverrini, and specific fluorophore-labeled probes. Mean melting temperature of O. viverrini DNA from the cercariae and each of two positive snails by shedding test was 66.3 ± 0.1. The O. viverrini infection rate in snails was 2.47% (2/81) by cercarial shedding test but was 8.52% (4/47) by real-time FRET PCR method. The real-time FRET PCR method is rapid and effective in examining a large number of snail samples simultaneously. Validation using molecular evidence from this procedure provides another tool for surveying the prevalence of O. viverrini-infected snails in Southeast Asian countries.

IN HIS NEWS FOCUS STORY "MAYHEM ON THE MEKONG" (12 AUGUST, P. 814), R. STONE REPORTS concerns about hydropower development projects on the lower Mekong River and its tributaries. The ecological transformations induced by water resource development are especially critical in tropical areas, where favorable conditions are created for the transmission of vector-borne diseases. With regard to large hydroelectric projects, there has been a misconception that public health prevention measures are too costly; thus, they have been neglected or enacted at a minimal level (1). Water projects have been shown to have direct and indirect effects on diseases such as malaria (2, 3), schistosomiasis (4, 5), and hepatitis C (6). However, there is a paucity of comprehensive, in-depth assessment of the global health and environmental burden attributable to the development and operation of large dams. One exception is the 1070-MW Nam Theun 2 hydropower station in Laos. The company that operates the dam, along with its partners and stakeholders, has developed policies that balance hydroelectric production with responsible and coherent social and environmental programs, including the strengthening of the provincial public health infrastructure. This strategy could serve as a model for others. As part of this approach, increased resources have been provided for local mother and child care, curative and preventative medicine, and psychosocial well-being. Adequate water supplies and sanitation have been provided, mosquito and gastropod vector populations responsible for disease transmission are monitored, and targeted vector control strategies have been implemented (7). To cope with the occurrence of potential infectious hazards, the company has developed a tailored outbreak response preparedness plan to be used in conjunction with the national plan. Surprisingly, the implementation of such measures has been proven feasible at an acceptable cost ratio (0.2% of the overall project development budget) (8).Twenty-fi ve years after Chernobyl, the Fukushima incident will undoubtedly make hydropower an increasingly attractive renewable energy resource for countries facing urgently rising needs for electricity to fuel their economies. A systematic, durable evaluation of the health status of dam-affected populations is vital to improve our understanding of the impact of dams and to develop appropriate mitigation strategies. Lending agencies and power companies constructing and operating these dams need to reevaluate their responsibilities concerning the public health impact on affected populations.