Risk Factors for Mosquito House Entry in the Lao PDR

Citation: Hiscox A, Khammanithong P, Kaul S, Sananikhom P, Luthi R, et al. ( Risk Factors for Mosquito House Entry in the Lao PDR Alexandra Hiscox 0 Phasouk Khammanithong 0 Surinder Kaul 0 Pany Sananikhom 0 Ruedi Luthi 0 Nigel Hill 0 Paul T. Brey 0 Steve W. Lindsay 0 Georges Snounou, Universite Pierre et Marie Curie, France 0 1 Institut Pasteur du Laos , Vientiane , Lao PDR, 2 London School of Hygiene and Tropical Medicine , London , United Kingdom , 3 Khammouane Provincial Health Office, Thakhek , Lao PDR, 4 Nam Theun 2 Power Company, Vientiane, Lao PDR, 5 School of Biological and Biomedical Sciences, Durham University , Durham , United Kingdom Background: Construction 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 Findings: Surveys 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/Significance: Construction 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. - Funding: This study was supported by the Fondation EDF Diversiterre. SWL was supported by the Research and Policy for Infectious Disease Dynamics (RAPIDD) Program of the Science and Technology Directory, Department of Homeland Security, and Fogarty International Center, National Institutes of Health. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The co-authors Surinder Kaul, Pany Sananikhom and Ruedi Luthi were under paid employment by the Environment and Social Division of NTPC during the time of the described study. However, the authors declare that this does not alter their adherence to all PLOS ONE policies on sharing data and materials. Mosquito house entry can be reduced through simple changes in house design, such as closing eaves, installing a ceiling, screening external doors and windows and a general improvement in quality of construction materials [1]. In these instances house entry rates are probably reduced by physically blocking or decreasing the number of holes through which a mosquito may gain access to a home. Houses can also be made less suitable for indoor resting mosquitoes by making them well lit, with few places for adult vectors to rest, and this is often cited as one of the reasons for the decline in malaria in Europe [2]. Raising houses on stilts can also reduce mosquito house entry [3,4] by interfering with host-seeking behaviour. Anecdotal evidence has suggested that the smoke created by burning biomass fuels inside houses may repel host-seeking mosquitoes, although an in-depth literature review [5] found little evidence that smoke from fires led to a corresponding reduction in malaria. Limiting exposure to mosquito bites should reduce the risk of exposure to infections such as Japanese encephalitis (JE) and malaria. For example, a recent randomised controlled trial of house screening in The Gambia showed that installing screened ceilings or full screening of houses with fly-screened doors and windows, and closing the eaves resulted in a 50% decline in the risk of anaemia due to malaria, a major killer of young children [6]. In Sri Lanka the incidence of malaria among residents of poor-quality housing was up to 2.5 fold higher compared with a population living in improved housing [7]. Although one study investigating risk factors for culicine mosquitoes in The Gambia found that closed eaves reduced the risk of house entry for this genus [8] a subsequent intervention study showed that culicines entered houses through doors and not the eaves [9]. Little is known about whether improvements in house construction can reduce mosquito house entry rates in other parts of the world, including South-East Asia. The Nam Theun 2 (NT2) hydroelectric project in south-central Lao PDR, is one of the largest recent development projects in South-East Asia. The project is predicted to generate an average income of US$80 million per year, with Lao government revenues expected to reach a total US$2 billion over the period of a 25 year concession agreement. Hydropower is generated by the force of water released from a reservoir measuring 450 km2 in area, descending 348 m to a power station. Flooding of a mountain plateau to create this reservoir resulted in the resettlement of 1,310 households and 6,300 people, into 16 villages settled along the southern shore line of the reservoir. Families were provided with a newly constructed wooden house built to considerably higher standards than traditional houses in the area. Preliminary studies carried out in 312 randomly selected houses in the resettlement area during 2009 indicated that resettlement style houses were at lower risk of house entry by putative JE vectors than a small sample of traditional houses (N = 15) and that houses located in more agricultural parts of the resettlement area were at increased risk of entry by this group of mosquitoes [10]. The specific objectives of the present study were to determine household-level risk factors for mosquito house entry in areas affected by the NT2 hydroelectric project and to relate these risk factors to improvements in housing design which could be incorporated into future development programmes. We sampled mosquitoes from the bedrooms of an equal number of traditional and resettleme (...truncated)