Untreated Villages Research Articles

Measuring effects of ivermectin-treated cattle on potential malaria vectors in Vietnam: A cluster-randomized trial.

Malaria elimination using current tools has stalled in many areas. Ivermectin (IVM) is a broad-antiparasitic drug and mosquitocide and has been proposed as a tool for accelerating progress towards malaria elimination. Under laboratory conditions, IVM has been shown to reduce the survival of adult Anopheles populations that have fed on IVM-treated mammals. Treating cattle with IVM has been proposed as an important contribution to malaria vector management, however, the impacts of IVM in this One Health use case have been untested in field trials in Southeast Asia. Through a randomized village-based trial, this study quantified the effect of IVM-treated cattle on anopheline populations in treated vs. untreated villages in Central Vietnam. Local zebu cattle in six rural villages were included in this study. In three villages, cattle were treated with IVM at established veterinary dosages, and in three additional villages cattle were left as untreated controls. For the main study outcome, the mosquito populations in all villages were sampled using cattle-baited traps for six nights before, and six nights after a 2-day IVM-administration (intervention) period. Anopheline species were characterized using taxonomic keys. The impact of the intervention was analyzed using a difference-in-differences (DID) approach with generalized estimating equations (with negative binomial distribution and robust errors). This intervention was powered to detect a 50% reduction in total nightly Anopheles spp. vector catches from cattle-baited traps. Given the unusual diversity in anopheline populations, exploratory analyses examined taxon-level differences in the ecological population diversity. Across the treated villages, 1,112 of 1,523 censused cows (73% overall; range 67% to 83%) were treated with IVM. In both control and treated villages, there was a 30% to 40% decrease in total anophelines captured in the post-intervention period as compared to the pre-intervention period. In the control villages, there were 1,873 captured pre-intervention and 1,079 captured during the post-intervention period. In the treated villages, there were 1,594 captured pre-intervention, and 1,101 captured during the post-intervention period. The difference in differences model analysis comparing total captures between arms was not statistically significant (p = 0.61). Secondary outcomes of vector population diversity found that in three villages (one control and two treatment) Brillouin's index increased, and in three villages (two control and one treatment) Brillouin's index decreased. When examining biodiversity by trapping-night, there were no clear trends in treated or untreated vector populations. Additionally, there were no clear trends when examining the components of biodiversity: richness and evenness. The ability of this study to quantify the impacts of IVM treatment was limited due to unexpectedly large spatiotemporal variability in trapping rates; an area-wide decrease in trapping counts across all six villages post-intervention; and potential spillover effects. However, this study provides important data to directly inform future studies in the GMS and beyond for IVM-based vector control.

Reconciling Evaluations of the Millennium Villages Project

The Millennium Villages Project was an integrated rural development program carried out for a decade in 10 clusters of villages in sub-Saharan Africa starting in 2005, and in a few other sites for shorter durations. An evaluation of the 10 main sites compared to retrospectively chosen control sites estimated positive effects on a range of economic, social, and health outcomes (Mitchell et al. 2018). More recently, an outside group performed a prospective controlled (but also nonrandomized) evaluation of one of the shorter-duration sites and reported smaller or null results (Masset et al. 2020). Although these two conclusions seem contradictory, the differences can be explained by the fact that Mitchell et al. studied 10 sites where the project was implemented for 10 years, and Masset et al. studied one site with a program lasting less than 5 years, as well as differences in inference and framing. Insights from both evaluations should be valuable in considering future development efforts of this sort. Both studies are consistent with a larger picture of positive average impacts (compared to untreated villages) across a broad range of outcomes, but with effects varying across sites or requiring an adequate duration for impacts to be manifested.

The influence of heating energy on indoor air quality and its association with socioeconomic status in rural Beijing

BACKGROUND AND AIM: Solid fuel combustion for cooking and heating is a dominant source of indoor fine particulate matter (PM2.5). To improve ambient air quality, China is implementing a national program to replace traditional coal stoves with clean energy devices and ban further use of coal for space heating. To date, the impact evaluation of this program on indoor air quality is very limited. METHODS: Three-hundred households among 50 rural villages spanning four districts in Beijing, including 10 treated villages (electricity-based space heating) and 40 untreated villages (coal-based space heating), were recruited to monitor indoor PM2.5 concentrations (PMS7003 Plantower) for 58 to 110 days during the wintertime heating season (November to March). A 24-h filter-based measurement of PM2.5 (Ultrasonic Personal Aerosol Samplers, Access Sensor Technologies, USA) was co-located in a subsample of 3 households per village. Outdoor PM2.5 concentrations were measured concurrently (2 sensor-based and 1 filter-based measurement per village). Filter-based PM2.5 samples were analyzed for mass, black carbon, and elemental composition. RESULTS:Overall, indoor PM2.5 concentrations were lower in treated villages than untreated villages, while no strong trends were observed for outdoor PM2.5. Indoor PM2.5 concentrations followed similar diurnal trends in both treated and untreated villages, although PM2.5 concentrations were more elevated overnight in untreated villages, possibly due to solid fuel burning in space heating stoves. Elemental composition will provide insight on infiltration of outdoor PM2.5 and its contribution to indoor air quality. CONCLUSIONS:Indoor air quality in treated villages was better compared to untreated villages, with the strongest evidence for this coming from the observed differences in diurnal patterns of indoor PM2.5 concentrations, indicative of overnight solid fuel burning in space heating stoves in untreated villages. The clean heating energy program shows benefit on indoor air quality even though it aims on improve ambient air quality. KEYWORDS: Indoor fine particulate matter, coal combustion, household energy transition, outdoor contribution, socioeconomic status, Beijing

The role of village spillover and stove use on wintertime outdoor PM2.5 in villages transitioning to clean heating in China

BACKGROUND AND AIM: In an effort to improve ambient air quality, the Beijing government is requiring that households in the municipality transition, at the village-scale, from coal-burning stoves to electric-powered heat pumps and natural gas boilers for household heating. Wintertime air quality in this region is subject to meteorological clustering and air pollution emissions from rural residential space heating with coal-burning stoves. Thus, to better understand how large-scale policies like the one being implemented perform, we conducted a village level analysis of outdoor air pollution patterning, accounting for meteorology, coverage of the policy, and home heating energy use. METHODS: We analyzed 283 1-week outdoor fine particulate matter (PM2.5) samples from 30 villages in 2 Beijing districts across 2 winter field seasons. In the first winter season (2018-2019) households in all 30 villages were heating with coal-burning stoves, whereas in the second season (2019-2020) households in 10 of those villages had ceased using coal for space heating and instead used electric heat pumps (treated). PM2.5 samples were analyzed for mass, black carbon (BC) and trace elements. Elemental and BC concentrations were included in a source apportionment model to identify the sources of elements in these villages. RESULTS:Median (interquartile range) PM2.5 concentrations (μg m-3) for treated villages were 31.2 (21.2) for season 1 and 29.7 (25.5) for season 2. For untreated villages, median concentrations were 28.8 (11.7) and 24.8 (19.0) for seasons 1 and 2, respectively. To contextualize the PM2.5 mass and source apportionment results, we discuss how these concentrations vary with respect to meteorological clustering, density of nearby treated and untreated villages, and self-reported and objective measures of home heating energy use. CONCLUSIONS:Our analysis and findings provide a framework and insights regarding influential factors that should be considered when assessing the effectiveness of similar household energy interventions. KEYWORDS: source apportionment, household energy transition, coal combustion, trace elements

Is biological larviciding against malaria a starting point for integrated multi-disease control? Observations from a cluster randomized trial in rural Burkina Faso.

To evaluate the impact of anti-malaria biological larviciding with Bacillus thuringiensis israelensis on non-primary target mosquito species in a rural African setting. A total of 127 villages were distributed in three study arms, each with different larviciding options in public spaces: i) no treatment, ii) full or iii) guided intervention. Geographically close villages were grouped in clusters to avoid contamination between treated and untreated villages. Adult mosquitoes were captured in light traps inside and outside houses during the rainy seasons of a baseline and an intervention year. After enumeration, a negative binomial regression was used to determine the reductions achieved in the different mosquito species through larviciding. Malaria larviciding interventions showed only limited or no impact against Culex mosquitoes; by contrast, reductions of up to 34% were achieved against Aedes when all detected breeding sites were treated. Culex mosquitoes were captured in high abundance in semi-urban settings while more Aedes were found in rural villages. Future malaria larviciding programs should consider expanding onto the breeding habitats of other disease vectors, such as Aedes and Culex and evaluate their potential impact. Since the major cost components of such interventions are labor and transport, other disease vectors could be targeted at little additional cost.

The effects of renewable energy-based village grid electrification on poverty reduction in remote areas: The case of Indonesia

This study attempts to investigate the potential role of renewable energy-based rural electrification to reduce poverty in remote non-grid villages and outermost islands, through the use of the renewable energy-based village-grids (RVGs) program in Indonesia. As the geographical characteristics of such areas are often the main inhibiting factors for electricity supply, this study assesses whether renewable-based off-grid electrification is able to reduce the number of poor and vulnerable people in the remote villages and through what intermediary mechanism it may play its role. Using a difference-in-differences (DID) approach, this study analyzes the effect of renewable energy-based plants in 217 remote villages in Indonesia by comparing outcomes for treated and untreated villages within one sub-district where the remote villages are located. The results show that the program has significantly reduced the number of poor and vulnerable people in the treated village by 91 people. Furthermore, this study also finds that the program was able to significantly increase the number of small-scale industries in the treated village by three units, suggesting that small-scale industries could potentially be the intermediate mechanism through which electricity has a positive effect on poverty alleviation. These results highlight the importance of an off-grid renewable energy-based electrification roll-out in reducing poverty in remote areas and outer islands of Indonesia.

Outdoor Transmission of Malaria

Recent assessments of controlling the vectors of malaria have shown that due to reliance of treatments inside houses, malaria transmission is still occurring as people are more active outdoors during the evening after sunset. During several visits to Cameroon, it was noticeable that, at least in the towns, there was considerable activity outdoors after sunset as people preferred to go shopping or socialise with friends when it was cooler. However, as in other countries in Africa, the emphasis has been put on the distribution of insecticide treated bednets while indoor residual spraying (IRS) has also been used. A pilot study in six villages in a malaria-endemic area examined different mosquito control interventions applied to entire villages to assess their impact on vectors, malaria incidence and the quality of life of the communities. One of the villages was left untreated during the year of the trial. One of the other villages which had been treated with IRS and bednets treated with ICON CS (lambda-cyhalothrin capsule suspension formulation) or another that had improved screening of houses combined with outdoor misting showed reduced numbers of mosquitoes collected from exit traps compared to the other treatments. More malaria sporozoites were detected in mosquitoes sampled in exit traps in the untreated village than in the treated villages. Malaria incidence several months after both IRS/ITN and screening/misting treatments was not significantly different from pre-treatment levels. In retrospect, the village with house improvement and outdoor misting was almost as effective as using both treated bed nets and IRS inside houses, indicating important transmission outdoors. A subsequent study showed that, as expected, the treated bed nets were of greater importance in protecting young children remaining under the nets throughout the night than adults.

Large-scale field trial of attractive toxic sugar baits (ATSB) for the control of malaria vector mosquitoes in Mali, West Africa

BackgroundThe aim of this field trial was to evaluate the efficacy of attractive toxic sugar baits (ATSB) in Mali, where sustained malaria transmission occurs despite the use of long-lasting insecticidal nets (LLINs). ATSB bait stations were deployed in seven of 14 similar study villages, where LLINs were already in widespread use. The combined use of ATSB and LLINs was tested to see if it would substantially reduce parasite transmission by Anopheles gambiae sensu lato beyond use of LLINs alone.MethodsA 2-day field experiment was conducted to determine the number of mosquitoes feeding on natural sugar versus those feeding on bait stations containing attractive sugar bait without toxin (ASB)—but with food dye. This was done each month in seven random villages from April to December 2016. In the following year, in seven treatment villages from May to December 2017, two ATSB bait stations containing the insecticide dinotefuran were placed on the outer walls of each building. Vector population density was evaluated monthly by CDC UV light traps, malaise traps, pyrethrum spray (PSCs) and human landing catches (HLCs). Female samples of the catch were tested for age by examination of the ovarioles in dissected ovaries and identification of Plasmodium falciparum sporozoite infection by ELISA. Entomological inoculation rates (EIR) were calculated, and reductions between treated and untreated villages were determined.ResultsIn the 2-day experiment with ASB each month, there was a lower number of male and female mosquitoes feeding on the natural sugar sources than on the ASB. ATSB deployment reduced CDC-UV trap female catches in September, when catches were highest, were by 57.4% compared to catches in control sites. Similarly, malaise trap catches showed a 44.3% reduction of females in August and PSC catches of females were reduced by 48.7% in September. Reductions of females in HLCs were lower by 19.8% indoors and 26.3% outdoors in September. The high reduction seen in the rainy season was similar for males and reductions in population density for both males and females were > 70% during the dry season. Reductions of females with ≥ 3 gonotrophic cycles were recorded every month amounting to 97.1% in October and 100.0% in December. Reductions in monthly EIRs ranged from 77.76 to 100.00% indoors and 84.95% to 100.00% outdoors. The number of sporozoite infected females from traps was reduced by 97.83% at treated villages compared to controls.ConclusionsAttractive toxic sugar baits used against Anopheles mosquitoes in Mali drastically reduced the density of mosquitoes, the number of older females, the number of sporozoite infected females and the EIR demonstrating how ATSB significantly reduces malaria parasite transmission.

Air Quality, Home Heating, and Well-Being under Beijing’s Ban on Household Coal Burning

OPS 02: Environmental epidemiology and policy, Room 315, Floor 3, August 28, 2019, 1:30 PM - 3:00 PM Background/aim: In response to severe and persistent haze, the Chinese Air Pollution Prevention and Control Action Plan includes regional coal consumption caps in key northern regions. In Beijing, the municipal government has designated coal restricted areas throughout the province, offering subsidies to nighttime electricity rates and for electric-powered heat pumps to replace traditional coal heating stoves. We compared treated and untreated villages in the Beijing province to investigate three dimensions of outcomes of the policy: fuel use and economic behavior, subjective well-being, and indoor environmental conditions. Methods: Our study design consists of 302 door-to-door surveys in six villages, with one treated and one un-treated village in each of three districts chosen to represent different socioeconomic and geographic conditions present in peri-urban Beijing. We measured indoor temperature and fine particulate matter levels (PM2.5) in a subset of homes in each village. Results: Coal use was absent in treated villages in two districts, and significantly lower in the treated as compared with the untreated village in one district where adherence to the coal ban was not complete. In homes in the two coal-restricted villages adhering to the coal ban, average (standard deviation) outdoor-subtracted, indoor 24-h PM2.5 concentrations (0.145 (0.218) mg-m-3) were lower compared with untreated homes (0.275 (0.244) mg-m-3). In the middle-income district, where the transition to electric heating was complete, satisfaction with life (SWL) and satisfaction with living conditions (SWC) were higher (+0.6 and +1.0 on the 0–10 scale) in the treated village than the untreated. By contrast, in the least affluent district, both satisfaction measures were lower (-1.0, -1.5) in the treated village compared with the untreated. Conclusions: Our results suggest that sudden household energy transition can be effective, given available technology for leap-frogging to high-efficiency electric heating, and generous public support for the program.

Human population movement can impede the elimination of soil-transmitted helminth transmission in regions with heterogeneity in mass drug administration coverage and transmission potential between villages: a metapopulation analysis

BackgroundSoil-transmitted helminth (STH) infections affect predominantly socio-economically disadvantaged populations in sub-Saharan Africa, East Asia and the Americas. Previous mathematical modelling studies have evaluated optimal intervention strategies to break STH transmission in clusters of villages. These studies assumed that villages are closed independent units with no movement of people in or out of communities. Here we examine how human population movement, for example, of seasonal migrant labourers, affect the outcome of mass drug administration (MDA) programmes.ResultsWe used a stochastic individual-based metapopulation model to analyse the impact of human population movement at varying rates on STH elimination efforts. Specifically, we looked at seasonal clumped movement events of infected individuals into a village. We showed that even if on average 75% of the entire resident population within a village are treated, an annual rate of 2–3% of the population arriving from an untreated source village can reduce the probability of STH elimination to less than 50% in high-prevalence settings. If a village is infection-free, an annual movement rate of 2–3% from an infected source village imposes a risk of re-introduction of STH of 75% or higher, unless the prevalence in the source village is less than 20%. Even a single arrival of 2–3% of the population can impose a risk of re-introducing STH of 50% or greater depending on the prevalence in the source village. The risk of re-introduction also depends on both the age group of moving individuals and STH species, since the pattern of cross-sectional age-prevalence and age-intensity profiles of infection in the human host are species-specific.ConclusionsPlanning for STH elimination programmes should account for human mobility patterns in defined regions. We recommend that individuals arriving from areas with ongoing STH transmission should receive preventive chemotherapy for STHs. This can most easily be implemented if migration is seasonal and overlaps with treatment rounds, e.g. seasonal migrant labour. Moreover, transmission hotspots in or near treatment clusters should be eliminated, for example, by implementing appropriate water, sanitation and hygiene (WASH) measures and targeting treatment to individuals living in hotspots.

Residual survival and local dispersal drive reinfestation by Triatoma dimidiata following insecticide application in Guatemala

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and transmitted by triatomine insect vectors. In Guatemala, insecticide spraying is an integral part of management of the main vector, Triatoma dimidiata. Spraying typically has low efficacy, which may be due to incomplete elimination from infested houses, within-village dispersal, or influx from other villages or sylvan environments. To evaluate how these mechanisms contribute to reinfestation, we conducted a time-course analysis of T. dimidiata infestation, abundance and household genetic structure in two nearby villages in Jutiapa, Guatemala; houses in the first village were surveyed, treated with insecticide if infested and then re-surveyed at eight and 22 months following spraying, while the second village served as an untreated control to quantify changes associated with seasonal dispersal. Insects were genotyped at 2–3000 SNP loci for kinship and population genetic analyses. Insecticide application reduced overall infestation and abundance, while the untreated village was stable over time. Nevertheless, within two years 35.5% of treated houses were reinfested and genetic diversity had largely recovered. Insects collected from reinfested houses post-spraying were most closely related to pre-spray collections from the same house, suggesting that infestations had not been fully eliminated. Immigration by unrelated insects was also detected within a year of spraying; when it occurred, dispersal was primarily local from neighboring houses. Similar dispersal patterns were observed following the annual dispersal season in the untreated village, with high-infestation houses serving as sources for neighboring homes. Our findings suggest that the efficacy of pyrethroid application is rapidly diminished by both within-house breeding by survivors and annual cycles of among-house movement. Given these patterns, we conclude that house structural improvements, an integral part of the Ecohealth approach that makes houses refractory to vector colonization and persistence, are critical for long-term reduction of T. dimidiata infestation.

Evaluation of the residual efficacy of indoor residual spraying with bendiocarb (FICAM WP 80) in six health districts in Senegal

BackgroundFrom 2011 to 2014, an indoor residual spray (IRS) programme for malaria vectors control was implemented in six health districts in Senegal. The main objective of the present study was to evaluate the efficacy of bendiocarb (FICAM WP 80) sprayed on different wall surfaces and its impact on malaria vectors. The entomological monitoring activities were carried out monthly in five treated sentinel villages and one control untreated village in each district.MethodsThe residual efficacy of bendiocarb applied at a dosage of 0.4 g/sq m was monitored for a period up to 9 months post-IRS using WHO cone bioassay method. This assay consisted to expose 2–5 days old unfed susceptible Anopheles coluzzii females to sprayed walls for a period of 30 min. The mortality rates after 24 h post-exposure were estimated and compared between the different types of walls sprayed in each sentinel village.ResultsThe results showed that the residual efficacy varied between the different sprayed walls, from one sentinel village to another and between the different campaigns. The FICAM had a residual efficacy of 3–6 months post-IRS on mud and cement wall surfaces. In some cases, the observed mortality rates were much higher than those reported elsewhere particularly during the first campaign in all the six districts.ConclusionsThe FICAM was found to be effective with a residual efficacy varying from 3 to 6 months. If the quality of the IRS application is excluded as a possible explanation of the short efficacy duration, the results suggest at least two rounds of treatments in order to cover the rainy season that lasts 5 to 6 months in the area. Such treatments could be carried out before the intensification of the rains in July and August in order to better cover the transmission period that occurs between late August and October in the area.

An evaluation of air quality, home heating and well-being under Beijing’s programme to eliminate household coal use

To mitigate health and environmental effects from coal-based home heating, the Beijing Municipality has implemented a programme in 3,700 villages that subsidizes electric heat pumps and electricity, and bans coal. Here, we estimate this programme’s impact on household energy use and expenditure, well-being and indoor environmental quality by comparing treated and untreated villages in three districts that vary in socioeconomic conditions. We find that, under this programme, households in high- and middle-income districts eliminated coal use with benefits to indoor temperature, indoor air pollution and life satisfaction. In a low-income district, the policy had partial effectiveness: coal use was contingent on household wealth, and there were fewer benefits to the indoor environment and negative impacts on well-being. These results suggest that a rapid household energy transition can be effective, but it is essential to appropriately control subsidies and fine-tune supports to limit transitional hardships for the less affluent. The Beijing Municipality has implemented a programme that subsidizes electric heat pumps and electricity, and bans coal. This study estimates the programme’s impact on household energy use and expenditure, well-being and indoor environment quality.

Biocontrol of rats in an urban environment in Southeast Asia using Sarcocystis singaporensis.

Upon request of the local administration a control campaign targeting commensal rats (Rattus rattus, R. exulans) was conducted in 30 sub-districts (villages) of the World Heritage town Luang Prabang, Northern Laos, using rat bait containing lethal quantities of the parasitic protist Sarcocystis singaporensis. The associated investigations assessed the short-term control efficacy, willingness of residents to co-operate (community approach), and temporal and spatial changes of the urban rat population in response to treatment. Biological rodent control significantly reduced rodent activity (percentage of positive tracking patches) in the town, from a mean of 25.3% (±12.8% SD) before (January-February) down to 8.0% (±4.4%) after (June) treatment. Reduction of rodent activity relative to three untreated villages was 83%. Similarly, residents observed significantly fewer rats on their properties after the campaign (mean percentage of households (HHs) per village with sightings), whereby reduction of sightings amounted to 57%. There was significant correlation between residents' observation rates and rodent activity. Among 94 rats trapped before and after treatment each, proportions of adult R. exulans and juvenile R. rattus were higher after rodent control, suggesting that a considerable part of the adult house rat population had been removed. Furthermore, a 5% post-campaign incidence of infection suggested that few rats had survived bait uptake. S. singaporensis may be used successfully as tactical biocontrol agent for culling of rats in urban environments. We propose additional components of a long-term rodent management strategy for the town, without which the impact of culling campaigns would be limited. © 2019 Society of Chemical Industry.

Untreated villages and factors associated with the absence of Community-Directed Treatment with Ivermectin (CDTI) in DRC.

The African Programme for Onchocerciasis Control (APOC), the main objective of which was the Community-Directed Treatment with Ivermectin (CDTI), was closed by the end of 2015. The purpose of this study was to describe untreated villages in DRC and to assess the factors associated with the absence of CDTI in endemic villages, between 2001 and 2014. This retrospective study was descriptive. Several annual technical reports of the National Onchocerciasis Task Force (NOTF) and national technical reports of CDTI projects were analysed; 21 projects implemented to control the disease were considered, representing the coverage of 42,778 endemic villages. Data were collected over a 3 month-period, between October and December 2016. Only 15,700 endemic villages were not treated through an annual CDT with Mectizan, i.e. 36.7%. The population at risk totalled 29,712,381 individuals and 7,681,995 of them were not treated, i.e. 25.9%. Eight projects recorded high proportions of untreated villages, i.e. 7,100 endemic entities (16.6%). Factors independently associated with non-treatment were the fear of serious side effects (adjusted OR: 10.6; 95% CI: 4.5-27.7), supply impaired by insecurity (adjusted OR: 15.9; 95% CI: 6.7-41.4) and geographical inaccessibility (adjusted OR: 19; 95% CI: 6.9-63.9). After 15 CDTI-cycles in DRC, the mean geographical coverage and therapeutic coverage rates reached 63.3% and 74.1%, respectively. The 2025 target of onchocerciasis eradication, as advocated by APOC, will not be reached. Untreated areas are partly responsible for such results. Many weaknesses persist in the National Program for Onchocerciasis Control (NPOC) and new strategies of disease control should be investigated.

Bionomics of Phlebotomus argentipes in villages in Bihar, India with insights into efficacy of IRS-based control measures.

BackgroundVisceral leishmaniasis (VL) is a deadly vector-borne disease. Approximately 90% of Indian VL cases occur in Bihar, where the sand fly, Phlebotomus argentipes, is the principal vector. Sand fly control in Bihar consists of indoor residual spraying (IRS), the practice of spraying the inner walls of village dwellings with insecticides. Prior researchers have evaluated success of IRS-control by estimating vector abundance in village houses, but the number of sampling periods (n = 2–3) were minimal, and outdoor-resting P. argentipes were neglected. We describe a large-scale field study, performed in 24 villages within two Bihari districts, during which P. argentipes were collected biweekly over 47-weeks, in cattle enclosures, houses, and outdoors in peri-domestic vegetation. The objectives of this study were to provide updated P. argentipes ecological field data, and determine if program-initiated IRS-treatment had led to noticeable differences in vector abundance.Principal findingsP. argentipes (n = 126,901) relative abundance was greatest during the summer months (June-August) when minimum temperatures were highest. P. argentipes were most frequently collected from cattle enclosures (~46% total; ~56% blood fed). Many sand flies were found to have taken blood from multiple sources, with ~81% having blood fed on humans and ~60% blood feeding on bovines. Nonparametric statistical tests were determined most appropriate for evaluating IRS-treatment. Differences in P. argentipes abundance in houses, cattle enclosures and vegetation were detected between IRS-treated and untreated villages in only ~9% of evaluation periods occurring during the peak period of human-vector exposure (June-August) and in ~8% of the total observations. No significant differences were detected between the numbers of P. argentipes collected in vegetation close to the experimental villages.ConclusionThe results of this study provide updated data regarding P. argentipes seasonal abundance, spatial distribution, and host preferances, and suggest vector abundance has not significantly declined in IRS-treated villages. We suggest that IRS be supplemented with vector control strategies targeting exophagic, exophilic P. argentipes, and that disease surveillance be accompanied by rigorous vector population monitoring.

The ecological complexity of the Thai-Laos Mekong River: I. Geology, seasonal variation and human impact assessment on river quality

The objective of this study is to assess the variation of pollution in the Thai–Laos Mekong associated with seasonal dynamics concomitant with the natural geological features and human activities that impact on the adverse quality of the river. The complex ecology of the 1500 km stretch of the Thai-Laos Mekong River has been studied in this paper to understand the relationship with the geomorphology, with the sub-tropical monsoonal climate and the impact of human activity. Sub-surface geology controls the nature and extent of the drainage basin and of the river channel. The volume flow of the river varies naturally and dynamically in phase with the rainfall; traditional models based on steady state hydraulics are inappropriate. Continuous erosion of the river banks and bed generates a sediment load of impure silt, mica, quartz and clay minerals that inhibits light penetration and limits the primary productivity of the river. The river separates two countries at different stages of development; it flows through or close to eight non-industrial conurbations (Populations 350,000–2,000,000) but is otherwise sparsely populated. The river is used for subsistence agriculture, village transport, fishing including aquaculture and as a source of domestic water. Hydroelectricity is generated from the Laos tributaries. The river is a depository for partially treated urban waste and untreated village waste, hence populations of E.coli bacteria sometimes render the water unsuitable for drinking unless treated with the highest value of 240/100ml found at station 7 during the summer season of 2003. Furthermore the river is polluted by trace metals, notably cadmium and mercury, and by Polycyclic Aromatic Hydrocarbons (PAHs), which are particularly concentrated in the sediments. Previous work has shown that cadmium and mercury exceed the Probable Effect Level (PEL) values of Canadian Environmental Quality Guidelines and that the PAH concentrations were also greater than the Interim Sediment Quality Guidelines (ISQG). Consequently the fish stock, a vital source of protein for the local human population maybe seriously affected. As conflict between the demands of human activities will be exacerbated by the continuing development of the basin; monitoring must be continued and a better model of the river's ecology is needed to predict the impact of development.

Abrupt spatial and numerical responses of overabundant foxes to a reduction in anthropogenic resources

Summary 1. Carnivore overabundance that results from exploitation of human derived resources can have numerous detrimental effects on local human populations and ecological communities. Experimental studies on the responses of overabundant carnivores to reductions of such resources are necessary to understand the effectiveness and impacts of resource reduction. 2. We conducted controlled experiments in two villages in which we drastically reduced the availability of anthropogenic food sources in half of each village. Spatial and numerical responses of radio‐collared red foxes Vulpes vulpes were recorded and contrasted with those of radio‐collared foxes in three similar untreated villages and pristine areas in the region. In total, we looked at survival rates of 134 foxes. 3. Prior to the resource manipulation, home range sizes (0·47 and 0·56 km2) and population densities (30 and 36 foxes km−2) in the two villages were comparable to documented low and high‐end values, respectively. 4. Fast and distinct spatial responses were observed in response to the resource manipulation, and were manifested in either increased home range size or home range shifts. In one village, foxes exposed to reduced resource availability more than doubled their home range size. 5. Survival rates of individuals in the treated areas were drastically reduced. Actual fox mortality in the two treated areas reached 100% and 64% within 12 months of the onset of resource manipulation. Estimated monthly survival in the two treated areas declined from 0·96–0·98 and 0·98–0·99 (∼0·69 and 0·78 derived annual survival) before treatment to 0·80–0·83 and 0·92–0·94 (∼<0·01 and 0·42 derived annual survival) after treatment, respectively. By contrast, average monthly survivorship in pristine areas was nearly 0·97 (∼0·69 annual survival) and in the untreated areas and other non‐treated villages was 0·95–0·99 (∼0·54–0·89 annual survival). 6. Synthesis and applications. This study demonstrates that sound waste disposal measures are very effective in controlling populations of overabundant carnivores. Contrary to common notion, the response of foxes to reduced resources was fast, manifested more by reduced survival than by successful dispersal into adjacent pristine areas. The results offer support to the Resource Dispersion Hypothesis regarding both home range size and density (suggested by the sharp decrease in survival) as a function of the spatial and temporal dispersion of resource.

Preliminary examination of integrated vector management in a tropical rainforest area of Cameroon

In the tropical rainforest area of Cameroon, people are affected by blackflies (Simulium spp.) and mosquitoes (Anopheles spp). Use of insecticide-treated bed nets (ITNs) has been promoted to protect vulnerable groups from mosquito bites, whereas historically indoor residual spraying (IRS) was the primary intervention. In a malaria-endemic area, a pilot study examined different mosquito control interventions applied to entire villages to assess their impact on vectors, malaria incidence and the quality of life of the communities. The Sanaga River near these villages was treated with insecticide to kill blackfly larvae. A medical survey of the six villages had shown that 20% of the population suffered from malaria, while 50% were infected with onchocerciasis and 5% with Loa loa. IRS+ITN using ICON CS (lambda-cyhalothrin capsule suspension formulation) or improved screening of houses combined with outdoor misting reduced the numbers of mosquitoes collected from exit traps compared to the other treatments. More sporozoites were detected in mosquitoes sampled in exit traps in the untreated village than in the treated villages. Malaria incidence several months after treatments was not significantly different from pre-treatment levels. Blackfly adult populations were reduced for several weeks following larvicide application but recovered when treatment was halted.

CHLAMYDIA ON CHILDREN AND FLIES AFTER MASS ANTIBIOTIC TREATMENT FOR TRACHOMA

There are various approaches to control trachoma. These include the elimination of the ocular strains of Chlamydia trachomatis that cause the disease and to decrease the spread of infection by other measures such as fly control. Here, we examined how these two are related (i.e., how treating children with antibiotics affects carriage of Chlamydia by flies). Flies were collected in villages that had received mass oral azithromycin distribution and were compared with flies in untreated villages. Polymerase chain reaction (PCR) was performed to detect chlamydial DNA on the flies. Conjunctival swabs were also taken to assay for chlamydial prevalence in the children. Chlamydia was found on 23% of the flies in the untreated villages but only 0.3% in treated villages. Prevalence of trachoma in children proved to be an excellent predictor of the prevalence on flies (correlation coefficient, 0.89). Thus, treating children with antibiotics may drastically reduce the role of flies as a vector.