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Temperature and head movement are relevant parameters when analyzing the farrowing behavior of sows. Obtaining these body parameters in a way that is nonintrusive to animals is a major challenge in the harsh farrowing pen environment. Due to the presence of large amounts of metal as well as the unpredictable behavior of animals, such environments are not ideal for wired communication platforms. Intrusive measuring equipment may cause animals to deviate from their normal behavioral patterns invalidating gathered sensor data. Using lightweight, highly mobile and wireless sensor equipment is thus essential for unobtrusive measurements. This article discusses the challenges involved in developing a lightweight and flexible wireless sensor network infrastructure platform used in the analysis of sow behavior during farrowing. The platform is based on the customizable wireless sensor platform Shimmer and the open source software frameworks TinyOS and SPINE. Embedded in hot melt adhesive, the Shimmer modules were used as ear tags providing biologists with head movement and temperature data throughout six months. Focus is on the technical aspects of developing a system faced with mutually exclusive and changing requirements in an iterative and progressive research project, drawing upon the experiences from several stages of live experiments with farrowing sows. [ABSTRACT FROM AUTHOR]

Abstract Background Malaria in The Gambia is highly seasonal, with transmission occurring as Anopheles gambiae s.l. populations expand during and immediately after a single annual rainy season that lasts from June to October. There has been very limited investigation of the ecology of vectors during the dry season, when numbers are very limited and distributions may be restricted. Methods Weekly adult mosquito collections (pyrethrum spray, light trap, and search collections from rooms, as well as light trap collections from animal shelters, abandoned wells and grain stores), and artificial sentinel breeding site surveys were performed in four villages near the upper tidal and partially saline part of the Gambia River in the last four months of an annual dry season (March to June). Mosquito species were identified by morphological and DNA analysis, and ELISA assays were performed to test for Plasmodium falciparum sporozoites and human blood meal components. Results Adults of An. gambiae s.l. were collected throughout the period, numbers increasing towards the end of the dry season when humidity was increasing. Adult collections were dominated by An. melas (86%), with An. gambiae s.s. (10%) and An. arabiensis (3%) also present throughout. Most females collected in room search and spray collections contained blood meals, but most from light traps were unfed. None of the females tested (n = 1709) contained sporozoites. Larvae (mostly An. gambiae s.s.) were recovered from artificial sentinel breeding sites in the two villages that had freshwater pools. These two villages had the highest proportions of An. gambiae s.s. adults, and experienced the most substantial increase in proportions of An. gambiae s.s. after the onset of rains. Conclusion During the dry season population minimum, An. melas was the predominant vector species, but differences among villages in availability of fresh-water breeding sites correlate with egg laying activity and relative numbers of An. gambiae s.s. adults, and with the increase in this species immediately after the beginning of the rains. Local variation in dry season vector persistence is thus likely to influence spatial heterogeneity of transmission intensity in the early part of the rainy season.

Competing Interests: The project was financially supported by the Wellcome Trust Africa Asia Programme Vietnam. The authors declare that they have no conflicts of interest.

Background: The emergence of insecticide resistance and outdoor transmission in malaria-endemic areas underlines the urgent need to develop innovative tools, such as spatial repellents (SR), that may circumvent this residual transmission. With limited options for effective insecticides, regular resistance monitoring is warranted for selecting and using appropriate tools. This study evaluates the pyrethroid knockdown resistance (kdr) allele before and after implementing a transfluthrin-based spatial repellent (SR) intervention in placebo-treated clusters., Methods: This study looks at the frequency distribution of the kdr allele in Sumba Island from June 2015 to August 2018. Insecticide susceptibility tests were carried out on female Anopheles sp. aged 3-5 days against permethrin 21.5 μg/ml, deltamethrin 12.5 μg/ml, and transfluthrin 10 μg/ml using CDC bottle assay. PCR sequencing of representative samples from adult mosquito collections and insecticide tests revealed the presence of kdr mutations (L1014F and L1014S) in the VGSC gene., Results: A total of 12 Anopheles species, Anopheles tesselatus, Anopheles. aconitus, Anopheles barbirostris, Anopheles kochi, Anopheles annularis, Anopheles maculatus, Anopheles sundaicus, Anopheles flavirostris, Anopheles balabacensis, Anopheles indefinitus, Anopheles subpictus, and Anopheles vagus were analysed. Anopheles vagus and An. sundaicus predominated in the larval populations. Susceptibility assays for all insecticides identified fully susceptible phenotypes in all species examined. Anopheles increasing frequency of kdr mutant alleles during the 3 year SR deployment was observed in both SR-treated and placebo areas, a statistically significant increase occurred in each arm. However, it is unclear how significant SR is in causing the increase in mutant alleles. The L1014S, knockdown resistance east type (kdr-e) allele was detected for the first time among the mosquito samples in this study. The L1014F, knockdown resistance west type (kdr-w) allele and heteroduplex form (wild-type-mutant) were found in almost all Anopheles species examined, including An. vagus, An. aconitus, An. subpictus, An. tesselatus, An. annularis, An. flavirostris and An. sundaicus., Conclusion: The presence of fully susceptible phenotypes over time, along with an increase in the frequency distribution of the L1014F/S mutations post-intervention, suggest drivers of resistance external to the study, including pyrethroid use in agriculture and long-lasting insecticidal nets (LLINs). However, this does not negate possible SR impacts that support resistance. More studies that enable the comprehension of possible SR-based drivers of resistance in mosquitoes need to be conducted., (© 2024. The Author(s).)

Skin diseases are a major public health concern in Indonesia, although access to specialized care in remote areas is limited. We initiated a low-cost teledermatology service in Sumba, a remote island in eastern Indonesia. Eighteen healthcare workers (HCWs) at five primary healthcare centers received training to manage common skin diseases and submit clinical cases beyond their expertise to an online platform. Submitted cases were reviewed by at least one dermatologist. Diagnostic agreement between HCWs and dermatologists was calculated. The HCWs participated in a satisfaction survey 2 years after project initiation. Since October 2020, of 10,384 patients presenting with skin complaints in a 24-month period, 307 (3%) were submitted for a teledermatology consultation. The most frequent skin diseases were infections and infestations (n = 162, 52.8%) and eczematous (85, 27.7%) and inflammatory (17, 5.5%) conditions. Fifty-three patients (17.3%) were diagnosed with a neglected tropical skin disease, including leprosy and scabies. Dermatologist advice was provided within a median of 50 minutes (interquartile range, 18-255 minutes), with 91.9% of consultations occurring within 24 hours. The diagnostic agreement level between HCWs and dermatologists significantly improved over time, from 46.9% in the first 6-month period (κ = 0.45; 95% CI, 0.37-0.54) to 77.2% in the last 6-month period (κ = 0.76; 95% CI, 0.67-0.86; global P < 0.001). The HCWs reported that the teledermatology service was extremely/very useful in supporting daily practice (100%) and improved their knowledge of skin diseases tremendously/a lot (92%). Teledermatology can improve accessibility and quality of skin services in medically underserved areas, providing opportunities for scalability and knowledge transfer to frontline HCWs.

Malaria vector control interventions in Sumba, Indonesia, have not been able to eliminate malaria. Human drivers of exposure to Anopheles bites were investigated as part of a larger clinical trial evaluating the impact of a spatial repellent product on malaria incidence. Human behavioral observations (HBOs) evaluating temporal and spatial presence, sleeping behaviors, and insecticide treated net (ITN) use, were collected parallel to entomological collections-indoor and outdoor human landing catches (HLCs), and house hold surveys. Data demonstrates that mosquito access to humans, enabled by structurally open houses, is evident by the similar entomological landing rates both inside and outside households. The presence of animals inside houses was associated with increased mosquito entry-however, the number of humans present inside houses was not related to increased mosquito landing. Analyzing mosquito landing rates with human behavior data enables the spatial and temporal estimation of exposure to Anopheles bites, accounting for intervention (ITN) presence and usage. Human behavior adjusted exposure to Anopheles bites was found to be highest in the early in the evening, but continued at lower levels throughout the night. Over the night, most exposure (53%) occurred when people were indoors and not under the protection of nets (asleep or awake) followed by exposure outside (44%). Characterized gaps in protection are outdoor exposure as well as exposure indoors-when awake, and when asleep and not using ITNs. Interestingly, in the primary trial, even though there was not a significant impact of the spatial repellent on vector biting rates by themselves (16%), when factoring in human behavior, there was approximately 28% less exposure in the intervention arm than in the placebo arm. The treated arm had less human behavior adjusted bites in all spaces evaluated though there was proportionally higher exposure indoors. This analysis points to the importance of using HBOs both towards understanding gaps in protection as well as how interventions are evaluated. To mitigate ongoing transmission, understanding context specific spatial and temporal exposure based on the interactions of vectors, humans and interventions would be vital for a directed evidence-based control or elimination strategy., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2022 Rozi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: The East Nusa Tenggara province, Indonesia, contributed to 5% of malaria cases nationally in 2020, with other mosquito-borne diseases, such as dengue and filariasis also being endemic. Monitoring of spatial and temporal vector species compositions and bionomic traits is an efficient method for generating evidence towards intervention strategy optimization and meeting disease elimination goals., Methods: The impact of a spatial repellent (SR) on human biting mosquitoes was evaluated as part of a parent cluster-randomized, double-blinded, placebo-controlled trial, in Sumba, East Nusa Tenggara. A 10-month (June 2015-March 2016) baseline study was followed by a 24-month intervention period (April 2016 to April 2018)-where half the clusters were randomly assigned either a passive transfluthrin emanator or a placebo control., Results: Human-landing mosquito catches documented a reduction in landing rates related to the SR. Overall, there was a 16.4% reduction (21% indoors, and 11.3% outdoors) in human biting rates (HBR) for Anopheles. For Aedes, there was a 44.3% HBR reduction indoors and a 35.6% reduction outdoors. This reduction was 38.3% indoors and 39.1% outdoors for Armigeres, and 36.0% indoors and 32.3% outdoors for Culex species. Intervention impacts on the HBRs were not significant and are attributed to large inter-household and inter cluster variation. Anopheles flavirostris, Anopheles balabacensis and Anopheles maculatus individually impacted the overall malaria infections hazard rate with statistically significance. Though there was SR-based protection against malaria for all Anopheles species (except Anopheles sundaicus), only five (Anopheles aconitus, Anopheles kochi, Anopheles tessellatus, An. maculatus and An. sundaicus) demonstrated statistical significance. The SR numerically reduced Anopheles parity rates indoors and outdoors when compared to the placebo., Conclusion: Evidence demonstrating that Anopheles vectors bite both indoors and outdoors indicates that currently implemented indoor-based vector control tools may not be sufficient to eliminate malaria. The documented impact of the SR intervention on Aedes, Armigeres and Culex species points to its importance in combatting other vector borne diseases. Studies to determine the impact of spatial repellents on other mosquito-borne diseases is recommended., (© 2022. The Author(s).)

Mosquitoes are important vectors that transmit pathogens to human and other vertebrates. Each mosquito species has specific ecological requirements and bionomic traits that impact human exposure to mosquito bites, and hence disease transmission and vector control. A study of human biting mosquitoes and their bionomic characteristics was conducted in West Sumba and Southwest Sumba Districts, Nusa Tenggara Timur Province, Indonesia from May 2015 to April 2018. Biweekly human landing catches (HLC) of night biting mosquitoes both indoors and outdoors caught a total of 73,507 mosquito specimens (59.7% non-Anopheles, 40.3% Anopheles). A minimum of 22 Culicinae species belonging to four genera (Aedes, Armigeres, Culex, Mansonia), and 13 Anophelinae species were identified. Culex quinquefasciatus was the dominant Culicinae species, Anopheles aconitus was the principal Anopheles species inland, while An. sundaicus was dominant closer to the coast. The overall human biting rate (HBR) was 10.548 bites per person per night (bpn) indoors and 10.551 bpn outdoors. Mosquitoes biting rates were slightly higher indoors for all genera with the exception of Anopheles, where biting rates were slightly higher outdoors. Diurnal and crepuscular Aedes and Armigeres demonstrated declining biting rates throughout the night while Culex and Anopheles biting rates peaked before midnight and then declined. Both anopheline and non-anopheline populations did not have a significant association with temperature (p = 0.3 and 0.88 respectively), or rainfall (p = 0.13 and 0.57 respectively). The point distribution of HBR and seasonal variables did not have a linear correlation. Data demonstrated similar mosquito-human interactions occurring outdoors and indoors and during early parts of the night implying both indoor and outdoor disease transmission potential in the area-pointing to the need for interventions in both spaces. Integrated vector analysis frameworks may enable better surveillance, monitoring and evaluation strategies for multiple diseases., Competing Interests: The authors have declared that no competing interest exist. Author Michael J. Bangs was unable to confirm their authorship contributions. On their behalf, the corresponding author has reported their contributions to the best of their knowledge.

A cluster-randomized, double-blinded, placebo-controlled trial was conducted to estimate the protective efficacy (PE) of a spatial repellent (SR) against malaria infection in Sumba, Indonesia. Following radical cure in 1,341 children aged ≥ 6 months to ≤ 5 years in 24 clusters, households were given transfluthrin or placebo passive emanators (devices designed to release vaporized chemical). Monthly blood screening and biweekly human-landing mosquito catches were performed during a 10-month baseline (June 2015-March 2016) and a 24-month intervention period (April 2016-April 2018). Screening detected 164 first-time infections and an accumulative total of 459 infections in 667 subjects in placebo-control households, and 134 first-time and 253 accumulative total infections among 665 subjects in active intervention households. The 24-cluster protective effect of 27.7% and 31.3%, for time to first-event and overall (total new) infections, respectively, was not statistically significant. Purportedly, this was due in part to zero to low incidence in some clusters, undermining the ability to detect a protective effect. Subgroup analysis of 19 clusters where at least one infection occurred during baseline showed 33.3% ( P -value = 0.083) and 40.9% ( P -value = 0.0236, statistically significant at the one-sided 5% significance level) protective effect to first infection and overall infections, respectively. Among 12 moderate- to high-risk clusters, a statistically significant decrease in infection by intervention was detected (60% PE). Primary entomological analysis of impact was inconclusive. Although this study suggests SRs prevent malaria, additional evidence is required to demonstrate the product class provides an operationally feasible and effective means of reducing malaria transmission.

A randomized, double-blinded, placebo-controlled study was conducted to examine the effect of spatial repellent (SR) in households at risk of malaria in Indonesia. Following presumptive radical cure for malaria in 180 adult men representing sentinels of new infection in four clusters within two villages, all households were given either metofluthrin or placebo mosquito coils. Weekly blood smear screening and human-landing mosquito catches were done throughout the 6 months intervention. Malaria infections occurred in 61 subjects living in placebo households and 31 subjects living in SR coil households, suggesting a 52% protective effect of SR. Likewise, anopheles indoor human landing rates were 32% lower in homes receiving SR coils. Differences in the malaria attack rate between SR- and placebo-treated homes was significant when not accounting for the effects of clustering. When the analysis was adjusted for intra-cluster correlation, the differences between SR- and placebo-treated homes were not statistically significant. The findings provide evidence of SR public health benefit and support a larger trial statistically powered to detect those effects., (© The American Society of Tropical Medicine and Hygiene.)

Background: For malaria control in Africa it is crucial to characterise the dispersal of its most efficient vector, Anopheles gambiae, in order to target interventions and assess their impact spatially. Our study is, we believe, the first to present a statistical model of dispersal probability against distance from breeding habitat to human settlements for this important disease vector., Methods/principal Findings: We undertook post-hoc analyses of mosquito catches made in The Gambia to derive statistical dispersal functions for An. gambiae sensu lato collected in 48 villages at varying distances to alluvial larval habitat along the River Gambia. The proportion dispersing declined exponentially with distance, and we estimated that 90% of movements were within 1.7 km. Although a 'heavy-tailed' distribution is considered biologically more plausible due to active dispersal by mosquitoes seeking blood meals, there was no statistical basis for choosing it over a negative exponential distribution. Using a simple random walk model with daily survival and movements previously recorded in Burkina Faso, we were able to reproduce the dispersal probabilities observed in The Gambia., Conclusions/significance: Our results provide an important quantification of the probability of An. gambiae s.l. dispersal in a rural African setting typical of many parts of the continent. However, dispersal will be landscape specific and in order to generalise to other spatial configurations of habitat and hosts it will be necessary to produce tractable models of mosquito movements for operational use. We show that simple random walk models have potential. Consequently, there is a pressing need for new empirical studies of An. gambiae survival and movements in different settings to drive this development.

Understanding local variability in malaria transmission risk is critically important when designing intervention or vaccine trials. Using a combination of field data, satellite image analysis, and GIS modeling, we developed a high-resolution map of malaria entomological inoculation rates (EIR) in The Gambia, West Africa. The analyses are based on the variation in exposure to malaria parasites experienced in 48 villages in 1996 and 21 villages in 1997. The entomological inoculation rate (EIR) varied from 0 to 166 infective bites per person per rainy season. Detailed field surveys identified the major Anopheles gambiae s.l. breeding habitats. These habitats were mapped by classification of a LANDSAT TM satellite image with an overall accuracy of 85%. Village EIRs decreased as a power function based on the breeding areas size and proximity. We use this relationship and the breeding habitats to map the variation in EIR over the entire 2500-km(2) study area.

Home treatment with antimalarials is a common practice in many countries, and may save lives by ensuring that more malaria cases receive prompt treatment. Through retrospective surveys we found that home treatment of young children with antimalarials was uncommon in rural Gambia. Few families kept medicines in the home in case of illness, 28% kept paracetamol and only 8% kept chloroquine. Less than 10% of cases of childhood 'malaria' had been treated with chloroquine at home, and 69% of those giving home medication did not know the correct dosage for a child. The most common course of treatment was the use of paracetamol and/or tepid sponging to reduce fever, before the child was taken to a government health facility. Treating a child with antimalarials at home was more costly than other forms of treatment. The low cost associated with the use of health services for children and the limited availability of antimalarials outside major towns contribute to the high use of government health services. This shows that that home treatment cannot be assumed to be the predominant mode of malaria treatment throughout Africa, and highlights the need for country-specific policies based on accurate local knowledge of treatment practices in both rural and urban areas.

A study was undertaken to identify the major larval habitats of the Anopheles gambiae (Giles) complex in rural Gambia. Mosquito larvae and pupae were sampled along transects and in specific habitats in the central region of the country during the rainy seasons of 1996 and 1997. The sampling showed that the major breeding sites were located on the flooded alluvial soils bordering the river. The largest numbers of larvae were found during September, one month after the peak rains. Polymerase chain reaction analysis of specimens showed that Anopheles melas (Theobald) was the dominant species in the flooded areas (81.5%), followed by A. gambiae sensu stricto (Giles) (18.0%) and A. arabiensis (Patton) (0.5%). By sampling in specific habitats it was evident that A. arabiensis was mainly breeding in rain-fed rice fields along the edge of the alluvial soils. Anopheles melas and A. gambiae s.s. often coexisted but whereas A. melas were found in water with a salinity of up to 72% sea water (25.2 g NaCl l(-1)), A. gambiae s.s. only occurred in water with up to 30% sea water (10.5 g NaCl l(-1)). Anopheles melas larvae were found in association with plant communities dominated by sedges and grasses (Eleocharis sp., Paspalum sp., Sporobolus sp.) and sea-purslane Sesuvium portulacastrum (L.) and the presence of cattle hoof prints, whereas A. gambiae s.s. larvae mainly occurred in association with Paspalum sp. and Eleocharis sp. The study showed that even during the peak rainy season, breeding of the A. gambiae complex is almost entirely restricted to the extensive alluvial areas along the river.

The World Health Organization has recommended the use of cattle for zooprophylaxis as a protective measure against malaria since 1982. However, concern has been raised about this practice, since some studies have shown that the presence of cattle may instead increase malaria prevalence. This study was designed to investigate the effect of passive zooprophylaxis on malaria in an area of moderate seasonal transmission in The Gambia, West Africa. The study was based on a paired-cohort of 204 children aged < 7 years, sleeping < 20 m or > 50 m from cattle, and surveys were done from 14 October to 2 December 1997. Entomological investigations showed that the presence of cattle did not alter the risk of malaria transmission in nearby houses. There was also no significant difference in the prevalence of Plasmodium falciparum between the 2 groups. Although the presence of cattle appeared to be protective against high parasitaemia, cattle were also associated with greater wealth of the children's families. Conditional logistic regression analysis showed that the decreased risk of high parasitaemia in the group with cattle present was an artefact associated with the higher general wealth of the cattle owners. We concluded that zooprophylaxis is not an effective intervention method against malaria in settings similar to The Gambia.

The causes of local variation in the prevalence of malaria were investigated in rural Gambia. Cross-sectional prevalence surveys were carried out among 1184 young children (aged 6 months-5 years) in 48 villages, at the end of the transmission season in 1996. Villages were categorized according to distance from the nearest vector breeding sites, and the patterns of malaria transmission, infection and disease compared. Children living in villages within 3 km of breeding sites experienced more infective bites, and higher prevalences of parasitaemia and spleen enlargement than less-exposed children living further away. Clinical illness, in contrast, was more common among infected children who were less exposed. Infected children living 3 km or more from breeding sites were more likely to have high-density parasitaemia (odds ratio [OR] = 1.98), fever (OR = 2.60) and high-density parasitaemia together with fever (OR = 3.17). Clinical attacks did not decline in older children, as seen amongst children who were more exposed. These findings show that significant differences in the risk of infection and clinical attacks can occur over very short distances. The age at which protective immunity is acquired may be delayed in villages where transmission intensity is lower, thus increasing the risk of a clinical attack following infection. Communities with the lowest vector densities may be those at greatest risk of disease.

The effect of zooprophylaxis on malaria transmission has not been studied on the African continent despite that the World Health Organization has recommended this intervention method since 1982. The effect of passive zooprophylaxis on malaria vector abundance, mosquito feeding preferences, and infectivity was studied in an area of moderate seasonal transmission in The Gambia. A paired cohort of 204 children <7 yr of age was selected and matched in groups for presence or absence of cattle (Bos taurus) within 20 m of their bedroom. Comparisons were made between mosquitoes collected from the bedrooms of the two groups of children. Other ruminants and equines were present in both groups of compounds. Most of the anopheline mosquitoes (98.5%) collected were Anopheles gambiae sensu lato. There was no difference in the geometric mean number of An. gambiae s.l. mosquitoes caught in houses near or far from cattle. The species composition of the An. gambiae complex was similar in both groups. Blood meal analysis of specimens collected in houses without cattle showed a human blood index (HBI) of 82% for An. Arabiensis (Patton), 56% for An. gambiae sensu stricto (Giles), and 36% for Anopheles Melas (Theobald), indicating that each of these sibling species fed readily on animals. The presence of cattle reduced the HBI of An. arabiensis but did not significantly alter the HBI of An. gambiae s.s. or An. melas. There was no significant difference between the groups in the sporozoite rates of An. gambiae s.l. nor in the estimated malaria transmission risk. These findings suggest that passive zooprophylaxis using cattle does not alter the individual exposure to malaria parasites in The Gambia.

A simple model for the influence of host availability on vector bloodmeal choice is applied to estimate the relative availabilities of humans, cattle and other host populations to malaria vectors in African communities, using published human blood indices and ratios of cattle to humans. Cattle were bitten < 0.01, 0.021 +/- 0.11, 1.61 +/- 0.16 and 1.61 +/- 0.46 times as often as humans by Anopheles funestus, An. gambiae sensu stricto and An. arabiensis in Segera, Tanzania, and An. gambiae sensu lato in The Gambia, respectively. No significant feeding upon host species other than cattle or humans was detected. Even though An. gambiae s.l. in The Gambia were mostly An. gambiae s.s., they were 77 times more likely to choose cattle over humans than An. gambiae s.s. in Tanzania. The model accurately predicted cattle blood indices for the An. arabiensis population in Tanzania (predicted = 0.99 +/- 0.21 x observed + 0.00 +/- 0.10; r2 = 0.66). The potential effect of increased cattle abundance upon malaria transmission intensity was simulated using fitted relative availability parameters and assuming vector emergence rate, feeding cycle length and survivorship were unaffected. The model predicted that increased cattle populations would not affect malaria transmission in Tanzania but could drastically reduce transmission in The Gambia or where An. arabiensis is the dominant vector. We define the availability of a host as the rate at which a typical individual host-seeking vector encounters and feeds upon that host in a single feeding cycle. Mathematical models based on this definition also represent promising tools for quantifying the dependence of vector longevity, feeding cycle length and dispersal upon host availability.

Bednets are thought to offer little, if any, protection against malaria, unless treated with insecticide. There is also concern that the use of untreated nets will cause people sleeping without nets to receive more mosquito bites, and thus increase the malaria risk for other community members. Regular retreatment of nets is therefore viewed as critical for malaria control. However, despite good uptake of nets, many control programmes in Africa have reported low re-treatment rates. We investigated whether untreated bednets had any protective benefit (in October and November 1996) in The Gambia where nets, although widely used, are mostly untreated. Cross-sectional prevalence surveys were carried out in 48 villages and the risk of malaria parasitaemia was compared in young children sleeping with or without nets. Use of an untreated bednet in good condition was associated with a significantly lower prevalence of Plasmodium falciparum infection (51% protection [95% CI 34-64%], P < 0.001). This finding was only partly explained by differences in wealth between households, and children in the poorest households benefited most from sleeping under an untreated net (62% protection [14-83%], P = 0.018). There was no evidence that mosquitoes were diverted to feed on children sleeping without nets. These findings suggest that an untreated net, provided it is in relatively good condition, can protect against malaria. Control programmes should target the poorest households as they may have the most to gain from using nets.

Background: Domestic flies are accepted vectors of diarrhoea, but their role in trachoma transmission has never been quantified and no study has shown that fly control decreases the prevalence of trachoma. We assessed the effect of fly control on public health in a pilot study in Gambian villages., Methods: We studied two pairs of villages--one pair in the 1997 wet season, and one pair in the 1998 dry season. For each pair, deltamethrin was sprayed for 3 months to control flies in one village whilst the other was used as a control. Fly populations were monitored with traps. We surveyed trachoma at baseline and at 3 months, and collected daily data on diarrhoea in children aged between 3 months and 5 years., Findings: Fly control decreased numbers of muscid flies by around 75% in the intervention villages compared with controls. Trachoma prevalence was similar at baseline (wet season, prevalence in intervention village 8.8% vs control 12.2%; dry season, 18.0% vs 16.0%), but after 3 months of fly control there were 75% fewer new cases of trachoma in the intervention villages (wet season 3.7% vs 13.7%; dry season 10.0% vs 18.9%; rate ratio and relative risk of pooled data 0.25 [adjusted 95% CI 0.09-0.64], p=0.003). There was 22% less childhood diarrhoea in the wet season (14% vs 19%, period prevalence ratio 0.78 [0.64-0.95], p=0.01), and 26% less diarrhoea in the dry season (6% vs 8%; 0.74 [0.34-1.59], p=0.60) compared with controls., Interpretation: Muscid flies are important vectors of trachoma and childhood diarrhoea in The Gambia. Deltamethrin spray is effective for fly control and may be useful for reducing trachoma and diarrhoea in some situations, but further research on sustainable fly-control methods is needed.

The impact of permethrin-impregnated bednets on resting and feeding behaviour of mosquito vectors of Wuchereria bancrofti, causing human lymphatic filariasis was studied in six pairs of villages (treated and untreated) before and after intervention. The study villages were in Kwale District, near the coast of Kenya, where Bancroftian filariasis is highly endemic, transmitted by a combination of both anopheline and culicine mosquito vectors. Mosquitoes were collected weekly in each village, indoors (using pyrethrum spray catches) and outdoors (using pit traps) during 3-4 months following the long rainy season. Of the filariasis vector species of mosquitoes collected in 1994 before intervention. 33.6% were members of the Anopheles gambiae complex, 30% were An. funestus and 36.4% were Culex quinquefasciatus. PCR analysis of the An. gambiae complex species collected in 1995 demonstrated that 98.5% were An. gambiae sensu stricto. 1% An. arabiensis and 0.5% An. merus. Introduction of impregnated bednets in 1995 significantly reduced the number of indoor-resting An. gambiae s.l. by 94.6% and An. funestus by 96.7%, but there was no change in the number of Cx quinquefasciatus collected indoors. The number of outdoor-resting An. gambiae s.l. was significantly reduced, whereas densities of An. funestus and Cx quinquefasciatus remained unaffected outdoors. ELISA analysis of mosquito bloodmeals showed a shift from human to animal feeding after the introduction of treated nets. The human blood index (HBI) for indoor resting Cx quinquefasciatus was reduced from 93.1% to 14.4%. Vector potential based on the HBI and mosquito density was estimated to be reduced by 99% for An. gambiae s.l., 98% for An. funestus and 97% for Cx quinquefasciatus and vectorial capacity would be suppressed even more by the impact on the vector survival rates (not measured). These results suggest that permethrin-impregnated bednets give effective personal protection against transmission of W. bancrofti by An. gambiae, An. funestus and Cx quinquefasciatus in East Africa.