Insecticide-treated Materials Research Articles

Evaluation of insecticide treated window curtains and water container covers for dengue vector control in a large-scale cluster-randomized trial in Venezuela.

Following earlier trials indicating that their potential in dengue vector control was constrained by housing structure, a large-scale cluster-randomized trial of insecticide treated curtains (ITCs) and water jar covers (ITJCs) was undertaken in Venezuela. In Trujillo, Venezuela, 60 clusters (6223 houses total) were randomized so that 15 clusters each received either PermaNet insecticide-treated window curtains (ITCs), permanent insecticide-treated water storage jar covers (ITJCs), a combination of both ITCs and ITJCs, or no insecticide treated materials (ITMs). A further 15 clusters located at least 5km from the edge of the study site were selected to act as an external control. Entomological surveys were carried out immediately before and after intervention, and then at 6-month intervals over the following 27 months. The Breteau and House indices were used as primary outcome measures and ovitrap indices as secondary. Negative binomial regression models were used to compare cluster-level values of these indices between the trial arms. Reductions in entomological indices followed deployment of all ITMs and throughout the trial, indices in the external control arm remained substantially higher than in the ITM study arms including the internal control. Comparing the ratios of between-arm means to summarise the entomological indices throughout the study, the combined ITC+ITJC intervention had the greatest impact on the indices, with a 63% difference in the pupae per person indices between the ITC+ITJC arm and the internal control. However, coverage had fallen below 60% by 14-months post-intervention and remained below 40% for most of the remaining study period. ITMs can impact dengue vector populations in the long term, particularly when ITCs and ITJCs are deployed in combination. ClinicalTrials.gov ISRCTN08474420; www.isrctn.com.

Climbing ability of Trogoderma granarium larvae on artificial household and insecticide-treated materials

The khapra beetle, Trogoderma granarium is a serious pest of stored grains in many nations. Larvae of T. granarium may be persistent in warehouse conditions due to the ability to enter facultative diapause. Thus, a better understanding of their behavior with respect to movement as they seek places of refuge or food may lead to improvements in the development of monitoring tools and control technologies. The distance that khapra beetle larvae walk on a variety of surfaces at different angles was examined for 10-min intervals. Certain surfaces such as plywood, sheetrock, tile, cement, and netting were much more easily climbed than plastic, painted cement, and metal. Movement would often increase when the surface inclination increased from 0° to 30°, but then decrease at 60° or 90°. Tape corridors promoted climbing, and those with paper-like surfaces such as masking tape or lab labeling tape provided the most benefit. Other tapes with slippery or textured surfaces did not promote climbing. We also tested the ability to move on plastic bag and netting material impregnated with insecticide at different angles. Regardless of insecticide treatment, plastic bags were much less amenable to larval movement than netting. At the same time, there was little effect of the insecticide on slowing movement in these brief trials. The results suggest that optimal placement of wall traps should include an assessment of the surface, and that incorporating insecticide-treated nets or bags into new technologies must account for larval mobility on such surfaces.

Spatial spillover analysis of a cluster-randomized trial against dengue vectors in Trujillo, Venezuela.

BackgroundThe ability of cluster-randomized trials to capture mass or indirect effects is one reason for their increasing use to test interventions against vector-borne diseases such as malaria and dengue. For the same reason, however, the independence of clusters may be compromised if the distances between clusters is too small to ensure independence. In other words they may be subject to spillover effects.MethodsWe distinguish two types of spatial spillover effect: between-cluster dependence in outcomes, or spillover dependence; and modification of the intervention effect according to distance to the intervention arm, or spillover indirect effect. We estimate these effects in trial of insecticide-treated materials against the dengue mosquito vector, Aedes aegypti, in Venezuela, the endpoint being the Breteau index. We use a novel random effects Poisson spatial regression model. Spillover dependence is incorporated via an orthogonalized intrinsic conditional autoregression (ICAR) model. Spillover indirect effects are incorporated via the number of locations within a certain radius, set at 200m, that are in the intervention arm.ResultsFrom the model with ICAR spatial dependence, and the degree of surroundedness, the intervention effect is estimated as 0.74—favouring the intervention—with a 95% credible interval of 0.34 to 1.69. The point estimates are stronger with increasing surroundedness within intervention locations.ConclusionIn this trial there is some evidence of a spillover indirect effect of the intervention, with the Breteau index tending to be lower in locations which are more surrounded by locations in the intervention arm.

Multisectoral approaches for the control of vector-borne diseases, with particular emphasis on dengue and housing.

The Sustainable Development Goals suggest an intersectoral approach for development and health, including for vector-borne diseases. Evidence-based policy recommendations exist for malaria and housing, but not for other, more underfunded, vector-borne diseases. This review aims to stimulate the process for developing policy recommendations for other vector-borne diseases and housing with the process as it was developed for dengue and Aedes control as an example and with suggestions for steps necessary for other vector-borne diseases. For dengue, some basic research on the efficacy of vector control in relation to housing exists, summary evidence highlights the lack of evidence and efficacy and policy recommendations remain difficult. For other vector-borne diseases, few studies have focused on protecting the house, combinations of effective interventions (e.g. intradomiciliary residual spraying, insecticide-treated materials and treatment of larval habitats with biological and chemical methods, which have proven to be effective) have not been studied and summary evidence is non-existent. In order to recommend vector control to protect the house against vector-borne diseases, basic research and summary evidence are needed, with an appropriate combination of the most efficacious interventions and linked to improvement of housing itself. Standards for such studies need to be developed.

Influence of blood meal and age of mosquitoes on susceptibility to pyrethroids in Anopheles gambiae from Western Kenya

BackgroundPhysiological characteristics (age and blood feeding status) of malaria vectors can influence their susceptibility to the current vector control tools that target their feeding and resting behaviour. To ensure the sustainability of the current and future vector control tools an understanding of how physiological characteristics may contribute to insecticide tolerance in the field is fundamental for shaping resistance management strategies and vector control tools. The aim of this study was to determine whether blood meal and mosquito age affect pyrethroid tolerance in field-collected Anopheles gambiae from western Kenya.MethodsWild mosquito larvae were reared to adulthood alongside the pyrethroid-susceptible Kisumu strain. Adult females from the two populations were monitored for deltamethrin resistance when they were young at 2–5 days old and older 14–16 days old and whether fed or unfed for each age group. Metabolic assays were also performed to determine the level of detoxification enzymes. Mosquito specimens were further identified to species level using the polymerase chain reaction (PCR) method.ResultsAnopheles gambiae sensu stricto was the predominant species comprising 96% of specimens and 2.75% Anopheles arabiensis. Bioassay results showed reduced pyrethroid induced mortality with younger mosquitoes compared to older ones (mortality rates 83% vs. 98%), independently of their feeding status. Reduced mortality was recorded with younger females of which were fed compared to their unfed counterparts of the same age with a mortality rate of 35.5% vs. 83%. Older blood-fed females showed reduced susceptibility after exposure when compared to unfed females of the same age (mortality rates 86% vs. 98%). For the Kisumu susceptible population, mortality was straight 100% regardless of age and blood feeding status. Blood feeding status and mosquito age had an effect on enzyme levels in both populations, with blood fed individuals showing higher enzyme elevations compared to their unfed counterparts (P < 0.0001). The interaction between mosquito age and blood fed status had significant effect on mosquito mortality.ConclusionThe results showed that mosquito age and blood feeding status confers increased tolerance to insecticides as blood feeding may be playing an important role in the toxicity of deltamethrin, allowing mosquitoes to rest on insecticide-treated materials despite treatment. These may have implications for the sustained efficacy of indoor residual spraying and insecticide-treated nets based control programmes that target indoor resting female mosquitoes of various gonotrophic status.

Interventions for the control of Aedes aegypti in Latin America and the Caribbean: systematic review and meta-analysis.

To determine the effectiveness and degree of implementation of interventions for the control of Aedes aegypti in Latin America and the Caribbean (LAC) as reported in scientific literature. We searched MEDLINE, EMBASE, CENTRAL, SOCINDEX, and LILACS, for experimental and observational studies, economic assessments and qualitative experiences carried out in LAC from 2000 to 2016. We assessed incidence and morbimortality of Aedes aegypti-related diseases and entomological indices: Breteau (containers), House, and Pupae per Person. We used GRADE methodology for assessing quality of evidence. Of 1826 records retrieved, 75 were included and 9 cluster randomised clinical trials could be meta-analysed. We did not identify any intervention supported by a high certainty of evidence. In consistency with qualitative evidence, health education and community engagement probably reduces the entomological indices, as do the use of insecticide-treated materials, indoor residual spraying and the management of containers. There is low certainty of evidence supporting the use of ovitraps or larvitraps, and the integrated epidemiological surveillance strategy to improve indices and reduce the incidence of dengue. The reported degree of implementation of these vector control interventions was variable and most did not extend to whole cities and were not sustained beyond 2years. We found a general lack of evidence on effectiveness of vector control in the region, despite a few interventions that showed moderate to low certainty of evidence. It is important to engage and educate the community, apart from achieving the implementation of integrated actions between the health and other sectors at national and regional level.

Sample size calculations for skewed distributions.

BackgroundSample size calculations should correspond to the intended method of analysis. Nevertheless, for non-normal distributions, they are often done on the basis of normal approximations, even when the data are to be analysed using generalized linear models (GLMs).MethodsFor the case of comparison of two means, we use GLM theory to derive sample size formulae, with particular cases being the negative binomial, Poisson, binomial, and gamma families. By simulation we estimate the performance of normal approximations, which, via the identity link, are special cases of our approach, and for common link functions such as the log. The negative binomial and gamma scenarios are motivated by examples in hookworm vaccine trials and insecticide-treated materials, respectively.ResultsCalculations on the link function (log) scale work well for the negative binomial and gamma scenarios examined and are often superior to the normal approximations. However, they have little advantage for the Poisson and binomial distributions.ConclusionsThe proposed method is suitable for sample size calculations for comparisons of means of highly skewed outcome variables.Electronic supplementary materialThe online version of this article (doi:10.1186/s12874-015-0023-0) contains supplementary material, which is available to authorized users.

Benefit of insecticide-treated nets, curtains and screening on vector borne diseases, excluding malaria: a systematic review and meta-analysis.

IntroductionInsecticide-treated nets (ITNs) are one of the main interventions used for malaria control. However, these nets may also be effective against other vector borne diseases (VBDs). We conducted a systematic review and meta-analysis to estimate the efficacy of ITNs, insecticide-treated curtains (ITCs) and insecticide-treated house screening (ITS) against Chagas disease, cutaneous and visceral leishmaniasis, dengue, human African trypanosomiasis, Japanese encephalitis, lymphatic filariasis and onchocerciasis.MethodsMEDLINE, EMBASE, LILACS and Tropical Disease Bulletin databases were searched using intervention, vector- and disease-specific search terms. Cluster or individually randomised controlled trials, non-randomised trials with pre- and post-intervention data and rotational design studies were included. Analysis assessed the efficacy of ITNs, ITCs or ITS versus no intervention. Meta-analysis of clinical data was performed and percentage reduction in vector density calculated.ResultsTwenty-one studies were identified which met the inclusion criteria. Meta-analysis of clinical data could only be performed for four cutaneous leishmaniasis studies which together showed a protective efficacy of ITNs of 77% (95%CI: 39%–91%). Studies of ITC and ITS against cutaneous leishmaniasis also reported significant reductions in disease incidence. Single studies reported a high protective efficacy of ITS against dengue and ITNs against Japanese encephalitis. No studies of Chagas disease, human African trypanosomiasis or onchocerciasis were identified.ConclusionThere are likely to be considerable collateral benefits of ITN roll out on cutaneous leishmaniasis where this disease is co-endemic with malaria. Due to the low number of studies identified, issues with reporting of entomological outcomes, and few studies reporting clinical outcomes, it is difficult to make strong conclusions on the effect of ITNs, ITCs or ITS on other VBDs and therefore further studies be conducted. Nonetheless, it is clear that insecticide-treated materials such as ITNs have the potential to reduce pathogen transmission and morbidity from VBDs where vectors enter houses.

Reducing Visceral Leishmaniasis by Insecticide Impregnation of Bed-Nets, Bangladesh

The effect of insecticide-treated materials on reducing visceral leishmaniasis (VL) is disputable. In Bangladesh, we evaluated the effect of a community-based intervention with insecticide impregnation of existing bed-nets in reducing VL incidence. This intervention reduced VL by 66.5%. Widespread bed-net impregnation with slow-release insecticide may control VL in Bangladesh.

A systematic review of mosquito coils and passive emanators: defining recommendations for spatial repellency testing methodologies

Mosquito coils, vaporizer mats and emanators confer protection against mosquito bites through the spatial action of emanated vapor or airborne pyrethroid particles. These products dominate the pest control market; therefore, it is vital to characterize mosquito responses elicited by the chemical actives and their potential for disease prevention. The aim of this review was to determine effects of mosquito coils and emanators on mosquito responses that reduce human-vector contact and to propose scientific consensus on terminologies and methodologies used for evaluation of product formats that could contain spatial chemical actives, including indoor residual spraying (IRS), long lasting insecticide treated nets (LLINs) and insecticide treated materials (ITMs). PubMed, (National Centre for Biotechnology Information (NCBI), U.S. National Library of Medicine, NIH), MEDLINE, LILAC, Cochrane library, IBECS and Armed Forces Pest Management Board Literature Retrieval System search engines were used to identify studies of pyrethroid based coils and emanators with key-words “Mosquito coils” “Mosquito emanators” and “Spatial repellents”. It was concluded that there is need to improve statistical reporting of studies, and reach consensus in the methodologies and terminologies used through standardized testing guidelines. Despite differing evaluation methodologies, data showed that coils and emanators induce mortality, deterrence, repellency as well as reduce the ability of mosquitoes to feed on humans. Available data on efficacy outdoors, dose–response relationships and effective distance of coils and emanators is inadequate for developing a target product profile (TPP), which will be required for such chemicals before optimized implementation can occur for maximum benefits in disease control.

Dengue vector management using insecticide treated materials and targeted interventions on productive breeding-sites in Guatemala

BackgroundIn view of the epidemiological expansion of dengue worldwide and the availability of new tools and strategies particularly for controlling the primary dengue vector Aedes aegypti, an intervention study was set up to test the efficacy, cost and feasibility of a combined approach of insecticide treated materials (ITMs) alone and in combination with appropriate targeted interventions of the most productive vector breeding-sites.MethodsThe study was conducted as a cluster randomized community trial using “reduction of the vector population” as the main outcome variable. The trial had two arms: 10 intervention clusters (neighborhoods) and 10 control clusters in the town of Poptun Guatemala. Activities included entomological assessments (characteristics of breeding-sites, pupal productivity, Stegomyia indices) at baseline, 6 weeks after the first intervention (coverage of window and exterior doorways made of PermaNet 2.0 netting, factory treated with deltamethrin at 55 mg/m2, and of 200 L drums with similar treated material) and 6 weeks after the second intervention (combination of treated materials and other suitable interventions targeting productive breeding-sites i.e larviciding with Temephos, elimination etc.). The second intervention took place 17 months after the first intervention. The insecticide residual activity and the insecticidal content were also studied at different intervals. Additionally, information about demographic characteristics, cost of the intervention, coverage of houses protected and satisfaction in the population with the interventions was collected.ResultsAt baseline (during the dry season) a variety of productive container types for Aedes pupae were identified: various container types holding >20 L, 200 L drums, washbasins and buckets (producing 83.7% of all pupae). After covering 100% of windows and exterior doorways and a small number of drums (where the commercial cover could be fixed) in 970 study households, tropical rains occurred in the area and lead to an increase of the vector population, more pronounced (but statistically not significant) in the control arm than in the intervention arm. In the second intervention (17 months later and six weeks after implementing the second intervention) the combined approach of ITMs and a combination of appropriate interventions against productive containers (Temephos in >200 L water drums, elimination of small discarded tins and bottles) lead to significant differences on reductions of the total number of pupae (P = 0.04) and the House index (P = 0.01) between intervention and control clusters, and to borderline differences on reductions of the Pupae per Person and Breteau indices (P = 0.05). The insecticide residual activity on treated curtains was high until month 18 but the chemical concentration showed a high variability. The cost per house protected with treated curtains and drum covers and targeting productive breeding-sites of the dengue vector was $ 5.31 USD. The acceptance of the measure was generally high, particularly in families who had experienced dengue.ConclusionEven under difficult environmental conditions (open houses, tropical rainfall, challenging container types mainly in the peridomestic environment) the combination of insecticide treated curtains and to a less extent drum covers and interventions targeting the productive container types can reduce the dengue vector population significantly.

Characterization of mosquito larval habitats and assessment of insecticide-resistance status of Anopheles gambiae senso lato in urban areas in southwestern Ghana

The study was carried out to characterize potential larval habitats in the city of Sekondi with the aim of assessing the relative importance of anthropogenic and natural water bodies as larval habitats. Insecticide-resistance status of Anopheles gambiae senso lato in the southwestern part of the coastal savannah zone in Ghana was also assessed against four different classes of insecticides. Larval surveys were carried out in two communities that are separated by a lagoon. Although the lagoon was a potential mosquito larval habitat, we showed that it was not an important mosquito breeding site. The major larval habitats were anthropogenic, resulting from human behavior. Some of the organically polluted breeding sites were inhabited by both An. gambiae s.l. and Culex quinquefasciatus larvae. The data also showed that An. gambiae s.l. has currently developed a strong resistance to DDT and pyrethroid insecticides in southwestern Ghana, where the species was reported to be susceptible about a decade ago. The use of insecticides in households was implicated as a possible cause of the development of resistance among An. gambiae s.l. populations in the area. The management of insecticide resistance among malaria vectors needs urgent attention if insecticide-treated materials can continue to be used for malaria control.

Evaluation of the Effectiveness of Insecticide Treated Materials for Household Level Dengue Vector Control

ObjectiveTo assess the operational effectiveness of long-lasting insecticide treated materials (ITMs), when used at household level, for the control of Aedes aegypti in moderately infested urban and suburban areas.MethodsIn an intervention study, ITMs consisting of curtains and water jar-covers (made from PermaNet) were distributed under routine field conditions in 10 clusters (5 urban and 5 suburban), with over 4000 houses, in Trujillo, Venezuela. Impact of the interventions were determined by comparing pre-and post-intervention measures of the Breteau index (BI, number of positive containers/100 houses) and pupae per person index (PPI), and by comparison with indices from untreated areas of the same municipalities. The effect of ITM coverage was modeled.ResultsAt distribution, the proportion of households with ≥1 ITM curtain was 79.7% in urban and 75.2% in suburban clusters, but decreased to 32.3% and 39.0%, respectively, after 18 months. The corresponding figures for the proportion of jars using ITM covers were 34.0% and 50.8% at distribution and 17.0% and 21.0% after 18 months, respectively. Prior to intervention, the BI was 8.5 in urban clusters and 42.4 in suburban clusters, and the PPI was 0.2 and 0.9, respectively. In both urban and suburban clusters, the BI showed a sustained 55% decrease, while no discernable pattern was observed at the municipal level. After controlling for confounding factors, the percentage ITM curtain coverage, but not ITM jar-cover coverage, was significantly associated with both entomological indices (Incidence Rate Ratio = 0.98; 95%CI 0.97–0.99). The IRR implied that ITM curtain coverage of at least 50% was necessary to reduce A. aegypti infestation levels by 50%.ConclusionDeployment of insecticide treated window curtains in households can result in significant reductions in A. aegypti levels when dengue vector infestations are moderate, but the magnitude of the effect depends on the coverage attained, which itself can decline rapidly over time.

Determinants of uptake, short‐term and continued use of insecticide‐treated curtains and jar covers for dengue control

To evaluate the acceptance and long-term use of insecticide-treated (IT) materials for dengue vector control. In 2007, IT jar covers and/or curtains (PermaNet®) were distributed under routine conditions to 4101 households (10 clusters) in Venezuela and to 2032 households (22 clusters) in Thailand. The use of IT tools was measured at distribution (uptake), at 5/6 months (short-term use) and at 18/22 months (continued use) after distribution. Determinants of use were assessed with logistic regression analysis. The uptake of IT curtains was 76.7% in Venezuela and 92.3% in Thailand. It was associated with being a resident for >5 years (OR Venezuela 3.0 95% CI 2.0-4.4; OR Thailand 3.5 95% CI 1.7-7.3) and with pre-intervention use of ordinary curtains (OR Venezuela 2.2 95% CI 1.4-3.6). The continued use decreased significantly to 38.4% of households in Venezuela and 59.7% in Thailand and was, conditional on short-term use, only determined by the perceived effectiveness of IT curtains (OR Venezuela 13.0 95%CI 8.7-19.5; OR Thailand 4.9 95% CI 3.1-7.8). Disease knowledge and pre-intervention perception of mosquito nuisance were not associated with IT curtains' uptake or use. The uptake of IT jar covers in Venezuela was 21.5% and essentially determined by the presence of uncovered jars in the household (OR 32.5 95% CI 14.5-72.6). Their continued use, conditional on short-time use, was positively associated with the household use of Abate® (OR 7.8 95% CI 2.1-28.9). The use of IT curtains rapidly declines over time. Continued use is mainly determined by the perceived effectiveness of the tool. This poses a real challenge if IT curtains are to be introduced in dengue control programmes.

Population Genetic Structure of &lt;I&gt;Anopheles gambiae&lt;/I&gt; and &lt;I&gt;Anopheles arabiensis&lt;/I&gt; in Niger

The increasing usage of long-lasting insecticide-treated nets allows protection of millions of people from malaria infection. Monitoring studies should be planned during any wide-scale malaria control program integrating insecticide-treated materials, to evaluate their effects and effectiveness on epidemiologically relevant parameters. Such operational control interventions may be challenged by insecticide resistance spread within vector populations, as a result of wide insecticide pressure. A nationwide distribution of long-lasting insecticidal nets was implemented throughout Niger in 2005. We studied the population genetic structure of major malaria vectors across Nigerien Sahel, and investigated potential effects of this large malaria control intervention. Wild-caught Anopheles gambiae sensu lato females from seven villages and two wet seasons were genotyped at 12 microsatellite loci. The genetic diversity within both species appeared homogenous between villages and years. The estimated genetic differentiation among samples was very low within both species, indicating high gene flow across the area. An absence of differentiation was also found between 2005 and 2006 wet seasons, for all samples but one, showing that the net distribution did not impact significantly the genetic diversity and structure of vector populations in a single year. We provide valuable results participating to document effects of large malaria control programs, to maximize the efficiency of available tools in future interventions.

Multi‐modal Aedes aegypti mosquito reduction interventions and dengue fever prevention

To systematically review the effectiveness of biological, chemical and educational dengue fever prevention programs on the reduction of entomologic indicators. Searches of PubMed, GoogleScholar, CabDirect databases and reference lists yielded over 1000 articles containing mosquito abatement interventions. Inclusion criteria were: Vector control programs targeting Aedes aegypti and Aedes albopictus mosquitoes; Studies providing pre- and post-test data. Intervention effectiveness was assessed using Mulla's formula to determine percent reductions for all studies with control groups. Twenty-one studies were reviewed. Twelve dependent variables were presented, however, the Breteau, House and Container indices were the primary measurement tools for monitoring larval populations. Behavioural methods consisting of educational campaigns and maintaining water containers to reduce the mosquito population were applied in eight studies. Eight studies involved the use of biological methods such as predatory organisms or bacteria. Finally, eight studies used chemical control techniques including insecticide sprays, larvicides, insecticide-treated materials, and cleaning water of containers with household chemicals with three studies using a combination of intervention techniques. Post-intervention reduction in entomologic indices ranged from 100% to an increase of 13.9% from baseline. Little evidence exists to support the efficacy of mosquito abatement programs owing to poor study designs and lack of congruent entomologic indices. Creation of a standard entomological index, use of clustered and randomized-controlled trials, and testing the generalizability of proven methods are recommended for future research.

Susceptibility status of Anopheles gambiae sensu stricto (Diptera: Culicidae) to pyrethroid and carbamate insecticides in the Greater Accra region of Ghana, West Africa

Pyrethroids are the insecticides of choice for the treatment of bednets for malaria control. Pyrethroid resistance in Anopheles spp. vectors may adversely impact malaria control measures, and therefore it is important to know the initial level of pyrethroid resistance before pyrethroid-treated bednets are introduced. Furthermore, a search for replacement insecticides is necessary to manage any eventual high-resistance levels to pyrethroid insecticides that may affect the effectiveness of treated bednets. This study reports on the susceptibility of Anopheles gambiae s.s. exposed for 1 h to the pyrethroid insecticide permethrin and the carbamate insecticide propoxur, at eight localities in the Greater Accra region of Ghana. The observed mortality rates ranged between 21–92% and 92–100% to permethrin and propoxur, respectively. The results also showed a reduction in the knockdown time (KD50 and KD95) in propoxur (mean KD 50 = 20 min and mean KD 95 = 31 min) when compared with permethrin (mean KD 50 = 47 min and mean KD 95 = 87 min). The results suggest that permethrin may not be effective in all areas. Where pyrethroid resistance is a problem, propoxur could be an alternative for indoor residual spraying and for insecticide-treated materials such as curtains and eave screens.

Children in Burkina Faso Who Are Protected by Insecticide‐Treated Materials Are Able to Clear Drug‐Resistant Parasites Better than Unprotected Children

It has been suggested that reducing exposure to malaria by vector control might impair the development of naturally acquired immunity to malaria. It is also thought that an individual's ability to clear drug-resistant malarial parasites after treatment is enhanced by acquired immunity. To investigate the hypothesis that insecticide-treated materials may affect the acquisition of immunity to malaria, we compared the ability of children living in villages in which insecticide-treated curtains (ITCs) had been used for 6-8 years to clear resistant parasites after treatment with chloroquine (CQ) with that of children living in unprotected villages. A total of 1035 children aged 6-59 months with falciparum malaria were treated with CQ; 409 were subsequently identified as carrying parasites with the pfcrt-76T allele. More children from ITC villages cleared parasites harboring this allele than did children from non-ITC villages (34.1% vs. 24.0%; adjusted odds ratio [OR], 1.80 [95% confidence interval {CI}, 1.15-2.80]; P=.01). The difference in the clearance of parasites with the pfcrt-76T allele was seen in children aged 6-35 months (32.3% vs. 19.3%; adjusted OR, 2.34 [95% CI, 1.18-4.66]; P=.02) but not in older children (37.3% vs. 37.0%; adjusted OR, 1.09 [95% CI, 0.56-2.10]; P=.97). Rates of adequate clinical response among children carrying parasites with the pfcrt-76T allele were similar in ITC and non-ITC villages (75.1% vs. 68.6%; adjusted OR, 1.21 [95% CI, 0.61-2.39]; P=.58). Our data suggest that the children who were protected from malaria by ITCs acquired functional immunity more rapidly than did the control children.

Impact of mosquito proofing of night shelters in refugee camps in Kitgum, northern Uganda

To test the impact of long-lasting insecticide-treated netting, fitted to cover the eaves and ceilings of refugee shelters, on the incidence of nighttime mosquito biting. Entomological surveys in night-dwelling shelters at three camps for internally displaced persons in Kitgum, Uganda during August and November 2004: The impact of proofing against the nighttime incidence of mosquito biting was assessed through human landing catches and indoor resting catches in proofed and unproofed (control) shelters. Human landing catches were performed inside and outside four proofed and four control shelters at three locations, and indoor resting catches were performed in 37 proofed and 18 control shelters. The difference in biting rates was tested using paired and unpaired t-tests and multivariate analysis. Most mosquitoes caught during the survey were culicine (97%). The difference in landing rate (mlrph) differentials (outdoor-indoor) illustrated a significant (t = 3.26, P = 0.004) difference between mlrph between proofed (0.154) and control shelters (-0.110). Mean shelter density (msd) recorded during indoor resting catches was 6.7 times higher in the control shelters than in proofed shelters (P < 0.001). The number of blood-fed mosquitoes/person/night (bfmpn) was significantly higher (P < 0.001), by a magnitude of 17, in control shelters (one in five individuals receiving a bite) compared with proofed shelters (1 in 83 individuals). A multivariate analysis showed that the difference in biting rates was because of the intervention. The significantly lower mlrph, msd and bfmpn in proofed shelters demonstrate that the mosquito proofing strategies employed do reduce the exposure to mosquito biting in proofed compared with control shelters by a magnitude of 6-17. Although numbers of Anopheline mosquitoes were low, the biting rates of Anophelines were also significantly lower in proofed shelters compared with control shelters. Insecticide-treated netting appears to significantly reduce the mosquito nuisance-biting incidence. However, a higher incidence of Anopheline biting may be required to test the effect of proofing on malaria vectors and a subsequent study is therefore recommended.

Species abundance and insecticide resistance of Anopheles gambiae in selected areas of Ghana and Burkina Faso

The Ghanaian National Malaria Control Programme has prioritized insecticide-treated materials as a key strategy for malaria control. We report on a survey of the distribution of the molecular forms of Anopheles gambiae Giles (Diptera: Culicidae) and insecticide resistance (the kdr mutation), carried out by sampling mosquitoes from 11 locations in Ghana and one additional site in Burkina Faso. The molecular M and S forms of An. gambiae were found to occur in sympatry in southern Ghana. The S form predominated throughout its distribution in the coastal savannah, except at one location in the strand and mangrove zone where rice was cultivated. The M form was the only form collected in northern Ghana and was the predominant form (97.5%) in Burkina Faso. No M/S hybrids were detected. The kdr mutation was observed at very high frequencies (98-100%) within the S form but reached a maximum of only 3.38% in the M form in one population at an irrigation scheme in the Ghanaian coastal savannah zone.