Insecticide-impregnated bed nets for malaria control: varying experiences from Ecuador, Colombia, and Peru concerning acceptability and effectiveness. Efficacy of permethrin-treated bed nets in the prevention of mortality in young children in an area of high perennial malaria transmission in western Kenya. A trial of bed nets (mosquito nets) as a malaria control strategy in a rural area of The Gambia, West Africa. [Study of the impact of deltamethrin impregnated curtains on malaria morbidity in Ankazobe of the Madagascar highlands]. A trial of permethrin-treated bed nets in the prevention of malaria in Gambian children. The effectiveness of permethrin-impregnated bed nets against malaria for migrant workers in eastern Thailand. Do insecticide-treated curtains reduce all-cause child mortality in Burkina Faso? Insecticide-treated bednets reduce mortality and severe morbidity from malaria among children on the Kenyan coast. Deltamethrin impregnated bednets for the control of urban malaria in Kumba Town, South-West Province of Cameroon. Permethrin-impregnated curtains and bed-nets prevent malaria in western Kenya. Cyfluthrin (EW 050)-impregnated bednets in a malaria control program in Ghassreghand (Baluchistan, Iran). Effect of insecticide-treated bed nets on haemoglobin values, prevalence and multiplicity of infection with Plasmodium falciparum in a randomized controlled trial in Tanzania. Mortality and morbidity from malaria in Gambian children after introduction of an impregnated bednet programme. Insecticide-treated materials for malaria control in Latin America: to use or not to use? Pyrethroid-impregnated bed nets for personal protection against malaria for Afghan refugees. Protective efficacy of lambda-cyhalothrin treated nets in Anopheles gambiae pyrethroid resistance areas of Côte d'Ivoire. A controlled trial of lambda-cyhalothrin-impregnated bed nets and/or dapsone/pyrimethamine for malaria control in Sierra Leone. Permethrin-impregnated bed nets for the prevention of malaria in schoolchildren on the Thai-Burmese border. Impact of permethrin impregnated bednets on child mortality in Kassena-Nankana district, Ghana: a randomized controlled trial.
Between 1991 and 1994, an intervention program with permethrin- and lambdacyhalothrin-impregnated bed nets was carried out over a period of nine months in each of five endemic, malarious areas of Ecuador, Peru, and Colombia. This program was evaluated through household surveys, blood sampling, in-depth longitudinal studies, and entomologic analysis. Eighty-four communities (including approximately 35,000 individuals) were paired according to malaria incidence, size, and coverage with bed nets and then randomly allocated to intervention and control groups. The results showed that peoples' acceptance of the measure was related to their perception of an immediate protective effect against insects. The effectiveness of the bed nets, measured as a reduction of malaria incidence in intervention communities as against control communities, showed large variations between and within the study areas. The protective efficacy varied between 0% and 70% when looking only at the postintervention differences between intervention and control groups. The average protection was 40.8% when considering a four-month incidence of clinical malaria attacks and 28.3% when considering a two-week malaria incidence. Important factors for the success of the bed net program were insect susceptibility to pyrethroids, high coverage with impregnated bed nets, high malaria incidence, good community participation, high mosquito densities when people go to bed, and a high proportion of Plasmodium falciparum. In one area, where DDT spraying in the control communities was executed, the effectiveness of bed net impregnation was slightly better than that of spraying. A group-randomized controlled trial of insecticide (permethrin)-treated bed nets (ITNs) was conducted in an area of high perennial malaria transmission in western Kenya to test the effect of ITNs on all-cause mortality in children 1-59 months of age. Child deaths were monitored over a two-year period by biannual household census in Asembo (1997-1998) and in Gem (1998-1999). Overall, 1,722 deaths occurred in children 1-59 months followed for 35,932 child-years. Crude mortality rates/1,000 child-years were 51.9 versus 43.9 in control and ITN villages in children 1-59 months old. The protective efficacy (PE) (95% confidence interval) adjusted for age, study year, study site, and season was 16% (6-25%). Corresponding figures in 1-11- and 12-59-month-old children in control and ITN villages were 133.3 versus 102.3, PE = 23% (11-34%) and 31.1 versus 28.7, PE = 7% (-6-19%). The numbers of lives saved/1,000 child-years were 8, 31, and 2 for the groups 1-59, 1-11, and 12-59 months old, respectively. Stratified analysis by time to insecticide re-treatment showed that the PE of ITNs re-treated per study protocol (every six months) was 20% (10-29%), overall and 26% (12-37%) and 14% (-1-26%) in 1-11- and 12-59-month-old children, respectively. ITNs prevent approximately one in four infant deaths in areas of intense perennial malaria transmission, but their efficacy is compromised if re-treatment is delayed beyond six months. An intervention trial was undertaken in a rural area of The Gambia to assess the impact on malaria morbidity of the use of bed nets. Bed nets were allocated at random among a group of 16 Fula hamlets, where they were previously rarely used. The incidence of febrile episodes with associated malaria parasitaemias throughout the rainy season and the prevalence of splenomegaly and parasitaemia at the end of the rainy season were determined in 233 children aged 1-9 years who slept under bed nets and in 163 children who did not. Bed nets were used correctly by the children in the study cohort, but direct observations showed that a significant number of children left their nets for a period during the night. There was no significant difference in the incidence of clinical attacks of malaria or in any other malariometric measurement between the 2 groups. Thus, bed nets were not effective in reducing malaria morbidity in this group of children. The apparent protection from bed nets demonstrated in previous retrospective surveys may have been due to an increased number of infective bites being received by exposed individuals sleeping close to users of bed nets. nan A trial was undertaken in a rural area of The Gambia to investigate the impact of permethrin-treated bed nets on malaria. Two groups of children, matched for age, sex, and malaria exposure, were followed through the rainy season of 1985 for illness and febrile episodes. One group of 205 children slept under permethrin-treated bed nets (0.5 g/m2); 184 children who slept under placebo-treated nets formed the control group. At the end of the rains the children were examined for splenomegaly and blood samples were taken for determination of packed cell volume (PCV) and parasitaemia. Permethrin treatment of bed nets was well accepted and was without side-effects. Children who slept under treated nets had significantly fewer episodes of clinical malaria than control children. However, at the end of the rains there was no significant difference in the prevalence of splenomegaly or parasitaemia or in the mean PCV between the groups. It is suggested that permethrin treatment of nets may have a greater effect on the duration of probing by mosquitoes for a blood meal than on the number of bites received. A randomized, double-blind, field trial was carried out to compare the effectiveness of permethrin-treated bed nets with that of untreated nets as a method of malaria control for migrant workers in eastern Thailand. The study was conducted using 261 subjects in eastern rural areas that are known to be highly endemic for multidrug-resistant Plasmodium falciparum infection. One hundred twenty-six subjects used treated nets, while 135 used untreated nets. During the 35 weeks of observation, 23 subjects using treated nets and 33 workers using untreated nets developed 28 and 51 episodes of malaria, respectively (P = 0.029). The reduction in risk per subject due to treated nets was 0.06. The residual effects of permethrin were tested using a World Health Organization standard bioassay. Anti-mosquito activity was found to be present in the nets for more than 16 months. We conclude that because of the failure of the development of safe, effective, long-lasting prophylactic agents, integrating the use of impregnated nets with large-scale primary health care programs may be a partially effective method for controlling malaria in eastern Thailand. To evaluate whether insecticide-treated netting (ITN) reduces child mortality in different epidemiological settings, 4 large, randomized, controlled trials were conducted in Africa. Here we report the findings from the trial in Burkina Faso, in an area of hyperendemic and markedly seasonal malaria transmission. The trial involved 158 villages, with a total population of some 90,000, grouped into 16 geographical clusters. Ascertainment of mortality among children aged 6-59 months began in early 1993. In June/July 1994, 8 of the clusters, randomly selected, received permethrin-treated curtains. Follow-up of children and ascertainment of mortality continued until May 1996. A 15% reduction in all-cause mortality among children aged 6-59 months was observed over the 2-year period following the installation of the curtains (95% c.i. -4% to 30%). In the first year, post-intervention mortality was substantially lower in the clusters receiving curtains compared with the control clusters (rate ratio = 0.74; 95% c.i. 0.57, 0.95) but in the second year, there was no difference between mortality in the two groups (rate ratio = 0.99). The overall two-year impact of the intervention is consistent with the impacts observed in other trials which have demonstrated reductions in child mortality of from 17% to 33%. However, the year-by-year analysis raises some concerns about the long-term effect of ITN. Further follow-up of this population is warranted. New tools to prevent malaria morbidity and mortality are needed to improve child survival in sub-Saharan Africa. Insecticide treated bednets (ITBN) have been shown, in one setting (The Gambia, West Africa), to reduce childhood mortality. To assess the impact of ITBN on child survival under different epidemiological and cultural conditions we conducted a community randomized, controlled trial of permethrin treated bednets (0.5 g/m2) among a rural population on the Kenyan Coast. Between 1991 and 1993 continuous community-based demographic surveillance linked to hospital-based in-patient surveillance identified all mortality and severe malaria morbidity events during a 2-year period among a population of over 11000 children under 5 years of age. In July 1993, 28 randomly selected communities were issued ITBN, instructed in their use and the nets re-impregnated every 6 months. The remaining 28 communities served as contemporaneous controls for the following 2 years, during which continuous demographic and hospital surveillance was maintained until the end of July 1995. The introduction of ITBN led to significant reductions in childhood mortality (PE 33%, CI 7-51%) and severe, life-threatening malaria among children aged 1-59 months (PE 44%, CI 19-62). These findings confirm the value of ITBN in improving child survival and provide the first evidence of their specific role in reducing severe morbidity from malaria. This study was conducted from January to December 1992 in Kumba, a town situated in the rain forest region of the South-West Province of Cameroon, and consisted of a longitudinal survey including parasitological and clinical studies. Forty households were chosen for the study and randomly divided into two groups, each with approximately 240 inhabitants aged < or = 15 years. One group received deltamethrin impregnated bednets and the other group had no nets (control). For the months of April, June and August (rainy season), deltamethrin impregnated bednets did not reduce malaria prevalence significantly, but the overall malaria prevalence for all months of the study was significantly reduced (chi 2 MH = 9.17, P = 0.002). Enlarged spleen rates (chi 2 MH = 6.73, P = 0.009) and spleen sizes (P = 0.0002) were also significantly reduced by the nets. However, the reduction in the geometric mean parasite density (GMPD) was not significant. Even though some of these reductions were statistically significant, they were relatively low in a global context compared with previous work done mainly in rural areas. In an urban environment, parents and children usually stay up late, and probably receive many mosquito bites before going to sleep. The effectiveness of permethrin-impregnated (0.5 g/m2) bed-nets and curtains as malaria control measures was evaluated in Uriri, Kenya in 1988. One hundred five families were randomly assigned to 1 of 3 study groups (control, bed-net, or curtain). All participants were cured of parasitemia with pyrimethamine/sulfadoxine. Selective epidemiologic and entomologic parameters were measured weekly, while knowledge, attitude, and practices surveys were conducted at the beginning and end of the 15 week study. Plasmodium falciparum infections per person week at risk were significantly higher in the control group than in either the curtain group (5.42 vs. 2.35 cases/100 person weeks risk) or the bed-net group (5.42 vs. 3.77 cases/100 person weeks risk). The curtain group had fewer infections per person week at risk than the bed-net group (2.35 vs. 3.77 cases/100 person weeks risk). A difference was found in clinical malaria among the groups: 45% of persons in the bed-net and curtain groups vs. 30% of those in the control group reported no episodes of fever and chills (chi 2, P less than 0.05). Indoor resting Anopheles gambiae or An. funestus were found on 94 occasions in the control houses, but only twice in the treated houses during weekly visits to each house over the study period (chi 2 P less than 0.001). The pyrethrum knockdown method produced similar results with a total of 195, 23, and 3 An. gambiae and An. funestus collected in the control, bed-net, and curtain houses during the same period, respectively.(ABSTRACT TRUNCATED AT 250 WORDS) In a study carried out in the Ghassreghand Division (Baluchistan, Iran) from March through November 1995, efficacy of cyfluthrin-impregnated bednets was compared to that of untreated nets, in relation to malaria control. Ten villages with a total population of 4,572 and 3 villages with a total population of 1,935 were used as treatment and control, respectively. The collection, impregnation (target dosage of 40 mg active ingredient [AI]/m2), and redistribution of the nets (9% nylon, 52% light cotton, 30% medium cotton, and 9% heavy cotton), carried out in mid-April, were done by local health workers, supervised by the senior research staff. Anopheles culicifacies was considered to be the main vector of malaria in the named area. This species is mainly zoophilic, endophilic, and exophagic. The initial uptake of the insecticide was lower than the target dosage, with high variation (nylon, 12.5 +/- 5.4 mg AI/m2; light cotton, 33.3 +/- 26.1 mg AI/m2; medium cotton, 25.9 +/- 20 mg AI/m2; heavy cotton, 17.6 +/- 12.5 mg AI/m2). The use of impregnated mosquito nets (used primarily outside) had no significant effect on the incidence of malaria. No difference was detected in the parasite density of patients with positive slides. No significant effect was observed in the parous rate, human blood index, and sporozoite rate of anopheline vectors. Only the indoor resting densities of An. culicifacies and other malaria vectors were drastically reduced after the introduction of the cyfluthrin-impregnated nets into the treatment villages. The residual activity of cyfluthrin was lower than expected. The mortality of anophelines brought in contact with the treated nets for 3 min in bioassays dropped to less than 55% in 3 months. The loss of chemical activity was greatest for the light cotton nets, followed by the medium cotton nets. Cyfluthrin-treated nets were mildly irritating to host-seeking female anophelines in the laboratory. The protective rate of impregnation (all fabric kinds included) in preventing female mosquitoes from biting through the impregnated nets was initially 5-6 times that of the nonimpregnated nets. The study did not detect any significant difference between the use of untreated versus impregnated bednets in the Ghassreghand area. In planning future medium-scale trials, comparison of new compounds and formulations to the more widely used pyrethroids such as permethrin and deltamethrin is highly recommended. A randomized controlled trial of insecticide-treated bed nets (ITNs) was conducted in an area of high malaria transmission in Tanzania in order to assess the effects of ITNs on infection and anaemia. One hundred and twenty-two children, aged 5 to 24 months, were randomly allocated to 2 groups, one of which received ITNs. Outcome measures were assessed in 6 consecutive months with monthly cross-sectional surveys. These measures were haemoglobin values, Plasmodium falciparum prevalence and density, and multiplicity of infection determined by polymerase chain reaction-restriction fragment length polymorphism analysis (PCR-RFLP) of the msp2 locus. There was a significant increase in mean heamoglobin values and a significant decrease of 16.4% in microscopically determined P. falciparum prevalence in children in the ITN group six months after the start of the trial. Both effects were more pronounced in younger children. However, no significant difference was observed in parasite density or multiplicity of infection among infected children. Comparison with PCR results indicated that microscopically subpatent parasitaemia was more frequently found in children in the ITN group. This, together with the observed similar multiplicity in the 2 groups, suggests that infections are maintained despite ITN use, owing to the chronicity of infections. This study shows that ITNs reduce the risk of anaemia in highly exposed young children. The virtually unchanged multiplicity of infection indicates that the potentially protective concomitant immunity is not compromised. After the success of a controlled trial of insecticide-treated bednets in lowering child mortality, The Gambia initiated a National Insecticide Impregnated Bednet Programme (NIBP) in 1992 with the objective of introducing this form of malaria control into all large villages in The Gambia. Five areas (population 115,895) were chosen as sentinel sites for evaluation of the NIBP. During the first year of intervention a 25% reduction was achieved in all-cause mortality in children 1-9 years old living in treated villages (rate ratio 0.75 [95% CI 0.57-0.98], p = 0.04). If one area where the programme was ineffective was excluded, the reduction was 38% (0.62 [0.46-0.83), p = 0.001). A decrease in rates of parasitaemia and high-density parasitaemia, an increase in mean packed-cell volume (rate ratio 0.75 [95% CI 0.59-0.98], p = 0.04) and an improvement in the nutritional status of children living in treated villages were also detected. In a country such as The Gambia, where nets were widely used and which has a good primary health care system, it is possible to achieve insecticide-treatment of bednets at a national level with a significant reduction in child mortality; but at a cost which the country cannot afford. Studies on the protective efficacy of insecticide-treated materials (ITMs) in Plasmodium vivax endemic areas of Latin America have not yielded sufficient evidence for recommendation of their extensive use in the region. Therefore 2 randomized community trials have been conducted on the Pacific Coast of Nicaragua which analysed the minimum coverage of ITMs needed to be effective against malaria. For the characterization of the study area, epidemiological and entomological baseline surveys and household interview surveys were undertaken. Thereafter the communities were paired (6 pairs in the 1st year and 13 pairs in the 2nd year) according to 4-monthly reported malaria incidence rates, population size and bednet coverage, and then randomly allocated to intervention and control groups. In the intervention groups, bednets were impregnated with lambdacyhalothrin; in the control groups, people received general health education. Anopheles albimanus was found to be the main vector with marked indoor biting behaviour late in the evening. P. vivax (99%) clearly outweighed P. falciparum (1%) with low parasite prevalence rates in the asymptomatic general population (8%) and low parasite densities. The protective efficacy of ITMs varied according to the coverage achieved: protective efficacy was 68% in communities with an average ITM coverage of 50% (10 pairs); 31% in communities with an ITM coverage of 16-30% (4 pairs); and no protective efficacy in communities with ITM coverage below 16% (5 pairs). The comparison with other P. vivax endemic areas in Latin America showed that the vector's late biting behaviour and the indoor preference (where ITMs have a repellent effect) probably led to the favourable results in the study. In malaria endemic areas of Latin America, where P. vivax is predominant, studies on vector behaviour should be conducted in order to predict the impact of ITMs on malaria transmission. A field trial of permethrin-impregnated bed nets (PIBs) was conducted in 2 Afghan refugee villages in Pakistan. Nets were issued to only 10% of families (= 1398 people); this simulated a situation in which bed nets are gradually adopted by villagers in Afghanistan. A further 10% lacking bed nets were selected as controls from the same villages. An initial survey showed that 86% of household heads were aware that malaria was transmitted by mosquito bites, but only 2% had used bed nets before. Trial families were encouraged to attend the village health centres if they fell ill. Microscopy records showed that, between July and December 1991, 22.4% of the control group became infected with Plasmodium vivax and 13.0% contracted P. falciparum while in the intervention group only 9.9% contracted P. vivax (relative risk 0.58, confidence interval [CI] 95% 0.49-0.68) and only 3.8% contracted P. falciparum (relative risk 0.39, 95% CI 0.29-0.53). A single treatment of the nets with permethrin at 0.5g/m2 remained protective throughout the 6 months' transmission season. 73% of families claimed to use their nets every night; members of families who claimed to use nets less regularly showed an incidence similar to that of the control group. There was no sex or age difference in net use or protective efficacy. Headlouse infestation rates were reduced in PIB users. Few nets were washed, given away or sold. The prospect for PIBs as personal protection appears good, despite people's lack of previous experience. The efficacy of nets treated with lambda-cyhalothrin, a pyrethroid insecticide, on malaria infection and disease was assessed for the first time at the community level in Anopheles gambiae pyrethroid resistance areas. The study was carried out in northern Côte d'Ivoire, which is an area of kdr resistance. Four pairs of villages were selected and matched according to demographic, sociological, and ecological criteria. Among each pair, a village was randomly allocated to receive mosquito nets. More than 80% of beds were covered with nets treated with lambda-cyhalothrin and retreated after 6 months. In each village, 54 children aged 0-59 months were randomly selected and clinically monitored for 8 periods of 7 days throughout the year. Results showed that the efficacy of treated nets was maintained with a reduction of the prevalence of asymptomatic malaria infection by 12% and an estimated protective efficacy against malaria disease of 56%. A randomized controlled trial investigated the impact of community-wide use of mosquito nets impregnated with lambda-cyhalothrin alone or with dapsone/pyrimethamine (d/p) prophylaxis on clinical malaria due to perennially transmitted Plasmodium falciparum in children in the Bo district of Sierra Leone. The 17 study communities were pair-matched and randomly allocated to receive treated mosquito nets or no nets and the children (age range = 3 months-6 years) in each community were randomly allocated to receive d/p or placebo individually every two weeks. This resulted in each of the approximately 2,000 children recruited being in one of four study groups (impregnated mosquito nets and d/p prophylaxis, impregnated mosquito nets, d/p prophylaxis, and controls). The intervention phase of the study lasted 12 months. A total of 1,800 children attended more than 25% of the 48 total weekly morbidity surveillance surveys and were included in the analysis. The effects of the exclusive use of either treated mosquito nets or d/p prophylaxis on protection against clinical malaria due to P. falciparum was significantly similar (49% and 42%, respectively), while in combination this protective efficacy was significantly increased to 72% (95% confidence interval = 67-76%). Children in the control group had an average of 1.3 clinical malaria episodes per child annually compared with 0.65 episodes or 0.78 episodes for those using treated mosquito nets and d/p, respectively. Children using both treated mosquito nets and d/p prophylaxis had an average of 0.37 episodes per child. The interventions significantly reduced spleen rates and increased hematocrit values, and reduced the duration of episodes of clinical malaria. A double-blind controlled trial was undertaken from August 1990 to February 1991 among Karen children on the Thai-Burmese border to evaluate the effects on malaria incidence and prevalence of permethrin-treated bed nets. Three hundred and fifty schoolchildren, aged 4 to 15 years, were allocated at random to receive either a permethrin-impregnated net or a non-treated net. The incidence of malaria infections, confirmed by a blood film, was assessed during 6 months. Three surveys were conducted, on admission and 3 and 6 months later, to measure the prevalence of infections and spleen rates. Compliance was assessed by monthly home visiting. The use of permethrin-treated bed nets reduced the number of parasitaemic Plasmodium falciparum infections by 38% and the number of symptomatic episodes by 42%. The number of P. vivax malaria attacks was similar in each group. The prevalence of positive blood films in the 2 groups did not change significantly during the study. A reduction in spleen rate by 50% in both groups at the end of the study period could not be related to the overall use of nets. Compliance was high and no side-effect was reported. The long-term effects on morbidity and mortality need to be assessed after distribution of permethrin treated bed nets at the village level. A community-based randomized, controlled trial of permethrin impregnated bednets was carried out in a rural area of northern Ghana, between July 1993 and June 1995, to assess the impact on the mortality of young children in an area of intense transmission of malaria and no tradition of bednet use. The district around Navrongo was divided into 96 geographical areas and in 48 randomly selected areas households were provided with permethrin impregnated bednets which were re-impregnated every 6 months. A longitudinal demographic surveillance system was used to record births, deaths and migrations, to evaluate compliance and to measure child mortality. The use of permethrin impregnated bednets was associated with 17% reduction in all-cause mortality in children aged 6 months to 4 years (RR = 0.83; 95% CI 0.69-1.00; P = 0.05). The reduction in mortality was confined to children aged 2 years of younger, and was greater in July-December, during the wet season and immediately after (RR = 0.79; 95% CI 0.63-1.00), a period when malaria mortality is likely to be increased, than in the dry season (RR = 0.92, 95% CI 0.73-1.14). The ready acceptance of bednets, the high level of compliance in their use and the subsequent impact on all-cause mortality in this study has important implications for programmes to control malaria in sub-Saharan Africa.
ITNs are highly effective in reducing childhood mortality and morbidity from malaria. Widespread access to ITNs is currently being advocated by Roll Back Malaria, but universal deployment will require major financial, technical, and operational inputs.