Use Of Insecticide-impregnated Bed Nets Research Articles

A study of malaria vector surveillance as part of the Malaria Elimination Demonstration Project in Mandla, Madhya Pradesh

BackgroundUnderstanding of malaria vector density, distribution, insecticide resistance, vector incrimination, infection status, and identification of sibling species are some of the essential components of vector control measures for achieving malaria elimination goals.MethodsAs part of the malaria elimination demonstration project, entomological surveillance was carried out from October 2017 to October 2019 by collecting indoor resting mosquitoes using hand catch method. Susceptibility test was done for determining the insecticide resistance status of vector mosquito Anopheles culicifacies using standard protocols by the World Health Organization. The cone bioassay method was used for determining the efficacy and quality of insecticide sprayed. Mosquitoes collected from different ecotypes were identified and processed for parasite identification, vector incrimination and sibling species determination.ResultsThe two known malaria vector species (Anopheles culicifacies and Anopheles fluviatilis) were found in the study area, which have been previously reported in this and adjoining areas of the State of Madhya Pradesh. The prevalence of An. culicifacies was significantly higher in all study villages with peak in July while lowest number was recorded in May. Proportion of vector density was observed to be low in foothill terrains. The other anopheline species viz, Anopheles subpictus, Anopheles annularis, Anopheles vagus, Anopheles splendidus, Anopheles pallidus, Anopheles nigerrimus and Anopheles barbirostris were also recorded in the study area, although their prevalence was significantly less compared to the An. culicifacies. In 2017, An. culicifacies was found to be resistant to dichloro-diphenyl-trichloroethane (DDT) and malathion, with possible resistance to alphacypermethrin and susceptible to deltamethrin. However, in 2019, the species was found to be resistant to alphacypermethrin, DDT, malathion, with possible resistance to deltamethrin. The bioassays revealed 82 to > 98% corrected % mortality of An. culicifacies on day-one post-spraying and 35 to 62% on follow-up day-30. Anopheles culicifacies sibling species C was most prevalent (38.5%) followed by A/D and E while B was least pre-dominant (11.9%). Anopheles fluviatilis sibling species T was most prevalent (74.6%) followed by U (25.4%) while species S was not recorded. One An.culicifacies (sibling species C) was found positive for Plasmodium falciparum by PCR tests in the mosquitoes sampled from the test areas.ConclusionBased on the nine entomologic investigations conducted between 2017–2019, it was concluded that An. culicifacies was present throughout the year while An. fluviatilis had seasonal presence in the study areas. Anopheles culicifacies was resistant to alphacypermethrin and emerging resistance to deltamethrin was observed in this area. Anopheles culicifacies was confirmed as the malaria vector. This type of information on indigenous malaria vectors and insecticide resistance is important in implementation of vector control through indoor residual spraying (IRS) and use of insecticide-impregnated bed nets for achieving the malaria elimination goals.

High mosquito burden and malaria transmission in a district of the city of Douala, Cameroon

BackgroundRapid demographic growth in Douala city, Cameroon, has resulted in profound ecological and environmental changes. Although demographic changes can affect anopheline mosquito breeding sites, there is a lack of understanding about the epidemiological impact that such changes might have on vector ecology and malaria transmission.MethodsA 12-month entomological study was conducted in a highly populated district of Douala called Ndogpassi. Adult mosquitoes were collected using two methods: 1) human landing catches (HLC); and 2) Centers for Disease Control and Prevention (CDC) light traps; these methods were used twice monthly from January to December 2011. Mosquito genus and species were identified with morphological and molecular diagnostic tools. The sampling efficiency of the CDC light trap and HLC were compared. Anopheles gambiae infection with Plasmodium falciparum was detected using ELISA. Susceptibility to DDT, permethrin, and deltamethrin insecticides were also determined.ResultsA total of 6923 mosquitoes were collected by HLC (5198) and CDC light traps (1725). There was no equivalence in the sampling efficiency between light traps and human landing catches (P > 0.01). With 51% of the total, Culex was the most common, followed by Anopheles (26.14%), Mansonia (22.7%) and Aedes (0.1%). An. gambiae ss (M form) comprised ~98% of the total anophelines collected. An. gambiae had a biting rate of 0.25 to 49.25 bites per human per night, and was the only species found to be infected with P. falciparum. A P. falciparum infection rate of 0.5% was calculated (based on enzyme-linked immunosorbent assays using the circumsporozoite surface protein). The entomological inoculation rate was estimated at 31 infective bites per annum. Insecticide susceptibility tests on An. gambiae females revealed a mortality rate of 33%, 76% and 98% for DDT, permethrin and deltamethrin, respectively. The West African kdr allele (L1014F) was detected in 38 of the 61 An. gambiae analyzed (62.3%).ConclusionsThe present study revealed seasonal malaria transmission in Douala. High levels of An. gambiae were detected along with a high prevalence of insecticide resistance in this vector population. These findings highlight the need to promote use of insecticide-impregnated bed nets in Douala.

Pyrethroid induced behavioral responses of Anopheles dirus, a vector of malaria in Thailand

Contact and noncontact behavioral actions of wild-caught Anopheles dirus in response to the operational field dose of three synthetic pyrethroids (bifenthrin, α-cypermethrin and λ-cyhalothrin) were evaluated using an exito-repellency test chamber. DEET was used as the repellency standard for comparison with the other three synthetic pyrethroids. Results showed that test specimens rapidly escaped from the test chamber when exposed to direct contact with a surface treated with each of the three synthetic pyrethroids and DEET. Alpha-cypermethrin demonstrated the strongest irritant action (84.9% escape), followed by DEET (77.0%), λ-cyhalothrin (68.6%) and bifenthrin (68.3%). In the noncontact configuration, fewer mosquitoes escaped from the test chambers as compared to contact trials, although a significant escape response was still observed as compared to the controls (P<0.05). We conclude that An. dirus exhibits both irritant and repellent actions in response the three pyrethroids testing in this study. The information obtained will allow us to better understand the behavioral responses of vectors to various chemicals and provide guidance when designing control strategies for targeting specific disease vectors.

Búsqueda activa de casos de leishmaniasis visceral zoonótica en población infantil indígena y canina colombiana

Carrying out an active search for cases of canine and human zoonotic visceral leishmaniasis (LVZ) by determining IgG antibodies against Leishmania infantum by indirect immunofluorescence (IFAT) and assessing the risk factors associated with the disease occurring in a Colombian endemic area. 580 indigenous children aged less than five and 270 cross-bred dogs from 5 rural areas near the town of Coyaima (Tolima) were evaluated by determining their antibodies using the Colombian Leishmania infantum (infantum) MOHOM/ COL/CLO44B strain as antigen. 527 households in the area were surveyed to assess the risk factors and protective measures being taken. No sero reactivity to Leishmania infantum antigens by IFAT test was observed in the child population. Leishmania infantum antibodies were observed in 68.5 % of the dogs (185/270). The survey found deficiencies in the housing's sanitary conditions. The use of insecticide-impregnated bed-nets was evident in 48 % (130/270) of the dwellings, as were poor knowledge of the disease and a low demand for traditional medical services (41.5 %). Control measures must be strengthened for interrupting the reservoir-vector-human transmission chain, evaluating health authorities' strategies for promoting protective habits and improving living conditions and the susceptible population's environment.

Current status of malaria and potential for control.

Malaria remains one of the world's worst health problems with 1.5 to 2.7 million deaths annually; these deaths are primarily among children under 5 years of age and pregnant women in sub-Saharan Africa. Of significance, more people are dying from malaria today than 30 years ago. This review considers the factors which have contributed to this gloomy picture, including those which relate to the vector, the female anopheline mosquito; to human activity such as creating new mosquito breeding sites, the impact of increased numbers of people, and how their migratory behavior can increase the incidence and spread of malaria; and the problems of drug resistance by the parasites to almost all currently available antimalarial drugs. In a selective manner, this review describes what is being done to ameliorate this situation both in terms of applying existing methods in a useful or even crucial role in control and prevention and in terms of new additions to the antimalarial armory that are being developed. Topics covered include biological control of mosquitoes, the use of insecticide-impregnated bed nets, transgenic mosquitoes manipulated for resistance to malaria parasites, old and new antimalarial drugs, drug resistance and how best to maintain the useful life of antimalarials, immunity to malaria and the search for antimalarial vaccines, and the malaria genome project and the potential benefits to accrue from it.

Malaria control in central Malaita, Solomon Islands: 1. The use of insecticide-impregnated bed nets

The present study investigated the use of insecticide-impregnated bed nets by communities in central Malaita, Solomon Islands. Qualitative and quantitative data were collected by: (1) questionnaire administration to 124 care-givers of children aged 0–10 years of age; (2) 20 focus group discussions; (3) two structured observations of bed net re-impregnation, and (4) interviews with key informants. Ninety-four percent of all care-givers had bed nets, but only 62% had sufficient bed nets for all household members. Fifty-two percent used bed nets throughout the year and 70% of care-givers reported that all their children slept under bed nets. Although coastal householders considered malaria and mosquitoes more of a problem than inland householders, overall bed net compliance did not differ. Factors affecting bed net ownership were cost and community expectation of free bed nets. Bed net use was affected by four factors: (1) seasonality (99% used bed nets during the rainy season, 52% used them all year); (2) mosquito nuisance (59% of respondents reported that protection against mosquitoes was the main reason for using a bed net); (3) weather (68% of care-givers would not use a bed net if the weather was hot), and (4) low density of mosquitoes (respondents who used bed nets as protection against mosquito nuisance were more likely not to use bed nets when mosquitoes were few than those who used bed nets for malaria protection (odds ratio (OR), 3.9; 95% confidence interval (CI), 1.4–12.0). Protection against malaria was the main reason children slept under bed nets. Children from households where bed nets were used for malaria protection were more likely to sleep under bed nets than children from households where nets were used as protection from mosquitoes only (OR, 2.7; 95% CI, 1.3–5.9). Other factors that affected children’s bed net use were, age (users were significantly younger than non-users; χ 2=7.9, degrees of freedom=1, P=0.005) and sufficiency of bed nets (OR, 2.0; 95% CI, 1.3–7.0).

Malaria control in central Malaita, Solomon Islands 2. Local perceptions of the disease and practices for its treatment and prevention

Government health policy for malaria control in Solomon Islands has three main objectives: (1) early diagnosis and treatment of malaria at a health service; (2) reduction of human-vector contact through widespread use of insecticide-impregnated bed nets; and (3) provision of malaria chemoprophylaxis for pregnant women. Social research was carried out in thirteen villages in central Malaita to determine local attitudes toward malaria and to estimate the level of participation in malaria control activities. Interviews with 124 care-givers who had children 0–10 years of age, 20 focus group discussions and four evening structured observations were research methods used. Antimalarial drugs were the most favoured treatment, and use of traditional medicines and healers were reportedly minimal. Twenty-five percent of respondents reported keeping chloroquine at home and 42% said they would use chloroquine before seeking diagnosis and treatment from a health service. Structured observations suggest that protection against mosquitoes is poor during the evening. Fifty-two percent of respondents reported using fire and 32% said they used bed nets to protect themselves from mosquitoes. Participants had contradictory beliefs on the threat of malaria during pregnancy and the safety of taking chloroquine prophylaxis. Implications of malaria treatment and prevention practices are discussed, and recommendations for improving malaria control are presented.

Acceptability and use of insecticide impregnated bednets in northern Ghana

A district-wide study was undertaken in a rural population of northern Ghana to identify factors influencing the acceptance and use of insecticide-impregnated bednets (IIBNs). A series of focus group discussions were conducted during 2 years of implementation of IIBNs to gauge community reactions to the introduction of the nets and a structured questionnaire was administered to approximately 2000 randomly selected individuals. Although the IIBNs were accepted and used because they provided protection from mosquito bites, seasonal factors, patterns of use, and questions of cost were key factors likely to influence the dissemination and effectiveness of bednets. Use of the bednets was highly seasonal. Almost all recipients used their IIBNs in the rainy season (99%), corresponding to the period of high mosquito density and 20% used them in the dry seasons, the period of low mosquito density. Mothers with young children were more likely to wash the bednets frequently (because the children soiled the bednets with faeces and urine), resulting in no protection from the insecticide. Provision of wider bednets, or the provision of plastic sheets with the bednets or possible incorporation of the insecticide in washing soaps could improve protection for young children. The success of the promotion of IIBNs in malaria control programmes will depend on the cost of the package and the time of year that it is delivered. Financing mechanisms for individual and village groups are discussed. Social research effectively monitored the intervention in this study, and it should be included as an important component of national malaria control programmes.

Evaluating the community education programme of an insecticide-treated bed net trial on the Kenyan coast.

Increased interest in the potential contribution of insecticide-impregnated bed nets (ITBN) to malaria control has led to research efforts to determine the impact and sustainability of ITBN programmes in differing environments. There is a need to develop effective, feasible educational strategies that will both inform and motivate community members, and thus maximize the correct usage of ITBN. This is especially true in communities where indigenous usage of bed nets is low. This paper describes the educational component of a randomized controlled community intervention trial of ITBN, with childhood malaria morbidity as an outcome. The educational approach and messages for the ITBN trial were developed from anthropological survey data collected 4 years before the trial, and from community surveys conducted by project researchers. Low levels of understanding amongst mothers of the aetiological link between mosquitos and malaria led to the exclusion of the term 'malaria' from the initial educational messages promoting the use of ITBN. Appropriate individuals within the existing district health care structure were trained as community educators in the project. These educators conducted intensive teaching in the community through public meetings and group teaching in the first 6 months of the trial. The impact of these initial activities was assessed through interviews with a random sample of 100 mothers and 50 household heads. This allowed the identification of messages which had not been well understood and further educational methods were chosen to address the areas pinpointed. The community assessment also demonstrated that, in 1994, over 90% of mothers understood a protective role for bed nets against malaria and the ITBN education messages were changed to take account of this. The school programme was evaluated through determining outreach (the number of households accessed), changes in participant children's knowledge, post-teaching assessment of mothers' knowledge and discussions with parent-teacher associations. It was shown that 40% of intervention homes with children in the target group were accessed, participant children learned the educational messages well (scores increased from a pre-teaching mean of 59% to a post-teaching mean of 92%) and a high level of awareness of the ITBN trial was achieved in these homes (75%). However, specific messages of the education programmed were not well transferred to the home (30%). The discussion emphasises the need for allocation of adequate resources for education in programmes dependent on achieving a change in community practices. We also describe the value of ongoing communication between programme planners and a target population in maximizing the effectiveness of messages and methods used.

The effectiveness of insecticide-impregnated bed nets in reducing cases of malaria infection: a meta-analysis of published results.

The use of insecticide-impregnated bed nets to minimize human-vector contact may reduce the incidence of malaria. Consequently, several field trials have evaluated their effectiveness as a malaria prevention strategy. A meta-analysis of published reports of field trials that measured the incidence of infections was performed to provide a measure of the effectiveness of insecticide-treated bed nets in preventing clinical malaria. Subsetted analyses were performed on the 10 field trials to calculate pooled incidence rate ratios of infection among the study groups. For the studies comparing insecticide-impregnated bed nets with untreated bed nets, the summary incidence rate ratio for acquiring malarial infections was 0.757 (95% confidence interval [CI] = 0.612-0.938), representing a reduction of 24%. For the studies comparing permethrin-impregnated bed nets with controls without bed nets, the summary incidence rate ratio was 0.497 (95% CI = 0.417-0.592) (Rothman-Boice heterogeneity statistics = 17.27 [P = 0.004] and 23.55 [P = 0.0003], respectively). These data suggest that insecticide-impregnated bed nets are effective in preventing malaria, decreasing the incidence rate ratio by approximately 50% in field trials performed to date.

Observations of human behavior influencing the use of insecticide-impregnated bednets to control malaria in Sabah, Malaysia.

Observational and survey methodologies were used to probe human behavioral factors influencing the use of insecticide-impregnated bednets to control malaria in rural Sabah, Malaysia. One aim was to investigate why a field trial of such nets in an interior area yielded disappointing results. A second aim was to gather baseline data prior to a field trial proposed for a coastal area. Interior villagers reported a significantly higher net usage rate than that observed directly, suggesting that subject self-reports need to be validated in some way. The poor results of the interior field trial appeared related to reluctance to regularly use nets, which were not in wide use previously. Prospects for reducing malaria transmission through bednets appeared better for the coastal area since nearly half of observed villagers were sleeping in them. However, significantly more coastal than interior villagers were observed watching television at night, an activity that may increase malaria risk by keeping villagers awake and out of bednets.

Malaria: drug use and the immune response.

Malaria is a controllable disease, yet the resources required - human, technical and financial - are massive, and are currently beyond the vast majority of the 96 countries where the disease is endemic. The control measures most widely applied are vector control through spraying or use of insecticide-impregnated bednets, and chemotherapy. The biological problems to add to the resource issues are well known; increasing resistance of anopheline mosquitoes to the most widely used insecticides, and the progressive development of drug resistance in the parasite populations, especiallyPlasmodium falciparum.