Effect Of Insecticide-treated Bed Nets Research Articles

Attitudes and Practices of Insecticide Treated Bed Nets Usage among Rural Dwellers in Oyo State, Nigeria

Aim: Malaria, a life-threatening disease transmitted to humans by the bites of infected female Anopheles mosquitoes, continues to be a significant public health issue, particularly in sub-Saharan Africa. This study was aimed at understanding the attitudes and practices regarding the use of insecticide-treated bed nets (ITNs) among rural dwellers in Oyo state, Nigeria.
 Methodology: The study adopted a cross-sectional design. The questionnaire was developed based on the objectives of the study. Sample size was calculated using the Fisher’s formula. The minimum sample size was 278 and was adjusted to 306 to account for non-response rate of 10%. A multi-stage cluster sampling technique was employed to select the participants.
 Results: The primary understanding of the purpose of ITNs was prevention of mosquito bites (59.67%), and prevention of malaria (40.33%). However, only 74% believed that ITNs could effectively prevent malaria and just 66% considered ITNs safe for use. The practice of ITN usage was quite high, with 93% of respondents possessing ITNs in their households. ITNs were obtained predominantly through free distribution (49%) or purchase (29.67%). Use of ITNs varied among participants, with 28.67% always using it, 41% often using it, and 7% never using it. The reasons for not always using ITNs included discomfort sleeping under it (49%) and perceptions of heat (30%). An analysis of the factors affecting the usage of ITNs indicated a significant association with the age, marital status, level of education, knowledge of ITNs, and beliefs about ITN's effectiveness and safety. The usage of ITNs was particularly low among younger respondents, those who were single or widowed/divorced/separated, those with no formal education or primary education, and those who were unaware of ITNs or did not believe in their effectiveness or safety.
 Conclusion: This study reveals a gap between knowledge and practice in ITN use, with significant barriers being discomfort and a lack of belief in the effectiveness of ITNs. While ownership rates are high, usage rates, especially consistent usage, is low. This was due to misconceptions, especially around the efficacy and safety of ITNs. Moreover, maintenance practices are suboptimal.

Malaria Control with Bed Nets; Assessment of Corelates of its Effectiveness for Pregnant Women in Kwaebibirem

Objective: This study aimed to investigate correlates of the effectiveness of Insecticide-treated Bed Nets (ITNs) for prevention of malaria through pregnancy till delivery.Methodology: The hospital-based cross sectional study enrolled 413 Antenatal Care (ANC) attendants at the maternity ward of the Kade government hospital. Differential patterns of use of ITNs among women who had malaria during pregnancy and women who did not have malaria during pregnancy were compared across various variables. Self-reported information by participants were objectively validated from maternal health record books, patient folders and other relevant maternal health registers.Results: ITNs are an important malaria prevention and control intervention among pregnant women who report using them during pregnancy. The period prevalence of malaria through pregnancy however remained high among adolescents irrespective of ITNuse while tertiary educational background and exposure to Intermittent Preventive Therapy with Sulfadoxine-pyrimethamine (IPTp-SP) reduced risk of malaria in pregnancy irrespective of ITN use.Conclusion: Malaria morbidity was generally higher among pregnant women who did not use bed nets during pregnancy despite variations by maternal age, area of residence, gestational age, occupation type, marital status, parity, maternal educational background and IPTp-SP status.Recommendations: Strategies aimed to reduce the period prevalence of malaria during pregnancy should be intensified particularly targeting adolescents. Barriers to sustained universal access to ITNs and IPTp-SP should be eliminated while policies aimed toincrease formal education should be prioritized.

A periodic dengue model with diapause effect and control measures

In order to investigate the effects of egg diapause on mosquito populations and dengue fever, the transmission dynamical model of dengue fever with diapause effect is established, incorporating temperature, photoperiod and control measures such as the release of Wolbachia-infected male mosquitoes and the use of insecticide-treated bed nets (ITNs). Firstly, the results of mosquito population dynamics on mosquito reproduction number are given. Secondly, the threshold dynamics of dengue transmission based on mosquito population dynamics are obtained. Thirdly, the relevant parameters of the model are estimated by collecting temperature, photoperiod and population data of Guangzhou, China. Further, the theoretical results are validated and the effects of seasonality, diapause, ITNs using and Wolbachia-infected male mosquitoes releasing on mosquito populations and dengue transmission are numerically analyzed. Finally, the control thresholds of mosquito populations and the disease are given under different conditions.

The Effect of Antimalarial Campaigns on Child Mortality and Fertility in Sub-Saharan Africa

We examine the extent to which recent declines in child mortality and fertility in Sub-Saharan Africa can be attributed to insecticide-treated bed nets (ITNs). Exploiting the rapid increase in ITNs since the mid-2000s, we employ a difference-in-differences estimation strategy to identify the causal effect of ITNs on mortality and fertility. We show that the ITN distribution campaigns reduced all-cause child mortality, but surprisingly increased total fertility rates in the short run in spite of reduced desire for children and increased contraceptive use. We explain this paradox in two ways. First, we show evidence for an unexpected increase in fecundity and sexual activity due to the better health environment after the ITN distribution. Second, we show evidence that the effect on fertility is positive only temporarily – lasting only 1-3 years after the beginning of the ITN distribution programs – and then becomes negative. Taken together, these results suggest the ITN distribution campaigns may have caused fertility to increase unexpectedly and temporarily, or that these increases may just be a tempo effect -- changes in fertility timing which do not lead to increased completed fertility.

Effect of insecticide-treated bed nets on visceral leishmaniasis incidence in Bangladesh. A retrospective cohort analysis

BackgroundVisceral leishmaniasis (VL) is a parasitic disease, transmitted by the sand fly species Phlebotomus argentipes in the Indian sub-continent. Effective vector control is highly desirable to reduce vector density and human and vector contact in the endemic communities with the aim to curtail disease transmission. We evaluated the effect of long lasting insecticide treated bed nets (LLIN) and bed nets impregnated with slow-release insecticide tablet K-O TAB 1-2-3 (jointly insecticide-treated nets or ITN) on VL incidence in a highly endemic sub-district (upazila) in Bangladesh.MethodsSeveral distributions of LLIN or K-O TAB 1-2-3 for self-impregnation of bed nets at home took place in Fulbaria upazila, Mymensigh district from 2004 to 2008 under three research projects, respectively funded by CDC, Atlanta, USA (2004) and WHO-TDR, Geneva, Switzerland (2006 & 2008). We included all households (n = 8142) in the 20 villages that had benefited in the past from one of these interventions (1295 donated LLIN and 11,918 local bed nets impregnated with K-O TAB 1-2-3) in the “exposed cohort”. We recruited a “non-exposed cohort” in villages with contemporaneously similar incidence rates who had not received such vector control interventions (7729 HHs from nine villages). In both cohorts, we visited all families house to house and ascertained any VL cases for the 3 year period before and after the intervention. We evaluated the incidence rate (IR) of VL in both cohorts as primary endpoint, applying the difference-in-differences method.ResultsThe study identified 1011 VL cases (IR 140.47/10,000 per year [py]) before the intervention, of which 534 and 477 cases in the intervention and control areas respectively. The IR was 144.13/10,000 py (534/37050) and 136.59/10,000 py (477/34923) in the intervention and control areas respectively, with no significant difference (p = 0.3901) before the intervention. After the intervention, a total of 555 cases (IR 77.11/10,000 py) were identified of which 178 (IR 48.04/10,000 py) in the intervention and 377 (107.95/10,000 py) in the control area. The intervention area had a significant lower IR than the control area during follow up, rate difference = –59.91, p<0.0001. The IR during follow up was significantly reduced by 96.09/10,000 py in the intervention area (p<0.0001) and 28.63/10,000 py in control area (p<0.0001) compared to baseline. There was a strong and significant overall effect of the ITN intervention, δ = –67.45, p <0.0001. Sex (OR = 1.36, p<0.0001) and age (OR = 0.99, p<0.0001) also had a significant effect on VL incidence. Male had a higher risk of VL than female and one year increase in age decreased the likelihood of VL by about 0.92%. Two third of the VL incidence occurred in the age range 2 to 30 years (median age of VL patients was 17 years).ConclusionVL incidence rate was significantly lower in the ITN intervention cohort compared to control in Bangladesh. Some bias due to more intense screen-and-treat activities or other interventions in the intervention area cannot be ruled out. Nonetheless, given their feasibility and sustainability, ITNs should be considered for integrated vector control during the maintenance phase of the VL elimination programme.

Experimental hut to study the indoor behaviour and effects of insecticide-treated bednets on phlebotomine sand flies (Diptera: Psychodidae).

BACKGROUNDBehavioural effects of insecticides on endophagic phlebotomine sand fly vectors of Leishmania are poorly understood mainly because of the lack of an experimental hut (EH) in which to study them.OBJECTIVE To build an EH to evaluate the effects of long-lasting insecticide-treated nets (LLINs) on Lutzomyia longiflocosa.METHODS The study had two phases: (1) Laboratory experiments using tunnel tests to select the traps for the EH; and (2) EH construction and evaluation of the effects of deltamethrin and lambda-cyhalothrin LLINs on L. longiflocosa females inside the EH.FINDINGS Phase 1: The horizontal-slit trap was the best trap. This trap collected the highest percentage of sand flies, and prevented them from escaping. Therefore, this trap was used in the EH. Phase 2: The main effects of LLINs on L. longiflocosa in the EH were: landing inhibition, inhibition from entering the bednet, induced exophily, and high mortality (total and inside exit traps).CONCLUSIONS The EH was effective for evaluating the effects of LLINs on endophagic sand flies. Although both types of LLINs showed high efficacy, the lambda-cyhalothrin-treated LLIN performed better. This is the first report of induced exophily in sand flies.

Emerging Pyrethroid Resistance among Anopheles arabiensis in Kenya.

.Vector control programs, particularly in the form of insecticide-treated bed nets (ITNs), are essential for achieving malaria elimination goals. Recent reports of increasing knockdown resistance (kdr) mutation frequencies for Anopheles arabiensis in Western Kenya heightens the concern on the future effectiveness of ITNs in Kenya. We examined resistance in An. arabiensis populations across Kenya through kdr mutations and World Health Organization–recommended bioassays. We detected two kdr alleles, L1014F and L1014S. Kdr mutations were found in five of the 11 study sites, with mutation frequencies ranging from 3% to 63%. In two Western Kenya populations, the kdr L1014F allele frequency was as high as 10%. The L1014S frequency was highest at Chulaimbo at 55%. Notably, the kdr L1014F mutation was found to be associated with pyrethroid resistance at Port Victoria, but kdr mutations were not significantly associated with resistance at Chulaimbo, which had the highest kdr mutation frequency among all sites. This study demonstrated the emerging pyrethroid resistance in An. arabiensis and that pyrethroid resistance may be related to kdr mutations. Resistance monitoring and management are urgently needed for this species in Kenya where resistance is emerging and its abundance is becoming predominant. Kdr mutations may serve as a biomarker for pyrethroid resistance in An. arabiensis.

Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide-treated bed nets.

In spite of widespread insecticide resistance in vector mosquitoes throughout Africa, there is limited evidence that long‐lasting insecticidal bed nets (LLINs) are failing to protect against malaria. Here, we showed that LLIN contact in the course of host‐seeking resulted in higher mortality of resistant Anopheles spp. mosquitoes than predicted from standard laboratory exposures with the same net. We also found that sublethal contact with an LLIN caused a reduction in blood feeding and subsequent host‐seeking success in multiple lines of resistant mosquitoes from the laboratory and the field. Using a transmission model, we showed that when these LLIN‐related lethal and sublethal effects were accrued over mosquito lifetimes, they greatly reduced the impact of resistance on malaria transmission potential under conditions of high net coverage. If coverage falls, the epidemiological impact is far more pronounced. Similarly, if the intensity of resistance intensifies, the loss of malaria control increases nonlinearly. Our findings help explain why insecticide resistance has not yet led to wide‐scale failure of LLINs, but reinforce the call for alternative control tools and informed resistance management strategies.

Effect of insecticide-treated bed nets on house-entry by malaria mosquitoes: The flight response recorded in a semi-field study in Kenya

Insecticide-treated nets are currently a major tool to reduce malaria transmission. Their level of repellency affects contact of the mosquito with the net, but may also influence the mosquito’s entry into the house. The response of host-seeking malaria mosquitoes approaching the eave of an experimental house was recorded within a large screen house. We compared entry- and exit rates in relation to the presence in the house of different insecticide-treated bed nets (ITNs) with an untreated net. Mosquitoes were lured towards the house by dispensing a synthetic host-odour blend from within the net in the house. Complementary WHO bioassays revealed that the treated nets caused high knock-down- and mortality responses to the Anopheles gambiae sensu stricto strain tested.The proportion of mosquitoes that came into view of the cameras and subsequently entered the house did not differ between treated nets and the untreated net. Treated nets did not affect proportions of mosquitoes that exited the house and departed from view around the eave. However, the percentage of house-leaving and re-entering mosquitoes when an insecticide- treated net was present, was lower than in the presence of an untreated net.Our results indicated that there was no spatial repellent effect from pyrethroid-treated nets that influences house-entry at eave level. It is argued that the toxic effect of treated bed nets resulted in a reduced number of mosquitoes re-entering the house, which could thereby affect malaria transmission in neighbouring, unprotected houses.

Effects of community-level bed net coverage on malaria morbidity in Lilongwe, Malawi

BackgroundThe protective effect of insecticide-treated bed nets against individual-level malaria transmission is well known, however community-level effects are less understood. Protective effects from community-level bed net use against malaria transmission have been observed in clinical trials, however, the relationship is less clear outside of a controlled research setting. The objective of this research was to investigate the effect of community-level bed net use against malaria transmission outside of a bed net clinical trial setting in Lilongwe, Malawi following national efforts to scale-up ownership of long-lasting, insecticide-treated bed nets.MethodsAn annual, cross-sectional, household-randomized, malaria transmission intensity survey was conducted in Lilongwe, Malawi (2011–2013). Health, demographic, and geographic-location data were collected. Participant blood samples were tested for Plasmodium falciparum presence. The percentage of people sleeping under a bed net within 400-m and 1-km radii of all participants was measured. Mixed effects logistic regression models were used to measure the relationship between malaria prevalence and surrounding bed net coverage. Each year, 800 people were enrolled (400 <5 years; 200 5–19 years; 200 ≥20 years; total n = 2400).ResultsFrom 2011 to 2013, malaria prevalence declined from 12.9 to 5.6%, while bed net use increased from 53.8 to 78.6%. For every 1% increase in community bed net coverage, malaria prevalence decreased among children under 5 years old [adjusted odds ratio: 0.98 (0.96, 1.00)]. Similar effects were observed in participants 5–19 years [unadjusted odds ratio: 0.98 (0.97, 1.00)]; the effect was attenuated after adjusting for individual-level bed net use. Community coverage was not associated with malaria prevalence among adults ≥20 years. Supplemental analyses identified more pronounced indirect protective effects from community-level bed net use against malaria transmission among children under 5 years who were sleeping under a bed net [adjusted odds ratio: 0.97 (0.94, 0.99)], compared to children who were not sleeping under a bed net [adjusted odds ratio: 0.99 (0.97, 1.01)].ConclusionsMalawi’s efforts to scale up ownership of long-lasting, insecticide-treated bed nets are effective in increasing reported use. Increased community-level bed net coverage appears to provide additional protection against malaria transmission beyond individual use in a real-world context.

Effectiveness of insecticide-treated bednets in malaria prevention in Haiti: a case-control study.

Insecticide-treated bednets (ITNs) are effective in preventing malaria where vectors primarily bite indoors and late at night, but their effectiveness is uncertain where vectors bite outdoors and earlier in the evening. We studied the effectiveness of ITNs following a mass distribution in Haiti from May to September, 2012, where the Anopheles albimanus vector bites primarily outdoors and often when people are awake. In this case-control study, we enrolled febrile patients presenting to outpatient departments at 17 health facilities throughout Haiti from Sept 4, 2012, to Feb 27, 2014, who were tested with malaria rapid diagnostic tests (RDTs), and administered questionnaires on ITN use and other risk factors. Cases were defined by positive RDT and controls were febrile patients from the same clinic with a negative RDT. Our primary analysis retrospectively matched cases and controls by age, sex, location, and date, and used conditional logistic regression on the matched sample. A sensitivity analysis used propensity scores to match patients on ITN use propensity and analyse malaria among ITN users and non-users. Additional ITN bioefficacy and entomological data were collected. We enrolled 9317 patients, including 378 (4%) RDT-positive cases. 1202 (13%) patients reported ITN use. Post-hoc matching of cases and controls yielded 362 cases and 1201 matched controls, 19% (333) of whom reported consistent campaign net use. After using propensity scores to match on consistent campaign ITN use, 2298 patients, including 138 (7%) RDT-positive cases, were included: 1149 consistent campaign ITN users and 1149 non-consistent campaign ITN users. Both analyses revealed that ITNs did not significantly protect against clinical malaria (odds ratio [OR]=0·95, 95% CI 0·68-1·32, p=0·745 for case-control analysis; OR=0·95, 95% CI 0·45-1·97, p=0·884 for propensity score analysis). ITN and entomological data indicated good ITN physical integrity and bioefficacy, and no permethrin resistance among local mosquitoes. We found no evidence that mass ITN campaigns reduce clinical malaria in this observational study in Haiti; alternative malaria control strategies should be prioritised. The Global Fund to Fight AIDS, Tuberculosis, and Malaria, and the US-based Centers for Disease Control and Prevention (CDC).

An Epidemiological Model of the Effects of Insecticide-Treated Bed Nets on Malaria Transmission.

Insecticide-treated bed nets (ITNs) have become a central tool for malaria control because they provide personal and community-wide protection through their repellent and insecticidal properties. Here we propose a model that allows to assess the relative importance of those two effects in different epidemiological contexts and we show that these two levels of protection may oppose each other. On the one hand, repellency offers personal protection to the users of ITNs. The repellent action, however, is a two-edged sword, for it diverts infectious mosquitoes to non-users, thereby increasing their risk. Furthermore, with increasing ITN coverage, the personal protection effect of repellency decreases as mosquitoes are forced to perform multiple feeding attempts even on ITN users. On the other hand, the insecticidal property, which offers community-wide protection by killing mosquitoes, requires that mosquitoes contact the insecticide on the ITN and is thus counteracted by the repellency. Our model confirms that ITNs are an effective intervention method by reducing total malaria prevalence in the population, but that there is a conflict between personal protection, offered by repellency, and community-wide protection, which relies on the ITN’s insecticidal properties. Crucially, the model suggests that weak repellency allows disease elimination at lower ITN coverage levels.

Safety of insecticide-treated mosquito nets for infants and their mothers: randomized controlled community trial in Burkina Faso.

BackgroundInsecticide-treated bed nets (ITNs) are now the main tool for malaria prevention in endemic areas. Synthetic pyrethroids are the only group of insecticides recommended by the World Health Organization for the use on ITNs. There are only few studies which have specifically investigated potential adverse effects of frequent exposure to ITNs in the vulnerable group of young infants and their mothers.MethodsThis study was nested into a large randomized controlled ITN effectiveness trial. Ninety newborns and their mothers were selected from the study population for participation. Together with their mothers they were protected with ITNs from birth (group A, n = 45) or from age 6 months (group B, n = 45) and followed up for 18 weeks (daily visits in the first 4 weeks, weekly visits thereafter). Potential side effects related to synthetic pyrethroids (deltamethrin) exposure were systematically investigated by trained field staff. The frequency and duration of respective symptoms was compared between the two study groups.ResultsA total of 180 participants (90 mothers and 90 infants) were followed up over the study period without any loss to follow up. There were no significant differences in the frequency and duration of side effects between the two study groups, except that the frequency of headache was significantly higher in group A compared to group B mothers (p = 0.01).ConclusionsThe study provides further evidence for ITNs being sufficiently safe in children and even in newborns. The association with headache in mothers could be explained by them handling the ITNs more intensely or it could be a chance finding.

A cohort study of the effectiveness of insecticide-treated bed nets to prevent malaria in an area of moderate pyrethroid resistance, Malawi.

BackgroundInsecticide-treated bed nets (ITNs) are the cornerstone of malaria control in sub-Saharan Africa but their effectiveness may be compromised by the spread of pyrethroid resistance among malaria vectors. The objective of this investigation was to assess the effectiveness of ITNs to prevent malaria in an area of Malawi with moderate pyrethroid resistance.MethodsOne deltamethrin ITN was distributed in the study area for every two individuals in each household plus one extra ITN for households with an odd number of residents. A fixed cohort of 1,199 children aged six to 59 months was seen monthly for one year and at sick visits to measure malaria infection and use of ITNs. Insecticide resistance among malaria vectors was measured. The effect of ITN use on malaria incidence was assessed, adjusting for potential confounders using generalized estimating equations accounting for repeated measures.ResultsThere were 1,909 infections with Plasmodium falciparum over 905 person-years at risk (PYAR), resulting in an observed incidence of 2.1 infections per person-year (iPPY). ITNs were used during 97% of the PYAR. The main vector was Anopheles funestus: mortality in WHO tube assays after exposure to 0.05% deltamethrin was 38% (95% confidence interval (CI) 29–47), and resistance was due to elevated oxidase enzymes. After adjusting for potential confounders, the incidence of malaria infection among ITN users was 1.7 iPPY (95% CI 1.5-2.1) and among non-bed net users was 2.6 iPPY (95% CI 2.0-3.3). Use of ITNs reduced the incidence of malaria infection by 30% (rate ratio 0.7; 95% CI, 0.5-0.8) compared to no bed nets.ConclusionITNs significantly reduced the incidence of malaria infection in children in an area with moderate levels of pyrethroid resistance and considerable malaria transmission. This is the first study to show that ITNs provide protection in areas where pyrethroid-resistant An. funestus is the major malaria vector. Malaria control programmes should continue to distribute and promote ITNs in areas with low to moderate pyrethroid resistance; however, insecticide resistance may intensify further and it is not known whether ITNs will remain effective at higher levels of resistance. There is an urgent need to identify or develop new insecticides and technologies to limit the vulnerability of ITNs to insecticide resistance.

A genetic model of the effects of insecticide-treated bed nets on the evolution of insecticide-resistance.

The evolution of insecticide-resistance in malaria vectors is emerging as a serious challenge for the control of malaria. Modelling the spread of insecticide-resistance is an essential tool to understand the evolutionary pressures and dynamics caused by the application of insecticides. We developed a population-genetic model of the spread of insecticide-resistance in a population of Anopheles vectors in response to insecticides used either as adulticides (focussing on insecticide-treated bed nets (ITNs)) or as larvicides (either for the control of malaria or, as an inadvertent side-product, in agriculture). We show that indoor use of insecticides leads to considerably less selection pressure than their use as larvicides, supporting the idea that most resistance of malaria vectors is due to the agricultural use of the insecticides that are also used for malaria control. The reasons for the relatively low selection pressure posed by adulticides are (i) that males are not affected by the ITNs and, in particular, (ii) that the insecticides are also repellents, keeping mosquitoes at bay from contacting the insecticide but also driving them to bite either people who do not use the insecticide or alternative hosts. We conclude by discussing the opposing public health benefits of high repellency at an epidemiological and an evolutionary timescale: whereas repellency is beneficial to delay the evolution of resistance, other models have shown that it decreases the population-level protection of the insecticide.

Effect of a Malaria Control Program on the Prevalence of Malaria, Fever and Anaemia in Children under Five Years in the Hohoe Municipality of Ghana: A Comparative Analysis of Cross-Sectional Surveys

Background: Malaria and anaemia continue to adversely impact the health of children in Ghana. Hohoe is an area of intense and prolonged, seasonal malaria transmission. In 2006, malaria control programme activities which provided In-secticide Treated Bed-Nets (ITNs) to resident children under five years and Artemisinin Combination Therapies (ACTs) for the management of malaria were introduced into the Hohoe Municipality. Before the introduction of the control programme, baseline surveys were carried out in communities in the Hohoe municipality to determine the prevalence of malaria, fever, anaemia, malaria parasite density, gametocytaemia and ITN ownership and use in June and November 2006 ahead of the intervention programme. Similar surveys were conducted in 2010 after the intervention to assess changes in the earlier indicators in the same communities. This report presents an evaluation of the intervention by comparing findings before and after the malaria control interventions. Methods: In 2010, two community-based surveys were carried out in thirty communities among children aged five years and below. The first one was at the beginning of the rainy and high malaria transmission season in June and the other was in November at the end of the rainy season. The surveys were to determine the prevalence of malaria, fever, anaemia and ITN ownership, use and effectiveness among children less than 5 years. Data were collected in the form of interviews using questionnaire and collection of biological samples. Findings were compared to those similar surveys conducted in the same communities and age groups in 2006. Pr-testi was used to analyze two sample tests for proportions and t-test was used for means. Findings: Malaria prevalence decreased by 20% [9.0% vs. 7.2%; p = 0.0.40], fever decreased by 47.8% [2.3% vs. 1.2%; p = 0.008] and anaemia decreased by 32.9% [7.8% vs. 5.3%; p = 0.002]. ITN ownership increased by 67.9% [20.8% vs. 64.8%; p < 0.001], ITN use increased by 64.2% [15.1% vs. 42.2%; p < 0.001] and ITN effectiveness increased by 41.7% [20.0% vs. 34.3%; p < 0.001]. The proportion of children with high density parasitaemia reduced by 17.9% [2.8% vs. 2.3%; p = 0.223]. Gameto-cytaemia decreased by 82.5% [0.8% vs. 0.14%; p = 0.002. Similarly data comparing 2006 and 2010 post-rainy season showed that malaria prevalence decreased by 16.8% [40.4% vs. 33.6%; p < 0.001], fever decreased by 14% [5.0% vs. 4.3%; p = 0.347] and anaemia decreased by 64.2% [12% vs. 4.3%; p < 0.001]. The proportion of children with high density parasitaemia also reduced by 69.5% [10.5% vs. 3.2%; p < 0.001] and gametocytaemia decreased by 78.5% [0.8% vs. 0.17%; p = 0.008]. Conclusion: This study suggested that there was an association between the current intervention and reduction in the prevalence of malaria, fever and anaemia. High parasite density and gametocytaemia prevalence have also significantly reduced over the five years of the introduction of the control measures. There has also been a significant increase in the ownership and use of ITNs.

Effects of vector-control interventions on changes in risk of malaria parasitaemia in sub-Saharan Africa: a spatial and temporal analysis.

In the past decade, decreases in clinical episodes and deaths due to malaria have been mainly associated with the expansion of vector-control measures, such as insecticide-treated bednets and indoor residual spraying. Malaria indicator surveys gather information about key malaria indicators through national representative household surveys. We aimed to estimate changes in risk of malaria parasitaemia at high spatial resolution in sub-Saharan Africa, and to quantify the effects of malaria interventions at national and subnational levels. In this spatial and temporal analysis, we analysed data from the six sub-Saharan countries that had publicly available data from two malaria indicator or demographic and health surveys with malaria measurements done in 2006-08 and 2010-12: Angola, Liberia, Mozambique, Senegal, Rwanda, and Tanzania. We used Bayesian geostatistical models to estimate the present malaria risk and to establish the change relative to the period between the last two national surveys. We applied Bayesian variable selection procedures to select the most relevant insecticide-treated-bednet measure for reducing malaria risk, and did spatial kriging over the study region to produce intervention coverage maps. We estimated the contribution of bednets and indoor residual spraying on changes in malaria risk, after adjustment for climatic and socioeconomic factors. Spatially varying coefficients of intervention coverage enabled estimation of their effects at subnational level. In all countries, the probability of decrease in parasitaemia varied substantially between regions. Insecticide-treated bednets were an important intervention for reducing malaria risk, according to different definitions of coverage. An overall effect of insecticide-treated bednets at country level was significant only in Angola (-0·64, 95% credible interval -0·98 to -0·30) and Senegal (-0·34, -0·64 to -0·05); however, in all countries, we detected significant effects of bednets and indoor residual spraying at local level. The described methodology is useful for the identification of regions where changes in malaria risk have taken place, and to describe the geographical pattern of malaria. Intervention effects vary in space, which might be driven by local endemicity levels. The produced maps provide a visual aid for national malaria control programmes to identify where targeted strategies and resources are most needed or likely to have the greatest effect on reducing the risk of parasitaemia.

Clustering of vector control interventions has important consequences for their effectiveness: a modelling study.

Vector control interventions have resulted in considerable reductions in malaria morbidity and mortality. When universal coverage cannot be achieved for financial or logistical reasons, the spatial arrangement of vector control is potentially important for optimizing benefits. This study investigated the effect of spatial clustering of vector control interventions on reducing the population of biting mosquitoes. A discrete-space continuous-time mathematical model of mosquito population dynamics and dispersal was extended to incorporate vector control interventions of insecticide treated bednets (ITNs), Indoor residual Spraying (IRS), and larviciding. Simulations were run at varying levels of coverage and degree of spatial clustering. At medium to high coverage levels of each of the interventions or in combination was more effective to spatially spread these interventions than to cluster them. Suggesting that when financial resources are limited, unclustered distribution of these interventions is more effective. Although it is often stated that locally high coverage is needed to achieve a community effect of ITNs or IRS, our results suggest that if the coverage of ITNs or IRS are insufficient to achieve universal coverage, and there is no targeting of high risk areas, the overall effects on mosquito densities are much greater if they are distributed in an unclustered way, rather than clustered in specific localities. Also, given that interventions are often delivered preferentially to accessible areas, and are therefore clustered, our model results show this may be inefficient. This study provides evidence that the effectiveness of an intervention can be highly dependent on its spatial distribution. Vector control plans should consider the spatial arrangement of any intervention package to ensure effectiveness is maximized.

The Impact of Pyrethroid Resistance on the Efficacy of Insecticide-Treated Bed Nets against African Anopheline Mosquitoes: Systematic Review and Meta-Analysis

Pyrethroid insecticide-treated bed nets (ITNs) help contribute to reducing malaria deaths in Africa, but their efficacy is threatened by insecticide resistance in some malaria mosquito vectors. We therefore assessed the evidence that resistance is attenuating the effect of ITNs on entomological outcomes. We included laboratory and field studies of African malaria vectors that measured resistance at the time of the study and used World Health Organization-recommended impregnation regimens. We reported mosquito mortality, blood feeding, induced exophily (premature exit of mosquitoes from the hut), deterrence, time to 50% or 95% knock-down, and percentage knock-down at 60 min. Publications were searched from 1 January 1980 to 31 December 2013 using MEDLINE, Cochrane Central Register of Controlled Trials, Science Citation Index Expanded, Social Sciences Citation Index, African Index Medicus, and CAB Abstracts. We stratified studies into three levels of insecticide resistance, and ITNs were compared with untreated bed nets (UTNs) using the risk difference (RD). Heterogeneity was explored visually and statistically. Included were 36 laboratory and 24 field studies, reported in 25 records. Studies tested and reported resistance inconsistently. Based on the meta-analytic results, the difference in mosquito mortality risk for ITNs compared to UTNs was lower in higher resistance categories. However, mortality risk was significantly higher for ITNs compared to UTNs regardless of resistance. For cone tests: low resistance, risk difference (RD) 0.86 (95% CI 0.72 to 1.01); moderate resistance, RD 0.71 (95% CI 0.53 to 0.88); high resistance, RD 0.56 (95% CI 0.17 to 0.95). For tunnel tests: low resistance, RD 0.74 (95% CI 0.61 to 0.87); moderate resistance, RD 0.50 (95% CI 0.40 to 0.60); high resistance, RD 0.39 (95% CI 0.24 to 0.54). For hut studies: low resistance, RD 0.56 (95% CI 0.43 to 0.68); moderate resistance, RD 0.39 (95% CI 0.16 to 0.61); high resistance, RD 0.35 (95% CI 0.27 to 0.43). However, with the exception of the moderate resistance category for tunnel tests, there was extremely high heterogeneity across studies in each resistance category (chi-squared test, p<0.00001, I² varied from 95% to 100%). This meta-analysis found that ITNs are more effective than UTNs regardless of resistance. There appears to be a relationship between resistance and the RD for mosquito mortality in laboratory and field studies. However, the substantive heterogeneity in the studies' results and design may mask the true relationship between resistance and the RD, and the results need to be interpreted with caution. Our analysis suggests the potential for cumulative meta-analysis in entomological trials, but further field research in this area will require specialists in the field to work together to improve the quality of trials, and to standardise designs, assessment, and reporting of both resistance and entomological outcomes.

The elusive effect of water and sanitation on the global burden of disease

About 2.5 billion people lack access to improved sanitation, and 1 billion have no access to any form of sanitation (UNICEF 2013). About 780 million people lack access to an improved water source, a figure that is based on a fairly generous definition incorporating little with respect to reliability, proximity and convenience of access (UNICEF 2013). While the ancient Romans may already have been aware of it (Bradley 2012), water and sanitation came to be regarded as key to improve health in the growing cities of Europe and America in the late 19th and early 20th centuries. A number of notable observational studies were carried out that even with the limited epidemiological tools available at the time all but proved the direct link between water, sanitation and health (Snow 1860; Pringle 1910). By contrast, in the early days of development aid in the post-colonial era, water and sanitation were often not regarded as a health issue, but primarily provided with the aim of making people’s life easier and enable developmental activities. Whoever tried to argue for more investment on health grounds was faced by a lack of epidemiological studies conducted in low-income settings, which led to a renewed interest in research from the 1970s.