Combination of Insecticide Treated Nets and Indoor Residual Spraying in Northern Tanzania Provides Additional Reduction in Vector Population Density and Malaria Transmission Rates Compared to Insecticide Treated Nets Alone: A Randomised Control Trial

Indoor residual spraying (IRS) combined with insecticide treated nets (ITN) has been implemented together in several sub-Saharan countries with inconclusive evidence that the combined intervention provides added benefit. The impact on malaria transmission was evaluated in a cluster randomised trial comparing two rounds of IRS with bendiocarb plus universal coverage ITNs, with ITNs alone in northern Tanzania. From April 2011 to December 2012, eight houses in 20 clusters per study arm were sampled monthly for one night with CDC light trap collections. Anopheles gambiae s.l. were identified to species using real time PCR Taq Man and tested for the presence of Plasmodium falciparum circumsporozoite protein. ITN and IRS coverage was estimated from household surveys. IRS coverage was more than 85% in two rounds of spraying in January and April 2012. Household coverage with at least one ITN per house was 94.7% after the universal coverage net campaign in the baseline year and the proportion of household with all sleeping places covered by LLIN was 50.1% decreasing to 39.1% by the end of the intervention year. An.gambiae s.s. comprised 80% and An.arabiensis 18.3% of the anopheline collection in the baseline year. Mean An.gambiae s.l. density in the ITN+IRS arm was reduced by 84% (95%CI: 56%-94%, p = 0.001) relative to the ITN arm. In the stratum of clusters categorised as high anopheline density at baseline EIR was lower in the ITN+IRS arm compared to the ITN arm (0.5 versus 5.4 per house per month, Incidence Rate Ratio: 0.10, 95%CI: 0.01–0.66, p-value for interaction <0.001). This trial provides conclusive evidence that combining carbamate IRS and ITNs produces major reduction in Anopheles density and entomological inoculation rate compared to ITN alone in an area of moderate coverage of LLIN and high pyrethroid resistance in An.gambiae s.s.     

Modeling the Effects of Integrating Larval Habitat Source Reduction and Insecticide Treated Nets for Malaria Control

Integrated vector management for malaria control has received a lot of recent interest. Attacking multiple points in the transmission cycle is hoped to act synergistically and improve upon current single-tool interventions based on the use of insecticide-treated bed nets (ITNs). In the present study, we theoretically examined the application of larval habitat source reduction with ITNs in reducing malaria transmission. We selected this type of environmental management to complement ITNs because of a potential secondary mode of action that both control strategies share. In addition to increasing vector mortality, ITNs reduce the rate at which female mosquitoes locate human hosts for blood feeding, thereby extending their gonotrophic cycle. Similarly, while reducing adult vector emergence and abundance, source reduction of larval habitats may prolong the cycle duration by extending delays in locating oviposition sites. We found, however, that source reduction of larval habitats only operates through this secondary mode of action when habitat density is below a critical threshold. Hence, we illustrate how this strategy becomes increasingly effective when larval habitats are limited. We also demonstrate that habitat source reduction is better suited to human populations of higher density and in the presence of insecticide resistance or when the insecticidal properties of ITNs are depleted.     

Prevention of Malaria in Pregnancy with Intermittent Preventive Treatment and Insecticide Treated Nets in Mali: A Quantitative Health Systems Effectiveness Analysis

Introduction

The objectives of the study were to evaluate the health system effectiveness of ANC for the delivery of a dose of IPTp and an ITN to women attending ANC during eligible gestation, and to identify the predictors of systems effectiveness.

Methods

A cross sectional study was undertaken in 10 health facilities including structured non-participant observations of the ANC process for 780 pregnant women followed by exit interviews. The proportion of pregnant women receiving a dose of IPTp-SP and an ITN was assessed. Predictors of each ineffective intermediate process were identified using multivariable logistic regression.

Results

Overall, 0% and 24.5% of pregnant women of eligible gestation on the first visit to ANC received a dose of IPTp-SP by DOT at the district and community levels respectively. Ineffective intermediate processes were ‘given IPTp-SP at the ANC’ 63.9% and 74.0% (95% CI 62.0, 83.3), and ‘given IPTp-SP by DOT’ 0% and 34.3% (95% CI 10.5, 69.8), at district and community levels, respectively. Delivery of ITNs was effective where they were in stock; however stock-outs were a problem. Predictors of receiving IPTp-SP at the district level were 4 to 6 months gestation, not reporting symptoms of malaria at ANC visit and the amount of money spent during the visit. At the community level, the predictors were 4 to 6 months gestation, maternal education below primary level, routine ANC visit (not for an illness), palpation of the abdomen, and expenditure of money in ANC.

Conclusion

In Segou District, the delivery of IPTp-SP was ineffective; whilst ITN delivery was effective if ITNs were in stock. Predictors of receiving IPTp-SP at the district and community levels included gestational age, the amount of expenditure during the ANC visit and no illness.     

Efficacy,Safety and Cost of Insecticide Treated Wall Lining,Insecticide Treated Bed Nets and Indoor Wall Wash with Lime for Visceral Leishmaniasis Vector Control in the Indian Sub-continent: A Multi-country Cluster Randomized Controlled Trial

BackgroundWe investigated the efficacy, safety and cost of lime wash of household walls plus treatment of sand fly breeding places with bleach (i.e. environmental management or EM), insecticide impregnated durable wall lining (DWL), and bed net impregnation with slow release insecticide (ITN) for sand fly control in the Indian sub-continent.MethodsThis multi-country cluster randomized controlled trial had 24 clusters in each three sites with eight clusters per high, medium or low sand fly density stratum. Every cluster included 45–50 households. Five households from each cluster were randomly selected for entomological measurements including sand fly density and mortality at one, three, nine and twelve months post intervention. Household interviews were conducted for socioeconomic information and intervention acceptability assessment. Cost for each intervention was calculated. There was a control group without intervention.FindingsSand fly mortality [mean and 95%CI] ranged from 84% (81%-87%) at one month to 74% (71%-78%) at 12 months for DWL, 75% (71%-79%) at one month to 49% (43%-55%) at twelve months for ITN, and 44% (34%-53%) at one month to 22% (14%-29%) at twelve months for EM. Adjusted intervention effect on sand fly density measured by incidence rate ratio ranged from 0.28 (0.23–0.34) at one month to 0.62 (0.51–0.75) at 12 months for DWL; 0.72 (0.62–0.85) at one month to 1.02 (0.86–1.22) at 12 months for ITN; and 0.89 (0.76–1.03) at one months to 1.49 (1.26–1.74) at 12 months for EM. Household acceptance of EM was 74% compared to 94% for both DWL and ITN. Operational cost per household in USD was about 5, 8, and 2 for EM, DWL and ITN, respectively. Minimal adverse reactions were reported for EM and ITN while 36% of households with DWL reported transient itching.InterpretationDWL is the most effective, durable and acceptable control method followed by ITN. The Visceral Leishmaniasis (VL) Elimination Program in the Indian sub-continent should consider DWL and ITN for sand fly control in addition to IRS.     

Effectiveness of Antenatal Clinics to Deliver Intermittent Preventive Treatment and Insecticide Treated Nets for the Control of Malaria in Pregnancy in Kenya

Background

Malaria in pregnancy can have devastating consequences for mother and baby. Coverage with the WHO prevention strategy for sub-Saharan Africa of intermittent-preventive-treatment (IPTp) with two doses of sulphadoxine-pyrimethamine (SP) and insecticide-treated-nets (ITNs) in pregnancy is low. We analysed household survey data to evaluate the effectiveness of antenatal clinics (ANC) to deliver IPTp and ITNs to pregnant women in Nyando district, Kenya.

Methods

We assessed the systems effectiveness of ANC to deliver IPTp and ITNs to pregnant women and the impact on low birthweight (LBW). Logistic regression was used to identify predictors of receipt of IPTp and ITN use during pregnancy.

Results

Among 89% of recently pregnant women who attended ANC at least once between 4–9 months gestation, 59% reported receiving one dose of SP and 90% attended ANC again, of whom 57% received a second dose, resulting in a cumulative effectiveness for IPTp of 27%, most of whom used an ITN (96%). Overall ITN use was 89%, and ANC the main source (76%). Women were less likely to receive IPTp if they had low malaria knowledge (0.26, 95% CI 0.08–0.83), had a child who had died (OR 0.36, 95% CI 0.14–0.95), or if they first attended ANC late (OR 0.20, 95% CI 0.06–0.67). Women who experienced side effects to SP (OR 0.18, CI 0.03–0.90) or had low malaria knowledge (OR 0.78, 95% CI 0.11–5.43) were less likely to receive IPTp by directly observed therapy. Ineffective delivery of IPTp reduced its potential impact by 231 LBW cases averted (95% CI 64–359) per 10,000 pregnant women.

Conclusion

IPTp presents greater challenges to deliver through ANC than ITNs in this setting. The reduction in public health impact on LBW resulting from ineffective delivery of IPTp is estimated to be substantial. Urgent efforts are required to improve service delivery of this important intervention.     

A Qualitative Health Systems Effectiveness Analysis of the Prevention of Malaria in Pregnancy with Intermittent Preventive Treatment and Insecticide Treated Nets in Mali

Introduction

Delivery of intermittent preventive treatment with sulphadoxine-pyrimethamine to pregnant women (IPTp-SP) through antenatal clinic (ANC) in Mali is low, and whilst ANC delivery of insecticide treated nets (ITNs) is higher, coverage is still below national and international targets. The aim of this study was to explain quantitative data from a related study which identified ineffective processes in the delivery of these interventions in one district in Mali.

Methods

In-depth interviews were conducted with health workers at the national, regional, district and health facility levels on their perceptions of reasons for the ineffective processes identified in the quantitative study, and their reported practices. Themes were coded for each ineffective process, and within these a health systems lens was used. Content analysis was used for emergent themes within this framework. MindMaps were used to display the findings.

Results

Intervention specific factors for the ineffective delivery of IPTp-SP included misunderstanding of the upper limit of the gestational age at which SP could be given and side effects of SP. Incorrect practices had been recommended in training and supervision of health workers. Pregnant women who were ill on attendance at ANC were not consistently managed across health facilities. The most common reason for not offering women an ITN on their first ANC visit was if they were from outside the health facility catchment area. Broader health systems issues influencing the effectiveness of delivery of each of these interventions were also identified.

Conclusion

In this setting, intervention-specific factors resulted in the ineffective delivery of IPTp-SP. These relate to complex policy guidelines, lack of guidance on how to implement the guidelines, and the institutionalising of practices that undermine the national guidelines. Interventions may be implemented and show real gains in the shorter-term whilst waiting for broader health systems issues to be addressed.     

Assessing Insecticide Hazard to Bumble Bees Foraging on Flowering Weeds in Treated Lawns

Maintaining bee-friendly habitats in cities and suburbs can help conserve the vital pollination services of declining bee populations. Despite label precautions not to apply them to blooming plants, neonicotinoids and other residual systemic insecticides may be applied for preventive control of lawn insect pests when spring-flowering weeds are present. Dietary exposure to neonicotinoids adversely affects bees, but the extent of hazard from field usage is controversial. We exposed colonies of the bumble bee Bombus impatiens to turf with blooming white clover that had been treated with clothianidin, a neonicotinoid, or with chlorantraniliprole, the first anthranilic diamide labeled for use on lawns. The sprays were applied at label rate and lightly irrigated. After residues had dried, colonies were confined to forage for six days, and then moved to a non-treated rural site to openly forage and develop. Colonies exposed to clothianidin-treated weedy turf had delayed weight gain and produced no new queens whereas those exposed to chlorantraniliprole-treated plots developed normally compared with controls. Neither bumble bees nor honey bees avoided foraging on treated white clover in open plots. Nectar from clover blooms directly contaminated by spray residues contained 171±44 ppb clothianidin. Notably, neither insecticide adversely impacted bee colonies confined on the treated turf after it had been mown to remove clover blooms present at the time of treatment, and new blooms had formed. Our results validate EPA label precautionary statements not to apply neonicotinoids to blooming nectar-producing plants if bees may visit the treatment area. Whatever systemic hazard through lawn weeds they may pose appears transitory, however, and direct hazard can be mitigated by adhering to label precautions, or if blooms inadvertently are contaminated, by mowing to remove them. Chlorantraniliprole usage on lawns appears non-hazardous to bumble bees.     

Treated Filter Paper Bioassay for Detection of Insecticide Resistance in Haematobia irritans exigua de Meijere (Diptera: Muscidae)

This paper reports on the standardisation of an assay, whereby buffalo flies Haematobia irritans exigua de Meijere from a laboratory population which had not been exposed to insecticides for 8 years were confined in Petri dishes containing filter paper treated with known concentrations of insecticide. Mortality was assessed after 2 and 4 h and mean LC₅₀ and LC₉₉ values for each of 11 insecticides were calculated. the bioassay technique had acceptable repeatability and was simple to perform. Field populations of northern Queensland buffalo fly were assayed using the technique and were found to have high levels of pyrethroid resistance and little or no organophosphate resistance.     

Combining Organophosphate Treated Wall Linings and Long-lasting Insecticidal Nets for Improved Control of Pyrethroid Resistant Anopheles gambiae

Background

New approaches to delivering insecticides need to be developed to improve malaria vector control. Insecticidal durable wall lining (DL) and net wall hangings (NWH) are novel alternatives to indoor residual spraying which can be produced in a long-lasting format. Non-pyrethroid versions could be used in combination with long-lasting insecticidal nets for improved control and management of insecticide resistant vector populations.

Methods

Experimental hut trials were carried out in Valley du Kou, Burkina Faso to evaluate the efficacy of pirimiphos methyl treated DL and NWH either alone or in combination with LLINs against pyrethroid resistant Anopheles gambiae ss. Comparison was made with pyrethroid DL. Mosquitoes were genotyped for kdr and ace-1R resistant genes to investigate the insecticide resistance management potential of the combination.

Results

The overall kdr and ace-1^R allele frequencies were 0.95 and 0.01 respectively. Mortality with p-methyl DL and NWH alone was higher than with pyrethroid DL alone (>95% vs 40%; P<0.001). Combining pyrethroid DL with LLINs did not show improvement in mortality (48%) compared to the LLIN alone (44%) (P>0.1). Combining p-methyl DL or NWH with LLINs reduced biting rates significantly (8–9%) compared to p-methyl DL and NWH alone (>40%) and killed all An gambiae that entered the huts. Mosquitoes bearing the ace-1^R gene were more likely to survive in huts with p-methyl DL alone (p<0.03) whereas all resistant and susceptible genotypes were killed by the combination.

Conclusion

P-methyl DL and NWH outperformed pyrethroid DL. Combining p-methyl DL and NWH with LLINs could provide significant epidemiological benefits against a vector population which is resistant to pyrethroids but susceptible to organophosphates. There was evidence that the single intervention would select kdr and ace-1^R resistance genes and the combination intervention might select less strongly. Technology to bind organophosphates to plastic wall lining would be worth developing.     

昆虫对有机磷杀虫剂的抗性

有机磷杀虫剂在害虫的防治中多年来一直被作为一种有效的化学农药来使用。随着杀虫剂的大量使用,大部分害虫对这些杀虫剂产生了不同程度的抗性,导致杀虫剂剂量不断加大、防治效果降低,同时也造成了严重的环境污染。近年来,对昆虫有机磷杀虫剂抗性机制的研究发现,害虫对有机磷杀虫剂产生抗性的主要原因是由于其作用靶标物乙酰胆碱酯酶(AchE)对杀虫剂敏感性下降、AchE或普通酯酶活性上升等。本文就近年来国内外关于昆虫对有机磷杀虫剂抗性机制的研究进行综述,以期对害虫的抗性监测及抗性治理提供有用的参考。