Personal protection of long lasting insecticide-treated nets in areas of Anopheles gambiae s.s. resistance to pyrethroids

BACKGROUND: The development of mosquito nets pre-treated with insecticide, Long Lasting Impregnated Nets (LLINs) that last the life span of the net, is a solution to the difficulty of the re-impregnation of conventional nets. Even if they showed a good efficacy in control conditions, their efficacy in the field, particularly in areas with resistance of Anopheles gambiae to pyrethroids, is not well documented. This study compares wide (Olyset(®)) and small (Permanet(®)) mesh LLINs in field conditions, using entomological parameters. METHODS: The two LLINs were tested in a rice-growing area of south-western Burkina Faso (West Africa) with year around high density of the main malaria vector An. gambiae s.s. In the study village (VK6), there is a mixed population of two molecular forms of An. gambiae, the S-form which dominates during the rainy season and the M-form which dominates the rest of the year. The two LLINs Olyset(® )and Permanet(® )were distributed in the village and 20 matched houses were selected for comparison with four houses without treated nets. RESULTS: Mosquito entrance rate was ten fold higher in control houses than in houses with LLINs and there was no difference between the two net types. Among mosquitoes found in the houses, 36 % were dead in LLIN houses compared to 0% in control houses. Blood feeding rate was 80 % in control houses compared to 43 % in LLIN houses. The type of net did not significantly impact any of these parameters. No mosquitoes were found inside Permanet(®), whereas dead or dying mosquitoes were collected inside the Olyset(®). More than 60% of mosquitoes found on top or inside the nets had had blood meals from cattle, as shown by ELISA analysis. CONCLUSION: The percentage of blood-fed mosquitoes in a bed net study does not necessarily determine net success. The efficacy of the two types of LLINs was comparable, during a period when the S-form of An. gambiae was carrying the kdr gene. Significantly higher numbers of mosquitoes were collected in control houses compared to intervention houses, indicating that the LLINs provided an additional deterrent effect, which enhanced their expected prevention capacity

Median knock-down time as a new method for evaluating insecticide-treated textiles for mosquito control

<p>Abstract</p> <p>Background</p> <p>Insecticide treated bed nets are major tools for the Roll Back Malaria campaign. There are two types of Long-Lasting Insecticide-treated Nets (LNs) on the market: coated nets and insecticide-incorporated nets. Nets provided to this market need a recommendation from the World Health Organization to be purchased by donors and NGOs. During laboratory study (phase I), the first step consists in evaluating the wash resistance of a new LN product. When insecticide-incorporated nets are washed, it takes time to regenerate the insecticidal activity, i.e. insecticide must migrate to the net surface to be accessible to mosquitoes. The interval of time required for regeneration must be carefully determined to ensure the accuracy of further results. WHOPES procedures currently recommend the determination of the regeneration time by using mortality data. However, as mortality cannot exceed 100%, a LN that regenerates a surface concentration exceeding the dosage for 100% mortality, will have its regeneration time underestimated.</p> <p>Methods</p> <p>The Median Knock Down Time (MKDT) was determined as function of insecticide dosage on an inert surface, glass, and on polyester nettings using an acetone solution or a simple emulsion. Dosage response was also established for mortality data. The same method was then applied to a commercially polyethylene netting, currently under WHOPES evaluation, to determine the dynamics of regeneration as function of repeated washings. The deltamethrin content of these nets was estimated by Capillary Gas Chromatography (GC-ECD).</p> <p>Results</p> <p>MKDT was a linear function of log insecticide dosage on glass as on nettings. Mortality data were either 0 or 100% for most concentrations except for a narrow range. MKDT was log linear function of total deltamethrin content in a commercial polyethylene net exposed to washings. The regeneration time of this net increased with the number of washes and MKDT became higher. A new, easy and rapid method to determine MKDT is suggested.</p> <p>Discussion</p> <p>The MKDT is linearly correlated to log dosage on a given substrate and shows no saturation as mortality data do. It is suited to determine regeneration time of a product that is exposed to a stress, like washing or heating, where the process impacts on the bio-availability of the insecticide. Mortality data are useful for measuring product efficacy, whereas MKDT are better to measure dynamics of surface concentration like regeneration after a stressing process. Change in MKDT can be used to illustrate the loss of insecticide due to washing, but the slope of the curve is product and surface-dependent.</p

Strength of bed nets as function of denier, knitting pattern, texturizing and polymer

Abstract Background Bursting strength is a standard method for evaluating mosquito net strength. This article suggests that tension strength with one grab and one hook better represent how holes are generated in bed nets in real life. Methods Measurements of bursting strength and tension strengths in the two directions are analysed for eight model nets created for the study. The nets were made in the most commonly used denier (75 and 100 D) and mesh (156 holes/inch2) for multifilament polyester yarns, texturized or not, and with 4 or 6 sided holes. All were made from one polyester quality. Data was arranged in a randomized, complete block design and analysed for significant variables and their interactions. Data was then subjected to regression analyses using net square metre weight as a weighting factor with stepwise removal of variables. This revealed how the four textile variables interacted and allowed for making predictions for the strength of commercial nets in polyester or polyethylene. Results For the model nets, higher denier provided higher bursting strength and tension strengths, texturizing weakened nets and four-sided holes were stronger than six-sided holes. Even when compensating for square metre weight, 100 D nets are stronger than 75 D nets. Results for the commercial polyester net nets are less clear, probably because of different qualities of polyester. Tensile strength: a 75 denier net knitted tightly to provide the same square metre weight as a standard 100 denier net therefore does not obtain the same strength. Polyethylene nets are made of mono-fibre yarns and, therefore, have higher tension strength in both directions than multifilament polyester nets. For bursting strength results overlap for 100 denier yarns of both yarn types. As a class, commercial polyethylene nets are stronger than commercial polyester net whatever method is used for evaluation. Conclusion Tension strength measured in the length and width directions of the net using one hook and one clamp provide new relevant data as this method more closely imitates the cause of tear holes in nets as they occur in real life use. Using this methodology, the commercial monofilament yarn polyethylene nets are significantly stronger than the commercial multifilament polyester nets. This test method should be applied for nets used for years in the field.</p

Migration of additive molecules in a polymer filament obtained by melt spinning: Influence of the fiber processing steps

International audienceThe purpose of this study is to understand the influence of the yarn processing on the migration of additives molecules, especially insecticide, within polyethylene (PE) yarns. Yarns were manufactured in the laboratory focusing on three key-steps (spinning, post-stretching and heat-setting). Influence of each step on yarn properties was investigated using tensile tests, differential scanning calorimetry and wide-angle X-ray diffraction. The post-stretching step was proved to be critical in defining yarn mechanical and structural properties. Although a first orientation of polyethylene crystals was induced during spinning, the optimal orientation was only reached by post-stretching. The results also showed that the heat-setting did not significantly change these properties. The presence of additives crystals at the yarn surface was evidenced by scanning-electron microscopy. These studies performed at each yarn production step allowed a detailed analysis of the additives’ ability to migrate. It is concluded that while post-stretching decreased the migration rate, heat-setting seems to boost this migration

PermaNet 2.0 Long-Lasting Insecticidal Mosquito Net

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Prevention of mosquito nuisance among urban populations in Burkina Faso

This paper addresses the problems of mosquito control in urban areas of Burkina Faso. The main objectives are to examine relevant socio-cultural aspects in relation to a mosquito control intervention using a biolarvicide with main emphasis on local perceptions of mosquito nuisance and existing practices of mosquito control, including the cost of protective measures at household level. This is the report of an inter-disciplinary research project carried out in the two major towns of Burkina Faso, Bobo-Dioulasso and Ouagadougou, in 1999 and 2000, respectively. Both quantitative and qualitative methods were used in the ethnographic part of the study. Two questionnaire surveys were conducted in both study areas: one prior to the intervention (n=1083) and the other after the intervention of the treatments with bio-larvicide (n=956). In addition, 70 in-depth interviews and 17 focus group discussions (FGDs) were conducted. The findings show that mosquitoes are considered an important problem in the urban areas, both as a nuisance and a health risk and that the local population is very active in applying mosquito control measures at the household level. The intervention project was received positively by the local population with a decline in the perceived level of annoyance. The causal relationship between mosquitoes and malaria is clear, but the explanatory framework of the relationship between mosquitoes and other diseases is still under debate. The most common prevention methods are mosquito coils and aerosol spray, even though bed nets are perceived to be the most efficient and effective method. The investments in coils and aerosol sprays alone would mean an increase of 40% in the national figures for health expenditure at household level.Mosquitoes Prevention Urban population Malaria Cost Burkina Faso