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      A longitudinal study of the durability of long-lasting insecticidal nets in Zambia

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          Abstract

          Background

          A key goal of malaria control is to achieve universal access to, and use of, long-lasting insecticidal nets (LLINs) among people at risk for malaria. Quantifying the number of LLINs needed to achieve and maintain universal coverage requires knowing when nets need replacement. Longitudinal studies have observed physical deterioration in LLINs well before the assumed net lifespan of 3 years. The objective of this study was to describe attrition, physical integrity and insecticide persistence of LLINs over time to assist with better quantification of nets needing replacement.

          Methods

          999 LLINs distributed in 2011 in two highly endemic provinces in Zambia were randomly selected, and were enrolled at 12 months old. LLINs were followed every 6 months up to 30 months of age. Holes were counted and measured (finger, fist, and head method) and a proportional hole index (pHI) was calculated. Households were surveyed about net care and repair and if applicable, reasons for attrition. Functional survival was defined as nets with a pHI <643 and present for follow-up. At 12 and 24 months of age, 74 LLINs were randomly selected for examination of insecticidal activity and content using bioassay and chemical analysis methods previously described by the World Health Organization (WHO).

          Results

          A total of 999 LLINs were enrolled; 505 deltamethrin-treated polyester nets and 494 permethrin-treated polyethylene nets. With 74 used to examine insecticide activity, 925 were available for full follow-up. At 30 months, 325 (33 %) LLINs remained. Net attrition was primarily due to disposal (29 %). Presence of repairs and use over a reed mat were significantly associated with larger pHIs. By 30 months, only 56 % of remaining nets met criteria for functional survival. A shorter functional survival was associated with having been washed. At 24 months, nets had reduced insecticidal activity (57 % met WHO minimal criteria) and content (5 % met WHO target insecticide content).

          Conclusions

          The median functional survival time for LLINs observed the study was 2.5–3 years and insecticide activity and content were markedly decreased by 2 years. A better measure of net survival incorporating insecticidal field effectiveness, net physical integrity, and attrition is needed.

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          Long-term field performance of a polyester-based long-lasting insecticidal mosquito net in rural Uganda

          Albert Kilian, Wilson Byamukama, Olivier Pigeon … (2008)
          Background In order to evaluate whether criteria for LLIN field performance (phase III) set by the WHO Pesticide Evaluation Scheme are met, first and second generations of one of these products, PermaNet®, a polyester net using the coating technology were tested. Methods A randomized, double blinded study design was used comparing LLIN to conventionally treated nets and following LLIN for three years under regular household use in rural conditions. Primary outcome measures were deltamethrin residue and bioassay performance (60 minute knock-down and 24 hour mortality after a three minute exposure) using a strain of Anopheles gambiae s.s. sensitive to pyrethroid insecticides. Results Baseline concentration of deltamethrin was within targets for all net types but was rapidly lost in conventionally treated nets and first generation PermaNet® with median of 0.7 and 2.5 mg/m2 after six months respectively. In contrast, second generation PermaNet® retained insecticide well and had 41.5% of baseline dose after 36 months (28.7 mg/m2). Similarly, vector mortality and knockdown dropped to 18% and 70% respectively for first generation LLIN after six months but remained high (88.5% and 97.8% respectively) for second generation PermaNet® after 36 months of follow up at which time 90.0% of nets had either a knockdown rate ≥ 95% or mortality rate ≥ 80%. Conclusion Second generation PermaNet® showed excellent results after three years of field use and fulfilled the WHOPES criteria for LLIN. Loss of insecticide on LLIN using coating technology under field conditions was far more influenced by factors associated with handling rather than washing.
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            Evidence for a useful life of more than three years for a polyester-based long-lasting insecticidal mosquito net in Western Uganda

            Albert Kilian, Wilson Byamukama, Olivier Pigeon … (2011)
            Background Long-lasting insecticidal nets (LLIN) are now standard for the prevention of malaria. However, only products with recommendation for public use from the World Health Organization should be used and this evaluation includes the assessment of net effectiveness after three years of field use. Results for one of the polyester-based products, Interceptor® is presented. Methods In five villages, 190 LLIN and 90 nets conventionally treated with the insecticide alpha-cypermethrin at 25 mg/m2 were distributed randomly and used by the families. Following a baseline household survey a net survey was carried out every six months to capture use, washing habits and physical condition of the nets. Randomly selected nets were collected after 6, 12, 24, 36 and 42 months and tested for remaining insecticide content and ability to knock-down and kill malaria transmitting mosquitoes. Results During the three and a half years of observation only 16 nets were lost to follow-up resulting in an estimated attrition rate of 12% after three and 20/% after 3.5 years. Nets were used regularly and washed on average 1.5 times per year. After three and a half years 29% of the nets were still in good condition while 13% were seriously torn with no difference between the LLIN and control nets. The conventionally treated nets quickly lost insecticide and after 24 months only 7% of the original dose remained (1.6 mg/m2). Baseline median concentration of alpha-cypermethrin for LLIN was 194.5 mg/m2 or 97% of the target dose with between and within net variation of 11% and 4% respectively (relative standard deviation). On the LLIN 73.8 mg/m2 alpha-cypermethrin remained after three years of use and 56.2 mg/m2 after three and a half and 94% and 81% of the LLIN still had > 15 mg/m2 left respectively. Optimal effectiveness in bio-assays (≥95% 60 minute knock-down or ≥ 80% 24 hour mortality) was found in 83% of the sampled LLIN after three and 71% after three and a half years. Conclusions Under conditions in Western Uganda the tested long-lasting insecticidal net Interceptor® fulfilled the criteria for phase III of WHO evaluations and, based on preliminary criteria of the useful life, this product is estimated to last on average between three and four years.
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              Monitoring long-lasting insecticidal net (LLIN) durability to validate net serviceable life assumptions, in Rwanda

              Emmanuel Hakizimana, Beatus Cyubahiro, Alphonse Rukundo … (2014)
              Background To validate assumptions about the length of the distribution–replacement cycle for long-lasting insecticidal nets (LLINs) in Rwanda, the Malaria and other Parasitic Diseases Division, Rwanda Ministry of Health, used World Health Organization methods to independently confirm the three-year LLIN serviceable life span recommendation of WHO. Methods Approximately 3,000 coded LLINs, distributed as part of a national campaign, were monitored in six sites, by means of six–monthly visits to selected houses. Two indicators, survivorship/attrition, a measure of the number of nets remaining, and fabric integrity, the proportion of remaining nets in either ‘good’, ‘serviceable’ or ‘needs replacement’ condition, based on holes in the net material, were tracked. To validate the assumption that the intervention would remain effective for three years, LLIN coverage, calculated using either survivorship, or integrity, by removing nets in the ‘needs replacement’ category from the survivorship total, was compared with the predicted proportion of nets remaining, derived from a net loss model, that assumes an LLIN serviceable life of three years. Results After two years, there was close agreement between estimated LLIN survivorship at all sites, 75% (range 64-84%), and the predicted proportion of nets remaining, 75%. However, when integrity was considered, observed survivorship at all sites, declined to 42% (range 10-54%). Conclusions More than half, 58%, of the LLINs fell into the ‘needs replacement’ category after two years. While these nets were counted for survivorship, they were judged to be of little-to-no benefit to a user. Therefore, when integrity was taken into account, survivorship was significantly lower than predicted, suggesting that net serviceable life was actually closer to two, rather than three years, and, by extension, that the impact of the intervention during year three of the LLIN distribution-replacement cycle could be well below that seen in years one and two.
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                Author and article information

                Contributors
                Kathrine R. Tan: +1 (404) 718-4701 , ktan@cdc.gov
                Jane Coleman: jane.coleman@jhpiego.org
                Barbara Smith: bsmith@peacecorps.gov
                Busiku Hamainza: bossbusk@gmail.com
                Cecilia Katebe-Sakala: Cecilia.katebesakala@bayer.com
                Casey Kean: caseykean@gmail.com
                Ashley Kowal: Ashleyk9155@gmail.com
                Jodi Vanden Eng: jvandeneng@cdc.gov
                Tiffany K. Parris: tparris@cdc.gov
                Carla T. Mapp: cmapp@cdc.gov
                Stephen C. Smith: scsmith2@cdc.gov
                Robert Wirtz: rwirtz@cdc.gov
                Mulakwa Kamuliwo: mkamuliwo@yahoo.co.uk
                Allen S. Craig: acraig@cdc.gov
                Journal
                Journal ID (nlm-ta): Malar J
                Journal ID (iso-abbrev): Malar. J
                Title: Malaria Journal
                Publisher: BioMed Central (London )
                ISSN (Electronic): 1475-2875
                Publication date (Electronic): 19 February 2016
                Publication date PMC-release: 19 February 2016
                Publication date Collection: 2016
                Volume: 15
                Electronic Location Identifier: 106
                Affiliations
                [ ]Center for Global Health, Malaria Branch, Centers for Disease Control and Prevention, 1600 Clifton Rd. MS A6, Atlanta, GA 30333 USA
                [ ]Jhpiego, an affiliate of Johns Hopkins University, Washington, DC USA
                [ ]Peace Corps, West Coast Region, San Francisco, CA USA
                [ ]Zambia National Malaria Control Centre, Lusaka, Zambia
                [ ]Bayer (Pty) Ltd, Isando, South Africa
                [ ]Success Academy Charter Schools, Brooklyn, NY USA
                [ ]Society for Family Health, Lusaka, Zambia
                [ ]Center for Global Health, Division of Parasitic Diseases and Malaria, Centers for Disease Control and Prevention, Atlanta, GA USA
                [ ]National Center for Enteric, Zoonotic, and Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA USA
                [ ]Center for Global Health, Entomology Branch, Centers for Disease Control and Prevention, Atlanta, GA USA
                [ ]Center for Global Health, Polio Eradication Branch, Centers for Disease Control and Prevention, Atlanta, GA USA
                Article
                Publisher ID: 1154
                DOI: 10.1186/s12936-016-1154-4
                PMC ID: 4759777
                PubMed ID: 26891696
                SO-VID: 576c34a6-9c2d-474f-a1aa-2d55017938fd
                Copyright © © Tan et al. 2016
                License:

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                Date received : 14 November 2015
                Date accepted : 9 February 2016
                Funding
                Funded by: US President's Malaria Initiative
                Categories
                Subject: Research
                Custom metadata
                issue-copyright-statement © The Author(s) 2016

                ScienceOpen disciplines: Infectious disease & Microbiology
                Keywords: long-lasting insecticidal nets,durability,attrition
                Data availability:
                ScienceOpen disciplines: Infectious disease & Microbiology
                Keywords: long-lasting insecticidal nets, durability, attrition

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