Last data update: May 06, 2024. (Total: 46732 publications since 2009)
Records 1-14 (of 14 Records) |
Query Trace: Swamidoss I[original query] |
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Evaluation of the residual efficacy and physical durability of five long-lasting insecticidal nets (LLINs) in Senegal
Diouf EH , Diouf M , Dieme C , Swamidoss I , Ngom EHM , Senghor MW , Mbaye M , Konaté A , Coulibaly Y , Tine D , Dia I , Dotson EM , Faye O , Konaté L . Malar J 2022 21 (1) 210 BACKGROUND: The preventive and curative strategies of malaria are based on promoting the use of long-lasting insecticidal nets (LLINs) and treating confirmed cases with artemisinin-based combination therapy. These strategies have led to a sharp decline in the burden of malaria, which remains a significant public health problem in sub-Saharan countries. The objective of this study was to determine and compare the residual efficacy of LLINs recommended by the World Health Organization. METHODS: The study was conducted in six villages in two sites in Senegal located in the Sahelo-Sudanian area of the Thiès region, 70 km from Dakar and in Mbagame, a semi-urban zone in the Senegal River Valley. A census was conducted of all sleeping places in each household to be covered by LLINs. Five brands of LLIN were distributed, and every six months, retention rates, net use, maintenance, physical integrity, insecticide chemical content, and biological efficacy were examined for each type of LLIN. RESULTS: A total of 3012 LLINs were distributed in 1249 households in both sites, with an average coverage rate of 94% (95% CI 92.68-95.3). After 36 months, the average retention rate was 12.5% and this rate was respectively 20.5%, 15.1%, 10%, 7%, and 3% for Olyset Net(®), Dawa Plus(®) 2.0, PermaNet(®) 2.0, NetProtect(®) and Life Net(®), respectively. The proportion of LLINs with holes and the average number of holes per mosquito net increased significantly during each follow-up, with a large predominance of size 1 (small) holes for all types of LLINs distributed. During the three-year follow-up, bioassay mortality rates of a susceptible strain of insectary reared Anopheles coluzzii decreased in the following net types: in Dawa Plus(®) 2.0 (100% to 51.7%), PermaNet(®) 2.0 (96.6% to 83%), and Olyset Net(®) (96.6% to 33.3%). Mortality rates remained at 100% in Life Net(®) over the same time period. After 36 months, the average insecticide content per brand of LLIN decreased by 40.9% for Dawa Plus(®) 2.0, 31% for PermaNet(®) 2.0, 39.6% for NetProtect(®) and 51.9% for Olyset Net(®) and 40.1% for Life Net. CONCLUSIONS: Although some net types retained sufficient insecticidal activity, based on all durability parameters measured, none of the net types survived longer than 2 years. |
A Comparison of Surface and Total Deltamethrin Levels of Insecticide-Treated Nets and Estimation of the Effective Insecticidal Lifetime
Green M , Maxyay M , Pongvongsa T , Phompida S , Swamidoss I , Smith S , Irish S , Newton P . Am J Trop Med Hyg 2021 106 (1) 334-337 The ability to anticipate the useful lifetime of an insecticide-treated mosquito net (ITN) would provide a proactive approach for planning net distribution programs. Therefore, we used an exponential decay model of deltamethrin depletion to predict the effective insecticidal lifetime of PermaNet® 2.0 nets used in the Lao PDR. Residual deltamethrin was measured using two nondestructive analytical field methods; X-ray fluorescence (total levels) and a colorimetric field test (surface levels) at 12 and 24 months postdistribution. The model assumes that the 12-month depletion rate can be used to predict future levels. The median total and surface deltamethrin levels for the Lao nets at 12 months were 31.2 and 0.0743 mg/m2, respectively. By defining a failed net as having total deltamethrin levels of less than 15 mg/m2 or a surface level less than 0.0028 mg/m2, it was predicted that 50% of the group of nets will fail at about 27 months after distribution. Insecticide-treated bednets (ITNs) are recognized as important tools for reducing malaria transmission in malaria-endemic regions.1-3 The effectiveness of ITNs at reducing malaria transmission relies on their ability to act as chemical as well as physical barriers. Over time, the accumulation of holes, rips, and tears as well as depletion of insecticide potency, reduces the efficacy of ITNs. Although the accumulation of holes results in decreased personal protection, the presence of remaining insecticide still has the potential to reduce malaria.4 It has been suggested by mathematical models that 94% of transmission can be prevented if 80% of the population continues to use these nets.4 Thus, monitoring insecticide levels along with physical integrity are important in recognizing when an ITN is no longer effective. Although damage to the nets can be visually ascertained, monitoring insecticidal potency is often assessed by using mosquito bioassays or chemical techniques. Mosquito bioassays, such as the WHO Cone Test, are the "Gold Standard" for assessing ITNs. Although mosquito bioassays are important elements in evaluating net efficacy, it is difficult to compare net performance across geographical regions where mosquito behavior and insecticide resistance are quite variable. Therefore, this report focuses on measuring surface and total residual insecticide levels by chemical means as a practical way to monitor and predict net longevity. The chemical techniques used to measure insecticide levels usually result in the partial destruction of an ITN. Spectroscopic methods such as X-ray fluorescence (XRF)5,6 and surface level measurements such as the colorimetric field test for cyanopyrethroids (CFT)7 provide alternative insecticide analysis techniques that are nondestructive to the net, thus allowing the same net to be monitored for insecticide levels over time. The XRF method measures the total (TL) amount of insecticide per area and the CFT measures available insecticide on the net surface (SL) via an abrasion technique using filter paper. Deltamethrin adhered to the filter paper is measured using a colorimetric cyanopyrethroid analysis method.7 The deltamethrin molecule contains both cyano and bromine groups, thus allowing it to be detected by the CFT and XRF, respectively.5,7 In this report, we describe the use of both XRF and CFT methods were on the same net after 12 and 24 months of use. The objectives of this report are to apply an exponential decay model for predicting the effective longevity of ITNs based on TL and SL deltamethrin measured after 12 months of use. The model is based on an assumption that by 12 months, factors contributing to insecticidal loss, such as washing and storage habits have become routinely established, thereby resulting in a depletion rate constant, from which future levels can be predicted. |
Attrition, physical integrity and insecticidal activity of long-lasting insecticidal nets in sub-Saharan Africa and modelling of their impact on vectorial capacity
Briet O , Koenker H , Norris L , Wiegand R , Vanden Eng J , Thackeray A , Williamson J , Gimnig JE , Fortes F , Akogbeto M , Yadouleton AW , Ombok M , Bayoh MN , Mzilahowa T , Abílio AP , Mabunda S , Cuamba N , Diouf E , Konaté L , Hamainza B , Katebe-Sakala C , Ponce de León G , Asamoa K , Wolkon A , Smith SC , Swamidoss I , Green M , Gueye S , Mihigo J , Morgan J , Dotson E , Craig AS , Tan KR , Wirtz RA , Smith T . Malar J 2020 19 (1) 310 BACKGROUND: Long-lasting insecticidal nets (LLINs) are the primary malaria prevention and control intervention in many parts of sub-Saharan Africa. While LLINs are expected to last at least 3 years under normal use conditions, they can lose effectiveness because they fall out of use, are discarded, repurposed, physically damaged, or lose insecticidal activity. The contributions of these different interrelated factors to durability of nets and their protection against malaria have been unclear. METHODS: Starting in 2009, LLIN durability studies were conducted in seven countries in Africa over 5 years. WHO-recommended measures of attrition, LLIN use, insecticidal activity, and physical integrity were recorded for eight different net brands. These data were combined with analyses of experimental hut data on feeding inhibition and killing effects of LLINs on both susceptible and pyrethroid resistant malaria vectors to estimate the protection against malaria transmission-in terms of vectorial capacity (VC)-provided by each net cohort over time. Impact on VC was then compared in hypothetical scenarios where one durability outcome measure was set at the best possible level while keeping the others at the observed levels. RESULTS: There was more variability in decay of protection over time by country than by net brand for three measures of durability (ratios of variance components 4.6, 4.4, and 1.8 times for LLIN survival, use, and integrity, respectively). In some countries, LLIN attrition was slow, but use declined rapidly. Non-use of LLINs generally had more effect on LLIN impact on VC than did attrition, hole formation, or insecticide loss. CONCLUSIONS: There is much more variation in LLIN durability among countries than among net brands. Low levels of use may have a larger impact on effectiveness than does variation in attrition or LLIN degradation. The estimated entomological effects of chemical decay are relatively small, with physical decay probably more important as a driver of attrition and non-use than as a direct cause of loss of effect. Efforts to maximize LLIN impact in operational settings should focus on increasing LLIN usage, including through improvements in LLIN physical integrity. Further research is needed to understand household decisions related to LLIN use, including the influence of net durability and the presence of other nets in the household. |
Monitoring the durability of the long-lasting insecticidal nets MAGNet and Royal Sentry in three ecological zones of Mozambique
Abilio AP , Obi E , Koenker H , Babalola S , Saifodine A , Zulliger R , Swamidoss I , Ponce de Leon G , Alfai E , Blaufuss S , Olapeju B , Harig H , Kilian A . Malar J 2020 19 (1) 209 BACKGROUND: Malaria prevention with long-lasting insecticidal nets (LLINs) has seen a tremendous scale-up in sub-Saharan Africa in the last decade. To sustain this success, it is important to understand how long LLINs remain in the households and continue to protect net users, which is termed durability. This information is needed to decide the appropriate timing of LLIN distribution and also to identify product(s) that may be underperforming relative to expectations. Following guidance from the U.S. President's Malaria Initiative, durability monitoring of polyethylene 150-denier LLIN (Royal Sentry((R)) and MAGNet((R))) distributed during a 2017 mass campaign in Mozambique was implemented in three ecologically different sites: Inhambane, Tete, and Nampula. METHODS: This was a prospective cohort study in which representative samples of households from each district were recruited at baseline, 1 to 6 months after the mass campaign. All campaign LLINs in these households were labelled and followed up over a period of 36 months. The primary outcome was the "proportion of LLINs surviving in serviceable condition" based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from subsamples of campaign LLINs. RESULTS: A total of 998 households (98% of target) and 1998 campaign LLIN (85% of target) were included in the study. Definite outcomes could be determined for 80% of the cohort LLIN in Inhambane, 45% in Tete, and 72% in Nampula. The highest all-cause attrition was seen in Nampula with 74% followed by Inhambane at 56% and Tete at 50%. Overall, only 2% of campaign LLINs were used for other purposes. Estimated survival in serviceable condition of campaign LLINs after 36 months was 57% in Inhambane, 43% in Tete, and 33% in Nampula, corresponding to median survival of 3.0, 2.8, and 2.4 years, respectively. Factors that were associated with better survival were exposure to social and behavioural change communication, a positive net care attitude, and folding up the net during the day. Larger household size negatively impacted survival. Insecticidal performance was optimal up to 24 months follow-up, but declined at 36 months when only 3% of samples showed optimal effectiveness in Inhambane, 11% in Tete and 29% in Nampula. However, 96% of LLIN still had minimal effectiveness at 36 months. CONCLUSIONS: Differences in median survival could be attributed at least in part to household environment and net care and repair behaviours. This means that in two of the three sites the assumption of a three-year cycle of campaign distributions holds, while in the Nampula site either continuous distribution channels could be expanded or more intense or targeted social and behaviour change activities to encourage net care and retention could be considered. |
A random survey of the prevalence of falsified and substandard antibiotics in the Lao PDR
Tabernero P , Swamidoss I , Mayxay M , Khanthavong M , Phonlavong C , Vilayhong C , Yeuchaixiong S , Sichanh C , Sengaloundeth S , Green MD , Newton PN . J Antimicrob Chemother 2019 74 (8) 2417-2425 OBJECTIVES: In 2012, a stratified random survey, using mystery shoppers, was conducted to investigate the availability and quality of antibiotics sold to patients in the private sector in five southern provinces of the Lao People's Democratic Republic (Laos). METHODS: A total of 147 outlets were sampled in 10 districts. The active pharmaceutical ingredient (API) content measurements for 909 samples, including nine APIs (amoxicillin, ampicillin, ceftriaxone, ciprofloxacin, doxycycline, ofloxacin, sulfamethoxazole, tetracycline and trimethoprim), were determined using HPLC. RESULTS: All the analysed samples contained the stated API and we found no evidence for falsification. All except one sample had all the units tested with %API values between 75% and 125% of the content stated on the label. However, we identified the presence of substandard antibiotics: 19.6% (201/1025) of samples had their units outside the 90%-110% content of the label claim and 60.2% (617/1025) of the samples had units outside of the International Pharmacopoeia uniformity of content limit range. Amoxicillin had a high number of samples [67.1% (151)] with units above the limit range, followed by ciprofloxacin [58.8% (10)] and ofloxacin [57.4% (39)]. Ceftriaxone, trimethoprim and sulfamethoxazole had the highest number of samples with low API content: 57.1% (4), 51.6% (64) and 34.7% (43), respectively. Significant differences in %API were found between stated countries of manufacture and stated manufacturers. CONCLUSIONS: With the global threat of antimicrobial resistance to patient outcomes, greater understanding of the role of poor-quality antibiotics is needed. Substandard antibiotics will have reduced therapeutic efficacy, impacting public health and control of bacterial infections. |
Monitoring and predicting net longevity by measuring surface levels of insecticide: Implementing a faster, cost effective, nondestructive, and field-ready alternative to the World Health Organization Cone Test Bioassay
Calle DA , Rua-Uribe GL , Osorio L , Pineros-Jimenez JG , Swamidoss I , Vizcaino L , Beach R , Green MD . Am J Trop Med Hyg 2018 99 (4) 1003-1005 An important component of malaria control programs is the ability to assess the effectiveness of the insecticide in insecticide-treated nets (ITNs) during normal usage. The standard technique to measure insecticidal activity is the World Health Organization (WHO) cone test, which in many circumstances, may be difficult to implement. We have evaluated an alternative technique, the colorimetric field test (CFT) on a group of 24-month-old Permanet((R)) 2.0 nets collected in Colombia. The CFT, which measures surface levels (SL) of deltamethrin is compared with standard high-performance liquid chromatography (HPLC) and the WHO cone test. Effective concentrations of deltamethrin for 80% mortality (EC80) were determined from the CFT and HPLC results. Distribution of insecticide SL after 24 months of use reveal that sampling of the midsection best represents the condition of the entire net. We conclude that the CFT is a practical alternative to the WHO cone test for assessing ITN efficacy. |
Quality of Artemisinin-Containing Antimalarials in Tanzania's Private Sector--Results from a Nationally Representative Outlet Survey
ACT Consortium Drug Quality Project Team and the IMPACT2 Study Team , Swamidoss I , Green MD , Dwivedi P , Kachur SP . Am J Trop Med Hyg 2015 92 75-86 Ensuring that artemisinin-containing antimalarials (ACAs) are of good quality is a key component of effective malaria treatment. There are concerns that a high proportion of ACAs are falsified or substandard, though estimates are rarely based on representative data. During a nationally representative survey in Tanzania, ACAs were purchased from private retail drug outlets, and the active pharmaceutical ingredient (API) was measured. All 1,737 ACAs contained the labeled artemisinin derivative, with 4.1% being outside the 85-115% artemisinin API range defined as acceptable quality. World Health Organization (WHO) prequalified drugs had 0.1 times the odds of being poor quality compared with non-prequalified ACAs for the artemisinin component. When partner components of combination therapies were also considered, 12.1% were outside the acceptable API range, and WHO prequalified ACAs had 0.04 times the odds of being poor quality. Although the prevalence of poor quality ACAs was lower than reported elsewhere, the minority of samples found to be substandard is a cause for concern. Improvements in quality could be achieved by increasing the predominance of WHO prequalified products in the market. Continued monitoring of quality standards is essential. |
Quality of artemisinin-based combination formulations for malaria treatment: prevalence and risk factors for poor quality medicines in public facilities and private sector drug outlets in Enugu, Nigeria
Kaur H , Allan EL , Mamadu I , Hall Z , Ibe O , El Sherbiny M , Wyk AV , Yeung S , Swamidoss I , Green MD , Dwivedi P , Culzoni MJ , Clarke S , Schellenberg D , Fernandez FM , Onwujekwe O . PLoS One 2015 10 (5) e0125577 BACKGROUND: Artemisinin-based combination therapies are recommended by the World Health Organisation (WHO) as first-line treatment for Plasmodium falciparum malaria, yet medication must be of good quality for efficacious treatment. A recent meta-analysis reported 35% (796/2,296) of antimalarial drug samples from 21 Sub-Saharan African countries, purchased from outlets predominantly using convenience sampling, failed chemical content analysis. We used three sampling strategies to purchase artemisinin-containing antimalarials (ACAs) in Enugu metropolis, Nigeria, and compared the resulting quality estimates. METHODS: ACAs were purchased using three sampling approaches - convenience, mystery clients and overt, within a defined area and sampling frame in Enugu metropolis. The active pharmaceutical ingredients were assessed using high-performance liquid chromatography and confirmed by mass spectrometry at three independent laboratories. Results were expressed as percentage of APIs stated on the packaging and used to categorise each sample as acceptable quality, substandard, degraded, or falsified. RESULTS: Content analysis of 3024 samples purchased from 421 outlets using convenience (n=200), mystery (n=1,919) and overt (n=905) approaches, showed overall 90.8% ACAs to be of acceptable quality, 6.8% substandard, 1.3% degraded and 1.2% falsified. Convenience sampling yielded a significantly higher prevalence of poor quality ACAs, but was not evident by the mystery and overt sampling strategies both of which yielded results that were comparable between each other. Artesunate (n=135; 4 falsified) and dihydroartemisinin (n=14) monotherapy tablets, not recommended by WHO, were also identified. CONCLUSION: Randomised sampling identified fewer falsified ACAs than previously reported by convenience approaches. Our findings emphasise the need for specific consideration to be given to sampling frame and sampling approach if representative information on drug quality is to be obtained. |
A repeat random survey of the prevalence of falsified and substandard antimalarials in the Lao PDR: a change for the better
Tabernero P , Mayxay M , Culzoni MJ , Dwivedi P , Swamidoss I , Allan EL , Khanthavong M , Phonlavong C , Vilayhong C , Yeuchaixiong S , Sichanh C , Sengaloundeth S , Kaur H , Fernandez FM , Green MD , Newton PN . Am J Trop Med Hyg 2015 92 95-104 In 2003, a stratified random sample survey was conducted in the Lao People's Democratic Republic (Laos) to study the availability and quality of antimalarials in the private sector. In 2012, this survey was repeated to allow a statistically valid analysis of change through time. The counterfeit detection device 3 (CD-3) was used to assess packaging quality in the field. The availability of oral artesunate monotherapies had significantly decreased from 22.9% (22) of 96 outlets in southern Laos in 2003 to 4.8% (7) of 144 outlets in 2012 (P < 0.0001). All the samples collected in 2012 survey contained the correct active pharmaceutical ingredients (APIs) in contrast to the 21 (84%) falsified artesunate samples found in the 2003 survey. Although none of the medicines found in 2012 survey had evidence for falsification, 25.4% (37) of the samples were outside the 90-110% pharmacopeial limits of the label claim, suggesting that they were substandard or degraded. Results obtained from this survey show that patients are still exposed to poorly manufactured drugs or to ineffective medicines such as chloroquine. The quality of artemisinin-based combination therapies (ACTs) used in Laos needs to be monitored; since falsified ACTs would have devastating consequences in public health. |
Quality of antimalarials at the epicenter of antimalarial drug resistance: results from an overt and mystery client survey in Cambodia
Yeung S , Lawford HL , Tabernero P , Nguon C , van Wyk A , Malik N , DeSousa M , Rada O , Boravann M , Dwivedi P , Hostetler DM , Swamidoss I , Green MD , Fernandez FM , Kaur H . Am J Trop Med Hyg 2015 92 39-50 Widespread availability of monotherapies and falsified antimalarials is thought to have contributed to the historical development of multidrug-resistant malaria in Cambodia. This study aimed to document the quality of artemisinin-containing antimalarials (ACAs) and to compare two methods of collecting antimalarials from drug outlets: through open surveyors and mystery clients (MCs). Few oral artemisinin-based monotherapies and no suspected falsified medicines were found. All 291 samples contained the stated active pharmaceutical ingredient (API) of which 69% were considered good quality by chemical analysis. Overall, medicine quality did not differ by collection method, although open surveyors were less likely to obtain oral artemisinin-based monotherapies than MCs. The results are an encouraging indication of the positive impact of the country's efforts to tackle falsified antimalarials and artemisinin-based monotherapies. However, poor-quality medicines remain an ongoing challenge that demands sustained political will and investment of human and financial resources. |
Integration of novel low-cost colorimetric, laser photometric, and visual fluorescent techniques for rapid identification of falsified medicines in resource-poor areas: application to artemether-lumefantrine
Green MD , Hostetler DM , Nettey H , Swamidoss I , Ranieri N , Newton PN . Am J Trop Med Hyg 2015 92 8-16 The availability of falsified antimalarial drugs can be reduced with effective drug regulatory agencies and proper enforcement. Fundamental to these agencies taking action, rapid identification must be made as soon as they appear in the market place. Since falsified antimalarials occur mostly in developing countries, performing drug analysis presents itself with unique challenges. A fundamental factor in choosing a useful technique is affordability and simplicity. Therefore, we suggest a three-tiered drug evaluation strategy for identifying a falsified drug in resource-poor areas. Tier I is a simple comparison of a tablet's weight and dimensions with official specifications. Tier II uses inexpensive photometric devices (laser and fluorescence) to evaluate a tablet. Suspicious samples from Tier I and II assessments are then subjected to a colorimetric assay for active ingredients identification and quantification. In this article, we evaluate a novel colorimetric assay for the simultaneous assessment of both lumefantrine and artemether in co-formulated Coartem tablets, and integrate the method with two novel, low-cost, fluorescence and laser photometric devices. Image analysis software is used for the assessments. Although artemether-lumefantrine is used as an example, the strategy may be adapted to other medicines. |
The influence of diet on the use of near-infrared spectroscopy to determine the age of female Aedes aegypti mosquitoes
Liebman K , Swamidoss I , Vizcaino L , Lenhart A , Dowell F , Wirtz R . Am J Trop Med Hyg 2015 92 (5) 1070-5 Interventions targeting adult mosquitoes are used to combat transmission of vector-borne diseases, including dengue. Without available vaccines, targeting the primary vector, Aedes aegypti, is essential to prevent transmission. Older mosquitoes (≥ 7 days) are of greatest epidemiological significance due to the 7-day extrinsic incubation period of the virus. Age-grading of female mosquitoes is necessary to identify post-intervention changes in mosquito population age structure. We developed models using near-infrared spectroscopy (NIRS) to age-grade adult female Ae. aegypti. To determine if diet affects the ability of NIRS models to predict age, two identical larval groups were fed either fish food or infant cereal. Adult females were separated and fed sugar water +/- blood, resulting in four experimental groups. Females were killed 1, 4, 7, 10, 13, or 16 days postemergence. The head/thorax of each mosquito was scanned using a near-infrared spectrometer. Scans from each group were analyzed, and multiple models were developed using partial least squares regression. The best model included all experimental groups, and positively predicted the age group (< or ≥ 7 days) of 90.2% mosquitoes. These results suggest both larval and adult diets can affect the ability of NIRS models to accurately assign age categories to female Ae. aegypti. |
Falsified medicines in Africa: all talk, no action
Newton PN , Tabernero P , Dwivedi P , Culzoni MJ , Monge ME , Swamidoss I , Mildenhall D , Green MD , Jähnke R , de Oliveira MDS , Simao J , White NJ , Fernández FM . Lancet Glob Health 2014 2 (9) e509-10 Poor-quality medicines and medical products, both substandard and falsified, cause avoidable morbidity, mortality, drug resistance, and loss of faith in health systems, especially in low-income and middle-income countries.1, 2, 3 We report the analysis of two falsified medicines from Angola and discuss what lessons such a discovery could hold. | The tablets were seized at Luanda docks in June, 2012, after failing Minilab testing.4, 5 The seized shipment was enormous (1·4 million packets), and hidden in loudspeakers in a container from China.4 One sample was labelled as an adult course of the vital antimalarial drug artemether-lumefantrine, and as being manufactured by “Novartis Pharmaceutical Corporation”; it also bore an Affordable Medicines Facility—malaria logo (figure). Another sample was labelled as the broad-spectrum anthelmintic mebendazole, and as being manufactured by “Janssen-Cilag SpA”. |
Evaluation of a rapid colorimetric field test to assess the effective life of long-lasting insecticide-treated mosquito nets in the Lao PDR
Green MD , Mayxay M , Beach R , Pongvongsa T , Phompida S , Hongvanthong B , Vanisaveth V , Newton PN , Vizcaino L , Swamidoss I . Malar J 2013 12 (1) 57 BACKGROUND: Malaria morbidity and mortality have been significantly reduced through the proper use of insecticide-treated mosquito nets, but the extra protection afforded by the insecticide diminishes over time. The insecticide depletion rates vary according to location where wash frequency and wear are influenced by cultural habits as well as the availability of water. Monitoring of available insecticides on the net surface is essential for determining the effective life of the net. Therefore, a rapid and inexpensive colorimetric field test for cyanopyrethroids (Cyanopyrethroid Field Test or CFT) was used to measure surface levels of deltamethrin on insecticide-coated polyester nets (PowerNetsTM) in rural Lao PDR over a two-year period. METHODS: Net surface levels of deltamethrin were measured by wiping the net with filter paper and measuring the adsorbed deltamethrin using the CFT. A relationship between surface levels of deltamethrin and whole net levels was established by comparing results of the CFT with whole levels assayed by high-performance liquid chromatography (HPLC). An effective deltamethrin surface concentration (EC80) was determined by comparing mosquito mortality (WHO Cone Test) with CFT and HPLC results. Five positions (roof to bottom) on each of 23 matched nets were assayed for deltamethrin surface levels at 6, 12, and 24 months. Mosquito mortality assays (WHO Cone Tests) were performed on a subset of eleven 24-month old nets and compared with the proportion of failed nets as predicted by the CFT. RESULTS: At six months, the nets retained about 80% of the baseline (new net) levels of deltamethrin with no significant differences between net positions. At 12 months, ~15-40%, and at 24 months <10% of deltamethrin was retained on the nets, with significant differences appearing between positions. Results from the CFT show that 93% of the nets failed (deltamethrin surface levels ≤ EC80) at 24 months. This value is in agreement with 91% failure as determined by the WHO Cone Test on a subset of 11 nets. The CFT results show that 50% of the nets from Laos failed at 12 months of normal use. CONCLUSION: The CFT is a useful and accurate indicator of net efficacy and may be substituted for mosquito bioassays. |
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