A Colorimetric Test for the Evaluation of the Insecticide Content of LLINs Used on Bioko Island, Equatorial Guinea

Abstract

BackgroundInsecticide-treated nets and indoor residual spraying of insecticides are used as the major vector control interventions in the fight against malaria. Measuring the actual amount of deposits of insecticides on bed nets and walls is essential for evaluating the quality and effectiveness of the intervention. A colorimetric “Test Kit” designed for use as a screening tool, able to detect the type II pyrethroids on fabrics and sprayed walls, was used for the first time to detect deltamethrin on long-lasting insecticidal nets (LLINs) deployed on Bioko Island, Equatorial Guinea.MethodsLLINs were analysed using the colorimetric Test Kit performed in situ, which leads to the formation of an orange-red solution whose depth of colour indicates the amount of type II pyrethroid on the net. The kit results were validated by measuring the amount of extracted insecticide using high-performance liquid chromatography (HPLC) with diode array detection (DAD).ResultsDeltamethrin concentration was determined for 130 LLINs by HPLC-DAD. The deltamethrin concentration of these nets exhibited a significant decrease with the age from 65 mg/m2 (<12 months of use) to 31 mg/m2 (>48 months; p<0.001). Overall, 18% of the nets being used in households had <15 mg/m2 of deltamethrin, thus falling into the failed category as assessed by the colorimetric Test Kit. This was supported by the bioassay determined bio-efficacy of the nets with ≥80% mortality following the World Health Organization (WHO) minimal effectiveness criteria. The Test Kit was field evaluated in situ and found to be rapid, accurate, and easy to use by people without laboratory training. The Test Kit was shown to have a reliable linear relationship between depth of colour produced and deltamethrin concentration (R2 = 0.9135).ConclusionResults of this study show that this colorimetric test was a reliable method to assess the insecticidal content of LLINs under operational conditions. The Test Kit provides immediate results and offers a rapid, inexpensive, field-friendly alternative to the complicated and costly methods as HPLC and WHO cone bioassays which also need specialist staff. Thus, enabling National Malaria Programs to gain access to effective and affordable monitoring tools for use in situ.

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“…We demonstrate that the values generated by IQK™ were strongly correlated (r 2 =0.93) with those estimated using HPLC analysis, the gold standard method, thus further validating the assay accuracy. A similarly high correlation was reported between estimates using IQK™ kit bench-marked against HPLC during evaluation of residual deltamethrin concentrations in LLINs [55]. Consequently, it is not likely that the observed variation in the insecticide concentrations in this study were due to inaccuracy of the quantification methods.…”

“…concentrations. Previous studies have used IQK™ to quantify pyrethroids, bendiocarb and DDT, to quantify delivered and residual concentrations on a variety of sampling mediums including adhesive tape, felt pads, glue dots, long-lasting insecticidal nets (LLINs), and in scrapings from treated wall surfaces [37, 49, 53, 54, 55]. Unlike the previous methods, here we adapted the IQK™ assay conditions to quantify alpha-cypermethrin a.i.…”