A randomized and controlled comparison of the wash-resistances and insecticidal efficacies of four types of deltamethrin-treated nets, over a 6-month period of domestic use with washing every 2 weeks, in a rural area of Iran

Disease Control and Vector Biology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
Annals of Tropical Medicine and Parasitology (Impact Factor: 1.2). 10/2007; 101(6):519-28. DOI: 10.1179/136485907X193815
Source: PubMed

ABSTRACT In a randomized, prospective, 6-month-long field study in a rural area of Iran, the wash resistances of 200 nets (40 PermaNet, 40 Yorkool and 40 A-Z nets), that their manufacturers claimed be long-lasting insecticidal nets (LLIN), were compared with those of 40 nets conventionally treated with deltamethrin (using K-O Tab tablets). All the nets were kept in routine domestic use and subjected to standardized hand-washing at 2-week intervals. Wild-caught or laboratory-reared Anopheles stephensi were used for the bio-assays of insecticidal activity. The regular washing and domestic use led to reductions in the insecticidal activities of all the treated nets after 6 months. Although the PermaNet nets showed the smallest reduction, they were not significantly better than the conventionally treated nets, which still showed acceptable insecticidal activity after 6 months. The PermaNet and A-Z nets both performed significantly better than the Yorkool nets, which were slightly but not significantly worse than the conventionally treated nets. In questionnaire-based interviews, the local householders were found to wash their own (non-study) nets at median and mean frequencies of every 2 and 2.1 weeks, respectively. In conclusion, the PermaNet nets showed better wash resistance than any of the other commercial nets, and were the only commercial nets tested that truly appeared to be LLIN. There still appears to be scope, however, for the impregnation, and thus the wash-resistance, of even the PermaNet nets to be improved.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Insecticide-treated bednets play a cornerstone role in the efforts to control malaria. Bednets entomological efficacy is the determinant factor of their use to control malaria. In this study, we compared under laboratory conditions, the efficacy of two long-lasting nets (PermaNet® versus Interceptor®) and two treatments kits K-O TAB® (deltamethrin) versus Fendona 6SC® (alpha-cypermethrin) against Anopheles gambiae s.l. malaria vectors. The efficacy of washed and unwashed bednets was assessed by contact bioassays using World Health Organization (WHO) cones. Three to five-days-old mosquitoes were exposed to the netting for 3 min; the median and 95 % knockdown time, the after 24 h mortality was recorded for each type of bednet. The mortality after 24 h was equivalent for the Fendona 6SC® treated bednets and the K-O TAB® treated bednets [79.4 % confidence limits (CL) (73.9-84.6) and 74 % CL (68.3-80.0), respectively]. However, the Fendona 6SC® treated bednets were superior in 50 % knockdown time to the K-O TAB® treated bednets [7.8 min, CL (6.5-9.0) and 15. 2 min, CL (14.0-16.4), respectively]. Washed Interceptor® and PermaNet® bednets showed similar efficacy in terms of 50 % knockdown times. Mortality after 24 h was similar from the fifth to the twentieth wash, but PermaNet® performed better than Interceptor® for the first four washes and for unwashed bednets. This study showed that Fendona 6SC® kit and the Interceptor® bednets have exhibited consistent comparable efficacy in the laboratory compared to the well known and in use K-O TAB® kit and PermaNet® bednets.
    Parasitology Research 01/2014; DOI:10.1007/s00436-013-3742-3 · 2.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Wash resistance and field bioefficacy of PermaNet® 2.0 nets, long lasting insecticidal nets, against mosquitoes were evaluated in Assam, northeastern India. After repeated hand washings at 12-day intervals a decline in the mosquito killing ability of PermaNet nets was noted (trend χ2 38.9, p
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The method used to dry bednets after they have been treated with an insecticide solution may affect the levels of insecticide and the uniformity of the insecticide deposits on the dry nets. In an attempt to see how the drying method may affect the insecticide deposits on the dry net, and to select the best drying method, laboratory and field studies have recently been carried out (in the U.K. and Iran, respectively). Conventional polyester nets were each treated with a deltamethrin solution (made with one K-O Tab tablet in 500 ml water) and then dried, either while hanging vertically or laid horizontally on the floor, in the sun or shade. The concentrations of deltamethrin in 25-cm2 samples cut from the dry nets (from the inner folds, surface folds, and top and bottom of each net dried vertically, and from the upper and lower surfaces of each net dried horizontally) were then determined using high-performance liquid chromatography (HPLC). Drying the treated nets in the sun or the shade did not make a significant difference to deltamethrin concentrations on the nets. Mean deltamethrin concentrations were, however, higher on the lower parts of the nets that had been hung to dry vertically than on the upper parts of these nets, and greater on the upper surfaces of nets dried horizontally than on the lower surfaces of such nets. In general, the layers and folds of the nets that had been on the outside of the drying nets contained more deltamethrin than the inner folds. These patterns are consistent with the hypothesis that deltamethrin tends to accumulate at the points where the water from the insecticide solution evaporates from the drying nets and also, in the case of nets dried vertically, at the lower points of the drying nets (as the result of gravity). In order to obtain an even and adequate distribution of insecticide, it is therefore not necessary to dry the net in the shade. To achieve a uniform deposit of deltamethrin, the drying net should be folded as little as possible and dried quickly.
    Annals of Tropical Medicine and Parasitology 02/2009; 103(1):85-90. DOI:10.1179/136485909X385018 · 1.20 Impact Factor