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 M. H. KAYEDI *,{ , J. D. LINES * , A. A. HAGHDOOST *,{ and S. NAJAFI 1 * Disease Control and Vector Biology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, U.K. { Department of Parasitology, School of Medicine, Lorestan University of Medical Sciences, Goldasht, Khorramabad, Iran { Physiology Research Centre, Department of Social Medicine and Epidemiology, School of Medicine, Kerman University of Medical Sciences, Jomhory Eslamy Boulevard, Kerman, Iran 1 Kazeroun Field Station, School of Public Health, Tehran University of Medical Sciences, Kazeroun, Iran Received 9 May 2006, Revised 3 January 2007, Accepted 9 January 2007 In a randomized, prospective, 6-month-long field study in a rural area of Iran, the wash resistances of 200 nets (40 PermaNet TM , 40 Yorkool TM 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 TabH 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. One of the most beneficial antimalarial strategies developed in recent years has been the use of insecticide-treated nets (ITN) and the screening of rooms, to reduce exposure to the mosquito vectors that feed at night, indoors (Curtis, 1991, 1994; Curtis et al., 1992; Sexton, 1994; Curtis and Mnzava, 2000). The results of six major trials, in different areas of Africa, have indicated that the use of such nets can lead to significant reductions in mortality among young chil- dren (Alonso et al., 1991; Binka et al., 1997; D’Alessandro et al., 1995; Nevill et al., 1996; Habluetzel et al., 1997; Phillips- Howard et al., 2003a, b, c). Unfortunately, most ITN lose much of their insecticidal Reprint requests to: M. H. Kayedi, Department of Parasitology, School of Medicine, Lorestan University of Medical Sciences, Goldasht, Khorramabad, Iran. E-mail: kayedi78@yahoo.co.uk; fax: z98 66 1420 9040. Annals of Tropical Medicine & Parasitology, Vol. 101, No. 6, 519–528 (2007) # 2007 The Liverpool School of Tropical Medicine DOI: 10.1179/136485907X193815