Wash durability and optimal drying regimen of four brands of long-lasting insecticide-treated nets after repeated washing under tropical conditions.
BACKGROUND
The current study was undertaken to determine the optimal wash-drying regimen and the effects of different washing procedures on the efficacy, and durability of four brands of newly introduced long-lasting insecticide-treated nets (LLINs) under tropical conditions.


METHODS
In the current study, the following four LLINs were tested: Olyset, PermaNet 2.0, BASF and TNT. Nets were divided into three sets; one set was washed by hand rubbing and air-dried either hanging or spread on the ground in direct sunlight or hanging or spread on the ground under the shade. A second set was washed using the WHO protocol (machine) and the third set was washed by beating the nets on rocks. The biological activities of the nets were assessed by a three-minute bioassay cone test and the residual insecticide contents were determined using high performance liquid chromatography (HPLC) procedure.


RESULTS
Nets that were dried hanging under the shade retained more insecticide, 62.5% and recorded higher mortality compared to nets which were dried lying on the ground in direct sunlight 58.8%, nets dried under the shade spread on the ground 56.3%, and 57.8% for nets dried hanging in direct sunlight. It was also observed that nets washed by the standard WHO protocol, retained more insecticide and were more effective in killing mosquitoes compared to nets washed by local methods of hand rubbing and beating on rocks. There were significant differences between drying regimens (p < 0.0001) and between washing procedures (p < 0.001) respectively. However, the effect of net type was statistically insignificant. The statistical differences on individual nets were also compared, for PermaNet and TNT there were no significant differences observed between the four drying regimens (p = 0.7944 and 0.4703) respectively). For BASF and Olyset, the differences were significant (p < 0.001 and p > 0.0001).


CONCLUSIONS
The results of this study suggest that washing and drying regimen influence the insecticidal activity of LLINs. The standard WHOPES washing protocol underestimates the amount of insecticide washed from LLINs compared to the abrasive washing procedures that are used in the field. This suggests that there is need to educate net users to adopt a more gentle washing procedure while handling LLINs. The education should accompany net distribution campaigns.
Atieli
Francis K
FK
Kenya Medical Research Institute, Centre for Global Health Research, Kisumu, Kenya. Fatieli@ke.cdc.gov
Munga
Stephen O
SO
Ofulla
Ayub V
AV
Vulule
John M
JM
D000818:Animals; D001681:Biological Assay; D002851:Chromatography, High Pressure Liquid; D009033:Culicidae / Q000187:drug effects / Q000502:physiology; D006796:Household Work; D006801:Humans; D057148:Insecticide-Treated Bednets; D007306:Insecticides / Q000032:analysis / Q000494:pharmacology*; D016019:Survival Analysis; D014329:Tropical Climate
D007306:Insecticides
Trop Med Int Health. 2005 Oct;10(10):1022-9
16185237
Trop Med Int Health. 2009 May;14(5):597-602
19228347
Med Vet Entomol. 2005 Mar;19(1):72-83
15752180
Ann Trop Med Parasitol. 2007 Jul;101(5):449-56
17550651
Trop Med Int Health. 2005 Nov;10(11):1141-50
16262739
J Med Entomol. 2006 Sep;43(5):884-8
17017224
Trans R Soc Trop Med Hyg. 2008 Aug;102(8):811-6
18579169
J Am Mosq Control Assoc. 2006 Mar;22(1):107-10
16646331
Malar J. 2008 Mar 20;7:49
18355408
Anal Chem. 1987 Nov 1;59(21):2594-6
3688447
Am J Trop Med Hyg. 2007 Dec;77(6 Suppl):243-8
18165499