Deltamethrin and permethrin residue on long-lasting insecticidal nets after 18 months of use in a visceral leishmaniasis-endemic area in Nepal.

The insecticide residue on two types of long-lasting insecticidal nets (LLIN), Olyset Net and PermaNet 2.0, used in a visceral leishmaniasis-endemic village in eastern Nepal was quantified using HPLC. After two washes during 18 months of use the mean insecticide residues on PermaNet 2.0 and Olyset Net were 53.5 mg/m(2) (97.3% of the target dose) of deltamethrin and 911.8 mg/m(2) (91.2% of the target dose) of permethrin, respectively. These residues were close to the insecticide loads specified by the manufacturers of the two LLINs. The use of LLINs has been postulated as an alternative or complementary method to indoor residual spraying. Our results suggest that LLINs should be washed 4-5 times each year throughout their lifespan by specifically requesting villagers to wash nets on certain dates. The insecticide residue on the nets and their bioefficacy against sand fly vectors should be monitored after each wash, in various cultural settings, to assess their durability and long-term retention of the insectide.