Spraying houses in the Peruvian Andes with lambda-cyhalothrin protects residents against cutaneous leishmaniasis

household vector control trial was carried our in the Peruvian Andes to mea sure the effect of spraying inside walls and ceilings with lambda-cyhalothr in on the risk for residents of cutaneous leishmaniasis caused by Leishmani a peruviana. The mortality rates of Lutzomyia verrucarum measured with WHO contact bioassay cones set on adobe walls characteristic of the endemic reg ion indicated an LD95 for lambda-cyhalothrin of about 20 mg/m(2), and no re duction in effectiveness for at least 6 months on indoor adobe walls spraye d with 25 mg/m(2). A random selection of 112 houses were sprayed (starting in 1992/93) at 6-monthly intervals with a mean dose of 34 mg/m(2), leaving 154 control houses (with closely matched pre-intervention measurements of i ncidence and sandfly abundance). Comparisons of pre- and post-intervention sandfly indoor abundance, measured at regular intervals for up to 2 years u sing CDC light traps, in 22 sprayed and 21 control houses demonstrated that spraying significantly reduced the indoor abundance of Lu. verrucarum by a n average of 78% and of Lu. (Helcocyrtomyia) peruensis by 83%. Spraying was also associated with a significant reduction of 77% in the proportion of b loodfed sandflies collected in light traps. The proportion of susceptible h ouseholders acquiring leishmaniasis during the trial was significantly redu ced by 54% as a result of spraying. The observed impact of spraying was gre atest, 81% (95% confidence intervals 20-95%), when the cases detected durin g the first 6 months after the intervention were excluded from the analysis , suggesting a significant pre-patent period.