Insecticide-impregnated netting as a potential tool for long-lasting control of the leishmaniasis vector Lutzomyia longipalpis in animal shelters

Abstract

Background: Leishmaniasis remains a serious neglected disease, with more than 350 million people potentially at risk worldwide. Control strategies often rely on spraying residual insecticides to target populations of the sand fly vectors that transmit Leishmania parasites when blood-feeding. These programmes are often difficult to sustain effectively, as sand fly resting sites must be resprayed on a regular basis. Here, we investigate whether application of insecticide-impregnated netting to a surface could act as an alternative to residual spraying for controlling the American visceral leishmaniasis vector Lutzomyia longipalpis.

Methods: Female L. longipalpis from our laboratory colony were exposed for 1 h to three treatments applied to plywood surfaces: 2% permethrin-impregnated netting (Olyset®), 20 mg a.i.m-2 micro-encapsulated lambda-cyhalothrin (Demand CS®) and a no-treatment control. We compared the speed at which these treatments acted, by measuring the percentage of sand flies killed both immediately after exposure to the treatment for 1 hour, as well as the number that had died 24 h after the 1 hour exposure. We repeated the experiment at 6 and 12 months following application to test the effectiveness of each treatment over time.

Results: When first applied, the lambda-cyhalothrin killed more sand flies in the first hour than the permethrin-impregnated netting. However, the effectiveness of the lambda-cyhalothrin diminished over time, so that there was no difference between the two treatments at 12 months. Both killed more sand flies than the control. When measured 24 h following exposure, both test treatments had killed close to 100% of sand flies when first applied, but while the lethal effect of the netting was maintained at close to 100% over 12 months, the effectiveness of the residual insecticide diminished to approximately 80% after 6 months.

Conclusions: The results of these initial laboratory experiments indicate that covering surfaces with insecticide impregnated netting material may provide a longer-lasting solution for killing sand flies than residual spraying. Field trials are needed to identify the feasibility of treating surfaces with netting or similar impregnated materials as part of a control program. In targeting L. longipalpis, the greatest benefits may be seen in treating animal sheds with netting, where these sand flies aggregate in large numbers, and which can be difficult to treat repeatedly by conventional spraying.

Figure 1

Immediate efficacy of insecticide treatments. Percentage of sand flies killed immediately following 1 h exposure to plywood surfaces, untreated (control), covered with permethrin-impregnated netting or treated with lambda-cyhalothrin (insecticide). A-C: change in effectiveness of each treatment over time. F-values refer to ANOVA across all three time points, different letters indicate significant differences between time points (Tukey’s post-hoc test). D: comparison of effectiveness of each treatment at each time point. F-values refer to ANOVA across all three categories at each time point; different letters indicate significant differences between categories at each time point. * = P < 0.05, ** = P < 0.01, *** = P < 0.05. NS = Not Significant.

Figure 2

Efficacy of insecticide treatments over 24 h. Percentage of sand flies killed within 24 h following 1 h exposure to plywood surfaces, untreated (control), covered with permethrin-impregnated netting or treated with lambda-cyhalothrin (insecticide). A-C: change in effectiveness of each treatment over time. F-values refer to ANOVA across all three time points, different letters indicate significant differences between time points (Tukey’s post-hoc test). D: comparison of effectiveness of each treatment at each time point. F-values refer to ANOVA across all three categories at each time point; different letters indicate significant differences between categories at each time point. * = P < 0.05, ** = P < 0.01, *** = P < 0.05. NS = Not Significant.