Effectiveness of insecticide thermal fogging in hyrax dens in the control of leishmaniasis vectors in rural Palestine: A prospective study

Abstract

Background: Zoonotic cutaneous leishmaniasis (ZCL) is endemic in Palestine and transmitted by Phlebotomus sand flies. They inhabit dens of hyraxes, the reservoir animal. Control measures were implemented since 1996 but cases still occur. We estimated the effect of insecticide thermal fogging inside hyrax dens on sand fly density and leishmania infection.

Methodology/principal findings: During July-September 2019, we conducted a 12-week controlled interrupted time series study in two control and one intervention sites containing three hyrax dens each. We implemented Permethrin thermal fogging in the intervention site at week 6. We measured weekly and 36hrs post-intervention sand fly abundance inside dens using CDC light traps. We performed Next-Generation Sequencing to identify sand fly Leishmania spp. infection. We calculated the abundance reduction (AR) using Mulla's formula and negative binomial regression. Among 11427 collected sand flies, 7339 (64%) were females and 1786 (16%) were Phlebotomus spp. comprising ten species; P. sergenti was the dominant (n = 773, 43%). We report P. arabicus (n = 6) for the first time in Palestine. After fogging, Phlebotomus spp. AR was 93% at 36hrs, 18% and 38% at two and five weeks respectively and 41% during the complete post-intervention period. In the regression models, Phlebotomus spp. density in the intervention site decreased by 74% (IRR: 0.26, 95%CI: 0.11-0.57) at two weeks, 34% (IRR: 0.66, 95%CI: 0.48-0.90) at five weeks and 74% (IRR: 0.26, 95%CI: 0.12-0.59) during the complete period. The density of Leishmania infected sand flies decreased by 65% (IRR: 0.35, 95%CI: 0.26-0.48) at five weeks and 82% (IRR: 0.18, 95%CI: 0.07-0.42) for the complete period (zero infections until week two). Leishmania infection prevalence in the intervention site was 14% pre-intervention and 3.9% post-intervention.

Conclusions/significance: Fogging hyrax dens reduced sand fly abundance and leishmania infection during the 5-week post-intervention period and especially the first two weeks suggesting it could be an effective source-reduction measure for ZCL vectors. Future randomized controlled trials are needed to confirm the effectiveness of fogging hyrax dens on decreasing ZCL incidence.