Data for Community deployment of a synthetic pheromone of the sand fly Lutzomyia longipalpis co-located with insecticide reduces vector abundance in treated and neighbouring untreated houses : implications for control of Leishmania infantum

Methods

Houses within eight defined semi-urban blocks in an endemic municipality in Brazil were randomised to synthetic pheromone + insecticide or to placebo treatments. A similar number of houses located >100m from each block were placebo treated and considered as “True Controls” (thus, analysed as three trial arms). Insecticide was sprayed on a 2.6m2 surface area of the property boundary or outbuilding wall, co-located within one metre of 50mg synthetic pheromone in controlled-release dispensers.

Vector numbers captured in nearby CDC light traps were recorded at monthly intervals over 3 months post intervention. Recruited sentinel houses under True Control and pheromone + insecticide treatments were similarly monitored at 7–9 day intervals. The intervention effects were estimated by mixed effects negative binomial models compared to the True Control group.

Results: Dose-response field assays using 50mg of the synthetic pheromone captured a mean 4.8 (95% C.L.: 3.91, 5.80) to 6.3 (95% C.L.: 3.24, 12.11) times more vectors (female Lu. longipalpis) than using 10mg of synthetic pheromone. The intervention reduced household female vector abundance by 59% (C.L.: 48.7, 66.7%) (IRR = 0.41) estimated by the cross-sectional community study, and by 70% (C.L.: 56.7%, 78.8%) estimated by the longitudinal sentinel study.

Similar reductions in male Lu. longipalpis were observed. Beneficial spill-over intervention effects were also observed at nearby untreated households with a mean reduction of 24% (95% C.L.: 0.050%, 39.8%) in female vectors. The spill-over effect in untreated houses was 44% (95% C.L.: 29.7%, 56.1%) as effective as the intervention in pheromone-treated houses.

Ownership of chickens increased the intervention effects in both treated and untreated houses, attributed to the suspected synergistic attraction of the synthetic pheromone and chicken kairomones. The variation in IRR between study blocks was not associated with inter-household distances, household densities, or coverage (proportion of total households treated). Conclusions: The study confirms the entomological efficacy of the lure-and-kill method to reduce the abundance of this important sand fly vector in treated and untreated homesteads.

The outcomes were achieved by low coverage and using only 1–2% of the quantity of insecticide as normally required for IRS, indicating the potential cost-effectiveness of this method. Implications for programmatic deployment of this vector control method are discussed.<br><br>The raw dataset 'GVtrialdata26-1-21.xlsx' is in EXCEL format and describes the changes in Lutzomyia longipalpis sand fly numbers resulting from a household-based intervention with a synthetic pheromone + insecticide compared to two types of control houses ('True Controls' and 'Untreated' houses)in a Brazilian study site, following the protocols and as described by results published by Gonçalves et al, 2021.

PLoS Neglected Tropical Diseases, 15 (2). e0009080. doi:10.1371/journal.pntd.0009080. The variables are: trap_date: date of CDC light trap night round: sand fly trap sampling round prepost: defines pre- or post-intervention sample round. pre-intervention=1; post-intervention sample rounds>1 area: code of study location block: code for geographical block of houses sampled within area house: unique house ID number arm: intervention arm: 1=true control; 2=untreated control; 3=pheromone + insecticide treated houses female: female Lu. longipalpis sandflies captured male: male Lu. longipalpis sandflies captured flies: total Lu. longipalpis sandflies captured chicken: number of chickens kept by the household tab dog: number of dogs kept by the household tothosts: total humans, mammals, birds in the household nndist: nearest neighbouring house distance (metres)