Spatial modelling of sand fly vector's response to a synthetic sex-aggregation pheromone: impact on the incidence of visceral leishmaniasis in rural and urban settings

Background. Visceral leishmaniasis (VL) is a potentially fatal protozoan parasitic disease of humans and dogs. In the Americas, dogs are the reservoir and Lutzomyia longipalpis is the sand fly vector. A synthetic version of the vector9s sex-aggregation pheromone attracts conspecifics to co-located lethal insecticide, reducing reservoir infection and vector abundance. Mathematical models of spatially deployed interventions are lacking, thus best practise using this novel lure-and-kill vector control approach to reduce infection incidence has not been fully explored. Methods. We developed a predictive mathematical model of vector host-seeking behaviour combined with spatially explicit transmission models to evaluate changes in human and canine spatial infection incidence under variable pheromone implementation scenarios and demographic conditions. Results. The risk of human infection increased exponentially with canine incidence, but at different rates between rural and urban settings with spatial clustering of high forces of human infection related to their proximity to canine infected households. A predicted 70% household coverage using a cost-effective amount (50mg) of pheromone, plus insecticide, reduced rural and urban setting infection incidence by approximately 44% and 50% in dogs, and by 64% and 68% in humans, within 1-2 years. Near or complete transmission elimination in dogs and humans was achieved after 10 years intervention using 50mg of pheromone under 70% household coverage in urban settings when newly acquired (immigrant) dogs had no pre-existing infections, but in rural settings required 90% coverage using 500mg. The willingness to pay (WTP) price per 10mg unit of pheromone is likely to be <$3 USD, making it a cost-beneficial intervention compared to current alternative strategies. Conclusions. Integrated stochastic and spatial models capturing vector host-seeking behaviour, is a useful mathematical framework to evaluate spatially dependent intervention methods, fine-scale transmission dynamics, and to identify best practise.