Estimating the efficacy of community-wide use of systemic insecticides in dogs to control zoonotic visceral leishmaniasis: A modelling study in a Brazilian scenario

Abstract

Systemic insecticides in dogs have been suggested as a public health intervention to prevent human cases of Zoonotic Visceral Leishmaniasis (ZVL). But, currently there are no systemic insecticides for dogs registered against zoo-anthropophilic pool blood feeding phlebotomine flies. We predict the impact of community-wide use of systemic insecticide in dog populations as a public health measure to control transmission of Leishmania infantum to humans using a mathematical model. We developed a Susceptible-Exposed-Infected (SEI) compartmental model to describe L. infantum transmission dynamics in dogs, with a vectorial capacity term to represent transmission between L. infantum-hosting dogs via phlebotomine flies. For Infected (I) dogs two levels of infectiousness were modelled, high infectiousness and low infectiousness. Human incidence was estimated through its relationship to infection in the dog population. We evaluated outcomes from a wide range of scenarios comprising different combinations of initial insecticide efficacy, duration of insecticide efficacy over time, and proportion of the dog population treated (60%, 70% & 80%). The same reduction in human infection incidence can be achieved via different combinations of insecticide efficacy, duration and dog coverage. For example, a systemic insecticide with an initial efficacy of 80% and 6 months above 65% efficacy would require treating at least 70% of the dogs to reduce the human infection incidence by 50%. Sensitivity analysis showed that the model outcome was most sensitive to baseline values of phlebotomine fly daily survival rate and insecticide coverage. Community-wide use of systemic insecticides applied to the “L. infantum canine reservoir” can significantly reduce human incidence of L. infantum infection. The results of this mathematical model can help defining the insecticide target product profile and how the insecticide should be applied to maximise effectiveness.

Spatial and Temporal Variability of Visceral Leishmaniasis in Colombia, 2007 to 2018

“…gomezi for CL (Figure 6), and an abundance of reservoir mammals for the parasite, 37,75 which aid the pathogen's epidemiological circuit and, therefore, maintain the transmission rates. Regarding mammalian reservoirs, canines are the main reservoirs for the domestic and peri-domestic transmission of VL 76 in Brazil, 77,78 Spain, 79 and other endemic countries. Studies have been conducted to measure the impact of canines on the incidence of VL, and the effectiveness of euthanasia and other control strategies to interrupt transmission.…”

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

“…Deceased dogs were replaced by newly introduced dogs, which have a probability of being already infected. The VL transmission model is based on a localised vectorial capacity of the sand fly population transmitting infection between dogs [Dye, 1996; Gomez et al, 2018]. We modified the force of infection (FOI) to include a spatial dependence on a dispersal kernel function between infectious and susceptible dogs (Supplementary Information).…”

Vaccination against canine leishmaniasis in Brazil

“…Mathematical models have suggested that canine vaccination could have a limited to no effect on the infection incidence in humans, as compared with insecticideimpregnated collars (Sevá et al, 2016;Shimozako et al, 2017;Gomez et al, 2018).…”