Abstract:
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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. |