Poche, David Matthew (2015-11). Phlebotomine Sand Fly Control: Predicting the Impact of Alternative Sand Fly Control Methods, Using Simulation Modelling, on the Population Dynamics of Phlebotomus Argentipes (Diptera: Psychodidae) in Bihar, India. Master's Thesis.
Thesis
More cases of visceral leishmaniasis (VL) are reported in Bihar, India than any other region in the world. Attempts have been made to control the VL vector, the biting sand fly, Phlebotomus argentipes. Studies suggest that the insecticide fipronil, orally administered to cattle in drug-form, can control adult and larval sand flies. Hence, I developed an individual-based simulation model to estimate the effect of fipronil-treated cattle on sand fly population density in Bihar. The model represents daily sand fly population dynamics as a function of temperature-driven processes in a Bihari village and the impact of fipronil-induced adult and larval mortality on sand fly population density. Fipronil efficacy decreases over time in response to number of days post-cattle-treatment and is dependent on host preference (cattle) and oviposition site preference (cattle feces). Simulated treatment was performed with varying percentages of cattle treated and number of annual treatment applications to predict reduction in the mean number of simulated adult sand flies by the third year of treatment. Eight of 16 simulated treatment schemes resulted in reduction in the mean sand fly population of >50% within three years. Five of these simulations reduced the mean sand fly population by >67%, assumed to be a VL epidemic threshold. Two simulations eradicated sand fly populations. Additionally, simulated treatment schemes applied 12, 6, and 3 times per year showed an ability to suppress sand fly populations below an estimated epidemic threshold during the second and third years of treatment. Treating once per year is predicted to have little impact on vector abundance. Simulations predicted that sand fly population density can be reduced below the estimated epidemic threshold (>67%) if fipronil treatment is applied at a minimum 3 times per year over a 3-year period, a less cumbersome approach than 12 or 6 applications per year in the field. The sand fly populations are more sensitive to uncertainties surrounding sand fly oviposition site preference than host preference, suggesting that oviposition sites be investigated and targeted for control. A fipronil field trial and extensive oviposition site survey would best validate the model's potential to predict fipronil efficacy.
