Visceral leishmaniasis on the Indian Subcontinent: Efficacy of fipronil-based cattle treatment in controlling sand fly populations is dependent on specific aspects of sand fly ecology.

David M Poché,William E Grant,Hsiao-Hsuan Wang

doi:10.1371/journal.pntd.0008011

David M Poché, William E Grant + Show 1 more

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https://doi.org/10.1371/journal.pntd.0008011

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Abstract

BackgroundVisceral leishmaniasis (VL) is a deadly disease transmitted by the sand fly Phlebotomus argentipes on the Indian subcontinent, with a promising means of vector control being orally treating cattle with fipronil-based drugs. While prior research investigating the dynamic relationship between timing of fipronil-based control schemes and the seasonality of sand flies provides insights into potential of treatment on a large scale, ecological uncertainties remain. We investigated how uncertainties associated with sand fly ecology might affect our ability to assess efficacy of fipronil-based control schemes. To do this, we used a previously-described, individual-based, stochastic sand fly model to quantify how uncertainties associated with 1) the percentage of female sand flies taking blood meals from cattle, and 2) the percentage of female sand flies ovipositing in organic matter containing feces from treated cattle might impact the efficacy of fipronil-based sand fly control schemes.Principal findingsAssuming no prior knowledge of sand fly blood meal and oviposition sites, the probabilities of achieving effective sand fly population reduction with treatments performed 3, 6 and 12 times per year were ≈5–22%, ≈27–36%, and ≈46–54%, respectively.Assuming ≥50% of sand flies feed on cattle, probabilities of achieving efficacious control increased to ≈8–31%, ≈15–42%, and ≈52–65%. Assuming also that ≥50% of sand flies oviposit in cattle feces, the above probabilities increased further to ≈14–53%, ≈31–81%, and ≈89–97%.ConclusionsOur assessments of the efficacy of fipronil-based cattle treatments in controlling sand fly populations depend on our assumptions regarding key aspects of sand fly ecology. Assessments are most sensitive to assumptions concerning the percentage of sand flies ovipositing in feces of treated cattle, thus emphasizing the importance of identifying sand fly oviposition sites. Our results place the evaluation of fipronil-based cattle treatment within a broader ecological context, which could aid in the planning and execution of a largescale field trial.

Highlights

Visceral leishmaniasis (VL) is a virulent vector-transmitted disease with an estimated 50,000 to 90,000 new human cases occurring worldwide each year, out of which only 25–45% are estimated to be reported [1, 2]
Visceral leishmaniasis (VL) is a deadly disease transmitted by the sand fly Phlebotomus argentipes on the Indian subcontinent, with a promising means of vector control being orally treating cattle with fipronil-based drugs
Our assessments of the efficacy of fipronil-based cattle treatments in controlling sand fly populations depend on our assumptions regarding key aspects of sand fly ecology

Summary

Introduction

Visceral leishmaniasis (VL) is a virulent vector-transmitted disease with an estimated 50,000 to 90,000 new human cases occurring worldwide each year, out of which only 25–45% are estimated to be reported [1, 2]. Because the effectiveness of IRS is logically dependent on villagers and sand flies remaining indoors, alternative forms of sand fly control are needed to target outdoor vector populations. One such alternative may be the use of systemic insecticides (endectocides), which are used to control nematodes and arthropods affecting livestock [21]. Visceral leishmaniasis (VL) is a deadly disease transmitted by the sand fly Phlebotomus argentipes on the Indian subcontinent, with a promising means of vector control being orally treating cattle with fipronil-based drugs. Assuming no prior knowledge of sand fly blood meal and oviposition sites, the probabilities of achieving effective sand fly population reduction with treatments performed 3, 6 and 12 times per year were 5–22%, 27–36%, and 46–54%, respectively. Assuming that 50% of sand flies oviposit in cattle feces, the above probabilities increased further to 14–53%, 31–81%, and 89–97%

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