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About the Authors:
Orin Courtenay
* E-mail: [email protected]
Affiliations School of Life Sciences, University of Warwick, Coventry, United Kingdom, Zeeman Institute, University of Warwick, Coventry, United Kingdom
ORCID http://orcid.org/0000-0002-0188-6929
Nathan C. Peters
Affiliation: Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada
ORCID http://orcid.org/0000-0002-2548-9581
Matthew E. Rogers
Affiliation: Department of Disease Control, London School of Hygiene and Tropical Medicine, London, United Kingdom
Caryn Bern
Affiliation: Department of Epidemiology and Biostatistics, School of Medicine, University of California San Francisco, San Francisco, California, United States of America
ORCID http://orcid.org/0000-0001-8195-7303Abstract
Quantitation of the nonlinear heterogeneities in Leishmania parasites, sand fly vectors, and mammalian host relationships provides insights to better understand leishmanial transmission epidemiology towards improving its control. The parasite manipulates the sand fly via production of promastigote secretory gel (PSG), leading to the “blocked sand fly” phenotype, persistent feeding attempts, and feeding on multiple hosts. PSG is injected into the mammalian host with the parasite and promotes the establishment of infection. Animal models demonstrate that sand flies with the highest parasite loads and percent metacyclic promastigotes transmit more parasites with greater frequency, resulting in higher load infections that are more likely to be both symptomatic and efficient reservoirs. The existence of mammalian and sand fly “super-spreaders” provides a biological basis for the spatial and temporal clustering of clinical leishmanial disease. Sand fly blood-feeding behavior will determine the efficacies of indoor residual spraying, topical insecticides, and bed nets. Interventions need to have sufficient coverage to include transmission hot spots, especially in the absence of field tools to assess infectiousness. Interventions that reduce sand fly densities in the absence of elimination could have negative consequences, for example, by interfering with partial immunity conferred by exposure to sand fly saliva. A deeper understanding of both sand fly and host biology and behavior is essential to ensuring effectiveness of vector interventions.
Author summary
We review recent research that sheds light on the quantitative biology of leishmanial transmission between sand flies and mammalian hosts and use these insights to better understand transmission, the observed epidemiology of the disease, and their implications in choice of control strategy. Using animal models, we show how the parasite-induced processes manipulate sand fly blood-feeding behavior and the infectious metacyclic dose to promote host infection and to...