Abstract
BackgroundVectorial capacity and the basic reproductive number (R0) have been instrumental in structuring thinking about vector-borne pathogen transmission and how best to prevent the diseases they cause. One of the more important simplifying assumptions of these models is age-independent vector mortality. A growing body of evidence indicates that insect vectors exhibit age-dependent mortality, which can have strong and varied affects on pathogen transmission dynamics and strategies for disease prevention.Methodology/Principal FindingsBased on survival analysis we derived new equations for vectorial capacity and R0 that are valid for any pattern of age-dependent (or age–independent) vector mortality and explore the behavior of the models across various mortality patterns. The framework we present (1) lays the groundwork for an extension and refinement of the vectorial capacity paradigm by introducing an age-structured extension to the model, (2) encourages further research on the actuarial dynamics of vectors in particular and the relationship of vector mortality to pathogen transmission in general, and (3) provides a detailed quantitative basis for understanding the relative impact of reductions in vector longevity compared to other vector-borne disease prevention strategies.Conclusions/SignificanceAccounting for age-dependent vector mortality in estimates of vectorial capacity and R0 was most important when (1) vector densities are relatively low and the pattern of mortality can determine whether pathogen transmission will persist; i.e., determines whether R0 is above or below 1, (2) vector population growth rate is relatively low and there are complex interactions between birth and death that differ fundamentally from birth-death relationships with age-independent mortality, and (3) the vector exhibits complex patterns of age-dependent mortality and R0∼1. A limiting factor in the construction and evaluation of new age-dependent mortality models is the paucity of data characterizing vector mortality patterns, particularly for free ranging vectors in the field.
Highlights
The basic reproductive number (R0) and vectorial capacity are integral parts of the language, science, and control of vector-borne disease [1]
In order to better understand how variation in one of the most sensitive components of a vector’s role in pathogen transmission effect transmission dynamics and estimation of R0, we explored the consequences of a shift from age-independent to more biologically realistic age-dependent vector mortality
The new mathematical models derived and investigated in this paper extend the theoretical and empirical understanding of agedependent vector mortality in ways that can add to the conceptual basis of vector-borne disease prevention
Summary
The basic reproductive number (R0) and vectorial capacity are integral parts of the language, science, and control of vector-borne disease [1]. In distinction to previous works [8,9] we consider a set of models for vector mortality, which reflect different change of mortality with age. Vectorial capacity and the basic reproductive number (R0) have been instrumental in structuring thinking about vector-borne pathogen transmission and how best to prevent the diseases they cause. A growing body of evidence indicates that insect vectors exhibit age-dependent mortality, which can have strong and varied affects on pathogen transmission dynamics and strategies for disease prevention
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