Abstract
With escalating urbanization, the environmental, demographic, and socio-economic heterogeneity of urban landscapes poses a challenge to mathematical models for the transmission of vector-borne infections. Classical coupled vector–human models typically assume that mosquito abundance is either independent from, or proportional to, human population density, implying a decreasing force of infection, or per capita infection rate with host number. We question these assumptions by introducing an explicit dependence between host and vector densities through different recruitment functions, whose dynamical consequences we examine in a modified model formulation. Contrasting patterns in the force of infection are demonstrated, including in particular increasing trends when recruitment grows sufficiently fast with human density. Interaction of these patterns with seasonality in temperature can give rise to pronounced differences in timing, relative peak sizes, and duration of epidemics. These proposed dependencies explain empirical dengue risk patterns observed in the city of Delhi where socio-economic status has an impact on both human and mosquito densities. These observed risk trends with host density are inconsistent with current standard models. A better understanding of the connection between vector recruitment and host density is needed to address the population dynamics of mosquito-transmitted infections in urban landscapes.
Highlights
Vector-borne infections impose a major public health burden worldwide and affect livestock and wildlife, as the result of both established and recently emergent pathogens
Classical coupled vector –human models typically assume that mosquito abundance is either independent from, or proportional to, human population density, implying a decreasing force of infection, or per capita infection rate with host number. We question these assumptions by introducing an explicit dependence between host and vector densities through different recruitment functions, whose dynamical consequences we examine in a modified model formulation
Urban landscapes provide environmental settings for the persistence of urban malaria in South Asia, and the emergence, re-emergence, and establishment around the world of several infectious diseases transmitted by mosquitoes [4,5,6,7]
Summary
Vector-borne infections impose a major public health burden worldwide and affect livestock and wildlife, as the result of both established and recently emergent pathogens. We consider here a basic modification of classical models for the population dynamics of vector-borne infection and introduce an explicit dependence between host density and vector abundance through mosquitoes’ recruitment This modified system recognizes that increasing human densities are expected to generate increasing numbers of mosquito breeding sites and mosquito numbers, albeit with a likely asymptote. We argue that the condition needed for density dependence and for an increasing force of infection, namely a very small number of encounters between vectors and hosts (of less than one host per vector per week) [14], finds restricted application in urban landscapes In these environments, the abundance of breeding sites rather than host encounters is likely to act as the limiting factor determining the carrying capacity of vectors. Understanding how to include this currently missing link between host and vector abundance is critical to modelling the population dynamics of vector-borne infections in the heterogeneous landscapes of today’s urbanized world
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