Man Bites Mosquito: Understanding the Contribution of Human Movement to Vector-Borne Disease Dynamics

Ben Adams,Durrell D Kapan,Alison P Galvani

doi:10.1371/journal.pone.0006763

Abstract

In metropolitan areas people travel frequently and extensively but often in highly structured commuting patterns. We investigate the role of this type of human movement in the epidemiology of vector-borne pathogens such as dengue. Analysis is based on a metapopulation model where mobile humans connect static mosquito subpopulations. We find that, due to frequency dependent biting, infection incidence in the human and mosquito populations is almost independent of the duration of contact. If the mosquito population is not uniformly distributed between patches the transmission potential of the pathogen at the metapopulation level, as summarized by the basic reproductive number, is determined by the size of the largest subpopulation and reduced by stronger connectivity. Global extinction of the pathogen is less likely when increased human movement enhances the rescue effect but, in contrast to classical theory, it is not minimized at an intermediate level of connectivity. We conclude that hubs and reservoirs of infection can be places people visit frequently but briefly and the relative importance of human and mosquito populations in maintaining the pathogen depends on the distribution of the mosquito population and the variability in human travel patterns. These results offer an insight in to the paradoxical observation of resurgent urban vector-borne disease despite increased investment in vector control and suggest that successful public health intervention may require a dual approach. Prospective studies can be used to identify areas with large mosquito populations that are also visited by a large fraction of the human population. Retrospective studies can be used to map recent movements of infected people, pinpointing the mosquito subpopulation from which they acquired the infection and others to which they may have transmitted it.

Highlights

Our understanding of diseases such as malaria, yellow fever, onchocerciasis and filiarisis was profoundly affected when the medical scientists of the late 1800s revealed the role of insects as intermediate hosts known as vectors – carriers of disease from one primary host to another [1]
We shift focus from the vector to the host and develop a mathematical model to investigate the impact of human movement and mosquito patchiness on the dynamics and persistence of vector-borne disease at the city scale
Key issues for disease control in cities where successful vector control strategies have led to an overall rarity of mosquitoes include identifying reservoirs for the virus and understanding how it circulates in the urban environment

Summary

Introduction

Our understanding of diseases such as malaria, yellow fever, onchocerciasis and filiarisis was profoundly affected when the medical scientists of the late 1800s revealed the role of insects as intermediate hosts known as vectors – carriers of disease from one primary host to another [1]. Researchers interested in controlling these and other vector-borne diseases have rightly focused on the insect vector as the critical link between infected and susceptible hosts. Vector-borne diseases remain a significant problem, even in highly modernized industrial cities. We shift focus from the vector to the host and develop a mathematical model to investigate the impact of human movement and mosquito patchiness on the dynamics and persistence of vector-borne disease at the city scale. Key issues for disease control in cities where successful vector control strategies have led to an overall rarity of mosquitoes include identifying reservoirs for the virus and understanding how it circulates in the urban environment. Data from Puerto Rico show that human cases are clustered at the scale of households, where domestic mosquitoes are responsible for transmission, but not at the scale of city blocks [5]. Beyond individual households, persistent sources of infection and the routes by which it is spread remain unclear

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