Abstract
The characteristics of the host contact network over which a pathogen is transmitted affect both epidemic spread and the projected effectiveness of control strategies. Given the importance of understanding these contact networks, it is unfortunate that they are very difficult to measure directly. This challenge has led to an interest in methods to infer information about host contact networks from pathogen phylogenies, because in shaping a pathogen's opportunities for reproduction, contact networks also shape pathogen evolution. Host networks influence pathogen phylogenies both directly, through governing opportunities for evolution, and indirectly by changing the prevalence and incidence. Here, we aim to separate these two effects by comparing pathogen evolution on different host networks that share similar epidemic trajectories. This approach allows use to examine the direct effects of network structure on pathogen phylogenies, largely controlling for confounding differences arising from population dynamics. We find that networks with more heterogeneous degree distributions yield pathogen phylogenies with more variable cluster numbers, smaller mean cluster sizes, shorter mean branch lengths, and somewhat higher tree imbalance than networks with relatively homogeneous degree distributions. However, in particular for dynamic networks, we find that these direct effects are relatively modest. These findings suggest that the role of the epidemic trajectory, the dynamics of the network and the inherent variability of metrics such as cluster size must each be taken into account when trying to use pathogen phylogenies to understand characteristics about the underlying host contact network.
Highlights
The structure of human contact networks both facilitates and constrains the spread of pathogens
Research ranges from developing theoretical tools relating network structure and dynamics to the spread and control of pathogens [2,3,4,5,6,7,8,9], and in developing sampling strategies to learn more about networks [10,11,12]
The exterior branches of the three trees illustrate this qualitative dependence on the population dynamics: NBwNAwNC, and EBwEAwEC
Summary
The structure of human contact networks both facilitates and constrains the spread of pathogens. All sampling approaches used for measuring host contact networks share certain drawbacks: they access only a small portion of the population; they are sensitive to the choice of the individuals with whom the sample originates and they are not representative samples (though ideal respondent-driven sampling can give results independent of the seeding individuals [10]). They often cannot measure the dynamic aspects of contact networks, though individuals do report relationship durations in some cases [14]. Survey samples may not provide sufficient characterisation of the nature of contact networks to inform network simulation models or direct public health interventions to the optimal part of the network
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