Infodoc : Sciences, Techniques et Culture

Exchanges among agents, typically individuals or companies, fulfil various needs such as reproduction and economic profit, but can also support infectious disease transmission, impacting biological populations and potentially altering the disease-conducive exchanges. Epidemiological models increasingly account for reductions in infectious contact, such as risk-aversion behaviour in response to pathogen outbreaks. However, behavioural responses in exchange dynamics are not limited to risk-aversion; they are driven by different motivation and are constrained because resources are limited and exchanges are costly. Adaptive behaviour refers to change in agent behaviour, and potentially in exposure to risk, in response to disruption such as disease outbreak; the change may be through a[...]

Exchanges among agents, typically individuals or companies, fulfil various needs such as reproduction and economic profit, but can also support infectious disease transmission, impacting biological populations and potentially altering the disease-conducive exchanges. Epidemiological models increasingly account for reductions in infectious contact, such as risk-aversion behaviour in response to pathogen outbreaks. However, behavioural responses in exchange dynamics are not limited to risk-aversion; they are driven by different motivation and are constrained because resources are limited and exchanges are costly. Adaptive behaviour refers to change in agent behaviour, and potentially in exposure to risk, in response to disruption such as disease outbreak; the change may be through adaptation of social or economic mechanisms. Interaction constraints limit in different ways the capacity of agents to interact. They can limit the interaction of a given agent with everybody else (sparseness constraint), the rate and direction of exchanges (weighting and directional constraints), or the rate of encounter between agents (frictional constraint). While the sparseness constraint has been exhaustively studied, the epidemiological consequences of the three other constraints are poorly understood. Here, we use a combination of empirical analyses and mathematical modelling approaches to explore the influence of interaction constraints and adaptive behaviour on the combined dynamics of exchanges and infection. We can hence suggest relevant policies to prevent and mitigate exchange-driven epidemics. The examples investigated are sexually transmitted infection dynamics in sexual-contact networks, and epidemics in markets of animal livestock or ornamental plants. First, we show that differing patterns in agent contact structures and in epidemic dynamics arise when the networks are subject to combinations of interaction constraints. We identify analytical conditions when weighting and directional constraints limit the occurrence and severity of epidemic outbreaks, and translate these threshold conditions into disease-control strategies. These results hold in the case when agents are passive. Second, we account for adaptive behaviour encountered in markets that propagate infections and propose that the joint dynamics of markets and disease spread are limited by trade friction. This specific constraint creates a trade-off between the frequency and intensity of market transactions that can influence epidemics more strongly than risk-aversion. We finally suggest policy for limiting disease contagion in markets and minimise its adverse impact on trade. Our work demonstrates that the integration of differing standpoints at the crossroad of natural and social sciences is important in tackling the challenges posed by the emergence of exchange-driven epidemics. We believe our general approach can be transposed to other systems where agents exhibit adaptive behaviour and face interaction constraints, e.g. in ecology or in economics.