The influence of social behaviour on competition between virulent pathogen strains

Abstract

Infectious disease interventions like contact precautions and vaccination have proven effective in disease control and elimination. The priority given to interventions can depend strongly on how virulent the pathogen is, and interventions may also depend partly for their success on social processes that respond adaptively to disease dynamics. However, mathematical models of competition between pathogen strains with differing natural history profiles typically assume that human behaviour is fixed. Here, our objective is to model the influence of social behaviour on the competition between pathogen strains with differing virulence. We couple a compartmental Susceptible-Infectious-Recovered model for a resident pathogen strain and a mutant strain with higher virulence, with a differential equation of a population where individuals learn to adopt protective behaviour from others according to the prevalence of infection of the two strains and the perceived severity of the respective strains in the population. We perform invasion analysis, time series analysis and phase plane analysis to show that perceived severities of pathogen strains and the efficacy of infection control against them can greatly impact the invasion of more virulent strain. We demonstrate that adaptive social behaviour enables invasion of the mutant strain under plausible epidemiological scenarios, even when the mutant strain has a lower basic reproductive number than the resident strain. Surprisingly, in some situations, increasing the perceived severity of the resident strain can facilitate invasion of the more virulent mutant strain. Our results demonstrate that for certain applications, it may be necessary to include adaptive social behaviour in models of the emergence of virulent pathogens, so that the models can better assist public health efforts to control infectious diseases.

Prophylactic host behaviour discourages pathogen exploitation

“…More closely related to the current study are the conclusions of Pharaon and Bauch [16]. They show that host prophylactic behaviour in response to an endemic disease can allow the invasion of a pathogen strain that is more virulent than the resident.…”

“…Equations (2c) and (2d) capture dynamic features of the protector population that previous work has ignored. Modelling undertaken by Pharaon and Bauch [16] accounts for social learning but neglects changes due to demographics (births) and infection. Our equations, therefore, combine multiple processes to establish a more realistic model of changing host behaviour.…”

“…Individuals do not always adhere to beneficial measures such as taking medications [18], exercise regimes [19], or dietary restrictions [20], so we include group switching in our model to account for these types of effects. Following [16], we use the replicator dynamic [21] to model the total rate at which individuals move from one group to another. We assume that the decision to switch groups is driven by utility, as discussed in [22].…”

“…Ultimately, the replicator-dynamics model of switching gives us and where k is a constant that reflects the rate of social learning. We note that our model of switching makes the simplification (made elsewhere [16]) of assuming individuals have up-to-date information about the global state of the population. Our final model of disease dynamics can now be stated as, …”

“…Unfortunately, little is known about how hosts’ behavioural immune system impacts the evolution of pathogens. What work has been done in this area predicts that prophylactic behaviour exhibited by hosts can select for higher pathogen virulence [16]. This work, however, considers short-term evolutionary outcomes only, and does not completely link host behavioural changes with host demographics and disease dynamics.…”