Interplay between competitive and cooperative interactions in a three-player pathogen system

TL;DR

This study explores how simultaneous cooperation and competition among pathogens influence disease dynamics, revealing complex interactions and coexistence mechanisms through combined analytical and simulation approaches.

Contribution

It introduces a model integrating both cooperation and competition among pathogens, analyzing their combined effects on epidemiology with stability analysis and network simulations.

Findings

Cooperative interactions can lead to non-trivial dominance patterns.

Community structure enables coexistence of strains through ecological niches.

Complex phase diagrams emerge from combined cooperation and competition.

Abstract

In ecological systems heterogeneous interactions between pathogens take place simultaneously. This occurs, for instance, when two pathogens cooperate, while at the same time multiple strains of these pathogens co-circulate and compete. Notable examples include the cooperation of HIV with antibiotic-resistant and susceptible strains of tuberculosis, or some respiratory infections with Streptococcus pneumoniae strains. Models focusing on competition or cooperation separately fail to describe how these concurrent interactions shape the epidemiology of such diseases. We studied this problem considering two cooperating pathogens, where one pathogen is further structured in two strains. The spreading follows a susceptible-infected-susceptible process and the strains differ in transmissibility and extent of cooperation with the other pathogen. We combined a mean-field stability analysis with stochastic simulations on networks considering both well-mixed and structured populations. We observed the emergence of a complex phase diagram, where the conditions for the less transmissible, but more cooperative strain to dominate are non-trivial, e.g. non-monotonic boundaries and bistability. Coupled with community structure, the presence of the cooperative pathogen enables the co-existence between strains by breaking the spatial symmetry and dynamically creating different ecological niches. These results shed light on ecological mechanisms that may impact the epidemiology of diseases of public health concern.