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 human immunodeficiency virus 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 coexistence 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.
Highlights
— how does the presence of a synergistic infection alter the coexistence between competing strains?. We addressed these questions by providing a characterization of the phase space of dynamical regimes
We considered the case in which two pathogens, A and B, follow susceptible-infected-susceptible (SIS) dynamics, and we made the simplification that they both have the same recovery rate μ
We found that the interplay between competition and cooperation leads to a complex phase diagram whose properties cannot be anticipated from previous works that considered competition and cooperation separately. We showed that it is possible for a more cooperative strain to dominate over a more transmissible one, provided that the difference in transmissibility is not too high
Summary
Tuberculosis [1], human papillomavirus (HPV) [9] and P. falciparum [10], for example, appear to be facilitated by human immunodeficiency virus (HIV), whereas Str. pneumoniae benefits from some bacterial infections, e.g. Moraxella catarrhalis, and is negatively associated with others such as Sta. aureus [11,12] Competition, cooperation and their co-occurrence may fundamentally alter pathogen persistence and diversity, calling for a deep understanding of these forces and their quantitative effects on spreading processes. We introduced a three-player model where two pathogens cooperate, and one of the two is structured in two mutually exclusive strains This mimics a common situation, where e.g. resistant and susceptible strains of Str. pneumoniae cooperate with other respiratory infections [11] and allows us to address two important ecological questions:.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
