Interactions among multiple infectious agents are increasingly recognized as a fundamental issue in the understanding of global epidemics and at the basis of pathogens emergence and evolution. At the theoretical level, the modeling of cooperative and competitive contagion poses many interesting challenges and shows the presence of several interesting phenomena, not seen in single disease spreading.
In this talk, I'll introduce a framework based on multilayer networks that allows describing the spreading dynamics of two concurrent diseases. The model provides an analytical characterization of the epidemic thresholds of the two diseases for the general scenario of both cooperative and competing interactions. Moreover, I'll show, that under certain circumstances, finite and not vanishing epidemic thresholds are found even at the thermodynamic limit for scale-free networks. Finally, for the case of the same transmission network for both diseases, I'll also present some novel results on the nature of the epidemic transition.