Speaker: Qixin He (Purdue University)
Title: Multi-strain disease modelling to study long-term disease diversity and strain dynamics
Abstract: Strain diversity varies significantly among diseases. Some diseases exhibit extreme long-term diversity (such as pneumococcus and malaria), while others remain single-strain despite high mutation rates (such as measles and chickenpox). The persistence of strain diversity is influenced by a complex interplay of strain innovation, pathogen life history, transmission dynamics, and immune responses. Our goal is to identify the key factors that drive, maintain, or prevent long-term diversity. We developed Multi-Strain Eco-Evo Dynamics (MultiSEED), a theoretical framework to predict the long-term strain diversity observed in common diseases by integrating an n-strain status-based SIR (Susceptible-Infected-Recovered) model with continuous-time stochastic processes at the ecological and evolutionary time scales. The numerical framework enables fast calculation of the expected number of transient and long-persisting strains when supplied with epidemiological and genetic measures. Our results show that host population size largely determines the magnitude of strain diversity, while parasite innovation rates have a minor impact. The combination of basic reproduction number (R0) and resource recruitment rates determines the strain dynamics regime: while the parameter range of flu produces a constant strain replacement regime, characteristics of strep pneumonia and malaria ensure a co-existence regime of many strains.