S-I-R and Disease Spreading in Active Matter Models

The term active matter describes systems involving self propulsion, such as particles obeying driven diffusive or run-and-tumble dynamics. Active matter has been extensively studied in biological systems and for artificial swimmers made from active colloidal particles. Here we examine S-I-R (Susceptible-Infected-Recovered) dynamics on an active matter assembly of run-and-tumble disks. In the absence of the S-I-R dynamics, the system undergoes a motility-induced phase separation as a function of density and running time. We find that when we introduce S-I-R dynamics in which the mobility of infected particles is reduced, there can be an enhancement of motility-induced clustering followed by the disintegration of the clusters. We also find that the survival of susceptible particles to the time at which the infection is extinguished depends strongly on whether the particles are part of a cluster or not. In some cases, the formation of clusters can enhance the number of surviving susceptible particles due to the heterogeneities induced by the activity. We discuss the relevance of active matter models to epidemic modeling in systems with spatially heterogeneous transport.