Indirect transmission and the effect of seasonal pathogen inactivation on infectious disease periodicity

► A model for indirect disease transmission by a free living pathogen is presented. ► The ratio of the pathogen lifespan to the disease infectivity period is important. ► The effects of a seasonally forced pathogen inactivation rate were studied. ► A time delay exists between peak pathogen survival and peak disease incidence. ► The period of oscillation is independent of the duration of acquired immunity.