Understanding Host - Multipathogen Systems : Modeling the Interaction Between Ecol ogy and Epidemiology

We present a new mathematical framework for exploring the ecological and immunological interactions between multiple infectious diseases. The mechanism underlying the ecological interaction is the modulation of susceptible numbers for one pathogen as a result of quarantining or mortality following infection with a competitor. Immunological interactions are assumed to result from immunosuppression or crossimmunity to co-circulating pathogens, both during and after infection. This model is briefl y examined to explore the consequences of these factors for the coexistence of multiple infectious diseases. We show that strong competition among pathogens reduces the region of coexistence, while substantial immunosuppression acts to facilitate pathogen community per sis tence. The dynamics of this model in the presence of seasonal changes in contact rates are presented and compared with historical case notifi cation data for measles and whooping cough. We fi nish by highlighting how such a mathematical framework may be used to systematically investigate the role played by alternative competing mechanisms in shaping the observed dynamics of multipathogen systems.