STRUCTURED EPIDEMIC MODELS AND THE SPREAD OF INFLUENZA IN THE CENTRALCANADIAN SUB-ARCTIC

Patterns of transmission of infectious diseases within and among popul ations are strongly affected by population structure, which can either facilitate or limit interactions among people from different groups, Results from several theoretical studies show that nonrandom mixing am ong subgroups can affect the time when an infectious disease is introd uced to the population, the speed of propagation of the disease, and t he severity of an epidemic, Because many of these models focus on the effects of population structure, they are functionally similar to mode ls used to describe the genetic structure of a population, One major d ifference between genetic models and epidemic models is that genetic m odels, with a time scale of the order of generations, incorporate migr ations (or permanent movement) among subgroups, whereas epidemic model s, with a time scale of the order of days or weeks, must incorporate s hort-term mobility among subgroups, Such mobility can be included in m odels for epidemic spread by explicitly incorporating the process by w hich residents from different locations interact with one another. We present a derivation of a mobility model for epidemic processes and ap ply it to the spread of the 1918-1919 influenza epidemic among the Cre e and Metis people associated with three Hudson's Bay Company posts in the central Canadian Subarctic. The model distinguishes mobility from population effects. Results indicate that social organization (popula tion effects) and social responses to the epidemic were more important than movement patterns (mobility) in explaining the differential impa ct of this virgin soil epidemic on the three study communities.