Cities and villages: infection hierarchies in a measles metapopulation

An important issue in the dynamics of directly transmitted microparasites i s the relationship between infection probability and host density. We use m odels and extensive spatio-temporal data for the incidence of measles to ex amine evidence for spatial heterogeneity in transmission probability, in te rms of urban-rural hierarchies in infection rate. Pre-vaccination measles d ata for England and Wales show strong evidence for urban-rural heterogeneit ies in infection rate - the proportion of urban cases rises significantly b efore major epidemics. The model shows that this effect is consistent with a higher infection rate in large cities, though small towns have epidemic c haracteristics intermediate between town and country. Surprisingly, urban a nd rural areas of the same population size have a similar propensity for lo cal extinction of infection. A spatial map of urban-rural correlations reve als complex regional patterns of synchronization of towns and cities. The h ierarchical heterogeneities in infection persist into the vaccine era; thei r implications for disease persistence and control are discussed.