Note that equation (11) arises from the fact that w~N (vm) = (N (v) zN (vm) ). To represent daily commuting, with an infectious period of 5 days, we set x 2~5 , and choose w to give the required average number of commuters vcw. To seed a wildtype infection in the village we set I (v) 1~1 . In the village-city model, an emergence event is defined as having 100 infectious hosts with the fully adapted strain in the city.