Growing airline networks in Asia.

(A) Number of nodes (countries belonging to the Asian air transport network), the number of airlines, and total passenger flow in the Asian air transport network between 1982–2012. Records are not available for the period 1983–1991, so dashed lines represented imputed missing values obtained by linear interpolation. (B) Passenger flux in Asia in 1982, 2000 and 2012. The size of each node corresponds to the degree centrality of the country in the airline network. Color coded lines represent the volume of air passenger flux. Node colors correspond to the countries indicated on the right-hand side of the figure. Black points indicate countries for which no virus sequence was included in the genetic analyses. China shares one of the busiest Asian flight routes with Japan, which is indicated by an asterisk.