Thus, while the spatial pattern of relative risk is known to be largely associated with an abundance of free-grazing ducks and rice-cropping intensity, we found that several indicators of human activities were also associated with HPAI risk in Thailand during the second wave of the epidemic. This suggests that in addition to the ''rice paddy-free grazing duck system'', major cities, the highway network, and local road networks may also have played key roles in the spread of HPAI in Thailand. Through the transportation of potentially infected live poultry or contaminated poultry products, highways may have contributed to both the long distance and the local spread of the HPAI H5N1 virus. Local road networks were possibly involved in short-distance spread. In addition, major cities and highway junctions may have functioned as ''dissemination nodes'' for the HPAI H5N1 virus through the intense traffic of poultry products and poultry trading activities in their surrounding areas. Moreover, our results suggest that activities related to layer and broiler ducks may have played a more significant role than previously thought, as well as to a lesser extent -layer and broiler chickens.