Furthermore, we identified several statistically significant relationships between indicators of human activity and the relative risk for HPAI in chicken and duck populations. Human population density was the only anthropogenic risk factor thus far identified in previous research in Thailand. On the contrary to Tiensin et al. [24] , but in accordance with Gilbert et al. [8, 9] , our study found a progressive increase of HPAI risk with an increase of human population density for both chickens and ducks. In addition, we showed that areas located within a short distance radius around major cities and highway junctions constitute ''hot spots'' for HPAI risk. Cities are characterised by highly intense poultry trade activities involving live poultry markets, food markets, slaughterhouses, and poultry plants. This intensity may have resulted in increased possibilities of virus introduction and spread in surrounding areas. If the HPAI virus was transported through the road networks, the subdistricts located a short distance from the highway junction were more likely to be in contact with the virus than those situated further away. Highway junctions thus may have functioned as ''dissemination nodes'' for the HPAI H5N1 virus. A significant association was identified between a high HPAI risk and proximity to the closest highway. This may underline the role of the movement of poultry and poultry products during the second wave of the epidemic, not only in the long-distance spread of the HPAI virus, but also in the short distance dissemination in the areas surrounding the highways. Free-grazing ducks that are moved along the central plain for hundreds of kilometers and are known to be reservoirs of HPAI may have contributed to the spread of the disease [8, 20] . Other types of poultry also were moved from farms to slaughterhouses, markets, or fighting arenas, while farm inputs and poultry products such as eggs, meat, litter, and poultry manure were transported along collection circuits. The movement of live poultry, people, and infected material may have resulted in the spread of the virus between houses through direct or indirect transmission. Subdistricts with a high road density were associated with an increased risk of HPAI H5N1. Local poultry product and by-product business activities involve frequent contacts which revolve around road networks. Once the HPAI virus was introduced into a subdistrict, a dense road network may have facilitated its local spread.