Controlling the Highly Pathogenic Avian Influenza (HPAI) caused by the H5N1 virus in the poultry population is essential regarding the socioeconomic importance of the sector and for public health reasons. The disease is now endemic in several countries. Surveillance and control of HPAI H5N1 in the backyard poultry sector is particularly challenging, as farmers have been pointed out for underreporting outbreaks and avoiding control measures. However, the organization of this marketing chain is not well known. A value chain analysis was used to describe the organization of the supply chains of backyard poultry in Thailand, and identify key agents who may represent disease spreading nodes in the network. A field study was carried out to investigate the chains supplying native chickens to Phitsanulok city (a large city located in the central plain of Thailand). Quantitative data were collected on 473 backyard chicken farms, and on the 5 wet markets of the city. Qualitative data were collected on 17 poultry collectors and slaughterhouses, using semi-structured interviews. Findings from this study document the importance of native chickens and identify how bird collectors may spread the disease. The study describes the strategies developed by actors faced to an epidemic, and discusses the social and economical factors that influence those strategies. Trading sick chickens was one of the strategies developed by poultry collectors in case of outbreaks. This practice favoured disease spread but allowed limiting financial losses given the severe economic constraints. Results from this study should help tailoring the surveillance, control and incentive system to the backyard poultry sector in Thailand and in countries with similar context. (Texte intégral)