Martin, V., Zhou, X. Y., Marshall, E., Jia, B. B., Guo, F. S., FrancoDixon, M. A., DeHaan, N., Pfeiffer, D. U., Magalhaes, R. J. S., & Gilbert, M. Risk-based surveillance for avian influenza control along poultry market chains in South China: The value of social network analysis