Assessing reappearance factors of H7N9 avian influenza in China

H7N9, a kind of subgroup of influenza viruses, has lasted for over three years in China. Although it has not yet aroused large-scale outbreak in human, it reappeared and peaked every winter. According to the obtained information and literatures, possible reasons to induce recurrence of human cases every winter can be speculated as migration of birds, temperature cycling, or reopening of live poultry trading markets. However, which one is the major driving factor is unclear. As a result, a dynamical model about migrant birds, resident birds and domestic poultry, considering temperature-dependent decay rate of virus and periodical closure of trading markets, is established to determine internal critical driving factors, and to propose the most effective prevention measure by sensitivity analysis. By numerical analysis, it is concluded that temperature cycling may be the main driving mechanism of the periodicity of infected human cases. Closing trading markets is not the main factor, but it is the most effective measure to control the epidemic to be at a low level. Consequently, periodically closing trading markets is proposed to prevent and control the spread of epidemic.