H5N1/highly pathogenic avian influenza in Cambodia : evaluating poultry movement and the extent of interaction between poultry and humans

Since 2003, highly pathogenic avian influenza (HPAI), subtype H5N1, has spread across the Asian, African and European continents at an exceptional rate. To date, H5N1 remains primarily a pandemic within poultry populations with limited onward transmission to humans. Since there have been a limited number of human cases throughout the world, epidemiologic uncertainties exist regarding the extent of contact necessary to result in successful transmission between infected poultry and humans. In this thesis I undertook two large-scale surveys to evaluate poultry movement and the extent of interaction between humans and poultry to better define the risks of sustained transmission of H5N1 in poultry and onward transmission to humans. The thesis begins with a review of current knowledge on the epidemiology of HPAI, specifically subtype H5N1, and current options for its control worldwide and specifically within Cambodia. The first half of the thesis presents the methodology and results from a large-scale cross sectional survey of 3,600 rural subjects from 115 villages in six provinces throughout Cambodia. The results from this survey are used to explore animal ownership and husbandry, poultry mortality experienced and poultry mortality reporting, and the extent and frequency of poultry handling behaviours of subjects and how they differ by age and gender. The second half of the thesis presents results from a second cross-sectional survey of 715 rural villagers, 123 rural, peri-urban and urban market sellers and 139 middlemen from six Provinces and Phnom Penh, which was conducted to evaluate poultry movement and trading practices. The results from this survey are used to construct poultry movement networks using social network analysis techniques, to identify critical points for surveillance and to understand the potential transmission and control of HPAI over this network and to identify a spatial model to predict poultry movements. Finally in the last chapter the key findings are presented and discussed in the context of HPAI transmission in the region.