Swine influenza (SI) can result in a significant economic loss for the pig industry and potentially lead to pandemic influenza in humans. Although SI is prevalent in south China, the epidemiological characteristics of its occurrence in this area were not known prior to the study described in this thesis. This study was mainly conducted in Guangdong Province to: estimate the prevalence of SI; identify risk factors for SI infection in pig farms; assess the knowledge, beliefs and practices (KBP) of pig industry workers towards SI; describe the movement network of live pigs via the wholesale live pig markets; identify anthropogenic, meteorological and geographical factors associated with swine, human and avian influenza viral infection in pigs in south China; and provide evidence of the benefit of risk-based surveillance to address the pandemic influenza threat in south China.
A cross-sectional survey was conducted in 153 commercial pig farms in Guangdong Province. The farm-level prevalence of farmer-perceived SI during a six-month period was estimated to be 58% (95% CI: 48 - 68%). Statistically significant risk factors for SI were the presence of poultry on the farm (OR=3.24, 95% CI: 1.52-6.94), the ability of wild birds to enter the piggery (OR=2.50, 95% CI: 1.01-6.16) and failure to implement effective disinfection measures before workers entered the piggery (OR=2.65, 95% CI: 1.04-6.78).
A KBP study on local pig industry workers comprising 153 pig farmers, 21 pig traders and 16 pig trade workers revealed that only 33.7% of those surveyed believed that SI could infect humans, and many undertook practices that were unsafe for SI. The lack of awareness about the zoonotic risk of SI (OR = 3.19, 95%CI: 1.67 - 6.21) was associated with not using personal protective equipment when having contact with pigs.
Social network analysis on the movement of live pigs through four local wholesale live pig markets indicated that the source counties with the highest risk of having SI via the market trading system were in the central, northern and western regions of Guangdong Province. Risk-based control strategies were shown to result in a greater reduction of the magnitude of a potential epidemic of SI compared to a non-targeted control strategy.
Analysis of three year’s sero-surveillance data on SI highlighted that pig farms from south China had exposure to multiple strains of influenza A, including human and avian strains. Spatial modelling identified determinants, such as elevation above sea level, chicken density and the human population density, as important predictors for avian and human influenza infection in pigs within counties. The counties in the delta area of the Pearl River in Guangdong Province and those surrounding Poyang Lake in Jiangxi province had a higher risk of infection with avian or human influenza strains in pigs than other counties in Guangdong, Guangxi, Jiangxi and Fujian provinces.
It is concluded that SI is endemic in south China and, although there is the potential for the emergence of pandemic strains of porcine origin, improved on-farm biosecurity and changes to husbandry and trade practices could minimise the likelihood of a pandemic occurring
