One world, one health: the threat of emerging swine diseases. A North American perspective.

The predicted expansion of global livestock populations to meet the food and fibre demands of the growing human population raises numerous concerns, including the implications for disease emergence. The evolution of animal production in developed countries has been marked by substantial reduction in farm numbers with correspondingly larger herd sizes, specialization of enterprises, concentration or ownership and vertical integration. Innovations in the structure and operations of swine production have been largely driven by efforts to improve swine health, and the impact of several important swine diseases has declined. Productivity in swine production and the safety of pork products have increased markedly. The most significant emerging infectious diseases of pigs over the last decades have been highly host-specific viruses rather than multihost pathogens. While some bacterial pathogens of pigs have increased in importance in modern systems, improved management systems and biosecurity have enabled herd sizes to increase without negative impact on swine health. The most vulnerable scenario for disease emergence in swine, particularly for zoonotic agents, may be rapid expansion and intensification of swine industries in developing countries without incorporating the stringent biosecurity measures and veterinary oversight that have helped maintain the health and productivity of large herds in North America. Factors that may influence disease emergence in the long term include regulatory measures (particularly related to antimicrobial use), genetics and feeding practices.