Trends in the Emergence of Swine Pathogens

Introduction: From 1985 to 2010, global pork production increased by more than 80%. These changes to production scale have been accompanied by modifications to production systems. The transformations experienced by the industry raise concerns regarding the risk of emergence of new pathogens, which could drastically impact not only on pig health and welfare, but also on human health. The aim of this study was to assess the diversity of new swine pathogens that have been detected since 1985, and the spatio-temporal trend of these emergences. Methods: A systematic literature review was conducted to identify emerging pathogens. An emerging pathogen was defined as an infectious agent newly found to infect domestic swine under natural transmission conditions since 1985. A pathogen species was considered as emerging if at least one of its variants was classified as emerging. Results: A total of 186 new swine pathogen variants have been identified since 1985. These variants belonged to 98 emerging pathogen species, of which 77 were newly found to infect pigs. Although most new variants were bacteria, about half of the newly identified pathogen species were viruses, and the rate of detection of new virus species doubled during the previous decade (2000 to 2010). The emerging variants originated in 35 countries, with 63% being reported by 7 countries. These countries were also the largest pork producers worldwide. A substantial proportion (43%) of emerging swine pathogen species was zoonotic. Moreover, the pathogen species that have been recently discovered in high-income countries were more likely to be swine-specific than those recently discovered in low and middle-income countries, and also more likely to have been detected during outbreak investigations. Finally, the number of emerging drug-resistant variants increased over time. Conclusion: This review highlights the diversity of emerging swine pathogens. Whilst new specialist pathogen species, associated with higher virulence, were mainly discovered in industrial production settings, new generalist pathogen species, including zoonotic pathogens, were mainly detected in settings with less segregation between animal species and humans. While this trend is influenced by factors conditioning pathogen detection, it may also suggest that different scales and types of production systems may promote emergence of some pathogen types more than others. Considering the recent transformations undergone by the global swine industry, concerted efforts are needed towards improving risk-based surveillance and risk mitigation of emerging pathogens.