Global trends in infectious diseases of swine

Abstract

Pork accounts for more than one-third of meat produced worldwide and is an important component of global food security, agricultural economies, and trade. Infectious diseases are among the primary constraints to swine production, and the globalization of the swine industry has contributed to the emergence and spread of pathogens. Despite the importance of infectious diseases to animal health and the stability and productivity of the global swine industry, pathogens of swine have never been reviewed at a global scale. Here, we build a holistic global picture of research on swine pathogens to enhance preparedness and understand patterns of emergence and spread. By conducting a scoping review of more than 57,000 publications across 50 years, we identify priority pathogens globally and regionally, and characterize geographic and temporal trends in research priorities. Of the 40 identified pathogens, publication rates for eight pathogens increased faster than overall trends, suggesting that these pathogens may be emerging or constitute an increasing threat. We also compared regional patterns of pathogen prioritization in the context of policy differences, history of outbreaks, and differing swine health challenges faced in regions where swine production has become more industrialized. We documented a general increasing trend in importance of zoonotic pathogens and show that structural changes in the industry related to intensive swine production shift pathogen prioritization. Multinational collaboration networks were strongly shaped by region, colonial ties, and pig trade networks. This review represents the most comprehensive overview of research on swine infectious diseases to date.

Keywords: agricultural practices; emerging pathogens; global health; infectious diseases; livestock.

Fig. 1.

Most important pathogens of swine by region during 2006–2016, ranked in descending order by publication number. Asterisk indicates pathogens appearing on each regions list and thus excluded from regional lists.

Fig. 2.

Changes in publication count per year over time overall (A), and for FMD (B), influenza (C), and pseudorabies (D). Red lines represent count per year. Hashed lines and shading represent the fitted regression line (+SE) of a GLM with a negative binomial link function. A changepoint analysis was performed to estimate the year in which the slope changed and the slope before and after this changepoint. Horizontal line segments indicate the year of a slope changepoint. The blue line represents the expected trend based on overall publication counts (A), which was used to assess whether publication rates for specific pathogens were growing faster or slower than the general trend for swine diseases.

Fig. 3.

Publication counts according to geographic region for PED (A), pseudorabies (B), and P. multocida (C).

Fig. 4.

Proportion of publications in the past 10 y that focused on helminths/protozoa (A), bacteria (B), and diseases affecting production (C). Proportions were calculated for each country and then summarized by region. Colors represent regions with primarily developed (purple) and developing economies (green). Regions are listed in order of the percentage of the human population that is urban, which was used as a proxy for the extent of agricultural industrialization. Proportion of publications by viruses, zoonotic, and reportable pathogens are represented in SI Appendix, Fig. S3.

Fig. 5.

Multinational collaboration network. Links between countries were weighted according to an index of the frequency with which scientists from those two countries coauthored papers. Clusters represent communities of countries (indicated by color) that tended to coauthor papers with one another more often than with countries outside their cluster.