Studies on the pathogenesis of the infections caused by Streptococcus suis

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The reduction in livestock antimicrobial use and lack of vaccines led to the re-emergence of bacterial pathogens responsible for significant economic loss in the swine industry. Among them is Streptococcus suis, which causes serious systemic diseases in weened piglets in North America (NA) and is considered as one of the bacterial species of highest priority in the swine industry based on the need for intervention tools and the reduction of antimicrobial use. A total of 29 serotypes have been described, and serotype 2 is considered by far the most important, especially in Eurasia (EA). However, the situation in NA seems to be different and, in addition to serotype 2, other serotypes (e.g., serotype 1/2) are also predominant, although their virulence factors are unknown. Moreover, S. suis serorype 2 NA strains phenotypically/genotypically different from EA strains: they originate from different ancestors, possess different virulence potential and probably induce disease through different pathogenicity mechanisms. Indeed, almost all published studies on this serotype have been carried out on EA strains. Also, the presence of virulent strains does not always guarantee the development of disease, and co-factors are significant contributors. For example, the presence of mycotoxins in feed (such as deoxynivalenol) may affect intestinal epithelial cell permeability and/or the innate immune response of animals, increasing their susceptibility to S. suis infection. The long-term objective of this program is to expand fundamental knowledge on the pathogenesis of S. suis infections, including co-factors contributing to the disease. Our general hypothesis for this proposal is that virulence factors of NA strains differ from those of EA strains and, in addition, co-factors at the farm significantly contribute to the development of disease. Building on our expertise, the two main objectives over the next five years are to: 1) identify and characterize undescribed and conserved virulence factors of NA S. suis strains; 2) evaluate the role of mycotoxins (more specifically deoxynivalenol) as a co-factor in the development of S. suis-associated diseases. Different molecular methods and in-vitro/in vivo studies will help elucidate specific factors involved in the virulence and pathogenesis of the infection caused by NA strains. The effect of mycotoxins (and the mechanisms involved) at the intestinal and systemic levels will also be evaluated in vitro and in vivo. This program will provide new insights into the specific characteristics of NA strains of S. suis, revealing new virulence factors and mechanisms of pathogenicity. Results obtained with mycotoxins may further uncover important co-factors leading to the development of disease. The future development of a vaccine against this major pathogen and other strategies to mitigate risks of disease development are of utmost significance to the swine industry as it aims to reduce antimicrobial use.