Streptococcus suis in Asia: epidemiology, transmission and zoonotic risk at the animal-human interface.

Streptococcus suis is a swine-associated bacterial pathogen of zoonotic relevance in Asia, where its epidemiology reflects the intersection of widespread porcine carriage, diverse production systems and human exposure pathways. Across Asian swine populations, S. suis circulates endemically, with asymptomatic carriage established early in life and maintained through to slaughter, providing a persistent reservoir for both animal disease and zoonotic spillover. Reported detection frequencies and serotype composition of S. suis varied widely across countries and studies. While serotype 2 remained most consistently associated with invasive disease and human infection, non-serotype 2 and non-typeable strains still contributed substantial genetic and antimicrobial resistance diversity. The distribution of classical virulence determinants similarly reflected overlapping reservoirs of highly virulent and carriage-associated lineages rather than a strict pathogenic-commensal divide. Antimicrobial susceptibility patterns across Asia suggested sustained selective pressure from veterinary antimicrobial use, with widespread resistance to several commonly used classes. This was contrasted by generally preserved activity of selected β-lactams and critically important agents, with notable context-dependent exceptions. In humans, S. suis infection in Asia was observed to be predominantly foodborne or occupational, embedded within slaughter, handling and consumption practices rather than arising from rare or accidental exposure. Control experiences across Asian regions demonstrated that improved diagnostic recognition and surveillance can rapidly redefine disease burden. However, long-term risk reduction remains constrained by informal production systems, entrenched sociocultural practices and uneven regulatory implementation. In conclusion, the Asian S. suis landscape is characterised by endemic circulation in pigs, substantial regional and strain-level heterogeneity and persistent zoonotic risk linked to food and occupational exposure. Thus, S. suis exemplifies a One Health pathogen and effective control depends on a sustained, integrated approach across animal health, food systems and human clinical care.