Streptococcus suis disease in Southeast Asia: microbiology and epidemiology in humans and pigs

SUMMARY Streptococcus suis is a swine pathogen causing significant economic losses and an important zoonotic agent in humans. Southeast Asia is a high-incidence region, where infection is strongly linked to consumption of raw or undercooked pork and occupational exposure to pigs or pork products. Thailand and Vietnam report the highest case numbers, with additional cases in Indonesia (Bali), Malaysia, Singapore, Lao PDR, and Cambodia. Serotype 2 predominates in both humans and pigs, followed by serotype 14, while other serotypes (1, 4, 5, 7, 9, 16, 24, and 31) are also reported in humans. In pigs, a broader serotype range is observed, including 1 or 14, 2, 4, 5, 6, 7, 8, 9, 15, 16, 18, 21, 29, 31, and nontypeable strains. Human infections involve multiple clonal complexes (CC1, CC16, CC25, CC28, CC94, CC104, CC233, CC221/234, and CC1688), several overlapping with porcine lineages. The region is also challenged by increasing antimicrobial resistance, with rising non-susceptibility to macrolides and tetracyclines and occasional reduced susceptibility to penicillin. Diagnostic limitations due to misidentification, limited molecular tools, and reliance on conventional methods further complicate surveillance. The economic burden is substantial, driven by swine losses, treatment costs, outbreaks, and severe human disease. Vaccination remains suboptimal due to limited protection against genetically and antigenically diverse strains across serotypes and CCs. An urgent One Health approach integrating animal health, food safety, and human health is needed to monitor S. suis dynamics. Control measures should target farms, slaughterhouses, and retail markets while promoting community-accepted behavioral changes to reduce transmission risk.