Zoonotic Alert: Tracking Streptococcus suis Infections Across South America (1995-2024)

Streptococcus suis is a pig-associated bacterium capable of infecting humans and causing serious illness, including meningitis, sepsis, and streptococcal toxic shock-like syndrome (STSLS). Human infections generally occur among people who come into contact with pigs or pork products or who eat raw pork or barbecued pig blood dishes. 

The bacterium is phenotypically and genetically heterogeneous, with 29 recognized serotypes based on capsular polysaccharide composition, and more than 2,900 sequence types (STs) identified by multilocus sequence typing (MLST). It typically shows resistance to macrolides, lincosamides, and tetracyclines, with emerging resistance to β-lactams also being reported. 

Although serotype 2 is responsible for most human infections, other serotypes such as 1, 4, 5, 7, 9, 14, 16, 21, 24, and 31 have also been implicated. Most human cases of Streptococcus suis (S. suis) cases have been reported in East and Southeast Asia. In contrast, human infection with S. suis in Europe are less common, where it is recognized as an occupational hazard. Sporadic cases have also been reported in Hawaii, Australia, Togo, and Madagascar. Fewer than 10 cases of human S. suis infection have been reported in the continental U.S. and Canada, despite the presence of large-scale swine production farms. 

Researchers conducted comprehensive literature review across multiple databases and languages to identify reported human S. suis infections in South America. They identified 39 confirmed cases between 1995 and 2024. They also reported 8 new previously unreported cases from Argentina, confirmed by national laboratory surveillance and microbiological testing. 

For each new case, clinical and bacterial data were collected; PCR and mass spectrometry were used for confirmation. Whole-genome sequencing was also performed to examine the genetics, resistance traits, and relatedness of the bacteria. Phylogenetic analysis was used to explore the evolutionary relationships among the strains. This research study documented a total of 47 confirmed human S. suis cases in South America. 

Between 1995 and 2024, a total of 47 human cases of S. suis infection were identified in South America. Argentina accounted for the highest number of cases (29), including 21 previously reported, and eight new cases (2017-2023). Most of the cases were men from rural areas of Argentina with occupational exposure to pigs or their products, and nearly all presented with meningitis. Two deaths were recorded, one from the earlier group and one among the recent group. Infections were frequently associated with virulent strains such as ST1 of serotype 2. 

Brazil reported 5 cases involving occupational exposure and eating raw or undercooked pork. Hearing loss was a common complication. Chile confirmed 7 infections, all linked to pig exposure, including one case with a permanent loss of hearing. An additional potential case was inferred from genomic data. 

French Guiana reported one case linked to pig slaughter, resulting in hearing loss. Uruguay had five meningitis cases in rural pig handlers. Although serotyping was not performed and some patients experienced lasting neurological complications. 

This study demonstrates that human S. suis infections in South America, particularly in Argentina, are most frequently reported in regions with extensive small-scale and/or mixed pig farming systems where close contact with pigs is common and biosafety measures are limited, covering small-scale farming in rural or sparsely populated regions with extensive biosecurity measures shown in multi-species farming contexts with close animal contact. Argentina likely records the highest number of human S. suis cases due to both the prevalence of virulent strains in pigs and the country’s robust surveillance system.  

To curb the transmission of S. suis, the study emphasizes the need for improved farm-level biosafety practices, improved disease monitoring across the South America, and stronger regional and international collaboration. Argentina’s surveillance approach may serve as a model framework for neighboring countries. 

References: Bakpatina-Batako M, Li K, Lacouture S, et al. Human Streptococcus suis Infections, South America, 1995–2024. Emerging Infectious Diseases. 2025;31(7):1277-1286. doi:10.3201/eid3107.241835