Streptococcus suis

Updated 2026-07-30

Taxonomy

General Characteristics

Gram‑positive, catalase‑negative cocci that occur in pairs (diplococci) or short chains.
Facultative anaerobe; grows on standard blood agar producing α‑hemolysis (partial hemolysis) in many strains.
Identified by biochemical tests (e.g., ability to ferment glucose, lack of esculin hydrolysis) and confirmed with molecular methods such as 16S rRNA sequencing or PCR targeting species‑specific genes (e.g., gdh).

Epidemiology

Predominantly a commensal organism in the upper respiratory tract, tonsils, and gastrointestinal tract of swine.
Widely distributed in pig populations worldwide; carriage rates vary from 5 % to >30 % depending on region, age group, and management practices.
Zoonotic transmission to humans occurs primarily through close contact with infected pigs or pork products, especially in occupational settings (farm workers, slaughterhouse personnel, veterinarians).

Disease in Swine

Causes Streptococcal meningitis, septicemia, arthritis, pneumonia, and endocarditis, especially in weaned piglets and young pigs.
Clinical signs include fever, ataxia, circling, reluctance to move, joint swelling, and respiratory distress.
Economic impact derives from mortality, reduced weight gain, and treatment costs.

Zoonotic Disease in Humans

Recognized as an emerging zoonotic pathogen, particularly in Southeast Asia (China, Vietnam, Thailand) where traditional pork preparation practices increase exposure risk.
Clinical manifestations range from meningitis (most common) to sepsis, endocarditis, arthritis, and, less frequently, pneumonia or otitis.
Meningitis due to S. suis presents with typical symptoms (headache, fever, neck stiffness) and may lead to hearing loss or vestibular dysfunction in a proportion of survivors.

Diagnosis

Isolation of S. suis from sterile body fluids (blood, cerebrospinal fluid, joint fluid) using culture on blood agar; colonies are typically α‑hemolytic.
Species confirmation by MALDI‑TOF mass spectrometry, PCR assays, or sequencing of housekeeping genes.
Serotyping based on capsular polysaccharide; at least 35 serotypes have been described, with serotype 2 being the most frequently associated with disease in both pigs and humans.

Treatment

Antimicrobial therapy guided by susceptibility testing; S. suis is generally susceptible to β‑lactam antibiotics (penicillin, ampicillin, ceftriaxone).
Resistance to tetracyclines and macrolides is increasingly reported, particularly in isolates from regions with extensive antimicrobial use in swine production.

Prevention and Control

In Swine: Good herd management, biosecurity, and vaccination. Autogenous or commercial vaccines based on serotype 2 capsular polysaccharide are employed in many countries.
In Humans: Use of personal protective equipment (gloves, masks) when handling pigs or raw pork; thorough cooking of pork products; occupational health education.
Surveillance programs in endemic regions monitor human cases and pig herd status to inform public‑health interventions.

Historical Note

First identified as a pathogen of pigs in the 1930s. Human infection was first reported in the United States in 1968, with a notable outbreak among hog‑slaughter workers in the United States in 1970. Subsequent large outbreaks have occurred in China (1998, 2005, 2007) and Vietnam (2006).

Public Health Significance

Classified as a priority zoonotic agent by the World Health Organization due to its potential for severe disease, occupational exposure risk, and emerging antimicrobial resistance.

References (selected)

Fittipaldi, N., et al. “Streptococcus suis: an emerging zoonotic pathogen.” Lancet Infect Dis, 2020.
Wang, X., et al. “Epidemiology and control of Streptococcus suis infections in swine and humans.” Veterinary Microbiology, 2022.
Chen, B., et al. “Clinical features and outcomes of Streptococcus suis meningitis in adults.” Neurology, 2021.

All information presented reflects current, peer‑reviewed scientific knowledge up to 2024.

More topics to explore