From Stable to Lab-Investigating Key Factors for Sudden Deaths Caused by Streptococcus suis

Area of Science:

• Veterinary Microbiology
• Animal Pathology

Background:

• Streptococcus suis is a major swine pathogen causing endemic infections.
• Factors driving the transition from asymptomatic tonsillar colonization to severe disease remain unclear.
• Sudden deaths in zoo-housed fattening pigs were investigated.

Purpose of the Study:

• To characterize Streptococcus suis strains isolated from suddenly deceased zoo pigs and healthy controls.
• To investigate potential mechanisms behind the observed septic shock and disseminated intravascular coagulopathy.
• To assess the protective capacity of pig serum against pathogenic S. suis strains.

Main Methods:

• Genotypic and phenotypic characterization of S. suis isolates.
• Sequence typing (ST) and capsular (cps) type analysis.
• In vitro assays for bacterial growth, neutrophil extracellular trap induction, and blood survival.
• Reconstituted blood assays using serum from pigs of different age groups.

Main Results:

• Invasive S. suis strains from deceased pigs belonged to cps type 2 ST28.
• A tonsillar isolate from a healthy pig was identified as ST1173.
• Bacterial growth, NET induction, or blood survival did not fully explain the mortality.
• Serum from younger pigs showed varying protection against pathogenic cps type 2 strains.

Conclusions:

• Specific S. suis strains, particularly cps type 2 ST28, were associated with fatal septic shock in zoo pigs.
• Individual pig immunity, influenced by age, plays a role in protection against S. suis.
• Sequence typing of causative strains is essential for selecting appropriate autologous vaccine candidates.