Streptococcus suis serotype 9 endocarditis and subsequent severe meningitis in a growing pig despite specific bactericidal humoral immunity

Abstract

Introduction. Meningitis and endocarditis are common pathologies of Streptococcus suis infections in pigs and humans. S. suis serotype 9 strains contribute substantially to health problems in European pig production, and immune prophylaxis against this serotype is very difficult. Case presentation. We report the clinical course and histopathological picture of a 10-week-old growing pig following experimental intravenous infection with S. suis serotype 9. The piglet showed rapid onset of severe clinical signs of meningitis 11 days post-intravenous challenge following prime-booster vaccination. Histopathological findings revealed a diffuse fibrinosuppurative leptomeningitis. Additionally, a polyphasic endocarditis valvularis thromboticans with numerous bacterial colonies was diagnosed. Bacteriological culture of the brain and the mitral valve confirmed association with the challenge strain. However, virulent serotype 2 and 9 strains were killed in the blood of this piglet ex vivo prior experimental infection. Conclusion. Endocarditis induced by S. suis infection might develop and persist despite the presence of high specific bactericidal activity in the blood. Severe leptomeningitis is a putative sequela of such an endocarditis.