Abstract
Streptococcus suis is a pathogen of major economic significance to the swine industry and is increasingly recognized as an emerging zoonotic agent in Asia. In Vietnam, S. suis is the leading cause of bacterial meningitis in adult humans. Zoonotic transmission is most frequently associated with serotype 2 strains and occupational exposure to pigs or consumption of infected pork. To gain insight into the role of pigs for human consumption as a reservoir for zoonotic infection in southern Vietnam, we determined the prevalence and diversity of S. suis carriage in healthy slaughterhouse pigs. Nasopharyngeal tonsils were sampled from pigs at slaughterhouses serving six provinces in southern Vietnam and Ho Chi Minh City area from September 2006 to November 2007. Samples were screened by bacterial culture. Isolates of S. suis were serotyped and characterized by multi locus sequence typing (MLST) and pulse field gel electrophoresis (PFGE). Antibiotic susceptibility profiles and associated genetic resistance determinants, and the presence of putative virulence factors were determined. 41% (222/542) of pigs carried S. suis of one or multiple serotypes. 8% (45/542) carried S. suis serotype 2 which was the most common serotype found (45/317 strains, 14%). 80% of serotype 2 strains belonged to the MLST clonal complex 1,which was previously associated with meningitis cases in Vietnam and outbreaks of severe disease in China in 1998 and 2005. These strains clustered with representative strains isolated from patients with meningitis in PFGE analysis, and showed similar antimicrobial resistance and virulence factor profiles. Slaughterhouse pigs are a major reservoir of S. suis serotype 2 capable of causing human infection in southern Vietnam. Strict hygiene at processing facilities, and health education programs addressing food safety and proper handling of pork should be encouraged.
Highlights
Infections of Streptococcus suis constitute a major health problem in the swine industry worldwide
We studied the prevalence of S. suis in slaughterhouse pigs in southern Vietnam by systematic sampling of pig tonsils in three slaughterhouses which received pigs for slaughter from different farms in 6 provinces and HCMC area in southern Vietnam
We were interested in the prevalence of S. suis serotype 2 strains compared to other serotypes as strains carrying the serotype 2 polysaccharide capsule are responsible for the vast majority of human infections in Vietnam as well as worldwide [1,6]
Summary
Infections of Streptococcus suis constitute a major health problem in the swine industry worldwide. S. suis is an emerging zoonotic pathogen in Asia, and is increasingly recognized as a leading cause of bacterial meningitis cases and septicaemia in adult humans [1,2,3,4]. Additional serotypes reported to cause invasive disease in pigs include serotypes 1 to 9, 1/2 and 14 [1,3]. These strains are rarely found in human infection. Reported risk factors for S. suis infection in humans suggest the importance of both occupational and food-borne transmission [5,7]. Consumption of undercooked pork was identified as the most common risk factor in a retrospective cohort study in 66 patients infected with S. suis in Thailand [7]
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