Potentially hazardousStreptococcus suisstrains latent in asymptomatic pigs in a major swine production area of Thailand

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Carrier pigs have been considered as the major reservoir of Streptococcus suis and couldbe a significant source of human infection. Therefore, we investigated the prevalence and characteristics of latent S. suis in asymptomatic pigs in the pig-farming area of central Thailand, and compared the data to those previously reported in other regions.


We collected samples from 340 asymptomatic pigs. S. suis isolates from the samples were confirmed by species-specific PCR (recN PCR). The capsular polysaccharide synthesis gene (cps) types, virulence-associated gene profiles and sequence types (STs) of the isolates were investigated.

Results/Key findings.

The prevalence of S. suis found in this study was 37% (125/340 pigs). The most prevalent genotype was mrp−/epf−/sly−. Among the 16 cps-types identified in 135 isolates, cps-type 16 was the most frequent (11%), whereas 44% of the isolates were non-typable. In common with the strains causing human sepsis in Thailand, two cps-type 9 isolates and a cps-type 24 isolate from slaughtered pigs belonged to ST16 and ST221, respectively. All the isolated cps-type 2 strains were confirmed as serotype 2 by co-agglutination tests, and these belonged to ST104, the unique ST commonly found in Thai patients; however, in contrast to the endemic areas, the prevalence of serotype 2 strains was relatively low (2%) and no ST1 isolate was found.


Our results showed the population structure differences between S. suis in central Thailand and other regions; however, zoonotic S. suis is certainly latent in asymptomatic pigs in this intensive swine production area.

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