Identification of Streptococcus suis carriage in healthy pigs in Chiang Mai, Thailand

Abstract

Streptococcus suis (S. suis) belongs to the critical streptococcal swine pathogens affecting financial losses in pig production globally and being concerned as a zoonotic bacterial that causes a severe invasive disease emerging in pigs and humans. Serotype 2 is considered the major serotype and is the most pathogenic S. suis obtained from human cases, and the healthy pigs are known as the major reservoir of S. suis. In this cross-sectional study, S. suis prevalence was conducted in live pigs from 111 farms across Chiang Mai, Thailand. S. suis carriage rate and serotypes were determined from the bacteriological and multiplex PCR method from tonsil swab samples. We found that 18.2% (138/760) of tonsil swab samples and 54.1% (60/111) of pig farms were positive to S. suis, and only one (0.72%) from 138 isolates was identified as serotype 9. Meanwhile, all the remains were identified as non-serotype ½/1/2/7/9/14 strains. In addition, there was an independent relation between age-ranged, farm types, and production systems with S. suis-positive rates at the farm level. The results indicate that both intensive and smallholder production systems can generally be the source of S. suis carriage. Therefore, implementing good husbandry practices and S. suis-infection predisposing factors limiting that appropriate for each farm type is essential to minimize the opportunities of S. suis outbreak in humans.