Evaluation of methods used for detecting Streptococcus suis type 2 in tonsils, and investigation of the carrier state in pigs

Streptococcus suis type 2 was isolated from the tonsils of 143 (76 per cent) of 188 pigs from three herds by culturing on media containing a specific antiserum. Culture of frozen sections of tonsillar tissue was more sensitive than culture of swabs or deep scrapes. The specificity of an indirect fluorescent antibody test for identifying S suis type 2 in mixed cultures was conservatively estimated to be 0.89. The level of infection in one herd without a history of meningitis was lower than in two herds which had experienced repeated outbreaks. Differences between herds in the level of infection were due to differences in the number of organisms carried by pigs, more so than differences in the detectable carrier rate.