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Eighty 3-week-old crossbred pigs were randomly assigned to six groups (13–14 pigs/group). Group 1 pigs served as uninoculated controls, group 2 pigs were inoculated intranasally (IN) with Streptococcus suis serotype 2, group 3 pigs were inoculated IN with a modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine, group 4 pigs were inoculated IN with the same vaccine and with S. suis, group 5 pigs were inoculated IN with VR-2385 (a high-virulence strain of PRRSV), and group 6 pigs were inoculated IN with VR-2385 and S. suis. Pigs exposed to both PRRSV and S. suis were inoculated with PRRSV 7 days prior to S. suis inoculation. The pigs were 26 days old when inoculated with S. suis. Respiratory disease was significantly more severe in groups 5 and 6. Mortality rate was the highest in group 6 (87.5%). This rate was significantly higher than that observed in all other groups …