Evaluation of the effect of combined infection with Streptococcus suis serotypes 2 and 9 on clinical signs and pathology in pigs

Abstract

Streptococcus suis (S. suis) is a gram-positive bacterium that causes substantial economic losses in the pig industry. Infection with S. suis can cause meningitis, arthritis, endocarditis, septicaemia and bronchopneumonia. Of the 33 described serotypes, S. suis serotype 2 accounts for the majority of infections worldwide. In several European countries S. suis serotype 9 is emerging, whereas the prevalence of S. suis serotype 2 in field isolates of diseased pigs decreases. The cause of this replacement of serotype 2 by serotype 9 is unknown. In this research project the interaction of these serotypes is investigated in caesarean-derived, colostrum-deprived (CDCD)-pigs. The clinical and pathological findings shown by pigs inoculated with or contact exposed to S. suis serotype 2&9 were surveyed and compared to inoculation with or contact exposure to S. suis serotype 2 or 9 alone. The proposed hypothesis was that after combined infection via inoculation or contact exposure to S. suis serotype 2&9, S. suis serotype 9 suppresses S. suis serotype 2 and thereby reduces disease severity and increases survival of the pigs. This hypothesis can partially be proven. The co-infection did not alter the seriousness of clinical signs and the survival of the pigs inoculated with both serotypes. The survival of the pigs contact exposed to S. suis serotype 2&9, however, was increased after co-infection when compared to mono-infection with S. suis serotype 2. It can be concluded that S. suis serotype 9, partially, suppresses S. suis serotype 2 in inducing lethal infection.