Pathology and diagnosis of Streptococcus suis infections in pre-weaned piglets

Streptococcus suisis an emerging bacterial pathogen causing high mortality in nursery pigs. The prevalence of S. suis in piglets especially in nursery piglets of India is not known and needs to be addressed for its effective control. A total of 243 biological samples (152- nasal swabs; 57-palatine tonsils; 21-dead piglets and 13-joint fluids) were collected from both healthy and diseased preweaned piglets. Out of 209 samples from the asymptomatic piglets processed for microbiological investigations, 14 cultures were isolated (6.69%) while higher positivity was recorded by molecular method (68.4%) showing greater efficacy of molecular method for detection of S. suis infections in piglets. In diseased piglets, 5 isolates were recovered by routine culture method while40 cases (43.47%) were detected by molecular means. Majority of the isolates belonged to serotype 2 (9/19; 47.36%) followed by serotype 5 (5/19; 26.31%), serotype 7 (3/19; 15.78%) and serotype 9 (2/19; 10.52%). The predominant genotype was found to be mrp-/epf-/sly-/arcA- in both the cases. The piglets died of S. suis infections showed pneumonia, hepatitis, nephritis, splenitis, tonsillitis, enteritis with the demonstration of bacterial antigens at the site of lesions confirm its association with the development of the disease. Moreover, mouse pathogenecity testing of S. suis isolates confirm its pathogenic potential irrespective of its genotypes. This is the first report on documenting the prevalence and characterization of S. suis among healthy and diseased preweaned piglets of India.