Lesions caused by natural infection with Streptococcus suis type 9 in weaned pigs

In this paper we report on the spectrum and frequency of lesions observed in a prospective study of naturally occurring infections with Streptococcus suis type 9 (SS-9) in weaned pigs. SS-9 produced arthritis, meningitis, interstitial pneumonia, and endocarditis in 100%, 91%, 73%, and 42%, respectively, of pigs dying from the disease. The lesions were similar to those caused by S. suis type 2 (SS-2), however, SS-9 produced a different frequency of lesions. In SS-2 infections, bronchopneumonia is the most commonly observed lesion; meningitis, arthritis, and endocarditis are less frequently observed. Thus, SS-9 produced a different distribution of lesions from that reported for SS-2. Possible explanations for the differences found are discussed.