Multiple Serotypes and Strains of<i>Streptococcus Suis</i>in Naturally Infected Swine Herds

Abstract

We present a brief description of the epidemiology, clinical signs, and lesions in 21 accessions in which multiple serotypes of S. suis or multiple distinct isolates (strains) of the same capsular serotype of S. suis were identified. Isolates of the same capsular serotype that had different antibiogram profiles were considered to be distinct isolates or “strains” for the purposes of this study. Streptococcus suis isolates of the same capsular serotype and identical antibiogram profiles were considered to be identical organisms. These cases were selected to determine whether or not herds infected with multiple serotypes (or strains) of S. suis had unique features that might serve to distinguish these herds from those infected with a single serotype and strain of S. suis and to provide additional information on the development of this disease in swine. Selected cases were limited to those in which isolates were identified by capsular serotyping. Untypeable isolates of S. suis were not included in this study. Case selection criteria, data collection procedures, etc., were as previously described. 12 Of 277 accessions in which S. suis was identified, 21 accessions (7.6%) involving 37 pigs were cases in which 46 different isolates of S. suis were identified. The distribution of these isolates is shown in Tables 1 and 2. Because of the small sample size, statistical analyses were not performed. Although there was a slight increase in recovery of S. suis in the fall and winter months for all serotypes, S. suis was readily isolated throughout the year. In this study, there was a slight increase (approximately 5%) in the prevalence of serotypes 3, 7, and 8 and a decrease (approximately 10%) in the prevalence of serotype 2 from those reported previously. 12