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A retrospective study of 256 cases of naturally acquired Streptococcus suisinfections in swine submitted to the Indiana Animal Disease Diagnostic Laboratory from 1985 to 1989 was performed to determine the epidemiologic factors and antibiotic susceptibility patterns associated with S. suisserotypes 1–8 and 1/2. A standardized computer form was used to record the history, signalment, and clinical signs obtained from the records of selected cases and the microscopic lesions identified after review of the histopathology slides for each case. A computer statistics package (SAP) was used to evaluate the data. Although the number of recovered S. suisisolates increased in the fall and winter months, most serotypes were readily isolated throughout the year; only serotypes 1, 4, 7, and 1/2 increased in frequency of isolation in the fall, winter, and spring months. The majority (6 1.1%) of infected pigs in this study were < 12 weeks of age. More than 75% of pigs infected with serotypes 1, 6, 7, and 1/2 were < 12 weeks of age. There was extensive overlap in the age distributions for pigs with each serotype, and statistically significant differences for most serotypes were not observed. Fifty percent of pigs infected with S. suisserotypes 1 and 1/2 were 3–10 weeks of age, 50% of pigs infected with serotype 2 were 6–14 weeks of age, and 50% of pigs infected with serotypes 3, 4, 5, 7, and 8 were 2–16 weeks of age. Isolates of S. suiswere not uniformly susceptible to penicillin, and a large percentage of isolates were resistant to many antibiotics in common usage. The results of this study indicated that the various serotypes of S. suiscould not be readily separated based on antibiograms, epidemiologic factors (herd size, breed, etc.), or geographic location.

A retrospective study of 256 cases of naturally acquired Streptococcus suisinfections in swine submitted to the Indiana Animal Disease Diagnostic Laboratory from 1985 to 1989 was undertaken to describe the clinical signs, lesions, and coexisting organisms associated with S. suisserotypes 1–8 and 1/2. Infected pigs generally had clinical signs and gross lesions referable to either the respiratory system or to the central nervous system (CNS), but not both. Neurologic signs were inversely related to gross lesions in the respiratory tract (R2= −0.19, P= 0.003), as were respiratory signs and gross lesions in the CNS (R2= −0.19, P= 0.003). Suppurative bronchopneumonia was the most common gross lesion observed (55.2%, overall). Fibrinous and/or suppurative pleuritis, epicarditis, pericarditis, arthritis, peritonitis, and polyserositis were also reported. In 68% of the pigs, other bacteria in addition to S. suiswere isolated. Escherichia coli(35.0%) and Pasteurella multocida(30.0%) were the most commonly recovered bacterial agents. Mycoplasma and viral agents were identified less often, and their role in the development of streptococcosis was difficult to assess. In pigs infected with serotypes 2–5, 7, 8, and 1/2, suppurative meningitis with suppurative or nonsuppurative encephalitis, suppurative bronchopneumonia, fibrinopurulent epicarditis, multifocal myocarditis, and cardiac vasculitis were the most common microscopic lesions observed, whereas pigs infected with serotype 1 generally presented with suppurative meningitis and interstitial pneumonia. Microscopic lesions were morphologically similar among serotypes and were also similar to those reported with other pyogenic bacteria. The distribution of clinical signs and the gross and microscopic lesions in pigs infected with S. suisvaried among serotypes. However, these differences were not statistically significant and could not be used to distinguish between the various serotypes. These findings suggest that in pigs infected with S. suis,suppurative or fibrinopurulent inflammation in brain, heart, lungs, and serosae predominates and that bacterial culture is needed to confirm a diagnosis of streptococcosis in swine and to differentiate this disease from those caused by other pyogenic bacteria.