STREPTOCOCCUS-SUIS INFECTION IN SWINE - A RETROSPECTIVE STUDY OF 256 CASES .2. CLINICAL SIGNS, GROSS AND MICROSCOPIC LESIONS, AND COEXISTING MICROORGANISMS

A retrospective study of 256 cases of naturally acquired Streptococcus suis infections in swine submitted to the Indiana Animal Disease Diag nostic Laboratory from 1985 to 1989 was undertaken to describe the cli nical signs, lesions, and coexisting organisms associated with S. suis serotypes 1-8 and 1/2. Infected pigs generally had clinical signs and gross lesions referable to either the respiratory system or to the ce ntral nervous system (CNS), but not both. Neurologic signs were invers ely 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 gr oss lesion observed (55.2%, overall). Fibrinous and/or suppurative ple uritis, epicarditis, pericarditis, arthritis, peritonitis, and polyser ositis were also reported. In 68% of the pigs, other bacteria in addit ion to S. suis were 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 pig s infected with serotypes 2-5, 7, 8 and 1/2, suppurative meningitis wi th suppurative or nonsuppurative encephalitis, suppurative bronchopneu monia, fibrinopurulent epicarditis, multifocal myocarditis, and cardia c vasculitis were the most common microscopic lesions observed, wherea s pigs infected with serotype 1 generally presented with suppurative m eningitis and interstitial pneumonia. Microscopic lesions were morphol ogically similar among serotypes and were also similar to those report ed with other pyogenic bacteria. The distribution of clinical signs an d the gross and microscopic lesions in pigs infected with S. suis vari ed among serotypes. However, these differences were not statistically significant and could not be used to distinguish between the various s erotypes. These findings suggest that in pigs infected with S. suis, s uppurative 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 dise ase from those caused by other pyogenic bacteria.