Gross and histopathological findings in unusual lesions caused by Streptococcus suis in pigs. I. Cardiac lesions.

Unusual lesions caused by Streptococcus suis involved the heart of 48 pigs necropsied over a four-year period. Lesions included fibrinopurulent pericarditis (six pigs), hemorrhagic, necrotizing myocarditis resembling mulberry heart disease (21 pigs), and vegetative valvular endocarditis (21 pigs). Histologically, the myocarditis was characterized by focally extensive and diffuse hemorrhages and necrosis, with infiltrations of neutrophils and mononuclear cells, and thrombosis of small and large myocardial vessels. The 21 pigs with vegetative valvular endocarditis generally were over ten weeks old and had died suddenly. The left atrioventricular valve was affected in 18 hearts. Most of an affected valve was replaced by a layer of granulation tissue covered by a mixture of fibrin, inflammatory cells, necrotic debris and large numbers of coccoid bacteria.