History:

Three recently weaned pigs died in the preceding month and only a third of the group was eating and appeared clinically normal.

This particular 3.5 week old pig was depressed and lethargic, with pale oral mucous membranes. The pig was severely lame, with swelling of the stifle, hock and carpal joints. Manipulation of the affected joints elicited severe pain.

At necropsy, there was severe mitral valve endocarditis and a fibrinous polyarthritis.

Here you can see severe synovial villous hyperplasia (arrow) with synovial hyperaemia in the opened stifle joint.

A heavy growth of Erysipelothrix rhusiopathiae was cultured from the mitral valve thrombus.

In this low power view of the stifle synovium, note the exaggerated villous appearance of the intima and the normally abundant vasculature of the fibrofatty connective tissue which lies immediately beneath the intima.