''M. hyorhinis'' causes a chronic progressive polyserositis in pigs under 10 weeks old resulting in a fever, laboured breathing, lameness and swollen joints. Serofibrinous pleurisy, pericarditis and [[Peritonitis#In pigs|peritonitis]] occur. | ''M. hyorhinis'' causes a chronic progressive polyserositis in pigs under 10 weeks old resulting in a fever, laboured breathing, lameness and swollen joints. Serofibrinous pleurisy, pericarditis and [[Peritonitis#In pigs|peritonitis]] occur. |