Mycoplasma synoviae infection most frequently occurs as a subclinical upper respiratory tract infection.  It may also be seen as an air sac infection often occurring with infectious bronchitis.

Mycoplasma synoviae can become systemic causing acute to chronic disease affecting primarily the synovial membranes of joints and tendon sheaths, resulting in lameness in chickens and turkeys.

Mycoplasma synoviae can spread by both the vertical and horizontal routes in a similar manner to Mycoplasma gallisepticum except it is often more rapid. The disease is more difficult to eliminate in mixed age and free-range flocks.  Eradication is possible with good biosecurity and routine serological monitoring.