Ankylosing spondylitis is a systemic autoimmune disease of unknown cause, primarily affecting the axial joints, mainly involving the sacroiliac joints, and commonly occurring in young and middle-aged males. The symptoms of this disease are severe, progress rapidly, and there is a genetic predisposition, but it is not a contagious disease and does not have infectivity. If a patient with ankylosing spondylitis also contracts another infectious disease, it is because the other disease is infectious, not because ankylosing spondylitis is. It belongs to autoimmune diseases and cannot be cured, but can only be managed with medication to delay the onset of joint deformity.