Do viruses play an etiologic role in ankylosing spondylitis or psoriatic arthritis?

High venous blood levels of 2-5A, an adenylic acid polymer synthesized in the presence of double-stranded RNA and considered as a viral replication indicator, have been found in blood samples from ankylosing spondylitis and psoriatic arthritis patients, but not from patients with seropositive rheumatoid arthritis or acute chondrocalcinosis. These findings suggest the possibility that ankylosing spondylitis and psoriatic arthritis might be virus-induced diseases.