Chapter 9 - Molecular testing for polyoma viruses

Abstract

Polyoma viruses are genomically small, nonenveloped DNA viruses that are ubiquitous among humans. Primary infection is still poorly understood, since patients are either asymptomatic or disease is subclinical. The most important polyoma viruses in human medicine are the BK and JC viruses. Symptomatic infections caused by the BK and JC polyoma viruses present exclusively in immunocompromised patients. Both of these viruses replicate in the urothelium of urinary tract, but have been detected in other sites of latency. The principal diseases caused by the BK virus are nephropathy in patients that have undergone renal transplanation and hemorrhagic cystitis in patients undergoing hematopoietic stem cell transplantation. Although the JC virus replicates in the lower urinary tract, the most important disease caused by this virus is progressive multifocal leukoencephalopathy, which occurs predominantly in patients with altered T-cell immunity. The diagnosis and/or monitoring of patients with these diseases relies heavliy on quantitative polymerase chain reaction (PCR), and occasionally other diagnostic methods. A variety of other polyoma viruses have been described and will be discussed briefly. Among these, the Merkel cell polyoma virus is the most important, which is a cause of Merkel cell carcinoma.