BK and Other Polyomaviruses in Kidney Transplantation.

For more than 40 years, polyomaviruses (BK virus and JC virus) have been known to cause disease in human beings. Recently, 11 new polyomaviruses were discovered. However, the majority of these viruses are rare in renal transplant recipients and BK and JC viruses remain the most important polyomaviruses to impact this population. BK virus presents as BK virus nephropathy and has, in rare instances, been associated with hemorrhagic cystitis or ureteral strictures. JC virus can cause progressive multifocal leukoencephalopathy or nephropathy in this population as well, but is uncommon. Antiviral prophylactic and therapeutic interventions for these diseases are lacking to date, although reduction of immunosuppression has been associated with success in treating both BK virus nephropathy and JC virus-induced disease. Risk factors are not well defined and vary across studies. However, the cumulative degree of immunosuppression is regarded universally as an important contributor to BK virus replication. For these reasons, it is recommended to screen all renal transplant recipients prospectively for BK virus infection. Multicenter trials using standardized BK and JC virus screening methods are necessary to define risk factors better, and to determine the effect of prophylaxis and treatments for these polyomaviruses affecting renal transplant recipients.