Diagnosis and treatment of BK virus-associated transplant nephropathy

The incidence of polyoma virus infection, particularly that of BK virus (BKV) in kidney transplant recipients has been increasing steadily since early 1990s. The diagnosis is generally made by a renal allograft biopsy. However the diagnosis can sometimes be difficult because of the pathological similarities between BKV associated nephropathy (BKVAN) and acute cellular rejection. In addition to the difficulties in making a diagnosis, the treatment of BKVAN can also be very complex. Reduction in immunosuppression is generally advocated as the initial therapeutic option for the management of BKVAN. Despite reduced immunosuppression, BKV can persist in the renal allograft and lead to gradual loss of kidney function. Hence, new therapeutic options are being evaluated for treatment of BKVAN. Cidofovir, an anti-viral agent with known nephrotoxic effects, has been successfully used in very low doses to treat patients with BKVAN, with serial measurement of the blood and urine BKV load with PCR assays. More recently several other agents have also been utilized to treat BKVAN, with variable success. This chapter summarizes the current diagnostic modalities and therapeutic options for BKVAN.