Editorial comment to BK virus nephropathy: Clinical experience in a university hospital in Japan

The authors reported polyomavirus type BK (BKV) nephropathy in six out of 151 renal transplant recipients who underwent transplantation at their institution. The incidence of BKV nephropathy was approximately 5%. Graft loss occurred in two patients, but no graft loss was attributable to renal dysfunction related to BKV nephropathy. BKV virus nephropathy has been reported to be a common infectious complication in the USA and in European countries. Most US and European data show a 5–15% incidence of BKV nephropathy after renal transplantation with lost grafts in about 5% of the patients due to BKV nephropathy. In Japan, the incidence of BKV nephropathy after renal transplantation, as mentioned in this report, is lower than that in the USA and European countries. The reason for this discrepancy is not clear. Theoretically, the strength of immunosuppressive therapy should have a major impact on the occurrence of opportunistic infection, including BKV nephropathy. Perhaps the higher incidence of BKV nephropathy could be attributable to the use of more potent immunosuppressive regimens in the USA or European countries as compared to those in Japan. Adequate, but minimal immunosuppression appears to be the best option for preventing BKV nephropathy. A reduction of immunosuppression is an effective method for treatment at the onset of BKV nephropathy as well.