Prospective monitoring of BK virus replication in renal transplant recipients

Background. BK virus-associated nephropathy (BKVAN) can be diagnosed only with renal graft biopsy. De¢nitive diagnosis of BKVAN requires demonstration of BK virus (BKV) replication in renal allograft tissues. Non-invasive analysis of urine and blood is considered essential in screening renal transplant recipients. Patients and methods. This study evaluated prospectively the replication of BKV in plasma and urine with qualitative and quantitative real-time polymerase chain reaction in 32 de novo (group A) and 34 chronic (group B) renal transplant recipients and the long- term impact on graft function. Results. In group A, 456 samples (228 plasma, 228 urine) were examined and BKV was detected in 31 (31/228, 14%) samples of plasma and 57 (57/228, 25%) samples of urine in 20 (20/32, 62.5%) and 23 (23/32, 72%) recipients, respectively. Incidence of viremia and viruria increased during the ¢rst 6 months presenting a peak the third postoperative month (viremia: 28% and viruria: 31%). Immune suppressive treatment with tacrolimus showed signi¢cant relation with viremia. Renal graft function in de novo renal transplant recipients remained stable throughout the follow-up period without in£uence of BKV replication. In group B, incidence of viremia and viruria were 3% (1/34) and 9% (3/34) correspondingly, indicating that after the ¢rst post-transplant year the risk of BKV re-activation is diminished. Conclusion.The highest incidence of BK viremia and viruria is observed the third post-transplantation month, con¢rming previously published studies in Europe and the United States, and long-term follow up shows that BKV replication decreases signi¢cantly after the third post-transplant month and even transient viremia or viruria does not have an impact on renal function.