BACKGOUND: BK virus has emerged as a major cause of allograft loss in kidney transplant recipients over the past decade. The presence of BK virus in urine or blood indicates reactivation of the virus not necessarily accompanied by BK virus associated nephropathy. BK virus genotypes have been described based on the DNA sequence of VP1 region, and no data have been published on BK virus genotypes in Korea. In this study, we sought to determine BK virus genotypes and clinical characteristics associated with BK virus reactivation. METHODS: We isolated BK virus DNA from urine and blood of 103 kidney transplant recipients, and amplified VP1 region using polymerase chain reaction (PCR). The PCR products were sequenced and genotypes of BK virus (I-IV) were determined based on the nucleotide sequence 1744-1812 of the VP1 region. In addition, the clinical characteristics of the patients were analyzed to determine the risk factors of BK virus reactivation. RESULTS: Of 103 patients examined, 16 and 5 patients were shown to have BK viruria and viremia, respectively. Eight viral strains were demonstrated to be genotype I, but the other 8 strains neither matched with the genotypes from I to IV, nor did they fit into any other variants identified in the Western countries. Of note, 3 of these 8 unclassified strains were shown to have the same type of mutations. With respect to the risk factors of BK virus, tacrolimus and mycophenolate mofetil when combined with tacrolimus were found to be significantly associated with BK viruria and viremia. CONCLUSION: It appears that different variants of BK virus are prevalent in Korea compared with the Western countries, and that the reactivation of BK virus is significantly associated with tacrolimus.
Allografts ; Base Sequence ; BK Virus* ; DNA ; Genotype* ; Humans ; Kidney* ; Korea ; Polymerase Chain Reaction ; Risk Factors ; Tacrolimus ; Transplantation* ; Viremia