Analysis of 15 novel full-length BK virus sequences from three individuals: evidence of a high intra-strain genetic diversity

Prevalence of BK virus subtype I in Germany

The primary infection with human polyomavirus BK (BKV) occurs in early childhood and leads to viral latency within the urogenital tract. Up to 90% of the adult population are seropositive. In immunosuppressed patients, the BKV may be reactivated resulting in typical disease patterns like hemorrhagic cystitis and tubulointerstitial nephritis. Based on serological and molecular methods, BKV isolates were classified into four subtypes previously. Sixty specimens obtained from German renal and bone marrow transplant recipients were analyzed to gain data on the prevalence of BKV subtypes in Germany. With 90.9%, BKV subtype I was found to be predominant in both patient groups. 6.1% of BKV strains were classified as subtype IV. This pattern of phylogenetic distribution is similar to that demonstrated previously in England, Tanzania, the United States and Japan. Remarkably, there was one German BKV virus with a sequence which clusters together with strain SB in subtype II. The BKV subtype I was found to consist of at least three subgroups designated as Ia, Ib, and Ic. While the majority of the German sequences represent subgroup Ic, most of the Japanese sequences are clearly distinct. These findings support the hypothesis of distinct geographical prevalence of BKV subgroups. For the genotyping region, a relationship of BKV subgroups to disease patterns like hemorrhagic cystitis or tubulointerstitial nephritis could not be demonstrated.

A prospective longitudinal study of BK virus infection in 104 renal transplant recipients

BK virus (BKV) infection during the first year after renal transplantation was studied prospectively in 104 unselected consecutive patients. Viral DNA in urine (DNAuria) and plasma (DNAemia) samples was detected and quantified by real-time PCR. The noncoding control region (NCCR) of BKV isolates was sequenced. DNAuria and DNAemia occurred in 57% and 29% of patients, respectively. Three groups were defined, uninfected patients (group 1, n=45), patients with DNAuria (group 2, n=29) and patients with positive DNAemia (group 3, n=30). Active infection started within the first 3 months in 80% of patients. Cold ischemia duration over 24 h and the administration of tacrolimus were identified as significant risks factors for DNAuria, whereas it remains more frequently negative in patients receiving cyclosporine A. The risk for positive DNAemia was higher in patients with DNAuria (notably for viral load (VL)>4 log/mL) or treated with tacrolimus. No relationship was found with genetic variability in the NCCR sequence. Our data highlight the high frequency of active BKV infection after renal transplantation. Although high VL was detected in some patients, none developed a BKV nephropathy. A prospective follow-up of the whole population during the first year post renal transplantation is thus not useful to predict BKV disease.

Polymorphism in the genome of non-passaged human polyomavirus BK: implications for cell tropism and the pathological role of the virus

Worldwide studies have demonstrated that the human polyomavirus BK resides ubiquitously in the human population. After primary infection, which occurs mainly during childhood, the virus seems to establish a life-long harmless infection in the host. However, impaired immune functions may lead to reactivation of BK virus. The recent findings that associate BK virus with an increasing number of clinical conditions, including renal, pulmonary, ophthalmologic, hepatic, neurological, and autoimmune diseases, has resuscitated the interest in this virus as a pathogenic agent. This review focuses on polymorphisms in the genomes of non-passaged BK virus isolates from nonneoplastic tissues, with special focus on the transcriptional control region, the regulatory proteins large T-antigen and agnoprotein, and the major capsid protein VP1. The possible implications of genome diversity with respect to cell tropism, pathogenicity, and therapeutic strategies are discussed.