INTRODUCTION
BK virus (BKV) was first described by Gardner et al. in 1971, isolated in the urine and urinary epithelium of a renal transplant recipient with renal failure and ureteral stenosis[1]. BKV is a non-enveloped, 42 nm virus with a double-stranded circular DNA containing 5000 bases and an icosahedral capsid from the Papoavirus group in the Polyomaviridae family[2]. Primary infection is frequently seen in early childhood, sometimes with clinical signs of upper respiratory tract infection, and is usually asymptomatic[2]. After the primary infection, the virus exists in a latent state in the urogenital tract[2].
BKV seroprevalence is 80% in adults worldwide, and BKV infection is seen in 10-60% after renal transplantation. 5% (1-10) of these infections progress as BKV nephropathy (BKVN), and it is still a significant problem affecting allograft survival in the post-transplant period[3]. Alterations in immunosuppressive (IS) treatments and diagnostic approaches lead to epidemiological differences. The incidence of BKVN is higher in the first two years after transplantation and risk is increased in patients over 50 years of age, male gender, cases with high HLA incompatibility, with multiple allograft rejection episodes, and those who receive intensive triple IS therapy[3]. Patients may not show any symptoms other than impaired renal function. BKVN may present with interstitial nephritis, ureteral stenosis, hydronephrosis, and signs of a urinary tract infection. Progressive renal failure is approximately 30-60% in affected cases[2,3].
Early diagnosis of BKVN is essential. Since the disease is mostly silent, it is recommended to regularly monitor BKV DNA in blood and/or urine samples after transplantation[4]. It is recommended to reduce IS therapy in cases with BKV DNA levels above the critical threshold and to confirm both BKVN and the presence of concomitant rejection by performing a biopsy in patients with allograft dysfunction[4]. The crucial point in the treatment of BKVN is to reduce immunosuppression. In addition, cidofovir, intravenous immunoglobulin (IVIG), quinolones, and leflunomide therapy may be applied, but none of these treatments have strong evidence to be recommended[3].
The current knowledge of BKVN is mainly based on cross-sectional patient series with small numbers of cases. The studies reporting disease outcomes with large samples are rare in the literature. With this retrospective study, we aimed to contribute to the literature by analyzing our BKVN experience with the participation of transplantation centers in all provinces of our country.