BK polyomavirus (BKPyV) infection is significant due to its potential impact on the function and survival of the kidney allograft. The use of potent immunosuppressants can lead to reactivation and uncontrolled replication of the virus, which may result in BK polyomavirus-associated nephropathy (BKPyVAN) and, ultimately, graft loss. Treatment options are limited; therefore, early detection of BKPyV and reduction of immunosuppressants are crucial for disease management. Renal biopsy remains the gold standard for diagnosis, despite its invasive nature and the risk of false-negative results due to the focal nature of BKPyVAN. In our study, we used qPCR to detect the presence of BKPyV nucleic acids in 289 kidney samples, including 89 from kidney donors and 200 from transplant recipients, collected before and after transplantation. We confirmed the presence of BKPyV DNA in 7.0 % of the analysed Slovenian population without histological evidence of BKPyVAN. Based on the histological and immunohistochemical evaluations, the samples were divided into two groups: one with confirmed BKPyVAN and the other without the evidence of BKPyVAN (BKPyVAN-negative group). We compared the dynamics of infection between the two groups and found that the pre-transplant viral status was similar in both groups, suggesting the presence of a latent infection with self-limiting replication. In contrast, post-transplantation, the BKPyVAN group exhibited a significant increase in viral activity, characteristic of reactivation and progression to active infection. This distinction enabled us to differentiate latent infection from reactivation associated with the onset of BKPyVAN. The thesis is the first to confirm the presence of BKPyV infection in the Slovenian population and to evaluate whether nucleic acid detection in renal tissue can serve as a valuable supplementary diagnostic method for identifying BKPyV infection.
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