Polyomavirus BK-associated nephropathy is cause of kidney transplant morbidity and graft failure. Reported prevalence can vary significantly between centers, probably depending on the immunosuppressive regime used, averaging 5% and the reported incidence of allograft failure ranges from 15 to 50% of affected individuals.
Aim: To evaluate the evolution of BK virus nephropathy in our transplant center Materials: A descriptive, retrospective study of the clinical evolution of BK virus nephropathy in adult kidney transplant patients from 10 / 2011-10 / 2016. The diagnostic suspicion was through the technique of screening and / or renal dysfunction and confirm by kidney biopsy. Screening was performed by Polymerasa Chain Reaction for BKV(+ greater than 10 ⁴ copies / ml) at 2-6-9-12-month and then annually and after the treatment episode due to graft rejection. Patients with a diagnosis of BK nephropathy we decided 1- Reduction of immunosuppression (suspension of mycophenolate by leflunomide and tacrolimus reduction (maintaining dosages average 5ng / ml )or sirolimus,  corticoids and leflunomide), and following with 2-Evaluation of renal function ,3- Viral load, 4-antiHLA antibodies and 5-Renal biopsy . Half of the patients also received IVIG 400mg / kg / day for 5 days as a treatment.
Results:18/774 renal tx patients had BK nephropathy, at 553 ± 355 days of transplant. 6 for screening and the rest for renal dysfunction. Age 42 ± 12y, 50% women, 14 LD, 4 DD. 6/18 presented previous rejections 2 Mixed 4 cellular Kidney. Biopsies showed Stage I Nephropathy 8 patients (44.4%), S II 9 patients (50%) and S III 1 patient (5.6%). Average basal  creatinine (n = 18) 2.5 ± 0.18, 6 months (n = 16) 3.1 ± 1.6, 12 m (n = 15) 2.7 ± 0.8, 24 m (n = 10) 2.62 ± 0.8, 36m (n = 6) 2.9 ± 0.2. .2 patients presented by biopsy, cellular rejection at 3 months of the diagnosis, treated with steroid pulses. No development of de novo antiHLA DSA was observed in this group of patients. The negativization of the viral load BKV was at 3 months in 5 patients and the rest at 6 months. Only 12 renal biopsies were performed(X 12m) , presenting an increase in interstitial infiltration and tubulitis in 2patients). Loss of grafts in 3 patients (16.6%), 2/18 at 4 months and 1/18 at 10 months. There were no deaths.
Conclusions:A low incidence (2,34%) of BK virus nephropathy is observed in this population. There were no differences in the evolution of patients treated with / without IVIG (pNS) especially in the negativization of viral load. Higher percentage of living donors (77%) with BK nephropathy due  probably immunosuppression charge and / or unidentified serology of BK virus in donors.