BK virus

Background

Very high seroprevalence with asymptomatic infection ocurring in childhood
Disease is seen in immunosuppressed patients, especially renal transplant recipients
BKV nephropathy is seen in 1 to 10% of renal transplant recipients
BKV ureteric stenosis is seen in about 3% of renal transplant recipients
Hemorrhagic cystitis is seen in 10 to 25% of hematopoietic stem cell transplantation recipients

Typically a cause of nephropathy in renal transplant patients
Onset is 10 to 13 months post-transplant, with a wide range of 6 days to 5 years
Presents with slowly increasing creatinine levels
- Occasional hematuria and fever

Causes urinary obstruction and AKI in the donor kidney, usually without pain since it is not innervated

Complicates 10 to 25% of hematopoietic stem cell transplantations, most commonly in the context of GVHD
Symptoms include hematuria, dysuria, urinary urgency and frequency, and suprapubic pain
Clotting hematuria can cause urinary obstruction and renal failure

Nephropathy: screening with urine or blood PCR followed by biopsy if concurrent renal dysfunction to confirm the diagnosis
BKV Transplantation Associated Virus Infections Working Group developed a consensus definition1
- Proven: demonstration of active BKV within renal tissue by IHC for SV40 or ISH
- Probable: requires all of the following:
  - Renal biopsy not performed or inadequate specimen
  - Renal transplant recipient receiving immunosuppression
  - Renal allograft dysfunction (≥20% rise in serum creatinine from baseline)
  - No likely alternative process
  - Significant BKPyV DNAemia in plasma on repeated measurement
    - For well-validated assays, >4 log₁₀ copies/mL corresponds to biopsy-confirmed disease

Hemorrhagic cystitis: urine PCR is relatively non-specific, although a high viral load may be supportive
Urine cytology may show decoy cells, though they are also seen in CMV and adenovirus

There is no directed therapy
Nephropathy is typically managed by decreasing immunosuppression, monitoring viremia for response
Ureteral stenosis is similarly managed, but may require surgical intervention
Hemorrhagic cystitis is managed supportively, with continuous bladder irrigation, analgesia, hydration, and transfusion of platelets or erythrocytes as needed
- Target for platelets is >50k

In renal transplant patients, monitor for viremia monthly after transplant, decreasing immunosuppression if positive

^ Hannah Imlay, Paul Baum, Daniel C Brennan, Kimberly E Hanson, Michael R Hodges, Aimee C Hodowanec, Takashi E Komatsu, Per Ljungman, Veronica Miller, Yoichiro Natori, Volker Nickeleit, Jules O’Rear, Andreas Pikis, Parmjeet S Randhawa, Deirdre Sawinski, Harsharan K Singh, Gabriel Westman, Ajit P Limaye. Consensus Definitions of BK Polyomavirus Nephropathy in Renal Transplant Recipients for Clinical Trials. Clinical Infectious Diseases. 2022;75(7):1210-1216. doi:10.1093/cid/ciac071.