BK virus

Background

Microbiology

• Double-stranded DNA virus in the Polyomaviridae family

Epidemiology

• 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

Clinical Manifestations

Nephropathy

• 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

Ureteral Stenosis

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

Hemorrhagic Cystitis

• 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

Other Syndromes

• Very rarely causes encephalitis and pneumonitis

Diagnosis

Nephropathy

• 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 definition
  • 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

Other

• 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

Management

• 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

Prevention

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