In a renal transplant patient with worsening renal function and biopsy showing basophilic intranuclear inclusions, which virus is most likely responsible?

• A. BK virus (polyomavirus)
• B. CMV (cytomegalovirus)
• C. Adenovirus
• D. EBV (Epstein-Barr virus)

Answer: (A)

Reactivation of BK virus in a kidney transplant patient under immunosuppression is a common cause of allograft dysfunction. BK is a polyomavirus that remains latent in renal tissue and can reactivate when immune control is reduced, leading to BK virus nephropathy with tubulointerstitial inflammation and tubular injury. The biopsy finding of basophilic intranuclear inclusions in renal tubular epithelial cells is a classic clue to BK virus infection, reflecting viral replication within the nucleus of those cells. Clinically this often presents as a rising creatinine without another clear etiology. Diagnosis is strengthened by detecting BK DNA in blood or urine by PCR and by the characteristic histology on biopsy. Management focuses on reducing immunosuppression to restore viral control; antiviral therapies exist but evidence is limited. Although CMV can affect transplant recipients as well, it typically shows different histologic features (owl’s eye intranuclear inclusions) and often presents with systemic symptoms or organ-specific disease rather than isolated nephropathy.