Viruses are relatively uncommon but important cause of renal infection. Viral pathogens such as cytomegalovirus (CMV), polyomaviruses (JC or BK virus), and adenoviruses are able to replicate in the kidney, and symptomatic infection with these agents can be associated with significant morbidity and mortality in immunocompromised hosts such as renal allograft recipients. Of these, CMV is a particular problem in kidney transplant recipients and can result in temporary or irreversible renal dysfunction. CMV disease in immunocompromised patients is usually due to reactivation of the latent virus. Renal manifestation of CMV infection may include tubulointerstitial nephritis and glomerulopathy. Classic histologic findings in CMV nephritis include evidence of interstitial nephritis and characteristic owl's eyes representing intracellular inclusions. Antiviral therapy is usually reserved for immunocompromised hosts. BK polyomaviruses also have tropism for urinary epithelium. Symptomatic renal disease with polyomaviruses has only been described in immunocompromised patients, and clinical manifestations in this patient population may include tubulointerstitial nephritis, ureteral stenosis, and hemorrhagic cystitis. Similar to CMV, renal disease with BK virus in kidney transplant recipients is primarily due to reactivation of the latent virus. BK nephritis should be suspected in patients with allograft dysfunction who are found to have decoy cells in urinalysis, and the diagnosis is usually confirmed based on histopathologic findings and BK virus PCR (polymerase chain reaction). Reduction in immunosuppression is the cornerstone of therapy in BK virus nephritis. Renal infection with adenovirus is rare but has been associated with necrotizing tubulointerstitial nephritis in kidney transplant recipients and hemorrhagic cystitis in bone marrow transplant patients. Other viruses that may cause renal injury include Coxsackie and hantavirus groups.
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