Human Polyomaviruses

Abstract Polyomaviruses (PyVs) were discovered in the 1950s as infectious agents that pass bacterium‐tight filters and form different tumors in rodents, hence their name. The multifunctional large tumor antigen protein successfully maintained the bidirectional gene expression, which is a hallmark of the circular PyV genomes. Biopsy‐proven BK polyomavirus nephropathy is characterized by cytopathic changes in renal tubular epithelial cells, showing enlarged nuclei with intranuclear inclusions, rounding up, and cell detachment. Nucleic acid testing (NAT) is the most widely used diagnostic approach to detect viral DNA genomes in specimens from patients with suspected human polyomavirus (HPyV) infection. The diagnostic value of qualitative NATs in the clinical routine resides primarily in the analysis of sterile or NAT‐negative human materials, which must be obtained by clean invasive procedures. The assessment of HPyV‐specific immune responses is of increasing interest for evaluating the risk of primary infection or reactivation as well as identifying predictors of insufficient or reconstituted immune control.