After polyomavirus BK was recognized as a pathogen causing severe nephropathy in transplant recipients, infections in renal transplant patients receiving more potent immunosuppressive medication have raised increasing concern. As no effective treatment of BK-virus nephropathy is available, the prevention of this condition, which often leads to graft loss, is of outmost importance. Recently, new data of the pathogenesis of replication and immune responses to BK virus have been reported. In addition to the well-characterized direct effects caused by clinical CMV infections, also multiple indirect immunomodulatory effects of CMV have been postulated. Experimental data of the indirect effect of CMV have associated CMV with acute and chronic injury of the kidney graft, but in the recent years, also some clinical evidence has associated persistent CMV infection of the transplant with detrimental long-term effects.
The aim of this chapter is to review the pathophysiology of the effect of viruses to the kidney allograft, with special emphasis on the two probably most important viruses challenging the survival of the graft, namely polyomavirus BK and cytomegalovirus.