Leflunomide an Immunosuppressive Drug for Antiviral Purpose in Treatment for BK Virus-Associated Nephropathy After Kidney Transplantation

BK virus is a polyomavirus belonging to the papovaviridae branch. In addition to BK, the human polyomavirus family includes John Cunningham virus (JCV), Washington University virus (WUV), Karolinska Institute virus (KIV) and Merkel cell viruses (Boothpur et al. 2010). BK virus is a virus without a shell and it has a double-stranded circular nonenveloped DNA. It was first discovered and isolated in 1971 just like JC virus, responsible for Progressive Multifocal Leukoencephalopathy (PML). Contamination usually occurs during early childhood through the airway without clinical symptoms. BK virus seroprevalence in general population is around 60%. The main latency areas are the kidney and the urothelium. Asymptomatic BK virus infection is often acquired in childhood and the virus persists in a dormant state in urothelium and kidneys of healthy and immunocompetent individuals, where it can be reactivated under immunosuppression (Nickeleit et al. 2000a; Brocker et al. 2011).