ABSTRACT
John Cunningham virus (JCV) is a double-stranded DNA polyomavirus isolated in 1971 by Padgett et al. from the brain of a patient with Hodgkin disease. Viral DNA is transcripted on both strands and it encodes for the early genes counterclockwise and for the late genes clockwise. JCV belongs to the group of polyomaviruses along with BK virus, simian vacuolat-ing virus, and the new members KI virus, WU virus, and Merkel cell virus. Infection with JCV is widespread in the general population with more than 80% being seropositive by adulthood. Clinical presentation of the disease is extremely varied; the most common symptoms include visual disturbances, behavioral alterations, and hemiparesis. Clinical trials of potential PML therapies that have reasonable risk—benefit ratios are urgently needed, so that the high morbidity and mortality rates associated with this condition in immunocompromised patients can be prevented.
