PATHOGENS

• JC virus, a ubiquitous, neurotropic ds-DNA polyomavirus, infects primarily oligodendrocytes, as well as astrocytes and neurons.[2]
• Primarily affects deep and subcortical white matter of brain and can expand into cortical gray matter. Rarely involves spinal cord. Spares optic nerve.[7]
• Virus resides in extraneural reservoirs, i.e., lymphoid tissue, kidney, and bone marrow. Excreted in urine of healthy individuals and those with PML.[10]
• Seroprevalence of 70-80%, antibody not protective, those with deficient cellular response, e.g. HIV/AIDS, organ transplantation, hematologic malignancies, and those receiving immunosuppressive therapies, are at risk for PML.[1]