The JC Virus, or John Cunningham Virus, is a common virus that typically remains dormant in the body after initial infection. It is part of the Polyomavirus family and is often found in healthy individuals without causing any symptoms. Most people become infected during childhood, and the virus can be detected in urine and blood. In individuals with weakened immune systems, such as those with HIV/AIDS or those undergoing certain treatments, the JC Virus can reactivate and lead to a serious condition called Progressive Multifocal Leukoencephalopathy (PML). PML affects the brain and can cause severe neurological symptoms, making early detection and management crucial for affected individuals.