JCV, or John Cunningham Virus, is a type of virus that belongs to the Polyomavirus family. It is commonly found in the general population and usually remains dormant in healthy individuals. However, it can cause serious health issues in people with weakened immune systems, such as those with HIV/AIDS or those undergoing immunosuppressive therapy. In healthy individuals, JCV typically does not cause symptoms. However, in immunocompromised patients, it can lead to a rare but severe neurological condition known as Progressive Multifocal Leukoencephalopathy (PML). PML affects the brain's white matter and can result in significant neurological impairment or even death.