The full form of JCV is John Cunningham Virus

The JC virus, or John Cunningham virus, is a common germ. More than half of all adults have been exposed to it. It doesn’t cause problems for most people, but it can be dangerous if you have a weak immune system. There’s no known way to keep yourself from getting it.

The virus was first discovered in 1971. A doctor found it in the brain of a man with Hodgkin’s lymphoma and named the virus after them.

Experts don’t know how it’s spread, but it’s thought that many people pick it up as kids through food or water that has the virus in it. It settles in your urinary tract, bone marrow, tonsils, or brain. It can stay there for years, and most people never know they have it.