Human polyomavirus 2 - formerly called John Cunningham (JC) virus - infects about 70 to 90 percent of all people worldwide without most even noticing it. But once it enters the body, the genetic material of the pathogen remains dormant there. If the immune system is weakened or shut down by a serious illness or immunosuppressive drugs, the virus is reactivated and multiplies. It can migrate into the central nervous system via the blood. Then there is a risk for progressive multifocal leukoencephalopathy (PML). This rare brain infection gradually destroys brain tissue and often leads to death within a few weeks. ...
