You're likely already infected with a brain-eating virus you've never heard of

The JC virus (human polyomavirus 2) silently infects an estimated 50–90% of adults worldwide via the fecal-oral route, persisting asymptomatically for life. In rare cases, the virus reactivates, rearranges its genome, and invades the brain, causing progressive multifocal leukoencephalopathy (PML)—a devastating disease that destroys myelin sheaths and leads to severe neurological damage or death. Once extremely rare, PML surged during the HIV/AIDS epidemic but declined after the introduction of HAART in 1996, though survivors often suffer lasting brain damage.