A Common Virus, A Selective Killer (IMAGE) Brown University Caption A computer-enhanced image shows the general structure of viruses in the family polyomavirinae. A member of that family -- the JC virus, occurring in 70 percent of humans -- can cause a rare brain disease that is almost always fatal. Credit Provided Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.