By Dan Rodricks, The Baltimore Sun (TNS) Every 25 to 30 years, the eminent virologist Robert Gallo has said, a gap occurs in the study of viruses, and the results are devastating. It’s one of the reasons why Gallo, director of the Institute of Human Virology in Baltimore, established the Global Virus Network, a collaboration of disease experts in 32 countries who share information and watch for trouble.