It’s one of the most common viruses in America, and one that causes the most guilt and shame. It can get inside almost any kind of human cell, reproduce in vast numbers, and linger for years in the body, causing everything from recurrent genital blisters to sores around the mouth. Its complications can kill, and it may increase susceptibility to many nerve and brain disorders. But until now, scientists haven’t fully understood how the herpes simplex virus (HSV) manages to do all of this. And that has stood in the way of developing more targeted, effective treatments against it to help those infected. New research from the University of Michigan Medical School may help change that. An estimated 45 million Americans have genital herpes and millions more have the more visible oral variety. Once someone is infected, they’re infected for a lifetime. New medicines for herpes infection are badly needed; currently, antiviral drugs can quell symptoms of an outbreak, but not eliminate the virus. And, there’s increasing evidence that HSV may damage the nerve cells in which it hides between outbreaks, possibly contributing to neurological disease. In a presentation Sunday at the International Congress of Virology and in two new papers in the Journal of Virology, U-M researchers are reporting the discovery of a receptor that appears to function as one “lock” that HSV opens to allow it to enter human cells. They’ve also found the gene that controls the production of that receptor, deciphered some aspects of the receptor’s structure, and developed a pig-cell system that could be used to test new anti-herpes drugs. The findings may help explain why the oral and genital herpes virus has such a successful track record: The receptor, dubbed B5, is made by most cells for another purpose not yet understood. HSV appears to have evolved a way to latch onto it, and fool the cell into letting the virus in. And since most cells express the gene for the B5 receptor, this may be a reason HSV can get into most kinds of cells.