Fibres may be more important than viral load in determining transmission rates. A component found in semen can enhance HIV transmission by as much as 100,000-fold, researchers have found. The results, if verified in a clinical setting, could identify a new way to help prevent the spread of the disease. "I think this is tremendous," says Christopher Pilcher, an HIV researcher at the University of California, San Francisco, who was not affiliated with the study. "It raises a lot of really fundamental questions about how HIV is transmitted." Over 80% of HIV infections are acquired through sexual intercourse, primarily via...