Epstein-Barr virus (EBV) is a member of the human herpes virus family that infects more than 95 percent of the U.S. population. Most infections occur in childhood and cause no symptoms; in adolescents and adults, EBV often causes infectious mononucleosis. It has also been associated with certain forms of cancer. Chronic Epstein-Barr virus (CAEBV) is a rare disease, primarily of children and young adults, that leads to life-threatening infections.