The Epstein-Barr virus is a member of the herpes family of viruses. It is one of the most common viruses. In the United States, for instance, it is estimated that up to 95% of adults have encountered the Epstein-Barr virus (EBV) during their lifetime. Once infected with EBV, a person will carry the virus for life, mostly in the white blood cells. Periodically the virus is shed in the saliva, and this is the most likely way of spreading it to others.
In children younger than five, infection with the Epstein-Barr virus usually causes no symptoms at all. In older children, symptoms are usually mild. They may mimic a cold or go unnoticed. In teenagers and young adults, the Epstein-Barr virus sometimes causes more severe symptoms. This disease is called infectious mononucleosis. The most common symptoms are fatigue and fever, sore throat and swollen lymph nodes. At this age, EBV infection usually occurs through intimate contact with another infected person; thus it is sometimes called the "kissing disease." It will run its course in about two weeks, though fatigue may last six weeks or more. The Epstein-Barr virus causes more serious complications in rare cases.
People sometimes use the term Epstein-Barr virus to mean infectious mononucleosis specifically, but the Epstein-Barr virus causes other kinds of disease too. The virus seems to be capable of infecting the epithelial cells of the salivary glands and the white blood cells known as B-lymphocytes. Epstein-Barr virus causes a carcinogenic effect in these cells and is implicated in Burkitt's lymphoma and nasopharyngeal carcinoma, in particular. Epstein-Barr virus also causes rare forms of cancer, particularly in persons with damaged immune systems. Patients with AIDS may develop oral hairy leukoplakia, a malignancy of the salivary cells. Transplant patients, who must have their immune systems suppressed to avoid organ rejections, may develop lymphoproliferative disease, which is an immune system malignancy resulting from the viral infection of B-cells.