MONONUCLEOSIS, INFECTIOUS

Infectious mononucleosis is an illness caused by the Epstein-Barr virus. The symptoms of "mono," as the disease is colloquially called, include extreme fatigue, fever, sore throat, enlargement of the lymph nodes in the neck, armpit, and throat, sore muscles, loss of appetite, and an enlarged spleen. More infrequently, an individual will experience nausea, hepatitis, jaundice (which indicates malfunction of the liver), severe headache, chest pain, and difficulty breathing. Children may display only a few or none of these symptoms, while all can be present in adolescents.

The illness can be passed from person to person via the saliva. In adolescents, mononucleosis was once known as "the kissing disease" since kissing is a route of transmission of the Epstein-Barr virus. Given the relative ease of transmissions, epidemic outbreaks of mononucleosis can occur in environments such as schools, hospitals and the workplace.

Infectious mononucleosis is usually self-limiting. Recovery occurs with time and rest, and is usually complete with no after effects. Analgesics can help relieve the symptoms of pain and fever in adults. However, children should avoid taking aspirin, as use of the drug in viral illnesses is associated with the development of Reye syndrome, which can cause liver failure and even death.

Recovery from mononucleosis is not always complete. In some people there can be a decrease in the number of red and white blood cells, due either to damage to the bone marrow (where the blood cells are produced) or to enhanced destruction of the red blood cells (a condition known as hemolytic anemia). Another temporary complication of the illness is weakened or paralyzed facial muscles on one side of the face. The condition, which is called Bell's palsy, leaves the individual with a drooping look to one side of the face. Much more rarely, very severe medical complications can arise. These include rupture of the spleen, swelling of the heart (myocarditis), malfunction of the central nervous system, and Guillain-Barré syndrome. The latter condition is a paralysis resulting from disruption of nervous system function.

The illness is diagnosed in a number of ways. Clinically, the presence of fever, and inflammation of the pharynx and the lymph nodes are hallmarks of the illness. Secondly, the socalled "mono spot" test will demonstrate an elevated amount of antibody to the virus in the bloodstream. A third diagnostic feature of the illness is an increase in the number of white blood cells. These cells, which are also called lymphocytes, help fight viral infections.

Antibodies to the Epstein-Barr virus persist for a long time. Therefore, one bout of the illness usually bestows long-lasting immunity in an individual. Testing has demonstrated that most people have antibodies to the Epstein-Barr virus. Thus, most people have been infected with the virus at some point in their lives, but have displayed only a few minor symptoms or no symptoms at all. Many children are infected with the virus and either display no symptoms or become transiently ill with one of the retinue of infections acquired during the first few years of life. When the initial infection occurs during adolescence, the development of mononucleosis results 35–50% of the time. Understanding of the reasons for this failure to infect could lead to a vaccine to prevent infectious mononucleosis. As of 2002, there is no vaccine available.

The Epstein-Barr virus that is responsible for the illness is a member of the herpesvirus family. The virus is found all over the world and is one of the most common human viruses. In infectious mononucleosis, the virus infects and makes new copies of itself in the epithelial cells of the oropharynx. Also, the virus invades the B cells of the immune system.

For most patients, the infection abates after two to four weeks. Several more weeks may pass before the spleen resumes its normal size. A period of low activity is usually prescribed after a bout of mononucleosis, to protect the spleen and to help energy levels return to normal.

Epstein-Barr virus is usually still present after an infection has ended. The virus becomes dormant in some cells of the throat, in the blood, and in some cells of the immune system. Very rarely in some individuals, the latent virus may be linked to the appearance years later of two types of cancers; Burkitt's lymphoma and nasopharyngeal carcinoma.