Infectious mononucleosis is an illness caused by the Epstein-Barr virus (EBV), a member of the herpes family of viruses. Mononucleosis takes its name from the blood's mononuclear cells, white blood cells whose numbers increase in the bloodstream when a person has a mononucleosis infection. Although other viral infections, especially those caused by cytomegalovirus, can cause mononucleosis-like symptoms, classic mononucleosis is caused by EBV.

Mononucleosis can be passed from person to person in saliva, in coughs and sneezes, and through close (mouth-to-mouth) contact of mucous membranes during kissing. This is why mononucleosis has been nicknamed "the kissing disease." Young children usually become infected through contact with the saliva of sick playmates or family members. Although epidemics of mononucleosis sometimes happen, they usually affect persons living within the same home or institution, rather than larger communities of persons living in separate households.

Some studies suggest that most people are infected with EBV at some point in their lives, although the majority have few or no symptoms. Once this infection happens, the virus lingers in an inactive form within the body's white blood cells. Although EBV probably stays there for the rest of a person's life, it doesn't produce an active infection with symptoms.

What are the symptoms?

Most people usually think of fatigue as the main symptom of mononucleosis, and it's true that this can be a major complaint. Other classic symptoms of mononucleosis are fever, sore throat, and swollen glands (enlarged lymph nodes) in the neck, armpit, and throat. The spleen, an important abdominal organ that filters blood and produces antibodies, may become enlarged as well.

Loss of appetite, weakness, and sore muscles are other common symptoms, especially in adolescents. Nausea, hepatitis, jaundice, headache, stiffness, chest pain, and difficulty breathing have also been reported. Sometimes a widespread pink rash appears, especially in those who have been treated with ampicillin.

Younger children with mononucleosis may have no symptoms of infection, or they may have only vague complaints like malaise (a nonspecific "sick" feeling), loss of appetite, or fever. Of all age groups, adolescents are most likely to have the classic symptoms of fatigue, fever, sore throat, and swollen glands. Some of these young people suffer from such extreme fatigue that they stay in bed for days, and they may even feel too weak to walk around the house.

A strange "Alice in Wonderland" syndrome also has been reported by some patients with mononucleosis. Just as Alice did in her story, these patients see objects around them as being distorted in size.

In general, a susceptible person who has been exposed to someone with mononucleosis will probably come down with the illness in about ten days to 60 days.

How is it treated?

Doctors make the diagnosis of mononucleosis by collecting a blood sample and looking at it under a microscope to check for an abnormal number of white blood cells. Other types of blood tests may show an increase in antibody levels against EBV. (Antibodies are defensive immune proteins produced by the body in response to an infection.)

Right now, there is no antiviral medicine to treat mononucleosis effectively. Most cases can be cared for at home using nonprescription medicines, such as acetaminophen, to relieve fever and pain. Bed rest also helps many children with mononucleosis, especially if they are suffering from severe fatigue.

In some children with mononucleosis, loss of appetite is one symptom of a mild liver inflammation. In these cases, some experts recommend giving the child a diet high in carbohydrates and low in fat.

Since mononucleosis can cause enlargement of the spleen and make the spleen more susceptible to injury, many adolescents who are recovering from mononucleosis are advised not to participate in athletic events for three to four months. All patients with enlarged spleens should definitely avoid contact sports until the size of the spleen returns to normal.

Doctors sometimes use steroid medication to treat mononucleosis if the tonsils or lymph nodes in the throat become so enlarged that they interfere with breathing. Antibiotics may also be needed to treat a secondary bacterial throat infection in a person who already has the viral infection of mononucleosis.

When is it over?

Infectious mononucleosis is usually a self-limited illness, which means that it just runs its course and then goes away without too much of a problem. Fever and sore throat usually subside after about two weeks, but enlarged lymph nodes and spleen can persist for a few weeks more. In some cases, fatigue and weakness may last for months.

In rare cases, complications do occur. These may include blood disorders leading to dramatically lowered numbers of platelets (thrombocytopenia), white blood cells (agranulocytosis), or red blood cells (hemolytic anemia). Other less common complications include rupture of the spleen, inflammation of the heart muscle (myocarditis), inflammation of the brain or its covering membranes (encephalitis or aseptic meningitis), and a paralyzing disorder known as Guillain-Barré syndrome.

One attack of infectious mononucleosis is all that most people will ever have in a lifetime. Once a child has been infected with the virus, it will stay in his body in a dormant form. The virus is still present but will probably not actively produce another infection with symptoms.

How can I keep my kids from getting it?

Since there is no vaccine against EBV, the most parents can do to prevent mononucleosis is to have their children avoid contact with the saliva of infected persons. Also, any family member with mononucleosis should not share drinking glasses or cutlery with anyone else in the household.

When should I call my doctor?

Check with your doctor whenever your child has a combination of fever, sore throat, enlarged lymph nodes (swollen glands), and fatigue.