Karen Rutherford, age 16, of Montgomery, Ala., for her question:

WHAT CAUSES MONONUCLEOSIS?

Mononucleosis is an acute infectious disease that causes its victim fever, sore throat, extreme tiredness and enlarged lymph nodes. The organism that causes the disease is unknown, although most medical experts believe it is a virus.

Mononucleosis is sometimes called the "kissing disease." It is possible for the disease to be spread by kissing, but it can also be spread by coughing and sneezing.

Mononucleosis can be found in almost every part of the world. Primarily, it strikes people between the ages of 10 and 35.

The first symptoms of mononucleosis are extreme tiredness and a headache. The tiredness does not go away after the first long sleep, and then the victim usually also has a fever and a sore throat. The fever generally is between 100 and 103 degrees Fahrenheit. The sore throat is often followed by the appearance of red spots on the roof of the mouth, on about the seventh day of the illness.

Another thing that bothers the patient is enlarged lymph nodes, most frequently those in the neck. Lymph nodes in the armpits, groin and abdomen may also enlarge.

In about half of the mononucleosis cases, the spleen also enlarges. Occasionally it may become very large and rupture, requiring surgery.

Small skin lesions, pinkish in color, sometimes form a rash over the arms and chest.

Doctors discover an increase in the number of certain white blood cells called lymphocytes in the mononucleosis victim. Lymphocytes are called mononuclear cells because they have only a single nucleus.

Doctors say that the most beneficial therapy for mononucleosis is bed rest, since general treatments for the disease are limited. Aspirin and other pain medication along with a steriod drug called prednisone are sometimes prescribed.

The outlook for a person with the disease is good. About four weeks of rest is usually ordered by the doctor.

If a mononucleosis victim's spleen ruptures, emergency surgery is required. In some cases this can cause death, although this is uncommon.

Mononucleosis can continue for as along as two or three months in a few cases. The fever, however, usually disappears after 10 days.

Sometimes there is liver involvement with an occurrence of hepatitis. In a majority of the patients, this condition will subside after about five weeks.

Sometimes the heart can become involved with mononucleosis. There will be a rapid pulse and an irregular heartbeat.

Nervous system involvement is another occurrence that you'll sometimes find with mononucleosis.