Doe Simmons, age 15, of Laconia, N.H., for her question:

WHAT CAUSES MONONUCLEOSIS?

Mononucleosis is an acute infectious disease that primarily strikes younger people between the ages of 10 and 35. Doctors aren't absolutely sure what type of organism causes the disease although most believe it is a virus.

Sneezing, coughing and even kissing could spread mononucleosis. Some call it the "kissing disease" because of this.

First symptoms include a great tiredness, some fever, a sore throat and a headache. Then there is often a swelling of the lymph nodes and even an enlargement of the spleen.

Mononucleosis causes an increase in the number of certain white blood cells called lymphocytes. Patients with the disease also have a high concentration of a special antibody.

Treatment includes bed rest as probably the best therapy. Aspirin and other pain medication is often prescribed by the doctor, as well as throat spray and sometimes steroid drugs.