Dear Dr. Donohue • My daughter, 19, completed her first year of college and had been spending the summer at home as a waitress. In the middle of July, she felt bad and couldn't work. The family doctor examined her, took some blood and diagnosed infectious mononucleosis. He didn't give her any medicine. She is better. Can she safely go back to college? How did she get this? — R.T.

Answer • Infectious mononucleosis, "mono" for short, is a virus-caused illness. The virus' name is Epstein-Barr virus. It's found in the saliva of those infected, and it can persist for as long as 18 months. Most often, however, an infected person no longer has evidence of the virus after four months. Intermittent shedding of the virus can last for decades. Kissing has popularly been said to be the primary method of spread, but it is not the only way. Sharing a bottle of pop or the same glass used by one who still has virus in the saliva is another way to transmit the illness. It's nearly impossible to discover the source of infection.

The three distinctive signs of mono are sore throat, fever and swollen lymph nodes, particularly neck nodes. Fatigue is a universal complaint. Lab tests establish the diagnosis with certainty. The person's white blood cell count is high and composed mostly of lymphocytes.

No medicine exists for mono. Tylenol makes people comfortable. Three to four weeks is the usual length of time people feel sick. Your daughter will be ready for her next semester of college.

The most-talked-about complication of mono is rupture of the spleen, something that happens very rarely. If it occurs, it's most likely to do so from day two to day 21 of the illness. People ought not to play contact sports for at least four weeks from the onset of the illness.

To Readers • Fibromyalgia is a difficult illness to have and to explain. The booklet on it presents its details. Readers can order a copy by writing: Dr. Donohue — No. 305, Box 536475, Orlando, Fla. 32853-6475. Enclose a check or money order (no cash) for $4.75 with the recipient's printed name and address. Please allow four weeks for delivery.

Dear Dr. Donohue • Both my sister and I have white circles around the colored part of our eyes. What is it? — R.W.

Answer • Most likely it's arcus senilis. It's been said to indicate high cholesterol or high triglycerides. For most, however, it just happens without any change in cholesterol or triglycerides. It's nothing to worry about. Look around. You'll see that many people have it.

I don't know if it's a genetic trait. I can't find any information on that.

Write Dr. Donohue at P.O. Box 536475, Orlando, Fla. 32853-6475.