Sometimes called the "kissing disease" because it is most frequently spread through saliva, mononucleosis often is considered a teen illness. In fact, almost every adult (if tested) will show signs of having been infected by this virus, says Ben Hand, a primary-care physician in the department of medicine at Greater Baltimore Medical Center.

Just about everyone has heard of "mono." What causes this disease?

Mononucleosis or infectious mononucleosis is characterized by fever, sore throat or swollen lymph nodes, and it is caused by the Epstein-Barr virus, which is in the herpes family.

Who gets mononucleosis? Is there a particular population at greater risk than others?

That is an interesting question in that the Epstein-Barr virus is found throughout the world and is in all populations. About 90 [percent] or 95 percent of adults will show signs of having been infected by mononucleosis when tested, which means that almost everyone gets it in his or her lifetime. But many people will get it and never show signs of having it.

The clinical signs of mononucleosis tend to show up when the person contracts the virus between the ages of 10 and 19 years old. Lots of children are exposed to it, but if they are exposed to it before the age of 10, they rarely show any symptoms.

But as I mentioned, in many cases, the infection is subclinical, which means that you can have it and never know it.

Is there any time of year at which one is more likely to be at risk?

Not really, except maybe Valentine's Day because it is spread through saliva -- so kissing. It can be spread through sex, but mostly it is spread through saliva.

And after being infected, a person can be contagious for up to about 18 months, so it can basically be spread at just about any time.

Why doesn't mononucleosis seem to affect children younger than 10?

It isn't really understood why the clinical symptoms seem to happen in the teen years. And most likely, if little kids show symptoms, they will resemble those of a cold or some other respiratory illness.

Could you describe the symptoms?

The basic symptoms are fever in 80 [percent] to 90 percent of cases, malaise and fatigue in almost 100 percent of cases, swollen lymph nodes in the neck in almost 100 percent of cases, a sore throat in 80 [percent] to 90 percent of cases and an enlarged spleen in 50 [percent] to 70 percent of cases. Technically, an enlarged spleen would be considered a sign of the virus not a symptom, but we'll list it here.

How do you tell a cold from mononucleosis?

Strep throat, with its fever, sore throat and swollen glands, is more likely to resemble mononucleosis than a cold. Strep, however, is much less likely to come with the severe fatigue and malaise.

Colds typically involve the nasal symptoms -- runny nose and cough -- and these are less likely with mononucleosis.

We can order a blood test that will confirm mononucleosis.

What is the treatment?

There is no great anti-viral treatment for mononucleosis. Mostly, we treat the symptoms using acetaminophen or ibuprofen. We tell the patient to drink plenty of fluids, rest and make sure to get good nutrition. We also tell the patient to avoid contact sports for about four weeks; the reason is that you want to avoid the risk of rupturing the spleen.