“Mono” for short, this is an infection caused by the Epstein-Barr Virus (EBV). It’s most common in teenagers and young adults. It’s sometimes called the “kissing disease,” because it’s spread by saliva, but also as viruses spread into the air, however.
Mono begins with fever, sore throat, and feeling lousy. Lymph nodes swell (“swollen glands”), but often in unusual places, like behind the ear, back of the head, back side of the neck, armpit, or the elbow (on the pinky side). This may also happen with Syphilis, HIV, and other blood infections. It never occurs from common sore throat viruses or Strep Throat (then the nodes are under the jaw bone or front side of the neck).
There’s no treatment for Mono, because it’s a virus (see Differences Among Germs). It lasts around a month, goes away on its own, & never comes back. About 50% of adults have blood-test evidence of having had the disease at some point in their lives, because it can occur & go away without any symptoms. This is especially true among children (who get it without kissing anyone).
There are possible brain and nervous system complications, but they’re very rare. Since EBV affects the liver, it’s best not to drink alcohol until Mono goes away.
The spleen can swell during Mono. It can rupture, a 1-in-1,000 chance, causing fatal internal bleeding. Symptoms of rupture include new pain on the left side of the belly & under the lower left ribs, along with dizziness or shortness of breath. Mono patients should avoid sports for 3 weeks (vigorous sex too), and avoid strenuous or contact sports (and motorcycle accidents) for at least a month. For the serious eager athlete eager to return to play, an ultrasound after 3 weeks of illness can determine if the spleen is still enlarged.
The main blood test for Mono is called the “Monospot,” but in 25% of patients it doesn’t turn positive until the 2nd week of illness or later. Other tests that hint strongly for the disease are common liver enzymes (almost always elevated), and a complete blood count to look for lots of lymphocytes (a type of white blood cell), or atypical-looking lymphocytes. There are also special EBV antibody tests, that can be quite expensive.
In summary, the vast majority people with Mono who get symptoms feel lousy and wiped-out for several weeks. But then they get better, without any long-term problems. Athletes should get back into shape gradually (without social pressure to hurry faster). There’s a faddish diagnosis “Chronic Epstein-Barr Infection” to explain chronic fatigue, that’s almost impossible to prove, since EBV antibodies remain high for life. Chronic Fatigue Syndrome (now called “systemic exertion intolerance disease”) is not caused by EBV.