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Commonly known as "mono", infectious mononucleosis is a viral infection that can affect people of all ages -  although it is found most often among teens and young adults. About half of Canadian students have had mono by the time they start university or college. They usually catch it by kissing or having other intimate contact with someone already infected by the virus which is why mono is also called "the kissing disease."


The usual time between infection and the appearance of symptoms (incubation period) is believed to be 10 to 50 days, although 7 to 14 days is common for children and adolescents. People with mono often begin to feel sick several days to a week before any symptoms appear. Primary symptoms are:

  • extreme tiredness: The person may feel so tired that even walking around the house is too much. The fatigue is worse the first week or two, but then gradually dissipates. A very small number of people experience fatigue for a few months.
  • a really sore throat: A puslike exudate on the throat can sometimes be seen.
  • fever: It typically peaks at around 39.4º centigrade in the afternoon or evening.
  • swollen lymph glands: mostly in the neck and throat, but also in the armpits.

In about half of people with mono, the spleen is enlarged. (The spleen is the organ under the ribcage on the left side; it filters the blood and produces antibodies). An enlarged spleen can rupture if injured, which is why if you are an athlete and have mono you should check with your doctor before resuming your sport.

Not all people with mono, however, have signs or symptoms. In many cases, especially in younger children, the symptoms are so mild that the infection goes undiagnosed.

Note: Sometimes, if the antibiotics ampicillin or amoxicillin are prescribed to fight a presumed bacterial infection (streptococcal pharyngitis, for instance), the person with mono may develop an uncomfortable rash that is not an allergy to the antibiotic.


Mononucleosis is caused by the Epstein-Barr virus (EBV), a member of the herpesvirus family. This virus is very common; most Canadians (95 percent) have had it at one time or another, although they may have put what symptoms they had down to a cold or minor viral infection. When adolescents or young adults are infected with EBV, it causes infectious mononucleosis 35 to 50 percent of the time.

EBV remains dormant in the body even after the symptoms of mono disappear. Sometimes the virus reactivates and can be found in the person's saliva, but when that happens there aren't usually any symptoms of illness.


If you think you may have mono, visit your doctor who will check your symptoms and may also take a blood sample to send to the lab to confirm the presence of antibodies to EBV in your blood stream. Large numbers of white blood cells (mononuclear cells) in the bloodstream are also an indicator of mono and explain where the infection got its name. In addition, your doctor may take a swab of your throat to check for the presence of a bacterial infection (group A streptococcus).


There's no "cure" for mono so there's not much your doctor can do for you but help you to feel better while your body fights off the infection. Since there are no antiviral drugs available that have any affect on EBV, medication is limited to acetaminophen (e.g., Tylenol®) for fever and pain, and steroids (e.g., prednisone) if severe inflammation of the airways develops. If a bacterial infection is also found, your doctor may prescribe an antibiotic (although not ampicillin or amoxycillin).

People with mono are advised to rest until the symptoms have disappeared, typically 2 to 4 weeks, occasionally more. No heavy lifting or no contact sports for 3 weeks are also recommended. In most cases mono runs its course within a few weeks with no serious complications.


There is no vaccine to prevent mono. The only thing you can do is avoid contact with the saliva or respiratory secretions of people known to have mono but even that's not foolproof.


Serious complications are extremely rare. If the spleen ruptures, a splenectomy may have to be done, resulting in a weakened immune system for life. This is why it's so important to avoid playing contact sports as long as recommended.

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