Mononucleosis, Infectious

Infectious mononucleosis (in-FEK-shus mon-o-noo-klee-O-sis) is an illness caused by a virus * that may lead to symptoms such as fever, sore throat, swollen glands in the neck, and tiredness.


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Epstein-Barr virus


* virus (VY-rus) is a tiny infectious agent that lacks an independent metabolism (me-TAB-o-liz-um) and can only reproduce within the cells it infects.

Kim's Story

When Kim came down with a sore throat and headache, she thought maybe she had caught the flu. By the next day, though, she had a fever, and her throat was so swollen that she could hardly swallow. Worse yet, she felt so tired that she could barely drag herself out of bed. Kim's mother took her to the doctor's office, where a physical exam and blood test revealed that she had infectious mononucleosis. This is a common illness, especially in young people, that is caused by a virus. Mononucleosis, or "mono" for short, is often called the "kissing disease," and Kim took some teasing once she got better and went back to school. However, the doctor had explained to Kim that kissing someone with mono is just one way to catch the illness. It can also be spread by sharing a straw or cup, sneezing, or coughing.

What Is Infectious Mononucleosis?

Infectious mononucleosis is an illness that may lead to symptoms such as fever, sore throat, swollen glands in the neck, and tiredness. Although there are a number of infections that cause a mononucleosis-like condition, when people say mono they are referring to the infection caused by the Epstein-Barr virus (EBV). This is a common virus that may infect four out of five people by the time they are 40 years old. This virus is related to the ones that cause cold sores and chickenpox. EBV infects the blood cells and salivary (SAL-i-var-ee) glands (the glands that make saliva). Some people who are infected by this virus get mono, while others never develop symptoms. Once a person catches the virus, it stays in the body in a dormant or inactive condition for life, and it may show up in the saliva again from time to time. However, a person probably will not have the symptoms of mono again from the virus.

Mono is often called the "kissing disease." Andy Levin, Photo Researchers, Inc.
Mono is often called the "kissing disease."
Andy Levin, Photo Researchers, Inc.

EBV is spread through contact with infected saliva, by such means as kissing or sharing a straw or cup. It also can be passed by coughing or sneezing. If the symptoms of mono develop, they usually show up 2 to 7 weeks after exposure. Anyone of any age can catch EBV. When it strikes young children, though, it usually does not cause symptoms. EBV is more likely to cause problems in people who do not become infected until the teenage years or later. In fact, up to four out of five cases of full-blown mono occur in people between the ages of 15 and 30. The number of new cases peaks in those 15 to 17 years old. The disease is particularly common in teenagers and people in their twenties who are in high school, college, or the military.

Did You Know?

  • When people of all ages are taken into account, only about 50 out of every 100,000 Americans have mononucleosis symptoms each year.
  • Mononucleosis is much more common in young people, however, striking as many as 2 out of every 1,000 teenagers and twenty-somethings each year.

* tonsils are paired clusters of lymph tissues in the throat. They help protect the body from bacteria that enter through a person's nose or mouth.

What Are the Symptoms of Mononucleosis?

Mononucleosis usually is not a serious illness, and many people with mono have few or no symptoms at all. However, it can slow a person down for weeks or even months, since most people who get mono can feel very tired for several months. In teenagers and young adults, the ill-ness usually starts slowly, and the early symptoms are similar to those of the flu. They may include a general sense of not feeling well, along with tiredness, headache, chilliness, puffy eyelids, and loss of appetite. Other symptoms may develop later:

  • Sore throat
  • Tiredness
  • Fever. A fever of 101 degrees Fahrenheit to 105 degrees Fahrenheit lasts typically for about 5 days, and it sometimes comes and goes for up to 3 weeks.
  • Swollen glands. These are common in the neck, but they occur also under the arm and in the groin (the area where the inner thighs join the trunk).
  • Other symptoms. These can include swollen tonsils * , difficulty swallowing, bleeding gums, and a skin rash that lasts 1 or 2 days.

Occasionally, a more serious problem arises. Some people with mono have a swollen spleen * . In a few cases, the enlarged spleen may rupture, or break open, causing a sudden, sharp pain in the upper left part of the abdomen * . If this happens, emergency medical help is needed right away. To lower the risk of a ruptured spleen, people with mono often are advised not to lift heavy objects, do strenuous exercise, or take part in contact sports for 2 months after they get sick.

How Is Mononucleosis Diagnosed and Treated?

If mononucleosis is suspected, doctors will ask about symptoms and perform a physical exam. Many other viruses can cause symptoms similar to mono, however. To be sure of the diagnosis, the doctor may also order a blood test. One common test that can show indirectly the presence of EBV is called the Monospot test. If the results of the Monospot test are not clear, other blood tests may be needed.

There is no cure for mono. Antibiotics (an-ty-by-OT-iks), drugs that work against diseases caused by bacteria * , do not work against EBV. Rest is the only real treatment. In addition, drinking plenty of fluids can help relieve fever and a sore throat. Taking over-the-counter painkillers such as acetaminophen (a-set-a-MEE-no-fen) or ibuprofen (i-bu-PRO-fun), sucking on throat lozenges, or gargling several times a day with warm salt water may also help. The good news is that, even with no other treatment, the disease will almost always go away by itself, usually in 1 to 3 weeks. For some, however, it may take 2 to 3 months to feel totally back to normal.

* spleen is a large organ in the upper left part of the abdomen that stores and filters blood and also plays a role in making and breaking down blood cells.

* abdomen (AB-do-men), commonly called the belly, is the portion of the body between the chest and the pelvis.

* bacteria (bak-TEER-ee-a) are round, spiral, or rod-shaped single-celled microorganisms without a distinct nucleus that commonly multiply by cell division. Some types may cause disease in humans, animals, or plants.

See also
Viral Infections



Silverstein, Alvin, Virginia Silverstein, and Robert Silverstein. Mononucleosis. Springfield, NJ: Enslow Publishers, 1994.


U.S. National Institute of Allergy and Infectious Diseases, NIAID Office of Communications and Public Liaison, 31 Center Drive, Building 31, Room 7A-50, Bethesda, MD 20892-2520. Part of the U.S. National Institutes of Health (NIH), NIAID publishes a pamphlet called Infectious Mononucleosis.
Telephone 301-496-5717

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