Mononucleosis, Infectious

Mononucleosis Infectious 2360
Photo by: Lisa Eastman

Infectious mononucleosis (mah-no-nu-klee-O-sis), also known as mono, is an infectious illness usually caused by the Epstein-Barr (EP-steen BAR) virus (EBV). It often leads to fever, sore throat, swollen lymph nodes * , and tiredness.


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Burkitt's lymphoma


Epstein-Barr virus (EBV)


What Is Mononucleosis?

By the time they are 40, as many as 95 percent of adults in the United States have evidence in their blood of a previous EBV infection. Many of these infections are never recognized, especially if they occur in early childhood, because the symptoms look like those of other childhood viral illnesses. Some people infected with EBV have no symptoms. This occurs in many parts of the world where most people are infected early in life. In the United States, EBV infection is most common during adolescence and early adulthood (ages 15 to 25). One-third to one-half of teens who come into contact with the virus for the first time will develop symptoms of classic infectious mono: sore throat, swollen lymph nodes, fever, and extreme tiredness.

Mono most often is associated with acute * infection by EBV, but it is sometimes seen with acute cytomegalovirus * (CMV) infection, acute HIV * infection, and, rarely, other viruses.

Although the symptoms may be unpleasant, mono is generally a mild disease. After a person recovers, the virus remains dormant (inactive) in the body for life. It occasionally may reactivate but it rarely causes symptoms again. When people have been infected with the virus, whether or not they had symptoms, they usually will be immune * to future EBV-related illness.

How Common Is Mononucleosis?

EBV is one of the most common human viruses in the world. In the United States, cases of mono with symptoms most often are found in teens between the ages of 15 and 17. The illness occurs in 2 out of every 1,000 adolescents and young adults and is less common in other age groups.

* lymph (LIMF) nodes are small, bean-shaped masses of tissue that contain immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

* acute describes an infection or other illness that comes on suddenly.

* cytomegalovirus (sy-tuh-MEH-guh-lo-vy-rus), or CMV, infection is very common and usually causes no symptoms. It poses little risk for healthy people, but it can lead to serious illness in people with weak immune systems.

* HIV, or the human immunodeficiency (HYOO-mun ih-myoo-no-dih-FIH-shen-see) virus, is the virus that causes AIDS (acquired immunodeficiency syndrome).

* immune (ih-MYOON) means resistant to or not susceptible to a disease.

* respiratory tract includes the nose, mouth, throat, and lungs. It is the pathway through which air and gases are transported down into the lungs and back out of the body.

How Is Mononucleosis Spread?

Mono is contagious, although less so than the common cold. EBV passes from person to person primarily through contact with saliva. Kissing and sharing food, drinks, or utensils commonly spread the virus. Although EBV is present in the respiratory tract * , it usually is not transmitted by coughing or sneezing. Some people will become sick and be able to spread the virus for weeks, especially those who are infected but do not feel sick and pass the virus to others without realizing it. The virus usually remains inactive after the first infection, but some people may spread it from time to time throughout their life.

A person with mononucleosis typically has inflamed, pus-covered tonsils and may also have high fever and swollen lymph nodes. Dr. P. Marazzi/Science Photo Library
A person with mononucleosis typically has inflamed, pus-covered tonsils and may also have high fever and swollen lymph nodes.
Dr. P. Marazzi/Science Photo Library

How Do People Know They Have Mononucleosis?

Symptoms of mono develop between 4 and 6 weeks after infection and generally last 2 to 4 weeks. These include swollen lymph nodes, extreme tiredness, fever, sore muscles, and sore throat. Up to 50 percent of people with classic infectious mononucleosis will have a swollen spleen, and some will have an enlarged liver. Other symptoms may include loss of appetite, weakness, nausea (NAW-zee-uh), stiffness, headache, chest pain, and, rarely, jaundice * .

How Is Mononucleosis Diagnosed and Treated?

Symptoms of mono usually show up 1 to 4 weeks before the diagnosis is made. A physical exam, the patient's age, and sometimes a history of contact with an infected person help the doctor make the diagnosis. An adolescent patient with a lasting fever, sore throat, and swollen lymph nodes, with or without an enlarged spleen, is likely to have mono.

Blood tests will confirm the diagnosis. A blood count will show an increased number of lymphocytes * , and many of them will look unusual. A positive rapid screening test may confirm the diagnosis by revealing EBV in the blood, but this test can be negative, especially early in the illness. More accurate antibody * testing may be done to rule out other viruses that can cause mono-like illnesses. Antibody testing checks several antibodies to determine if there is a current infection or evidence of past infection.

There is no specific treatment for mono. Because it is a viral illness, antibiotics are not prescribed unless a secondary bacterial illness is present, such as strep throat. The best treatment for mono is rest. Over-the-counter medications such as acetaminophen (uh-see-teh-MIH-noh-fen) or ibuprofen may be taken to relieve fever and pain.

Steroids, medications that reduce inflammation, may be given to decrease swelling in the tonsils * and lymph nodes in the neck if a patient is experiencing difficulty swallowing or breathing. Playing contact sports is prohibited for someone who has mono because when the spleen and liver enlarge, they are more vulnerable to injury. Patients with mono are advised not to play contact sports for at least 1 month and to be examined and get a doctor's permission before they start again.

* jaundice (JON-dis) is a yellowing of the skin, and sometimes the whites of the eyes, caused by a buildup in the body of bilirubin, a chemical produced in and released by the liver. An increase in bilirubin may indicate disease of the liver or certain blood disorders,

* lymphocytes (LIM-fo-sites) are white blood cells, which play a part in the body's immune system, particularly the production of antibodies and other substances to fight infection.

* antibody (AN-tih-bah-dee) is a protein molecule produced by the body's immune system to help fight a specific infection caused by a microorganism, such as a bacterium or virus.

* tonsils are paired clusters of lymphatic tissue in the throat that help protect the body from bacteria and viruses that enter through a person's nose or mouth.

Kiss and Tell

Mono often is referred to as the "kissing disease" because the infection is spread primarily through direct contact with infected saliva.

Symptoms of mono usually clear up 1 to 2 months after they appear, but they can last as long as 4 months.

What Are Some Complications of Mononucleosis?

Recovery from mono is usually uneventful, but sometimes complications occur. An enlarged spleen may rupture, which is an emergency that needs surgery. Fifty percent of patients with infectious mononucleosis will have some liver inflammation, but only a small number will have significant inflammation, or hepatitis (heh-puh-TIE-tis). Blood problems that can result from the infection include anemia * , decreased white cells (cells that fight infection), and low numbers of platelets (cells that help the blood clot). Mononucleosis also can lead to encephalitis (en-seh-fuh-LYE-tis, inflammation of the brain), Guillain-Barre (GEE-yan bah-RAY) syndrome (an inflammation of the nerves, which causes muscle weakness and paralysis * ), and Bell's palsy (PAWL-zee, a temporary weakness or paralysis of the muscles on one side of the face). Myocarditis (my-ohkar-DYE-tis, an inflammation of the muscular walls of the heart) is a rare complication.

EBV also has been associated with cancers, such as lymphoma * , especially in patients with weak immune systems, such as people who have had organ transplants or who have HIV.

Can Mononucleosis Be Prevented?

There is nothing specific that a person can do to avoid contracting mono because EBV often is spread in the saliva of healthy people who have been infected in the past and who can still transmit the virus. Normal human behavior makes it practically impossible to prevent the spread of the disease.

EBV and Cancer

EBV has been linked to the development later in life of Burkitt's lymphoma (a rare blood disease of the lymph nodes seen mainly in Africa) and nasopharyngeal carcinoma (nay-zo-fair-inJEE-ul kar-sih-NO-muh, a cancer in the throat area seen mainly in China). EBV also is linked to lymphoma in the United States, most notably in people with weakened immune systems, such as people who have HIV.

* anemia (uh-NEE-me-uh) is a blood condition in which there is a decreased amount of oxygen-carrying hemoglobin in the blood and, usually, fewer than normal numbers of red blood cells.

* paralysis (pah-RAH-luh-sis) is the loss or impairment of the ability to move some part of the body.

* lymphoma (lim-FO-muh) refers to a cancerous tumor of lymphocytes, cells that normally help the body fight infection.



U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC is the U.S. government authority for information about infectious and other diseases. It posts information about mononucleosis at its website.
Telephone 800-311-3435

U.S. National Library of Medicine, 8600 Rockville Pike, Bethesda, MD 20894. The National Library of Medicine has a website packed with information on diseases such as mononucleosis, consumer resources, dictionaries and encyclopedias of medical terms, and directories of doctors and helpful organizations.
Telephone 888-346-3656

Website . KidsHealth is a website created by the medical experts of the Nemours Foundation and is devoted to issues of children's health. It contains articles on a variety of health topics, including mononucleosis.

See also
AIDS and HIV Infection
Cytomegalovirus (CMV) Infection
Hepatitis, Infectious

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