Mononucleosis, Infectious

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

What Is Mononucleosis?

By the time they are 40 years old, as many as 95 percent of all 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 situation 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 15–25). One-third to one-half of teens who come into contact with the virus for the first time develop symptoms of classic infectious mono: sore throat, swollen lymph nodes, fever, and extreme tiredness.

Kiss and Tell

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

Signs and symptoms of infectious mononucleosis.

Signs and symptoms of infectious mononucleosis.
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-in-JEE-ul kar-sih-NO-muh, a cancer in the throat area seen mainly in China). EBV is also linked to lymphoma in the United States, most notably in people with weakened immune systems, such as people who have HIV.

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 EBVrelated 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.

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 (nose, mouth, throat, and lungs), it usually is not transmitted by coughing or sneezing. Some people become sick and are 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.

How Do People Know They Have Mononucleosis?

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

How Is Mononucleosis Diagnosed and Treated?

Symptoms of mono usually show up one to four 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 can confirm the diagnosis. A blood count will show an increased number of lymphocytes * * testing may be done to rule out other viruses that can cause mono-like illnesses. Antibody testing checks several antibodies to determine whether 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-thecounter medications such as acetaminophen * 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 one month and to be examined and get a doctor's permission before they start again.

Symptoms of mono usually clear up one to two months after they appear, but they can last as long as four 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 have some liver inflammation, but only a small number have significant inflammation, or hepatitis * . 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-Barré (gee-YAN ba-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-oh-kar-DYE-tis, an inflammation of the muscular walls of the heart) is a rare complication.

EBV has also 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.

See also AIDS and HIV Infection • Cytomegalovirus (CMV) Infection • Encephalitis • Hepatitis • Myocarditis and Pericarditis


Books and Articles

Bradford, Alina. “Mono: Symptoms, Diagnosis and Treatment Options.” Live Science. December 24, 2014. (accessed October 28, 2015).

Crow, Diana. “The Epstein–Barr Virus Wears Chain Mail.” Scientific American. October 13, 2014. (accessed November 19, 2015).

“The Secret Life of the Epstein-Barr Virus.” . February 16, 2010. (accessed November 19, 2015).


Centers for Disease Control and Prevention. “Epstein-Barr Virus and Infectious Mononucleosis.” . html (accessed November 19, 2015).

Khanna, Rajiv. “Kissing the Epstein-Barr Virus Goodbye?” PBS Nova. (accessed November 19, 2015).

MedlinePlus. “Infectious Mononucleosis.” U.S. National Library of Medicine, National Institutes of Health. (accessed October 28, 2015).

Merck Manual: Consumer Version. “Infectious Mononucleosis.” (accessed November 19, 2015).


Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329. Toll-free: 800-232-4636. Website: (accessed October 28, 2015).

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

* acute describes an infection or other illness that comes on suddenly and usually does not last very long.

* cytomegalovirus (sy-tuh-MEHguh-lo-vy-rus) is a common infection usually causing no symptoms. It poses little risk for healthy people, but it can lead to serious illness in people with weak immune systems.

* HIV or human immunodeficiency virus (HYOO-mun ih-myoono-dih-FIH-shen-see) is the virus that causes AIDS (Acquired Immunodeficiency Syndrome), an infection that severely weakens the immune system.

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

* 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.

* strep throat is a contagious sore throat caused by a strain of bacteria known as Streptococcus.

* acetaminophen (uh-see-teh-MIH-noh-fen) is a medication commonly used to reduce fever and relieve pain.

* ibuprofen (eye-bew-PRO-fin) is a nonsteroidal anti-inflammatory drug (NSAID) used to reduce fever and relieve pain or inflammation.

* 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.

* hepatitis (heh-puh-TIE-tis) is an inflammation of the liver. Hepatitis can be caused by viruses, bacteria, and a number of other noninfectious medical conditions.

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

* paralysis (pah-RAHL-uh-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 the lymphocytes, cells that normally help the body fight infection.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)