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-steen BAR) virus (EBV). It often leads to fever, sore throat, swollen lymph nodes ^* , and tiredness.

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.

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.

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.

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.