Symptoms vary, but the most common are extreme fatigue, fever, sore throat, and swollen lymph nodes.
A blood test is done to confirm the diagnosis.
Acetaminophen or nonsteroidal anti-inflammatory drugs can relieve fever and pain.
Infection with the Epstein-Barr virus (EBV) is very common. EBV is a type of herpesvirus Overview of Herpesvirus Infections Some common viral infections are caused by herpesviruses. Eight different herpesviruses infect people: Three herpesviruses— herpes simplex virus type 1, herpes simplex virus type 2, and varicella-zoster... read more called herpesvirus 4. In the United States, about 50% of all children 5 years of age and nearly 95% of adults have had an EBV infection.
Most EBV infections cause no symptoms. Infectious mononucleosis typically develops in adolescents and young adults who are infected with EBV. Infectious mononucleosis is named for the large numbers of a certain type of white blood cell (mononuclear cells) in the bloodstream. Adolescents and young adults usually catch infectious mononucleosis by kissing someone infected with EBV.
After the initial infection, EBV, like other herpesviruses, remains in the body, mainly in white blood cells, for life. Infected people shed the virus periodically in their saliva. They can infect others during shedding, which causes no symptoms.
Rarely, EBV contributes to the development of several types of cancer, such as Burkitt lymphoma Burkitt Lymphoma Burkitt lymphoma is a very fast-growing non-Hodgkin lymphoma, a cancer of white blood cells that originates from B cells (B lymphocytes). Lymphomas (see also Overview of Lymphoma) are cancers... read more 
and certain cancers of the nose and throat (nasopharyngeal cancer Nasopharyngeal Cancer Nasopharyngeal cancers are cancers originating at the back of the nasal passage, from above the soft palate to the upper part of the throat. People often develop lumps in their neck or may have... read more ). It is thought that specific viral genes alter the growth cycle of infected cells and cause them to become cancerous. EBV does not cause chronic fatigue syndrome Chronic Fatigue Syndrome , as was once suspected.
Symptoms of Infectious Mononucleosis
In most children younger than 5 years, the infection causes no symptoms. In adolescents and adults, it may or may not cause infectious mononucleosis.
The usual time between infection and the appearance of symptoms is thought to be 30 to 50 days. This interval is called the incubation period.
The four main symptoms of EBV infectious mononucleosis are
Extreme fatigue
Fever
Sore throat
Not everyone has all four symptoms. Usually, the infection begins with a general feeling of illness (malaise) and low grade fever followed by sore throat and/or swollen lymph nodes. Fatigue is often severe and is usually most severe during the first 2 to 3 weeks but may last for months. The fever usually peaks at about 103° F (about 39.5° C) in the afternoon or early evening. The throat is often very sore, and puslike material may be present at the back of the throat. Most commonly, the lymph nodes of the neck are swollen, but any lymph node may be swollen. In some people, the only symptom is swollen lymph nodes (sometimes mistakenly called "swollen glands").
The spleen is enlarged in about 50% of people with infectious mononucleosis. In most infected people, an enlarged spleen causes few if any symptoms, but it may rupture, particularly if injured. Rupture of the spleen Spleen Injury Because of the spleen’s position in the upper left side of the abdomen, a severe blow to the stomach area can damage the spleen, tearing its covering, the tissue inside, or both. An injured... read more is life threatening. The liver may also enlarge slightly. Sometimes the area around the eyes is swollen.
Rashes develop infrequently. However, people with an EBV infection who take the antibiotic ampicillin may be more likely to develop a rash.
Other very rare complications include seizures, nerve damage, behavioral abnormalities, inflammation of the brain (encephalitis Encephalitis Encephalitis is inflammation of the brain that occurs when a virus directly infects the brain or when a virus, vaccine, or something else triggers inflammation. The spinal cord may also be involved... read more ) or tissues covering the brain (meningitis Viral Meningitis Viral meningitis is inflammation of the layers of tissue that cover the brain and spinal cord (meninges) and of the fluid-filled space between the meninges (subarachnoid space) when it is caused... read more ), anemia, and blockage of airways by the swollen lymph nodes.
How long symptoms last varies. After about 2 weeks, symptoms subside, and most people can resume their usual activities. However, fatigue may persist for several more weeks and, occasionally, for months. Fewer than 1% of people die, usually because of complications such as encephalitis, rupture of the spleen, or blockage of the airways.
Diagnosis of Infectious Mononucleosis
A blood test
The symptoms of infectious mononucleosis also occur in many other viral and bacterial infections. Therefore, infectious mononucleosis is often unrecognized. However, swollen lymph nodes Swollen Lymph Nodes Lymph nodes are tiny, bean-shaped organs that filter lymph fluid. They are located throughout the body, but particular collections are found just under the skin in the neck, under the arms,... read more 
, particularly in the neck, strongly suggest infectious mononucleosis.
Usually, a simple blood test known as a heterophile antibody or monospot test is done to confirm the diagnosis. This test can sometimes be negative early in illness in adolescents and adults, and if doctors strongly suspect the infection, they can repeat the test about a week later. This test is much less reliable and often negative in young children with infectious mononucleosis. An alternative test to confirm the diagnosis is a specific antibody blood test for EBV. (Antibodies Antibodies One of the body's lines of defense ( immune system) involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and... read more 
are produced by the immune system to defend against a particular attacker, such as EBV.)
Often, a complete blood count is also done. Finding many characteristic mononuclear white blood cells (atypical lymphocytes) may be the first clue that the diagnosis is infectious mononucleosis.
Treatment of Infectious Mononucleosis
Initially rest
Pain relievers
Sometimes corticosteroids for certain complications
There is no specific treatment.
People with infectious mononucleosis are encouraged to rest during the first week or two, while symptoms are severe. After about 2 weeks, they may be more active. However, because of the risk of rupturing the spleen, heavy lifting and contact sports should be avoided for at least 1 month, until doctors confirm by examination or sometimes ultrasonography that the spleen has returned to normal size.
Acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs, such as aspirin or ibuprofen) can relieve fever and pain. However, aspirin should not be given to children because of the small risk that it may cause Reye syndrome Reye Syndrome Reye syndrome is a very rare but life-threatening disorder that causes inflammation and swelling of the brain and impairment and loss of function of the liver. The cause of Reye syndrome is... read more , which can be fatal.
Some complications, such as severe swelling of the airways, may be treated with corticosteroids.
Currently available antiviral drugs have little effect on the symptoms of infectious mononucleosis and should not be used.
