Infectious mononucleosis is caused by the Epstein-Barr virus (EBV). A milder form is caused by the cytomegalovirus (CMV). Both EBV and CMV are members of the herpes virus family.

In the U.S., most adults have been infected by age 30 with the EBV. This is a very common virus. When children are infected with it, they often don't have any noticeable symptoms. But uninfected teens and young adults who come in contact with the virus may develop infectious mononucleosis.

Even after the symptoms of infectious mononucleosis have gone away, the EBV will stay dormant in the throat and blood cells throughout that person's life. The virus can reactivate from time to time in the saliva or blood. But it almost always does not cause symptoms.

This illness usually lasts for 1 to 2 months. Each person may have different symptoms. But these are the most common symptoms of mononucleosis:

• Fever
• Swollen lymph glands in the neck, armpits, and groin
• Extreme fatigue
• Sore throat, including white patches in the back of the throat
• Enlarged spleen
• Head and body aches
• Liver problems, such as mild liver inflammation that can rarely cause temporary jaundice, a yellow discoloring of the skin and whites of the eyes due to abnormally high levels of bilirubin (bile pigmentation) in the bloodstream

Once a person has had mononucleosis, the virus remains dormant in the throat and blood cells for the rest of that person's life. He or she is usually not at risk for getting the illness again, unless his or her immune system is weakened.

The symptoms of mononucleosis may look like other health problems. Always talk with your healthcare provider for a diagnosis.

Your healthcare provider will ask about your symptoms. You may also need certain blood tests, such as:

• White blood cell count. The presence of certain types of white blood cells (atypical lymphocytes) may support the diagnosis.
• Antibodies. These may be in the blood in response to certain parts of the EBV or CMV.
• Heterophile antibody test. This is the so-called monospot test. If positive, it may mean you have infectious mononucleosis. But this test may be falsely positive if you actually have another condition. Or it can be falsely negative even if you have the illness.

Treatment will depend on your symptoms, age, and general health. It will also depend on how severe the condition is.

Antiviral antibiotics don't help the body get rid of the infection quicker. Treatment for mononucleosis may include:

• Getting rest to give the body's immune system time to kill the virus
• Drinking lots of liquids
• Taking over-the-counter medicine as directed for discomfort and fever
• Not playing contact sports or putting too much pressure on the stomach and right side of back area to avoid hurting the spleen
• Taking corticosteroids only when needed to reduce swelling of the throat and tonsils

Complications don’t happen often. They may include:

• Ruptured spleen
• Kidney inflammation
• Hemolytic anemia
• Nervous system problems, such as encephalitis, meningitis, and other health problems
• Inflammation of the heart muscle
• Heart rhythm problems
• Obstruction of the upper airways

It can't be prevented. But it is wise to not kiss or share dishes, food utensils, or personal items with anyone who has the infection and symptoms.