What is infectious mononucleosis (mono)?

Infectious mononucleosis is a type of infection. It causes swollen lymph glands, fever, sore throat, and often extreme fatigue. It’s often spread through contact with infected saliva from the mouth. Symptoms can take between 4 to 6 weeks to appear. They often don't last beyond 4 months. Transmission is hard to prevent because even people without symptoms can carry the virus in their saliva.

What causes mono?

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 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, 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.

What are the symptoms of mono?

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

• Rash

• 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. They are usually not at risk of getting the illness again, unless their immune system is weakened.

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

How is mono diagnosed?

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.

• EBV-specific 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 have another condition. Or it can be falsely negative even if you have the illness.

How is mono treated?

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

What are possible complications of mono?

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

Can mono be prevented?

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 while they remain symptomatic.

When should I call my healthcare provider?

If your symptoms get worse or you have new symptoms, let your healthcare provider know.

Key points about infectious mononucleosis (mono)

• Infectious mononucleosis causes swollen lymph glands, fever, sore throat, and extreme fatigue.

• The illness usually lasts for 1 to 2 months.

• Symptoms may include fever, constant fatigue, sore throat, enlarged spleen, rash, liver inflammation, and swollen lymph glands in the neck, armpits, and groin.

• Treatment includes getting rest, drinking lots of liquids, and taking over-the-counter medicines for discomfort and fever. You should also avoid too much pressure on the stomach area.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your provider if you have questions.