About Infectious Mononucleosis (Mono)

Key points

  • Infectious mononucleosis, also called “mono,” is a contagious disease.
  • Most people with mono get better in 2 to 4 weeks, but some may feel fatigued for several more weeks.
  • There is no vaccine to protect against infectious mononucleosis.
College student experiencing fatigue from mono.

What is it

Infectious mononucleosis is a contagious disease most commonly caused by Epstein-Barr virus (EBV). Other viruses can also cause this disease.

Infectious mononucleosis is common among teenagers and young adults, especially college students. At least 1 out of 4 teenagers and young adults who get infected with EBV will develop infectious mononucleosis.

Sign and symptoms

When you feel sick‎

Typical symptoms of infectious mononucleosis usually appear 4 to 6 weeks after you get infected with EBV. Symptoms may develop slowly and may not all occur at the same time.

Symptoms of infectious mononucleosis include:

  • Extreme fatigue
  • Fever
  • Sore throat
  • Headaches and body aches
  • Swollen lymph nodes in the neck and armpits
  • Swollen liver or spleen or both
  • Rash

Enlarged spleen and a swollen liver are less common symptoms. For some people, their liver or spleen or both may remain enlarged even after their fatigue ends.

While most people get better in 2 to 4 weeks, some may feel fatigued for several more weeks. Occasionally, the symptoms of infectious mononucleosis can last for 6 months or longer.

Causes and spread

EBV is the most common cause of infectious mononucleosis, but other viruses can cause this disease. Typically, these viruses spread most commonly through bodily fluids, especially saliva.

However, these viruses can also spread through blood and semen during sexual contact, blood transfusions, and organ transplantations.

Keep Reading: How EBV Spreads

Other causes

Other infections that can cause infectious mononucleosis include:


There is no vaccine to protect against infectious mononucleosis.

You can help protect yourself by not kissing people who have infectious mononucleosis; or sharing drinks, food, or personal items (like toothbrushes) with them.

Testing and diagnosis

Healthcare providers typically diagnose infectious mononucleosis based on symptoms.

Laboratory tests are not usually needed to diagnose infectious mononucleosis. However, specific tests may be needed for patients who do not have a typical case of infectious mononucleosis.

The blood work of patients who have infectious mononucleosis due to EBV infection may show:

  • More white blood cells (lymphocytes) than normal
  • Unusual looking white blood cells (atypical lymphocytes)
  • Fewer than normal neutrophils or platelets
  • Abnormal liver function

Treatment and recovery

Most people get better in 2 to 4 weeks. You can help relieve symptoms of infectious mononucleosis by:

  • Drinking fluids to stay hydrated
  • Getting plenty of rest
  • Taking over-the-counter medications for pain and fever

Do not take penicillin antibiotics

If you have infectious mononucleosis, you should not take penicillin antibiotics like ampicillin or amoxicillin. Based on the severity of the symptoms, a healthcare provider may recommend treatment of specific organ systems affected by infectious mononucleosis.

Avoid contact sports

Because your spleen may become enlarged as a result of infectious mononucleosis, you should avoid contact sports until you fully recover. Participating in contact sports can be strenuous and may cause the spleen to rupture.