Infectious Mononucleosis (Mono)

Physician checking lymph nodes on a young female patient's neck.

Infectious mononucleosis, or “mono”, is an infection that causes fever, inflamed tonsils, fatigue, and swollen lymph nodes. It is most commonly caused by the Epstein-Barr Virus (EBV) and transmitted from person to person, mainly through saliva, but also through other body fluids. It is not highly contagious, so becoming infected requires close contact with another person who is infected. After infection, people can shed the virus in their saliva for up to 6 months, but sometimes even longer.

What are the symptoms of mono?

People of any age can become infected with mono, but it is much less common for younger children to be symptomatic. The peak age for a symptomatic mono infection is between 15-24 years old.

The typical symptoms include:

Fever
Fatigue
Inflamed and enlarged tonsils
Swollen lymph nodes
Sore throat
Pain or difficulty with swallowing
Headaches
Nausea and low appetite

Most symptoms resolve within 1 month, but fatigue can be more severe and prolonged, sometimes lasting as long as 6 months.

An enlarged spleen can occur in about 50% of cases. People with mono who develop an enlarged spleen should not return to sports until their spleen has returned to normal size. This is because the enlarged spleen may rupture and bleed into the abdomen. Rupture of the spleen is a rare, but potentially life-threatening situation. Usually, the spleen starts to return to its normal size at around the third week of illness.

How is mono diagnosed?

Mono can often be diagnosed based on your symptoms and the physical exam done by your doctor. A blood test can help confirm the diagnosis by detecting the presence of EBV antibodies. Mono will also cause an abnormal increase in a type of white blood cell called a lymphocyte.

What is the treatment?

Mono is caused by a virus, so it is not treated with antibiotics. The main treatments are to help the patient feel more comfortable. Tylenol and/or Ibuprofen can be taken to relieve fever and pain. A saltwater gargle is recommended for sore throat and lots of rest can help with fatigue.

In rare cases, the pain with swallowing may be so significant that a hospital admission for IV fluids is required. Rarely, the swelling of the tonsils can become large enough that it blocks the airway. In these cases, steroids will be needed as well.

When can you return to work or school?

Since the virus can shed for a very long time and is not highly contagious, there are no restrictions on returning to school or work. Usually, return to school or work will be based on the level of fatigue and severity of other symptoms.