Symptoms and causes

Symptoms

Signs and symptoms of mononucleosis may include:

  • Fatigue
  • Sore throat, perhaps a strep throat that doesn't get better with antibiotic use
  • Fever
  • Swollen lymph nodes in your neck and armpits
  • Swollen tonsils
  • Headache
  • Skin rash
  • Soft, swollen spleen

The virus has an incubation period of approximately four to six weeks, although in young children this period may be shorter. Signs and symptoms such as a fever and sore throat usually lessen within a couple of weeks, but fatigue, enlarged lymph nodes and a swollen spleen may last for a few weeks longer.

When to see your doctor

If you've been experiencing the above symptoms, you may have mononucleosis.

If rest and a healthy diet don't ease your symptoms within a week or two or if your symptoms recur, see your doctor.

Causes

The most common cause of mononucleosis is the Epstein-Barr virus, but other viruses can also cause this disease.

Mononucleosis usually isn't very serious. Most adults have been exposed to the Epstein-Barr virus and have built up antibodies. They're immune and won't get mononucleosis again.

Complications

Complications of mononucleosis may be more serious than the disease itself.

Enlargement of the spleen

Mononucleosis may cause enlargement of the spleen. In extreme cases, your spleen may rupture, causing sharp, sudden pain in the left side of your upper abdomen. If such pain occurs, seek medical attention immediately — you may need surgery.

Liver issues

Problems with your liver also may occur:

  • Hepatitis. You may experience mild liver inflammation (hepatitis).
  • Jaundice. A yellowing of your skin and the whites of your eyes (jaundice) also occurs occasionally.

Less common complications

Mononucleosis can also result in the following less common complications:

  • Anemia — a decrease in red blood cells and in hemoglobin, an iron-rich protein in red blood cells
  • Thrombocytopenia — low count of platelets, which are blood cells involved in clotting
  • Heart problems — an inflammation of the heart muscle (myocarditis)
  • Complications involving the nervous system — meningitis, encephalitis and Guillain-Barre syndrome
  • Swollen tonsils — which can block breathing

The Epstein-Barr virus can cause much more serious illness in people who have impaired immune systems, such as people with HIV/AIDS or people taking drugs to suppress immunity after an organ transplant.