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What is mono?

Infectious mononucleosis, or mono, is a viral infection caused by the Epstein-Barr virus. It occurs most often in adolescents and young adults, but people can get it at any age.

Although people can be very sick, mono is usually not serious and requires little treatment. Most of the time, the body’s immune system overcomes mono on its own within one to two months.


Symptoms of mononucleosis are similar to other common viruses like the flu. Typical symptoms include:

  • Fever
  • Fatigue
  • Sore throat
  • Swollen lymph glands
  • Headache
  • Muscle weakness
  • Swollen tonsils
  • Rash
  • Swollen spleen or liver (very rare)

How is it diagnosed?

If you have these symptoms and they last for more than 2 weeks, see your physician. He or she can sometimes diagnose mono through a physical exam.

To confirm a diagnosis of mono, you may need additional tests including:

  • Blood test to check for elevated white blood cell levels
  • Mono spot test to look for specific antibodies to the Epstein-Barr virus in the blood
  • Throat swab to rule out streptococcal infections
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