Mononucleosis (mono) is an infection caused by a virus. It is marked by fever, lack of energy, and swollen glands.
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Mono is caused by the Epstein-Barr virus (EBV). Found mainly in saliva and mucus, it is passed from person to person by intimate behavior, such as kissing.
Many people get EBV during their lifetime. Here are factors that raise the chance that EBV will turn into mono:
Getting mono once means you will be immune to it in the future.
Signs of mono start 4 to 7 weeks after you were exposed to the virus. The first symptoms may be a sense of weakness that lasts about 1 week. Next, you may have:
You will be asked about your symptoms and health history. A physical exam will be done.
Your bodily fluids may be tested. This can be done with blood tests.
There is no way to cure mono or to shorten the length of the illness. It lasts 4-6 weeks, but the lack of energy may last longer.
During the first few weeks, you should not play contact sports or lift anything heavy. A swollen spleen puts you at high risk of splenic rupture. This needs surgery. In rare cases, it can be fatal.
Get plenty of rest. Other steps may be to:
You can prevent mono by:
Centers for Disease Control and Prevention
National Institute of Allergy and Infectious Diseases
About Kids Health—The Hospital for Sick Children
The College of Family Physicians of Canada
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Epstein-Barr virus infection. EBSCO DynaMed Plus website. Available at: https://www.dynamed.com/topics/dmp~AN~T904534/Epstein-Barr-virus-EBV-infection . Updated January 5, 2018. Accessed July 17, 2018.
Luzuriaga K, Sullivan JL. Infectious mononucleosis. N Engl J Med. 2010 May 27;362(21):1993-2000.
Mononucleosis. Academy of Family Physicians Family Doctor website. Available at:
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Updated October 24, 2017. Accessed July 17, 2018.
Last reviewed May 2018 by James Cornell, MD
Last Updated: 7/18/2018