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). It is passed from person to person through contact with someone else's saliva, such as through:
Many people get EBV during their lifetime. Things that raise the risk that EBV will turn into mono are:
Getting mono once means a person will be immune to it in the future.
Signs of mono start 4 to 7 weeks after a person was exposed to the virus. The first symptoms may be a sense of weakness that lasts about 1 week. Next, a person may have:
The doctor will ask about symptoms and past health. A physical exam will be done.
Blood tests may be done to look for signs of infection.
There is no way to cure mono or to shorten the length of the illness. It lasts 4 to 6 weeks, but the lack of energy may last longer.
The goal is to manage symptoms. Choices are:
To lower the risk of this problem:
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
Dunmire SK, Verghese PS, et al. Primary Epstein-Barr virus infection. J Clin Virol. 2018 May;102:84-92.
Ebell MH, Call M, et al. Does this patient have infectious mononucleosis?: The rational clinical examination systematic review. JAMA. 2016 Apr 12;315(14):1502-1509.
Epstein-Barr virus (EBV) infection. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/epstein-barr-virus-ebv-infection . Accessed October 28, 2020.
Mononucleosis. Family Doctor—Academy of Family Physicians website. Available at:
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Accessed October 28, 2020.
Last reviewed September 2020 by
EBSCO Medical Review Board James P. Cornell, MD
Last Updated: 4/30/2021