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Mononucleosis

Infectious mononucleosis (mono) is a condition usually caused by the Epstein-Barr virus (EBV) or, less commonly, cytomegalovirus (CMV).

Mono is sometimes called the "kissing disease" because it is spread through saliva, shared drinking cups and utensils, and close contact.

Symptoms (fever, sore throat, swollen lymph glands, enlarged tonsils, and extreme fatigue) appear approximately four to eight weeks after exposure. Infected persons "shed" the virus in their saliva and can be contagious for about  six months. The virus eventually becomes dormant but never fully goes away. It can be potentially activated again if your immune system is weakened. 

Mono is treated with rest and symptom management. Prescription drugs are rarely needed. 

Frequently Asked Questions

  • What causes mononucleosis?

    Infection by the Epstein-Barr virus (EBV) is the most common cause of mononucleosis, but other viruses can cause mono-like illnesses too, such as cytomegalovirus (CMV).

  • How do you get mononucleosis?

    Mononucleosis is primarily spread through bodily fluids, especially saliva, but also through mucus, blood, semen, and vaginal secretions. Sharing a cup, straw, or eating utensil can contribute to the spread of EBV. Blood transfusions and organ transplantations can also spread the virus. One out of 4 teens or young adults who get infected with EBV will develop mono.

  • How long does mononucleosis last?

    The incubation period for mono is four to eight weeks, which means that symptoms set in at least a month after you've been exposed to the virus. Some symptoms may only last for a few days, while others, such as fatigue, may persist for months. Mono symptoms  last for two to four weeks in most people.

  • How many times can you get mononucleosis?

    In most cases, you'll only get mono once, but as the EBV virus stays in your body for the rest of your life, it is possible that mono could make a comeback. This is rare, and generally only likely if your immune system is weakened by another infection such as HIV, an organ transplant, or pregnancy. It's also possible to get mono from a virus other than EBV, even if you already have EBV.

Key Terms

Page Sources
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  1. Centers for Disease Control and Prevention. Epstein-Barr Virus and Infectious Mononucleosis. About Infectious Mononucleosis. Updated September 28, 2020.

  2. Centers for Disease Control and Prevention. Epstein-Barr Laboratory Testing. Updated May 10, 2018.

  3. Kim HJ, Ko YH, Kim JE, et al. Epstein-Barr virus-associated lymphoproliferative disorders: Review and update on 2016 WHO classification. J Pathol Transl Med. 2017;51(4):352-358. doi:10.4132/jptm.2017.03.15

  4. Womack J, Jimenez M. Common questions about infectious mononucleosis. Am Fam Physician. 2015;91(6):372-376.

  5. Schechter S, Lamps L. Epstein-barr virus hepatitis: a review of clinicopathologic features and differential diagnosisArchives of Pathology & Laboratory Medicine. 2018;142(10):1191-1195. doi:10.5858/arpa.2018-0208-RA.

Additional Reading