Is Mononucleosis Contagious?

Infectious mononucleosis (mono) is a contagious infection caused mainly by the Epstein-Barr virus (EBV). Typically, the virus is spread through bodily fluids, especially saliva.

Mono is most common in young adults and teenagers: It is estimated that at least one out of four teenagers and young adults who get infected with EBV will develop mono. Roughly 90% of Americans will have caught the virus by the time they turn 35 years old.

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Is Mono Contagious? 

Mono is contagious. Many people refer to the infection as its nickname, the kissing disease, because it is most commonly passed from person to person through saliva. It can also spread through other bodily fluids such as semen and blood during sexual intercourse, blood transfusions, or organ transplants.

When Is Mono Contagious? 

Although mono is contagious, it is spread primarily through contact with saliva of an infected person. As soon as a person becomes infected with EBV, they can pass it on to others.

Research has shown that following the initial transmission of the virus, viral loads were found in both the mouth and the blood before any symptoms appeared. A viral load refers to the amount of virus that is present in the body. More specifically, it's the amount of virus that can be measured within a standard volume of blood or plasma. The larger the viral load, the more contagious a virus is.

How Long Is Mono Contagious? 

Although medical professionals aren't exactly sure how long mono is contagious, some reports suggest that it can be spread to others for roughly three months after the initial transmission.

The reason why it can be hard to pinpoint an exact length of time is due to the variations in both the incubation period and active infection period. The incubation period is the time between the initial contraction of a virus and the onset of symptoms, while the active infection period is when a person is experiencing symptoms.

Incubation Period

In people with mono, the incubation period ranges widely. Some people may start to experience symptoms within four weeks, but others may not experience any symptoms until eight weeks after they first become infected. On average, the incubation period is six weeks, and during that time, mono is highly contagious.

Active Infection Period

A person can also spread the infection while they're showing symptoms. The time span of when a person feels ill can also vary. While some people may recover quickly and experience symptoms for only two weeks, others may take four weeks or more to recover. According to the Centers for Disease Control and Prevention (CDC), some people with mono may even deal with symptoms for up to six months after they first contracted the virus.

Oral Shedding

Even if the viral load in the blood is low, the virus can still be spread through saliva because of oral shedding. Oral shedding is a term used to describe the ability of the virus to spread from the oral cavity or the throat of one person to that of another. In one older study published in 2005, researchers found that people were still able to spread mono to others for up to 32 weeks because of oral shedding.

EBV can also remain in the body for life, so there is a small risk that it can reactivate. During reactivation, you can again have an increased viral load and spread the virus to others.

Risks of EBV Reactivation

Although reactivation of EBV doesn't occur in everyone, some people may have a higher risk of this happening. Individuals who have a weakened immune system, for example, are more at risk of the virus reactivating than those who have a healthy immune system.

Mono Incubation Period

Research has shown that the incubation period for mono is, on average, anywhere from 32 to 49 days. You could become infected with mono and be completely unaware that you have the infection for over a month before any symptoms start to show. During this time, you can still pass it on to others.

To test for a mono infection, a doctor will likely use either a Monospot test or an EBV antibody test. They are designed to look for antibodies produced by the immune system in response to EBV. The EBV antibody test can determine if there is a recent infection or if one has occurred in the past.

When to See a Healthcare Provider

Mono may not present with any symptoms at all, especially in children. When symptoms do appear, they may include:

  • Fever
  • Headaches
  • Extreme fatigue
  • Rash
  • Sore throat
  • Body aches
  • Swollen liver or spleen
  • Swollen lymph nodes in the neck and armpits

The symptoms may develop slowly and can present at different times during an infection. For example, you could have a fever at one point and then a sore throat after the fever has subsided.

If your symptoms are particularly severe or last for longer than 10 days, you should see a healthcare provider. They will likely order tests to make sure that another infection isn't to blame for your symptoms. Knowing what type of infection you have will be the deciding factor when it comes to treatment, and although there are no antibiotics or treatments specifically for mono, you'll want to rule out any other conditions that require medications to treat.

If you do have mono and recovery is taking longer than three months, you should also make an appointment to see your healthcare provider. This is because when mono lasts that long, the symptoms are typically associated with a condition known as chronic active Epstein-Barr virus (CAEBV). Although CAEBV is rare, it can be serious and thus requires prompt medical treatment.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. About infectious mononucleosis.

  2. Cleveland Clinic. Mononucleosis.

  3. Grimm JM, Schmeling DO, Dunmire SK, Knight JA, Mullan BD, Ed JA, Brundage RC, Hogquist KA, Balfour HH Jr. Prospective studies of infectious mononucleosis in university students. Clin Transl Immunology. 2016 Aug 12;5(8):e94. doi:10.1038/cti.2016.48

  4. Kids Health. How long is mono contagious?

  5. Dunmire SK, Grimm JM, Schmeling DO, Balfour HH Jr, Hogquist KA. The incubation period of primary Epstein-Barr virus infection: viral dynamics and immunologic events. PLoS Pathog. 2015 Dec 1;11(12):e1005286. doi:10.1371/journal.ppat.1005286

  6. Balfour HH Jr, Holman CJ, Hokanson KM, Lelonek MM, Giesbrecht JE, White DR, Schmeling DO, Webb CH, Cavert W, Wang DH, Brundage RC. A prospective clinical study of Epstein-Barr virus and host interactions during acute infectious mononucleosis. J Infect Dis. 2005 Nov 1;192(9):1505-12. doi:10.1086/491740

  7. Fugl A, Andersen CL. Epstein-Barr virus and its association with disease - a review of relevance to general practice. BMC Fam Pract. 2019 May 14;20(1):62. doi:10.1186/s12875-019-0954-3

  8. Balfour HH Jr, Dunmire SK, Hogquist KA. Infectious mononucleosis. Clin Transl Immunology. 2015 Feb 27;4(2):e33. doi:10.1038/cti.2015.1

  9. MedlinePlus. Mononucleosis (mono) tests.

  10. Kimura H, Cohen JI. Chronic active Epstein-Barr virus disease. Front Immunol. 2017 Dec 22;8:1867. doi:10.3389/fimmu.2017.01867

By Angelica Bottaro
Angelica Bottaro is a professional freelance writer with over 5 years of experience. She has been educated in both psychology and journalism, and her dual education has given her the research and writing skills needed to deliver sound and engaging content in the health space.