How Long Is a Person Contagious With Mono?

how long is a person contagious with mono
After exposure to the virus, someone with mono can be contagious for months, even before symptoms start and after symptoms subside

Infectious mononucleosis, also called mono, is a contagious disease most commonly caused by the Epstein-Barr virus (EBV). It’s unclear how long someone with mono is contagious, although they are definitely contagious while they have symptoms.

However, if you are infected with the virus, it may take 4-8 weeks for symptoms to appear (incubation period). During this time, you can spread the infection to other people even if you may not be aware that you are sick (asymptomatic viral shedding). Once symptoms appear, they can last 2-4 weeks or even longer.

What about after symptoms subside? Studies suggest that you can be contagious for up to 6 months even after your symptoms go away.

This is because once you are infected, the virus stays dormant, or inactive, in your body for the rest of your life. The dormant virus can become active at any given time and find its way into your saliva, causing you to spread the virus to others without your being aware of it.

How is mono spread?

Mono is often called “kissing disease” as the virus commonly spreads through saliva. Sharing glasses or eating utensils can therefore spread the infection.

In some cases, mono can also spread through blood and semen during sexual contact, blood transfusions, and organ transplantations. 

Since it is quite tricky and difficult to know when a person is contagious, it’s important to take protective measures such as washing your hands frequently and avoiding sharing toothbrushes, drinks, and eating utensils with others.

What are signs and symptoms of mono?

Signs and symptoms of mono include:

Symptoms may appear after 4-8 weeks of getting exposed to the infection.

Generally, symptoms start to subside in 2-4 weeks, although fatigue may last much longer. And even after fatigue subsides, the liver or spleen or both may stay enlarged for a long time. For some people, symptoms may last for as long as 6 months.

How is mono diagnosed?

To diagnose mono, your doctor may take your medical history and perform a detailed medical examination. Generally, lab tests are not required for people who are showing typical symptoms. For people who don’t show any definitive symptoms, a blood test may be done to confirm a diagnosis. Typical findings in a blood test may show:

  • Increased white blood cells or WBCs (lymphocytes)
  • Unusual looking WBCs (atypical lymphocytes)
  • Reduced number of neutrophils (a type of WBCs) or platelets
  • Abnormalities in liver function test (LFT)


Bowel regularity means a bowel movement every day. See Answer
Centers for Disease Control and Prevention. About Infectious Mononucleosis.

Auwaerter PG. Patient education: Infectious Mononucleosis (mono) in Adults and Adolescents (Beyond the Basics). UpToDate.