Mononucleosis (mono) is a contagious infection caused by a herpes virus called Epstein-Barr. Other viruses can also cause mono. The infection is common among teenagers and young adults. People with mono experience extreme fatigue, fever and body aches. Treatments can ease symptoms until the illness goes away on its own.


What is mononucleosis?

Mononucleosis, or infectious mononucleosis (“mono”), is a very contagious viral infection that most commonly affects teenagers and young adults, but it can affect children, as well. Viruses — most often Epstein-Barr virus (EBV) — and certain infections cause the illness. Mono is sometimes called “the kissing disease” because it spreads easily through bodily fluids like saliva.

For most people, mono isn’t serious, and it goes away on its own without treatment. Still, extreme fatigue, body aches and other symptoms can interfere with school, work and daily life. With mono, you might feel sick for about a month.

How common is mononucleosis?

The Epstein-Barr virus (EBV) that causes mononucleosis is extremely common. About 95% of Americans get this infection by age 35. But not everyone who has the virus develops mono symptoms — some people only carry the virus.


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Symptoms and Causes

Symptoms of mononucleosis vary, ranging from headaches to swollen lymph nodes.
Mononucleosis symptoms vary, and they can be mild or severe.

What are the symptoms of mononucleosis?

Mononucleosis symptoms vary, and they can be mild or severe. They tend to come on gradually. If you get sick with mono, it’ll probably happen four to six weeks after you come in contact with Epstein-Barr virus. These symptoms may last for four weeks or longer:

What causes mononucleosis?

The Epstein-Barr virus causes over 90% of infectious mononucleosis cases. Other viruses and certain infections may also bring on the illness. The symptoms can develop because of:

How contagious is mononucleosis?

Viruses that cause mononucleosis are very contagious. You can pick them up through contact with an infected person’s bodily fluids, including saliva. These viruses spread through:

Is mono a sexually transmitted infection?

Epstein-Barr is a type of herpes virus. It’s different than the herpes simplex virus (HSV) that causes genital and oral herpes. Both viruses can be sexually transmitted. However, EBV is more likely to spread through other means like sharing drinks or kissing.

Can you have mononucleosis twice?

The Epstein-Barr virus stays in your body in an inactive form even after mononucleosis symptoms go away. But most people develop mono only once.

If EBV reactivates, it rarely causes symptoms. However, you may unknowingly spread the reactivated virus to others. And people with weakened immune systems may develop mono symptoms more than once.


Who might get mononucleosis?

There are two peaks when people acquire EBV: early school-age children and again around adolescence/young adulthood. Young children often don’t have symptoms, whereas teenagers and people in their 20s are most likely to get mono. About 1 in 4 people in this age group who get EBV come down with mono, but anyone can get it, no matter their age.

What are the complications of this condition?

Mononucleosis symptoms tend to gradually improve in about four weeks. Feelings of fatigue can linger for months. Some people miss some school or work as they recover.

An enlarged spleen that ruptures (bursts) is the biggest concern with mono in previously healthy people. This gland in your upper left abdomen (belly) helps filter blood. If your spleen bursts, it can bleed into your abdomen. Internal bleeding from a ruptured spleen can be life-threatening and requires emergency surgery.

To avoid a ruptured spleen, your healthcare provider may tell you to avoid strenuous exercise, contact sports and heavy lifting until you feel better.


Diagnosis and Tests

How is mononucleosis diagnosed?

Your healthcare provider will assess your symptoms to make a diagnosis. They’ll especially check for swollen lymph nodes in your neck and signs of an enlarged spleen or liver.

Blood tests detect antibodies that your body makes to fight the Epstein-Barr virus. Your provider may also check for a high number of white blood cells (lymphocytes) that indicate infection.

Management and Treatment

How is mononucleosis managed or treated?

There isn’t a vaccine or cure for mono. Antibiotics and antiviral medications that kill other viruses don’t work against mono. Instead, mononucleosis treatments focus on helping you feel better by relieving symptoms. Your self-care might include:

  • Rest: Mono makes you very tired. Sleep helps your body fight infection.
  • Hydration: Drink plenty of fluids to prevent dehydration.
  • Pain relievers: Nonsteroidal anti-inflammatory drugs (NSAIDs) ease fever, inflammation, headaches and muscle aches. These drugs include ibuprofen (Advil®) and naproxen (Aleve®). Acetaminophen (Tylenol®) also works.
  • Sore throat soothers: You can gargle with salt water and use throat lozenges.
  • Avoid sports: Physical activity can put too much pressure on an enlarged spleen, increasing the risk of rupture. You should avoid contact sports and strenuous exercise while you’re sick and for up to four weeks afterward.


Can mononucleosis be prevented?

There’s no vaccine for mononucleosis. The best way to prevent getting the viruses that cause mono is by practicing good hygiene. Don’t share foods, drinks or bodily fluids with someone who has mono or any signs of viral illness, like fever, cough, sore throat or fatigue.

Outlook / Prognosis

What is the prognosis (outlook) for people with mononucleosis?

Mononucleosis symptoms can be severe. They may temporarily affect your ability to lead an active life. Fortunately, these symptoms gradually improve with at-home supportive therapy.

You may experience lingering fatigue for several months. You’ll need to protect your health by getting enough rest and fluids during this time. You should also avoid strenuous activities to prevent a ruptured spleen.

Living With

When should I see my healthcare provider?

You should call your healthcare provider if you have mononucleosis and you experience:

  • Difficulty swallowing or breathing.
  • Dizziness or fainting.
  • Extreme muscle weakness in your arms or legs.
  • Intense body aches.
  • Persistent high fever.
  • Severe headaches.
  • Sharp pain in your upper left abdomen.

What questions should I ask my healthcare provider?

If you have mononucleosis, you may want to ask your healthcare provider:

  • What’s the best treatment for mononucleosis symptoms?
  • How long am I contagious?
  • What steps can I take to prevent infecting others with this virus?
  • How long will it take to recover from mono?
  • When can I go back to work or school?
  • When can I get back to exercise and physical activity?
  • Can I get mono again?
  • Should I look out for signs of complications?

Additional Common Questions

How does mononucleosis affect pregnancy?

Expectant birthing parents who develop mononucleosis from EBV typically have healthy pregnancies. Call your healthcare provider if you develop a fever, which can increase the risk of miscarriage and premature labor. While there’s a slight chance you may pass the Epstein-Barr virus to your baby during pregnancy or after childbirth while breastfeeding, most babies don’t develop mono symptoms. If a CMV infection caused mono during pregnancy, there’s a chance it may affect your infant and you should discuss this with your obstetrician.

A note from Cleveland Clinic

Most cases of infectious mononucleosis (mono) don’t cause serious problems. But symptoms like extreme fatigue, sore throat and body aches can disrupt school, work and life. Your healthcare provider can provide suggestions for finding relief. Rest and over-the-counter medications are often the best ways to ease symptoms. It’s also important to avoid strenuous physical activity that may rupture an enlarged spleen.

Medically Reviewed

Last reviewed on 01/09/2024.

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