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Mononucleosis (Mono)

What Is Mononucleosis?

Mononucleosis (mono) is a viral infection that causes a sore throat and fever. Cases often happen in teens and young adults. It goes away on its own after a few weeks of rest.

What Causes Mono?

Mononucleosis (pronounced: mah-no-noo-klee-OH-sus), or infectious mononucleosis, is caused by the Epstein-Barr virus (EBV). Most of us are exposed to EBV at some point while we're growing up. Infants and young kids infected with EBV usually have very mild symptoms or none at all. But infected teens and young adults often develop the symptoms that define mono.

What Are the Signs & Symptoms of Mononucleosis?

Signs of mono usually show up about 1–2 months after someone is infected with the virus. Its most common symptoms are sometimes mistaken for strep throat or the flu. These include:

  • fever
  • sore throat with swollen tonsils that may have white patches
  • swollen lymph nodes (glands) in the neck
  • being very tired

A person also can have:

  • headaches
  • sore muscles
  • weakness
  • belly pain with a larger-than-normal liver or spleen (an organ in the upper left part of the belly)
  • skin rash
  • loss of appetite

Is Mono Contagious?

Mono is contagious. It spreads from person to person through contact with saliva (spit). It's nicknamed "the kissing disease" because it can spread through kissing. It also spreads through coughing and sneezing, or when people share something with spit on it (like a straw, drinking glass, eating utensil, or toothbrush).

Mono can also spread through sex or blood transfusions, but this is much less common.

People who've been infected carry the virus for life, even after symptoms stop and even if they had no symptoms. The virus is then "dormant," or inactive. Sometimes the dormant virus "wakes up" and finds its way into a person's saliva. This means that they can be contagious from time to time over the course of their life, even when they have no symptoms.

How Is Mono Diagnosed?

To diagnose mono, doctors do an exam to check for things like swollen tonsils and an enlarged liver or spleen, common signs of the infection. Sometimes the doctor will do a blood test.

How Is Mono Treated?

The best treatment for mono is plenty of rest and fluids, especially early in the illness when symptoms are most severe. For fever and aching muscles, try taking acetaminophen or ibuprofen. Don't take aspirin. Aspirin has been linked to a serious disease in kids and teens called Reye syndrome, which can lead to liver failure and death.

How Long Does Mono Last?

Mono symptoms usually go away within 2 to 4 weeks. In some teens, though, the tiredness and weakness can last for months.

When you start feeling better, take it slow and don't overdo it. Although you can return to school after your fever is gone, you may still feel tired. Your body will tell you when it's time to rest — listen to it. By taking good care of yourself and resting as much as you need to, you will soon be back to normal, usually within a few weeks.

Can Mono Be Prevented?

There is no vaccine to protect against the Epstein-Barr virus. But you can help protect yourself by avoiding close contact with anyone who has it.

If you have mono, don't share the virus with your friends and family as you recover. Wash your hands well and often, sneeze or cough into a tissue or your elbow (not your hands), and keep your drinks and eating utensils to yourself. This is one time when your friends and family will thank you for being selfish.

What Else Should I Know?

Mono can make the spleen swell for a few weeks or longer. An enlarged spleen can rupture, causing pain and bleeding inside the belly, and needs emergency surgery. So doctors recommend that teens who have mono avoid contact sports for at least a month after symptoms are gone. Don't do any strenuous activities until your doctor says it's OK.

In most cases, mono symptoms go away in a matter of weeks with plenty of rest and fluids. If they seem to linger or get worse, or if you have any other questions, call your doctor.

Reviewed by: Yamini Durani, MD
Date Reviewed: Jun 1, 2023

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