Mononucleosis Infection: Causes & Common Questions

What is a mononucleosis infection?

Mononucleosis, also called mono, is a very common and highly contagious viral infection. It is often caused by the Epstein-Barr virus (EBV), but other viruses also cause it.

Symptoms include exhaustion, sore throat, swollen glands in your neck, and fever. The infection usually affects children, teenagers, and young adults.

Mono spreads mainly through saliva so it is easy to pass it on by kissing, sharing drinks or toothbrushes, coughing, and sneezing. It’s often nicknamed “the kissing disease.”

There is no vaccine, treatment, or cure, but you can treat the symptoms. It takes about 2 to 8 weeks to feel mostly better. Still, the fatigue can linger for months.

What are the symptoms of mono in adults?

Most people with EBV don’t have symptoms. But at least 1 in 4 teenagers and young adults who are infected with EBV will develop mono. Symptoms usually show up about 4 to 6 weeks after getting the virus.

Main symptoms

• Fever, usually highest in afternoon or evening
• Large, swollen glands in neck, armpit, or groin
• Sore throat
• Extreme fatigue, sometimes so bad that you just want to sleep day and night

Other possible symptoms

• Headache
• Muscle aches or weakness
• Rash (especially if antibiotics are taken)
• Sudden severe abdominal pain, which can be caused by an enlarged spleen. If this happens, see your doctor immediately or go to the ER.
• Inflammation of the liver and jaundice (yellowing of the skin)
• Swollen tonsils, which can make it hard to breathe and swallow. If this happens, see your doctor immediately or go to the ER.

What causes infectious mononucleosis?

Mononucleosis is most often caused by the virus EBV. A milder version can also be caused by the cytomegalovirus (CMV). Both EBV and CMV are members of the herpes virus family. The virus infects your immune cells (called B cells).

Even after symptoms have disappeared, the EBV remains dormant in the body for the rest of your life. But it usually never causes symptoms again.

Mono is very common. More than 50% of kids have had EBV by age 5. By adulthood, over 90% of people have had the virus. But only 40% of adults will have actually gotten the symptoms called mononucleosis.

You’re more likely to get the virus or experience worse symptoms if you:

• Are young and spend a lot of time in groups (like at high school or college)
• Work in the medical field
• Take medicine to suppress your immune system

Mononucleosis treatment

If you develop symptoms of mono, you should see a doctor to confirm the diagnosis and check for complications. If you have a very high fever (above 103ºF), are unable to swallow, or have a very sore throat, abdominal pain, inability to urinate, inability to drink fluids, or shortness of breath, see your doctor. If your doctor cannot see you on the same day, go to the emergency room.

Your doctor will diagnose you by your symptoms and will usually order a blood test for mono, CBC (infection-fighting blood cells), and liver function. You may also have a strep (bacterial cause of sore throat) test done to rule that out.

There isn’t any way to cure or shorten the length of the illness. Mono just has to run its course, which can take anywhere from 2 to 8 weeks. It is a virus so antibiotics do not help and can actually give you a bad rash.

Listen to your body, get plenty of rest, and do not push yourself. You may need to take time off from school or work or reduce your workload.

Some symptoms, like fatigue, may last for months. It's important to take care of yourself while sick so that your body can recover.

• Stay home from work or school until you feel well enough to go back.
• You should avoid contact sports for 6-8 weeks because your spleen can become enlarged and can rupture with contact sports.
• Get as much sleep as your body needs. Even if that means you’re in bed all day.
• Drink lots of fluids.
• Gargle with saltwater or use lozenges for a sore throat.
• Bring down a fever with ibuprofen (Advil). (Since mono can affect the liver, it is best not to take acetaminophen.)
• Treat pain or swelling, with ibuprofen or naproxen (Aleve).
• For a very swollen throat interfering with swallowing, your doctor may offer a steroid, such as prednisone.

Follow up

If you have mono, you will be contagious while you have symptoms and for several months after symptoms subside. Try to avoid sharing drinks or utensils or kissing others during this time.

Some people have an increase in liver enzymes in their blood showing liver damage. This is usually temporary but may need to be watched with follow-up blood testing.

Prevention

It’s hard to avoid catching mono because the virus is so common. You can reduce your risk of being infected by not sharing drinks, water bottles, vaping products, or utensils. If you know someone has it, don’t kiss them.