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.
Mononucleosis is an illness that commonly affects teenagers and young adults, but can affect children as well. Viruses, most commonly 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 improves 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.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
The Epstein-Barr virus (EBV) that causes mono is extremely common. Around 90% of Americans are infected with it by age 35. Not everyone who has the virus develops mono symptoms — some people only carry the virus.
There are often two peaks when people acquire EBV: early school age children and again around adolescence/young adulthood. Young children are often asymptomatic, whereas teenagers and people in their 20s are most likely to get mono. About one in four people in this age group who get EBV come down with mono, but anyone can get it, no matter their age.
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.
Viruses that cause mono are very contagious. You can pick them up through contact with an infected person’s bodily fluids, including saliva. These viruses spread through:
The Epstein-Barr virus stays in your body in an inactive form even after mono 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.
Over 90% of mono cases are caused by the Epstein-Barr virus. Other viruses and certain infections may also bring on the illness. The symptoms can develop because of:
Symptoms of mono vary, and they can be mild or severe. They tend to come on gradually. If you get sick with mono, it will probably happen four to six weeks after you come in contact with EBV. These symptoms may last for four weeks or longer:
Your healthcare provider will assess your symptoms to make a diagnosis. They will especially check for swollen lymph nodes in your neck and signs of an enlarged spleen or liver.
Blood tests detects antibodies that your body makes to fight the Epstein-Barr virus. Your doctor may also check for a high number of white blood cells (lymphocytes) that indicate infection.
There isn’t a vaccine or cure for mono. Antibiotics to fight bacterial infection and antiviral medications to kill other viruses don’t work against mono. Instead, treatments focus on helping you feel better by relieving symptoms. Your care might include:
Mono 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 individuals. This gland in the 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. Your healthcare provider may tell you to avoid strenuous exercise, contact sports and heavy lifting until you feel better.
There’s no vaccine for mono. 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.
Expectant moms who develop mono 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 mono was caused by a CMV infection during pregnancy there is a chance your infant may be affected and you should discuss this with your obstetrician.
Mono symptoms can be severe. They may temporarily affect your ability to lead an active life. Fortunately, these symptoms gradually improve with at-home treatments.
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.
You should call your healthcare provider if you have mono and you experience:
If you have mono, you may want to ask your healthcare provider:
A note from Cleveland Clinic
Most cases of mononucleosis (mono) don’t cause serious problems. However, 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.
Last reviewed by a Cleveland Clinic medical professional on 08/03/2020.
Learn more about our editorial process.