Symptoms of Mononucleosis

mother taking daughter's (6-7) temperature
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Mononucleosis (mono) is a viral infection that most often affects teens and young adults. Typical symptoms in that age group are sore throat, fever, swollen neck glands, enlarged tonsils, and fatigue. In younger children there may be only mild symptoms or none at all. Older adults are more likely to have jaundice and may not have a sore throat or swollen glands. It's common for people to have different combinations of symptoms and a range from mild to severe.

Frequent Symptoms

The incubation period for mono is about four to six weeks, which means that you or your child might not develop symptoms of mono until a month after being exposed to someone else with mono. For most children and teens, mononucleosis gets off to a slow start—typically three to five days of mild symptoms such as headache, malaise, and fatigue. The classic symptoms of mono then follow:

  • A severe sore throat
  • Red, swollen tonsils covered in pus
  • Swollen lymph glands (lymphadenopathy) in the neck and armpits, but also possible in the groin.
  • Fever, which can be as high as 104 F to 105 F and may last one to two weeks, and often peaks in the afternoon or early evening
  • Continued malaise and fatigue, which can be extreme
  • Achy muscles and headache
  • Rash that is pink and measles-like, more frequently seen after taking antibiotics
  • Nausea
  • Abdominal pain

The combination of symptoms, how severe they are, and how long they last vary from person to person.

 The younger the child, the less severe and the shorter the illness. Young children may have only brief, mild symptoms that last only a few days. In teens and young adults, mono is notorious for lasting a long time, although the usual course is two to four weeks in that age group. Some symptoms, such as fatigue, can last several more weeks to six months.

Rare Symptoms

Less common symptoms of mononucleosis include chest pain, cough, shortness of breath, high heart rate, hives, neck stiffness, nosebleed, and sensitivity to light. Swollen or inflamed testicles can also develop. An enlarged spleen (splenomegaly) or liver can develop after two or three weeks of illness. Spleen enlargement is seen in about half of the cases at some point in the illness. Jaundice is a sign of liver involvement, with a yellow tinge to the skin and the whites of the eyes.

Mono Symptoms in Young Children

Younger children usually have much more mild symptoms of mononucleosis as compared to teens and young adults. An infant might have no symptoms or mild symptoms. Small children with mono may just be a little irritable, with a decreased appetite. On the other hand, they may have mild upper respiratory infection symptoms, such as a cough, runny nose, or mild fever.

Some kids have atypical or unusual cases of mono—for instance, they develop an enlarged gland but no sore throat or fever. Or the only symptoms they have are a sore throat or a fever. In either case, one clue these symptoms may be due to mono is that they linger for much longer than seems normal.

You may never know a child has mono unless they have blood tests done showing they have the atypical lymphocytosis or antibodies that indicate mono.

Later in life, a positive test for the Epstein-Barr virus may then reveal the past infection. The good news is that no treatment is usually given for mononucleosis other than relieving symptoms, so there was no missed opportunity for medical intervention.

Mono Symptoms in Older Adults (40 and Older)

Older adults often show a fever lasting longer than two weeks and may not show the other common symptoms of swollen glands and sore throat. Their symptoms can persist longer. They are more likely to have jaundice and lab tests will show a high bilirubin level and liver enzyme levels and their white blood cell count will not be as elevated or show as many lymphocytes as is seen in younger people.

Complications/Sub-Group Indications

Complications can develop, with some being more frequent in certain age groups.

Complications in Children

Airway obstruction from enlarged tonsils is possible in young children and it can require hospitalization. Your pediatrician might mistake the symptoms of mononucleosis for a bacterial infection (such as strep throat) and prescribe an antibiotic, such as ampicillin, amoxicillin or related penicillin-like antibiotics. These antibiotics won't work because mono is a viral infection. Moreover, children sometimes develop a bad rash as a result of these medications.

Complications in Pregnancy and Breastfeeding

Infectious mononucleosis caused by Epstein-Barr virus appears to have little to no effect on pregnancy outcomes, although there is some possible correlation with early delivery and lower birth weight. An expectant mother with mono should take care to stay well-hydrated. A high fever could increase the risks to the fetus. Acetaminophen is preferred for reducing fever. Some women have reactivation of EBV during pregnancy. It is possible for EBV to be passed to the newborn during birth. However, babies often have no symptoms when they have an EBV infection and so this is not a health concern. Breast milk can contain EBV but it isn't clear whether this can produce an infection in a child.


Mono can result in your red blood cells dying and being removed from your bloodstream by the spleen sooner than normal. Your bone marrow might not be able to keep up with this more rapid turnover and you may have anemia.

Hepatitis with Jaundice

Inflammation and enlargement of the liver are more common in people older than 35. Liver involvement is usually mild, but you should not drink alcohol while you have mono symptoms.

Ruptured Spleen

The spleen may become enlarged due to mono. It is important that you avoid contact sports or strenuous activities in order to prevent a ruptured spleen, which is a rare complication. The spleen filters the blood and a ruptured spleen can cause massive internal bleeding that is often life-threatening. Emergency medical transport is needed. The spleen is not required for good health, but you may be more at risk of infection by Streptococcus pneumoniae and some other germs after it is removed.

Nervous System Complications

Rarely there is involvement of the nervous system. This can include Guillain-Barre syndrome, seizures, meningitis, or Bell's palsy.

Fulminant EBV Infection

It is rare, but people with weakened immune systems due to HIV, immunosuppressive therapy for organ transplant, or X-linked lymphoproliferative disorders can get uncontrolled EBV infection and can die from mononucleosis.

When to See the Doctor/Go to the Hospital

You should see the doctor when you have the symptoms of mononucleosis so you can get a diagnosis and rule out other diseases that may have different treatment recommendations. Don't rely on self-diagnosis as it could be another illness.

Besides EBV, other viruses can bring about mono-like symptoms. These include cytomegalovirus (CMV), adenovirus, human immunodeficiency virus (HIV), rubella, hepatitis A, and human herpesvirus-6. The parasite Toxoplasma gondii also can cause mono-like symptoms. If you are pregnant or may become pregnant, some of these other illnesses can be a risk for you or your baby. You may be given more tests to identify the cause of your mono symptoms.

After being diagnosed you may contract other illnesses that need medical attention. You can get strep throat on top of mono. If you or your child has a severe sore throat, one that is lingering, or swollen tonsils that are making it hard to breathe or swallow, see your doctor. Strep throat can be diagnosed with a rapid strep test. Antibiotics are needed to cure strep throat and avoid complications. You should also see the doctor if there are any breathing difficulties due to enlarged tonsils.

The signs of a ruptured spleen include a sudden, sharp abdominal pain on the upper left side. You need to get to a hospital immediately and it's appropriate to call 9-1-1. A ruptured spleen usually requires blood transfusion and splenectomy surgery to remove the spleen and stop the internal bleeding.

The symptoms of mono usually get better after four to six weeks. If they are continuing, you should see your doctor as it could be a different disease. Your doctor may perform additional tests to identify the cause of your symptoms.


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Epstein-Barr Virus (EBV) and Infectious Mononucleosis. American Pregnancy Association.

Mononucleosis. Cleveland Clinic.

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Womack J, Jimenez M. Common Questions About Infectious Mononucleosis. American Family Physician. 2015 Mar 15;91(6):372-376.