Mono is often caused by the Epstein-Barr virus (EBV). It may also be caused by cytomegalovirus (CMV). Both viruses are members of the herpes simplex virus family.

Mono is most often spread by contact with infected spit (saliva). But it can also be spread through blood or other body fluids. It's hard to keep it from spreading because even people with no symptoms can carry the virus in their saliva and infect other people.

Most healthy people who get the CMV virus have few or no symptoms. Some may develop symptoms. Mono caused by EBV causes symptoms more often.

Symptoms of mono can take between 4 to 6 weeks to appear. They can last for weeks or months. They usually don’t last beyond 4 months.

The most common symptoms of mono include:

• Fever
• Headache
• Extreme tiredness (fatigue)
• Swollen lymph glands in the neck, armpits, and groin
• Headaches and body aches
• Sore throat because of enlarged tonsils (tonsillitis). This can make it hard to swallow.
• Enlarged spleen
• Mild liver damage that can cause short-term yellowing of the skin and eyes (jaundice)
• Rash

Once a child gets mono, the virus stays inactive in the body for life. It only rarely can become active again. 

The symptoms of mono can be like other health conditions. Have your child see his or her healthcare provider for a diagnosis.

The healthcare provider will ask about your child’s symptoms and health history. The provider will give your child a physical exam. The symptoms may be enough to diagnose mono. The diagnosis may be confirmed with blood tests for:

• White blood cell count
• Antibodies
• Liver function

Treatment will depend on your child’s symptoms, age, and general health. It will also depend on how severe the condition is.

Prescription medicines are rarely needed in the treatment of mono. Antibiotics will not help your child's mono get better. In rare, more severe cases in which swelling of the throat and tonsils are making breathing hard or if the fever and fatigue last a long time, your child may need corticosteroids. If breathing becomes difficult, your child should see an ear, nose, and throat doctor (otolaryngologist). In most cases of mono, care to ease symptoms is all that is needed.

To ease symptoms, help your child:

• Get lots of rest
• Drink plenty of fluids to stay hydrated
• Take over-the-counter medicine for fever and discomfort

The spleen may become enlarged because of the virus. An enlarged spleen is at risk of rupture if your child is injured or in an accident, or if major pressure is put on the stomach area. To protect the spleen, your child should not play any contact sports until fully recovered.

Both EBV and CMV stay in a person's cells for life, even after the symptoms of the virus are gone. The virus can become active again, but it usually doesn't cause symptoms.