What is mononucleosis (mono)?
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.

How common is mononucleosis (mono)?
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.

Who might get mononucleosis (mono)?
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.

Is mono a sexually transmitted infection?
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.

Is mononucleosis (mono) contagious?
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:

Blood transfusions.
Coughing or sneezing.
Sexual contact.
Sharing food, drinks or eating utensils.
Organ transplants.
Can you get mononucleosis (mono) more than once?
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.

What causes mononucleosis (mono)?
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:

Cytomegalovirus (CMV).
Hepatitis A, Hepatitis B and Hepatitis C.
Herpes simplex virus (HSV).
Human immunodeficiency virus (HIV).
What are the symptoms of mononucleosis (mono)?
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:

Enlarged spleen or liver.
Extreme fatigue.
Loss of appetite.
Muscle aches or weakness.
Sore throat.
Swollen lymph nodes in the neck, armpits or groin.