Infectious Mononucleosis: Cause

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Cause

Mono is caused by the Epstein-Barr virus (EBV).

Cytomegalovirus (CMV) causes some cases of a mono-like illness. Much less commonly, a mono-like illness is caused by different viruses, such as hepatitis B, rubella, and HIV. Toxoplasma gondii, a single-celled parasite, can also cause a mono-like illness.

How mono is spread

Epstein-Barr virus (EBV) can be found in saliva and mucus (and sometimes tears). EBV is not spread by casual contact. You can live in the same house with a person who has mono and never become infected with the virus. But a person who has a weakened immune system may be at higher risk for infectious mono. It's possible that people who have had mono can spread the virus even though they no longer have symptoms.

• EBV lives and grows in the nose and throat. Any fluid that comes from these parts of the body, including saliva, tears, or mucus, can be infected with the virus. The virus (EBV) is spread when people come in contact with infected fluids.
• EBV can be spread through intimate contact or sharing of saliva. (A brief kiss on the lips is not likely to spread EBV. It is spread when saliva from an infected person gets into another person's mouth.)
• You can get EBV if you share a drinking glass or eating utensils with an infected person (through sharing saliva).
• In rare cases, someone can get an infection after receiving blood from a person who is infected with EBV.
• Most people get infected with EBV at some point in their lives but never get mono symptoms. EBV "sleeps" (is dormant) in the body. It can become active from time to time and spread to others. When it reactivates, most people do not have symptoms. Many healthy people carry the virus and spread it every now and then throughout their lives. Lifetime carriers of EBV are the most common source of EBV infection.

Contagious and incubation period

• You can pass the Epstein-Barr virus (EBV) to others for several weeks or months during and after the time you are first infected with EBV. The virus can also become active and spread to others from time to time throughout your life.
• There is a small risk of spreading EBV through blood products. If you know you have mono, you should not donate blood.
• It takes 4 to 6 weeks for symptoms to develop after you come in contact with EBV. This is called the incubation period.

Last updated:	September 19, 2007
Author:	Debby Golonka, MPH
Reviewed By:	Michael J. Sexton, MD - Pediatrics, W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Editors:	Susan Van Houten, RN, BSN, MBA, Pat Truman, MATC