Mono, or mononucleosis, is most often caused by the Epstein-Barr virus, or EBV, and is mainly spread through saliva. In teens and young adults, kissing is one of the most common ways the virus is passed from one person to another.
EBV may also spread when people share drinks, food, cups, eating utensils, or toothbrushes. Young children may be exposed through toys or other objects that have saliva on them. Less commonly, the virus can spread through blood, semen during sexual contact, blood transfusions, or organ transplants.
A person can spread EBV before symptoms appear and may continue to shed the virus in saliva for weeks afterward. The virus also remains in the body after infection and can become active again later, so there is no simple number of days after which transmission is completely impossible.
To lower the risk, avoid kissing and sharing drinks, utensils, toothbrushes, or other saliva-contaminated items with someone who has mono. If you develop symptoms that could be mono, a primary care doctor can evaluate you and determine whether testing is appropriate.