The symptoms associated with a diagnosis of mononucleosis typically last for one to two months, according to WebMD. After exposure to the virus, it usually takes four to six weeks for symptoms to start.
Mononucleosis is a viral infection to which teens and young adults are particularly susceptible. It is passed from person to person through saliva and mucus. After the incubation period, symptoms manifest in various forms. The most common complaints are fever, sore throat, fatigue, and swollen tonsils and lymph nodes and are often mistaken for symptoms of the common cold virus. The mononucleosis virus remains in your system forever once the symptoms leave, notes WebMD. However, the symptoms do not return.