The Epstein-Barr virus, or EBV, responsible for mononucleosis lies dormant in patients who were previously infected with it, and this virus reactivates periodically with no symptoms unless the patient's immune system is in a weakened state. Reactivated EBV can cause illness in patients suffering from AIDS whose immune systems are weak, according to Mayo Clinic.
Most people with infectious mononucleosis, also know as mono, only get it once. Rarely, symptoms may recur months or years later. When the virus reactivates, tests can detect it in the saliva, as described by Mayo Clinic.
Infectious mononucleosis spreads through saliva, and patients can get it by sharing a glass or food utensils with an infected person or by kissing them. Fortunately, mononucleosis is not as contagious as many other infections, such as the common cold. Adolescents and young adults are most likely to contract mononucleosis with all the symptoms and signs. Young children usually display few symptoms and often have the disease without anybody knowing, as Mayo Clinic explains.
The symptoms of mononucleosis include fever, sore throat, fatigue, weakness and swollen lymph glands. Occasionally, patients may also develop a swollen spleen. The recovery time normally ranges between two and four weeks, but patients may feel tired for a few months afterwards, as noted by MedicinePlus.