Mononucleosis (mono) is a disease usually caused by infection with the Epstein-Barr virus (EBV). It is transmitted from person to person via saliva and mucus and most often affects adolescents and young adults. In the United States, as many as 95 percent of adults between 35 and 40 years of age have already been infected with EBV, according to the U.S. Centers for Disease Control and Prevention (CDC).

Signs and symptoms of mono may vary among patients. Fatigue is one of the main symptoms of mono. Other symptoms include fever, sore throat and swollen lymph nodes. Young children who contract the virus often do not display any symptoms, or they experience minor symptoms similar to those associated with minor respiratory infections.

However, mono may cause various medical complications, including inflammation of the spleen and liver. Severe complications are most likely to appear in people who have impaired immune systems or who are taking medications to suppress their immune systems after an organ transplant.

Generally, the presence of fever, sore throat and swollen lymph nodes for between one and four weeks is enough for a physician to suspect a diagnosis of mononucleosis. Blood tests may be performed to confirm a current infection. Other blood tests may determine whether a patient was ever previously exposed to the virus that causes mono.

Generally, no medical treatment for mono is necessary. In most cases, patients may be advised to get adequate rest and consume plenty of fluids. Antibiotics are not used to treat mono because these drugs have no effect on viral infections. It may take two to three months before a person is fully recovered.

After a person is infected with EBV, the virus remains in the body for a lifetime. However, after initial exposure to the virus, people typically build up antibodies that help prevent a future infection. The virus may occasionally reactivate throughout a person’s life and be intermittently released into their saliva. This causes no symptoms of infection, but may expose others to the virus.