Infectious mononucleosis is a common viral disease often known simply as mono or the kissing disease that usually occurs in individuals between the ages of 15 and 35. The infection generally spreads via saliva exchange and is thought to be caused by the Epstein-Barr virus, a member of the herpesvirus family. Symptoms of mononucleosis are varied, but frequently include fever, fatigue, and sore throat.

Swelling of the lymph nodes is also common and is the origin of another alternate name for the disease, glandular fever. Less often, a rash, eyelid swelling, or muscle soreness, as well as the more serious and even less common onset of pneumonia, meningitis, hepatitis, or peripheral neuritis, may occur. In some cases, the spleen may become enlarged, and rupture of the organ is the primary cause of the rare instances of death associated with mononucleosis.

Currently there is no cure for infectious mononucleosis, treatment typically taking the form of bed rest, ingestion of fluids, and painkillers. Aspirin is usually avoided, however, because the pharmaceutical has been associated with Reye syndrome when used to treat children with viral diseases. Usually within a month, the body successfully recuperates from an infection of mononucleosis on its own, but some individuals may continue to feel unusually tired and weak for several months. Even after symptoms of mononucleosis subside, the virus may be exuded in saliva so that the patient is actually contagious for several months. Once exposed to the virus, there is an incubation period of 10 to 60 days, though one to two weeks before the onset of symptoms is most common for youths.

The Epstein-Barr virus that causes infectious mononucleosis is one of the most widespread human viruses in the world. It is estimated that 95 percent of the 35- to 40-year-old adult population in the United States has been infected. However, a significantly smaller percentage of individuals have ever experienced mononucleosis. This is because when humans are exposed to the disease at a very young age, they typically do not experience any symptoms of illness, but develop immunity to mononucleosis. If infection with the virus does not occur, however, until adolescence or young adulthood, then an individual has approximately a 50 percent chance of developing the disease. The only fluid of the body known to carry infectious Epstein-Barr virus is saliva, but the specialized white blood cells known as B lymphocytes may also contain the virus in a state of incomplete replication. When B lymphocytes do become infected, they are altered permanently, assuming some of the atypical growth characteristics of cancerous lymphocytes.

The vast majority of individuals that experience mononucleosis experience a full recovery with no complications. However, in rare instances, serious problems related to the disease may transpire. For instance, a patient may develop hemolytic anemia or other disorders of the blood if the bone marrow fails to produce enough red and white blood cells or if the body begins destroying either of these cell types as a result of infection. The Epstein-Barr virus that causes mononucleosis also can occasionally lead to a condition known as Bell’s palsy, in which the facial muscles on one side of the body may become unusually weak or even temporarily paralyzed, or to Guillain-Barré syndrome, which is characterized by a more general paralysis of the muscles. Other possible complications include inflammation or other involvement of the heart, spleen, and central nervous system.