Infectious mononucleosis (IM, mono), also known as glandular fever, is an infection usually caused by the Epstein–Barr virus (EBV).

[2] In young adults, the disease often results in fever, sore throat, enlarged lymph nodes in the neck, and fatigue.

[2] Symptoms may be reduced by drinking enough fluids, getting sufficient rest, and taking pain medications such as paracetamol (acetaminophen) and ibuprofen.

[18] In adolescence and young adulthood, the disease presents with a characteristic triad:[19] Another major symptom is feeling tired.

[25] The most prominent sign of the disease is often pharyngitis, which is frequently accompanied by enlarged tonsils with pus—an exudate similar to that seen in cases of strep throat.

[16] A small minority of people spontaneously present a rash, usually on the arms or trunk, which can be macular (morbilliform) or papular.

[16] Almost all people given amoxicillin or ampicillin eventually develop a generalized, itchy maculopapular rash, which however does not imply that the person will have adverse reactions to penicillins again in the future.

[34] About 5–7% of cases of infectious mononucleosis is caused by human cytomegalovirus (CMV), another type of herpes virus.

[35] This virus is found in body fluids including saliva, urine, blood, tears,[36] breast milk and genital secretions.

[36] However, it can cause life-threatening illness in infants, people with HIV, transplant recipients, and those with weak immune systems.

For those with weak immune systems, cytomegalovirus can cause more serious illnesses such as pneumonia and inflammations of the retina, esophagus, liver, large intestine, and brain.

Viral hepatitis, adenovirus, rubella, and herpes simplex viruses have also been reported as rare causes of infectious mononucleosis.

[39] The length of time that an individual remains contagious is unclear, but the chances of passing the illness to someone else may be the highest during the first six weeks following infection.

[43][44] The disease is diagnosed based on: The presence of an enlarged spleen, and swollen posterior cervical, axillary, and inguinal lymph nodes are the most useful to suspect a diagnosis of infectious mononucleosis.

On the other hand, the absence of swollen cervical lymph nodes and fatigue are the most useful to dismiss the idea of infectious mononucleosis as the correct diagnosis.

The insensitivity of the physical examination in detecting an enlarged spleen means it should not be used as evidence against infectious mononucleosis.

[26] Acute HIV infection can mimic signs similar to those of infectious mononucleosis, and tests should be performed for pregnant women for the same reason as toxoplasmosis.

[50] Other conditions from which to distinguish infectious mononucleosis include leukemia, tonsillitis, diphtheria, common cold and influenza (flu).

[51] The need for rest and return to usual activities after the acute phase of the infection may reasonably be based on the person's general energy levels.

[26] Nevertheless, in an effort to decrease the risk of splenic rupture, experts advise avoidance of contact sports and other heavy physical activity, especially when involving increased abdominal pressure or the Valsalva maneuver (as in rowing or weight training), for at least the first 3–4 weeks of illness or until enlargement of the spleen has resolved, as determined by a treating physician.

[53][54] Intravenous corticosteroids, usually hydrocortisone or dexamethasone, are not recommended for routine use but may be useful if there is a risk of airway obstruction, a very low platelet count, or hemolytic anemia.

[61] Splenomegaly is a common symptom of infectious mononucleosis and health care providers may consider using abdominal ultrasonography to get insight into the enlargement of a person's spleen.

[62] Serious complications are uncommon, occurring in less than 5% of cases:[63][64] Once the acute symptoms of an initial infection disappear, they often do not return.

Independent infections of mononucleosis may be contracted multiple times, regardless of whether the person is already carrying the virus dormant.

[70] In 1885, the renowned Russian pediatrician Nil Filatov reported an infectious process he called "idiopathic adenitis" exhibiting symptoms that correspond to infectious mononucleosis, and in 1889 a German balneologist and pediatrician, Emil Pfeiffer, independently reported similar cases (some of lesser severity) that tended to cluster in families, for which he coined the term Drüsenfieber ("glandular fever").

[75] The term "infectious mononucleosis" was coined in 1920 by Thomas Peck Sprunt and Frank Alexander Evans in a classic clinical description of the disease published in the Bulletin of the Johns Hopkins Hospital, entitled "Mononuclear leukocytosis in reaction to acute infection (infectious mononucleosis)".

[71][76] A lab test for infectious mononucleosis was developed in 1931 by Yale School of Public Health Professor John Rodman Paul and Walls Willard Bunnell based on their discovery of heterophile antibodies in the sera of persons with the disease.

The Epstein–Barr virus was first identified in Burkitt's lymphoma cells by Michael Anthony Epstein and Yvonne Barr at the University of Bristol in 1964.

[78] The link with infectious mononucleosis was uncovered in 1967 by Werner and Gertrude Henle at the Children's Hospital of Philadelphia, after a laboratory technician handling the virus contracted the disease: comparison of serum samples collected from the technician before and after the onset revealed development of antibodies to the virus.