PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Synonym: glandular fever
Infectious mononucleosis (IM) is usually a self-limiting infection, most often caused by Epstein-Barr virus (EBV), which is a human herpes virus. However, approximately 10% of those with IM are not acutely infected with EBV and many of these have symptoms attributable to cytomegalovirus (CMV) infection. IM is particularly common in adolescents and children.
- Clinical infection is most common in populations with many young adults, such as active-duty military personnel and college students.
- The incidence of IM shows no consistent seasonal peak.
- The incubation period is four to eight weeks.
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Most patients have few, if any, symptoms (most adults show serological evidence of previous EBV infection):
- Low-grade fever, fatigue and prolonged malaise. Fatigue and malaise may persist for several months after the acute infection has resolved.
- Sore throat; tonsillar enlargement is common, classically exudative and may be massive; palatal petechiae and uvular oedema.
- Fine macular non-pruritic rash, which rapidly disappears.
- Transient bilateral upper lid oedema.
- Lymphadenopathy, especially neck glands.
- Nausea and anorexia.
- Arthralgias and myalgias occur but are less common than in other viral infectious diseases and are rarely severe.
- Other symptoms include cough, chest pain and photophobia.
- Older adults and elderly patients often have few throat symptoms or signs and have little or no lymphadenopathy.
- Later signs include:
- Mild hepatomegaly and splenomegaly (splenic enlargement returns to normal or near normal usually within three weeks after the clinical presentation) with tenderness over the spleen.
- Jaundice occurs in fewer than 10% of young adults but in as many as 30% of infected elderly patients.
- Exudative pharyngitis is commonly confused with group A streptococcal pharyngitis. In one study of adolescent and adult patients presenting with sore throat, the presence of posterior cervical, inguinal or axillary adenopathy, palatine petechiae, splenomegaly, or atypical lymphocytosis was associated with an increased likelihood of mononucleosis.
- Bilateral periorbital oedema without generalised oedema may also be due to Kawasaki disease, allergic reactions or bilateral periorbital cellulitis.
- Other causes of prominent lymphadenopathy (see also separate Neck Lumps and Bumps article), including leukaemia, cancers of the head and neck and lymphomas.
- Atypical lymphocytes must be differentiated from abnormal lymphocytes, which are associated with lymphoreticular malignancies. Atypical lymphocytes are associated with various viral and non-infectious diseases, as well as drug reactions.
- Other causes of abnormal LFTs.
- Patients with negative Paul-Bunnell or Monospot® reactions for six weeks and those with a negative EBV-specific test result, should be tested for the causes of heterophile-negative IM. A growing number of pathogens have been associated with heterophile-negative mononucleosis-like illnesses - eg, CMV, rubella, human herpesvirus 6, HIV infection, adenovirus, herpes simplex virus, Streptococcus pyogenes and Toxoplasma gondii.
EBV IM can be diagnosed using a variety of unrelated non-EBV heterophile antibodies and specific EBV antibodies.
Following IM caused by EBV, 70-90% of patients produce IM heterophile antibodies (antibodies against an antigen produced in one species that react against antigens from other species). The heterophile antibodies are not specific for the virus. These antibodies can be detected by:
- Paul-Bunnell test: sheep red blood cells agglutinate in the presence of heterophile antibodies.
- Monospot® test: horse red blood cells agglutinate on exposure to heterophile antibodies. The Monospot® uses this in conjunction with the principle of the Davidsohn differential test. Sensitivity and specificity for Monospot® are 70-90% and 100% respectively.
Positivity increases during the first six weeks of the illness and so the heterophile antibody test results may be negative early in the course of EBV IM. The titre does not correlate with the severity of the disease. Agglutinins usually remain in the blood for 4-8 weeks but may remain positive in low levels for up to one year.
False positive results
Although virtual 100% specificity exists with the Monospot® test, other disorders may rarely produce a false positive result:
- Infection - eg, toxoplasmosis, rubella, CMV, HIV, herpes simplex virus, malaria, viral hepatitis.
- Malignancy - eg, lymphomas (particularly Burkitt's lymphoma), leukaemias, cancer of the pancreas.
- Connective tissue diseases - eg, rheumatoid arthritis, systemic lupus erythematosus.
False negative results
- May occur if testing is performed too early in the course of the illness. The false negative rate is as high as 25% in the first week of infection, 5-10% in the second week and 5% in the third week of infection.
- Heterophile antibody tests are less sensitive in patients aged younger than 10 years. False negative results are particularly common in children aged younger than 2 years. 40% of children aged 4 years or younger do not have detectable heterophile antibodies at any time during EBV infection.
- Patients who remain heterophile-negative after six weeks with a mononucleosis illness are considered to be heterophile-negative IM and should be tested for EBV-specific antibodies.
- EBV-specific antibody tests may also be useful if a false positive heterophile antibody test result is suspected. Patients who are heterophile-positive but specific antibody-negative should be considered for testing for possible causes of false positive heterophile antibodies (see list of causes under 'False positive results', above).
- The antibody response to specific EBV serological testing consists of measuring the antibody response to surface and core EBV viral proteins. The most useful EBV-specific antibodies are the viral capsid antigens (VCAs) and the EBV nuclear antigen (EBNA):
- There is a high agreement between the heterophile antibody tests and the VCA-IgM ELISA but the VCA-IgM ELISA is more sensitive.
- IgM antibodies directed against the VCA of EBV are useful in differentiating recent infection from previous infection. Following acute infection, the increase in IgM levels peaks after 4-8 weeks and IgM usually remains positive for as long as one year.
- Antibodies to EBNA are usually not detectable until 6-8 weeks after the onset of symptoms but can help to establish whether infection is recent.
- EBV IgG VCA antibodies rise later than the IgM VCA antibodies but remain elevated with variable titres for life.
- Persistent IgG does not indicate chronic IM and is not relevant in the assessment of chronic fatigue syndrome.
- False positive VCA antibody titre results may occur with other herpes viruses (eg, CMV) or with unrelated organisms (eg, T. gondii). However, false-positive cross-reactivity to specific EBV antibodies is very rare.
- There may be false-negative results early in the course of the infection and in young children (aged less than 2 years).
- A real-time polymerase chain reaction identifying IM DNA has been developed. This may be useful in cases of diagnostic doubt or where rapid diagnosis is helpful, such as in patients with a high risk of splenic rupture.
- FBC: raised white cell count with lymphocytosis and a relative atypical lymphocyte count greater than 20%. Thrombocytopenia may occur.
- ESR: the ESR is elevated in most patients with IM but is not elevated with group A streptococcal pharyngitis.
- LFTs: mild elevation of the serum transaminases (higher increases in serum transaminase levels suggest viral hepatitis).
- Throat swabs: growth of group A streptococci does not identify the cause of the pharyngitis; 30% of patients with IM have group A streptococcus in the oropharynx.
- Abdominal ultrasound may be required to assess for splenomegaly.
- Other investigations may be required to differentiate from other possible diagnoses - eg, lumbar puncture if there is meningism. Abdominal ultrasound may be required to assess for splenomegaly.
EBV is also associated with:
- Burkitt's lymphoma.
- B-cell lymphomas in patients with immunosuppression.
- Undifferentiated carcinomas - eg, cancer of the nasopharynx and cancer of the salivary glands.
- Duncan's syndrome: rare, X-linked recessive; defective T cells fail to destroy EBV-infected cells; associated development of autoimmune disease and lymphoma.
- Multiple sclerosis.
It is not recommended that affected children need to be excluded from schools and other childcare settings unless appropriate for their own well-being.
- Patients are traditionally advised to avoid contact sports for three weeks because of the risk of splenic rupture. An ultrasound study of 19 patients found that in 16 splenomegaly resolved in four weeks but in three it took eight weeks. The authors recommended that advice should be guided by ultrasound findings and this should perhaps be considered in patients who regularly participate in such sports.
- Avoid alcohol for the duration of the illness.
- Advise paracetamol for analgesia and control of fever.
- No specific antiviral therapy is available.
- There is insufficient evidence to recommend steroid treatment for symptom control in IM. Short courses of corticosteroids are beneficial for haemolytic anaemia, central nervous system involvement or extreme tonsillar enlargement.
- There has been interest in the use of antivirals such as aciclovir and valaciclovir in the treatment of IM but to date trials have been unpromising.
- Ampicillin and amoxicillin cause an itchy maculopapular rash and should not be given in any patient who might have IM.
- Patients may require hospital admission for intravenous fluids.
- Surgery is usually advocated for spontaneous splenic rupture but non-operative management may be appropriate.
- One study of military personnel suggested a role for vitamin D in shortening recovery times in patients with acute pharyngitis associated with infectious mononucleosis.
- Extreme tonsillar enlargement may result in upper airway obstruction.
- Myocarditis and cardiac conduction abnormalities are rare complications.
- Splenic rupture is rare but potentially lethal. Splenectomy increases susceptibility to various infections.
- Haemolytic anaemia, thrombocytopenia.
- Acute interstitial nephritis, glomerulonephritis.
- Neurological, including optic neuritis, transverse myelitis, aseptic meningitis, encephalitis and meningoencephalitis, cranial nerve palsies (especially facial palsy) or Guillain-Barré syndrome.
- Prolonged fatigue; depression.
- Usually asymptomatic or of short duration and self-limiting.
- Fatigue and myalgia may persist for several, or even many, months after the acute infection has resolved.
- If splenic rupture is recognised and surgery performed quickly, the prognosis is good.
Further reading & references
- Balfour HH Jr, Dunmire SK, Hogquist KA; Infectious mononucleosis. Clin Transl Immunology. 2015 Feb 27;4(2):e33. doi: 10.1038/cti.2015.1. eCollection 2015 Feb.
- Bravender T; Epstein-Barr virus, cytomegalovirus, and infectious mononucleosis. Adolesc Med State Art Rev. 2010 Aug;21(2):251-64, ix.
- Dowd JB, Palermo T, Brite J, et al; Seroprevalence of epstein-barr virus infection in u.s. Children ages 6-19, 2003-2010. PLoS One. 2013 May 22;8(5):e64921. doi: 10.1371/journal.pone.0064921. Print 2013.
- Maloney SR, Almarines D, Goolkasian P; Vitamin D levels and monospot tests in military personnel with acute pharyngitis: a retrospective chart review. PLoS One. 2014 Jul 10;9(7):e101180. doi: 10.1371/journal.pone.0101180. eCollection 2014.
- Odumade OA, Hogquist KA, Balfour HH Jr; Progress and problems in understanding and managing primary Epstein-Barr virus infections. Clin Microbiol Rev. 2011 Jan;24(1):193-209. doi: 10.1128/CMR.00044-10.
- Vouloumanou EK, Rafailidis PI, Falagas ME; Current diagnosis and management of infectious mononucleosis. Curr Opin Hematol. 2012 Jan;19(1):14-20. doi: 10.1097/MOH.0b013e32834daa08.
- Ebell MH; Epstein-Barr virus infectious mononucleosis. Am Fam Physician. 2004 Oct 1;70(7):1279-87.
- Ebell MH, Call M, Shinholser J, et al; Does This Patient Have Infectious Mononucleosis?: The Rational Clinical Examination Systematic Review. JAMA. 2016 Apr 12;315(14):1502-9. doi: 10.1001/jama.2016.2111.
- Foxworth M; About Epstein-Barr virus-associated infectious mononucleosis, Contemporary Paediatrics, 2012
- Hall DJ, Fromm JS; Drug reaction with eosinophilia and systemic symptoms syndrome in a patient taking phenytoin and levetiracetam: a case report. J Med Case Rep. 2013 Jan 3;7(1):2. doi: 10.1186/1752-1947-7-2.
- De Paschale M; Serological diagnosis of Epstein-Barr virus infection: Problems and solutions. World J Virol . 2012: 12; 1(1): 31-43.
- D’Alessandro D; What Causes a False Positive Monospot Test?, PediatricEducation.org, 2009
- Kang MJ, Kim TH, Shim KN, et al; Infectious mononucleosis hepatitis in young adults: two case reports. Korean J Intern Med. 2009 Dec;24(4):381-7. doi: 10.3904/kjim.2009.24.4.381. Epub 2009 Nov 27.
- Abrahams K; Determination of the Epstein-Barr virus by means of ELISA and real-time PCR and reproducibility thereof, 2011
- Eligio P, Delia R, Valeria G; EBV Chronic Infections. Mediterr J Hematol Infect Dis. 2010 Aug 10;2(1):e2010022. doi: 10.4084/MJHID.2010.022.
- Jiang SY, Yang JW, Shao JB, et al; Real-time polymerase chain reaction for diagnosing infectious mononucleosis in pediatric patients: A systematic review and meta-analysis. J Med Virol. 2016 May;88(5):871-6. doi: 10.1002/jmv.24402. Epub 2016 Jan 5.
- Guidance on infection control in schools and other childcare settings; Public Health England (September 2014)
- O'Connor TE, Skinner LJ, Kiely P, et al; Return to contact sports following infectious mononucleosis: the role of serial ultrasonography. Ear Nose Throat J. 2011 Aug;90(8):E21-4.
- Rezk E, Nofal YH, Hamzeh A, et al; Steroids for symptom control in infectious mononucleosis. Cochrane Database Syst Rev. 2015 Nov 8;(11):CD004402. doi: 10.1002/14651858.CD004402.pub3.
- Dunmire SK, Hogquist KA, Balfour HH; Infectious Mononucleosis. Curr Top Microbiol Immunol. 2015;390(Pt 1):211-40. doi: 10.1007/978-3-319-22822-8_9.
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Dr Colin Tidy
Dr Laurence Knott
Dr Helen Huins