What is infectious mononucleosis (mono)?

Infectious Mononucleosis (Mono)

Infectious mononucleosis (mono) is a common viral illness caused by the Epstein-Barr virus (EBV) that primarily affects adolescents and young adults, characterized by fever, sore throat, swollen lymph nodes, and fatigue. 1, 2

Cause and Transmission

• Caused by Epstein-Barr virus (EBV), a ubiquitous herpesvirus that infects over 90% of adults worldwide 3
• Primarily transmitted through saliva ("kissing disease"), but can also spread via blood and respiratory droplets 4
• Most common in adolescents and young adults aged 15-24 years 2
• Primary infection in children under 10 years is usually asymptomatic or presents with nonspecific symptoms 4

Clinical Presentation

Classic Triad:

• Fever
• Pharyngitis/tonsillitis (often severe)
• Cervical lymphadenopathy (swollen lymph nodes in neck) 2, 5

Other Common Symptoms:

• Fatigue (may be profound and last up to 3 months)
• Periorbital/palpebral edema (occurs in ~33% of patients)
• Splenomegaly (enlarged spleen in ~50% of cases)
• Hepatomegaly (enlarged liver in ~10% of cases)
• Maculopapular rash (in 10-45% of patients, more common if treated with ampicillin) 2

Diagnostic Approach

Laboratory Findings:

• Peripheral blood leukocytosis with lymphocytosis (lymphocytes >50% of white blood cells)
• Atypical lymphocytes (>10% of total lymphocyte count) 2

Diagnostic Tests:

1. Heterophile antibody test (Monospot): Most widely used initial test

   • Quick and convenient but has limitations in sensitivity, especially in children 1
   • False-positive results may occur in leukemia, pancreatic carcinoma, viral hepatitis, and CMV infection 1

2. EBV-specific antibody testing: Recommended when Monospot is negative but clinical suspicion remains high 1

   • Primary EBV infection: Positive VCA IgM and VCA IgG with negative EBNA1 IgG
   • Past infection (>6 weeks): Positive EBNA1 IgG (with or without VCA IgG) 1, 3

3. Paul-Bunnell test: Suboptimal for diagnosis compared to newer methods 1

Management

Treatment is primarily supportive as mono is generally self-limiting:

• Rest as tolerated
• Adequate hydration
• Pain relievers for sore throat and fever
• Avoid contact sports or strenuous exercise for at least 8 weeks or while splenomegaly is present to prevent splenic rupture 2

Medications:

• Acyclovir therapy does not improve outcomes in otherwise healthy individuals 1
• Steroids may be indicated for airway obstruction but not routinely recommended 1

Complications

• Splenic rupture (0.1-0.5% of cases) - most serious acute complication 2, 5
• Chronic fatigue syndrome (increased risk following mono) 2
• Airway obstruction from severe tonsillar enlargement
• Neurological complications (rare): encephalitis, Guillain-Barré syndrome
• Hematologic complications: hemolytic anemia, thrombocytopenia
• In immunocompromised patients: increased risk of lymphoproliferative disorders 1

Prevention

• No vaccine currently available 4
• Avoiding direct contact with saliva of infected individuals
• EBV IgG screening may be considered before initiation of immunomodulator therapy in certain patients 1

Special Considerations

• Approximately 10% of mono-like illnesses are not caused by EBV but by other pathogens such as cytomegalovirus (CMV) 6
• Patients on immunosuppressive therapy who develop primary EBV infection are at increased risk for severe complications and lymphoproliferative disorders 1