What virus causes mononucleosis (mono)?

Virus Causing Mononucleosis (Mono)

Infectious mononucleosis (mono) is primarily caused by the Epstein-Barr virus (EBV), which belongs to the herpesvirus family. 1, 2, 3, 4

Epidemiology and Transmission

• EBV is extremely common worldwide, with approximately 90-95% of adults showing evidence of past infection 1, 2
• Transmission occurs primarily through saliva (hence the nickname "kissing disease"), but can also occur via blood and respiratory droplets 2
• Highest viral shedding occurs during the symptomatic phase, but virus can be shed intermittently in saliva for up to 18 months after initial infection 1
• Most infectious during the first 4-8 weeks of illness 1

Clinical Presentation

Mono typically presents with a classic triad:

• Fever
• Pharyngitis (sore throat)
• Cervical lymphadenopathy (swollen lymph nodes in the neck) 3, 4

Additional common findings include:

• Fatigue (may be profound and last up to 3 months)
• Periorbital/palpebral edema (occurs in about one-third of patients)
• Splenomegaly (50% of cases)
• Hepatomegaly (10% of cases)
• Maculopapular rash (10-45% of cases), especially if treated with ampicillin 4

Diagnosis

The Infectious Diseases Society of America recommends a stepwise diagnostic approach:

1. Initial testing: Heterophile antibody test (Monospot) is recommended as the first diagnostic step by the American Academy of Pediatrics 1

   • Note: False-negative results occur in approximately 10% of patients, especially in children under 10 years 1

2. If Monospot is negative but clinical suspicion remains high: EBV-specific antibody testing is recommended, including:

   • Viral Capsid Antigen (VCA) IgM
   • Viral Capsid Antigen (VCA) IgG
   • Epstein-Barr Nuclear Antigen (EBNA) IgG 1

3. Interpretation of EBV serology:

   • Acute primary EBV infection: Positive VCA IgM and VCA IgG with negative EBNA IgG
   • Past infection (>6 weeks): Positive EBNA IgG (with or without VCA IgG) 1

4. Laboratory findings:

   • Peripheral blood leukocytosis
   • Lymphocytes ≥50% of white blood cell differential count
   • Atypical lymphocytes >10% of total lymphocyte count 4

Management

Treatment is primarily supportive:

• Rest and adequate hydration
• Pain relievers for sore throat and fever
• Gradual return to normal activities as tolerated 1

Important precautions:

• Avoid contact sports or strenuous exercise for at least 8 weeks or while splenomegaly is present (due to risk of splenic rupture) 1, 4
• Spontaneous splenic rupture occurs in 0.1-0.5% of patients and is potentially life-threatening 4

Special Considerations

• Children under 10 years typically have asymptomatic or nonspecific presentations 2
• Immunocompromised patients may have atypical presentations and are at increased risk for complications, including lymphoproliferative disorders 1
• EBV is a risk factor for chronic fatigue syndrome 4
• If symptoms persist beyond 6 months, consider referral to an infectious disease specialist 1

Prevention

• No vaccine is currently available 2, 4
• Preventive measures include:
  • Frequent handwashing
  • Avoiding sharing utensils, glasses, or food
  • Avoiding kissing or intimate contact during the acute phase
  • Covering coughs and sneezes 1