What causes infectious mononucleosis (mono)?

Causes of Infectious Mononucleosis (Mono)

Infectious mononucleosis (mono) is primarily caused by the Epstein-Barr Virus (EBV), which is transmitted mainly through saliva. 1, 2

Primary Causative Agent

• Epstein-Barr Virus (EBV): A member of the herpesvirus family that infects approximately 90-95% of adults worldwide 1
• EBV is a γ-herpesvirus that establishes lifelong latent infection after primary exposure 3
• The virus primarily targets B-lymphocytes, leading to the characteristic lymphocytosis seen in mono 2

Transmission Routes

• Primary transmission: Through intimate oral contact ("kissing disease") 1, 2
• Secondary routes:
  • Sharing utensils, glasses, or food with infected individuals 1
  • Blood transmission (less common) 4
  • Respiratory droplets (less common) 4

Epidemiology and Risk Factors

• Most commonly affects adolescents and young adults aged 15-24 years 2, 5
• Primary EBV infection in children under 10 years is usually asymptomatic or presents with nonspecific symptoms 4
• Highest viral shedding occurs during the symptomatic phase 1
• Virus can be shed intermittently in saliva for up to 18 months after initial infection 1
• The incubation period ranges from 4-7 weeks after exposure 4

Pathophysiology

When EBV enters the body, it:

1. Infects B-lymphocytes through the CD21 receptor
2. Causes proliferation of infected B-cells
3. Triggers a robust T-cell response (causing the atypical lymphocytosis)
4. Establishes lifelong latency in memory B-cells 3

Clinical Relevance

Understanding the cause of mono is important because:

• EBV infection is associated with potential long-term complications:

  • Risk factor for chronic fatigue syndrome 2
  • Associated with certain cancers (Hodgkin lymphoma, non-Hodgkin lymphoma, nasopharyngeal carcinoma) 5
  • Linked to some autoimmune diseases 5

• Immunocompromised patients are at higher risk for:

  • Severe complications from primary infection 1
  • EBV reactivation, particularly those on anti-TNF agents 1
  • Lymphoproliferative disorders 1

Prevention Considerations

Since EBV is ubiquitous and primarily transmitted through saliva:

• Avoiding close contact during periods of highest contagiousness (first 4-8 weeks) 1
• Practicing good hand hygiene 1
• Not sharing personal items with infected individuals 1
• Currently, no EBV vaccine is available 2, 4

Understanding that EBV is the primary cause of mono helps guide appropriate diagnostic testing, management expectations, and prevention strategies for this common infection.