Dermatology MCQ - Viral Infections - Infectious mononucleosis

A 19-year-old college student presents with a 5-day history of fever, severe sore throat, and fatigue. Physical examination reveals bilateral cervical lymphadenopathy, pharyngeal erythema, and tonsillar exudates. The patient also has palatal petechiae and mild hepatosplenomegaly. Laboratory studies show an absolute lymphocytosis with atypical lymphocytes on peripheral smear and a positive heterophile antibody test. Which of the following is the most likely causative agent and its primary mode of transmission?

A) Cytomegalovirus (CMV); transmission via respiratory droplets
B) Epstein-Barr virus (EBV); transmission via saliva
C) Group A Streptococcus; transmission via respiratory droplets
D) Human herpesvirus 6 (HHV-6); transmission via saliva
E) Adenovirus; transmission via fecal-oral route

Correct Answer: B) Epstein-Barr virus (EBV); transmission via saliva

Explanation

This presentation is classic for infectious mononucleosis (IM), most commonly caused by Epstein-Barr virus (EBV).

Key Clinical Features of Infectious Mononucleosis:

• Symptoms: The classic triad of fever, pharyngitis (often exudative), and lymphadenopathy (especially posterior cervical nodes). Severe fatigue is hallmark.

• Signs:

  • Palatal petechiae (50% of cases).

  • Hepatosplenomegaly (mild, but splenic rupture is a rare complication).

  • Periorbital edema (less common).

• Laboratory Findings:

  • Lymphocytosis with ≥10% atypical lymphocytes (activated CD8+ T cells).

  • Positive heterophile antibody test (e.g., Monospot) in 85% of cases by the second week of illness.

  • Elevated hepatic transaminases (mild hepatitis).

Virologic Features:

• Causative Agent: Epstein-Barr virus (EBV), a double-stranded DNA virus in the Herpesviridae family.

• Transmission: Primarily through saliva ("kissing disease"), but also via shared utensils, drinks, or other close contact.

• Pathogenesis: EBV infects B lymphocytes and epithelial cells of the oropharynx, leading to polyclonal B-cell activation and a robust cytotoxic T-cell response (atypical lymphocytes).

Why Not the Other Options?

• (A) Cytomegalovirus (CMV): Can cause a mononucleosis-like illness with fever and fatigue, but exudative pharyngitis and lymphadenopathy are less prominent. Heterophile antibody test is negative. Transmitted via bodily fluids (saliva, urine, blood).

• (C) Group A Streptococcus: Causes bacterial pharyngitis with exudates and lymphadenopathy, but atypical lymphocytes and hepatosplenomegaly are absent. Rapid strep test or culture is positive.

• (D) Human herpesvirus 6 (HHV-6): Causes roseola infantum (exanthem subitum) in children, not infectious mononucleosis in adults.

• (E) Adenovirus: Can cause pharyngitis and conjunctivitis ("pharyngoconjunctival fever"), but atypical lymphocytes and heterophile antibodies are absent.

Management:

• Supportive care: Rest, hydration, analgesics (e.g., acetaminophen for fever/pain).

• Avoid ampicillin/amoxicillin: These antibiotics cause a non-allergic maculopapular rash in >90% of patients with EBV IM.

• Corticosteroids: Considered only for severe complications (e.g., airway obstruction, hemolytic anemia).

Complications:

• Splenic rupture (avoid contact sports for 3-4 weeks).

• Airway obstruction (from tonsillar hypertrophy).

• Chronic active EBV infection (rare).

Prognosis:
Self-limiting in most cases, with fatigue resolving over weeks to months. EBV establishes lifelong latency in B cells.