Epstein-Barr virus and cytomegalovirus infection — branching viva

Opening question

Examiner: Take me through this adolescent. What is the diagnosis, and what is the significance of the rash? ^[2]

Candidate: The diagnosis is Epstein-Barr virus infectious mononucleosis. The triad of fever, exudative pharyngitis and posterior cervical lymphadenopathy, with splenomegaly and a positive Monospot, is classic. The maculopapular rash that appeared after amoxicillin is an EBV-driven immune phenomenon rather than a true penicillin allergy — it develops in nearly all patients with EBV mononucleosis given ampicillin or amoxicillin and resolves when the antibiotic stops. The clinical error was giving the antibiotic at all, because the sore throat is viral. ^{[6] [2]}

Examiner: Why does EBV produce this illness at all? ^[1]

Candidate: EBV enters through the oropharynx, infects the epithelium, and then infects B cells via the CD21 complement receptor. It drives polyclonal B-cell activation and establishes lifelong latency in memory B cells. But the symptoms of mononucleosis are largely the host CD8 cytotoxic T-cell response to those infected B cells — the atypical lymphocytes on the blood film are reactive T cells, not infected B cells. The illness is the immune response. ^{[1] [4]}