Mononucleosis is caused by which virus?

• A. Epstein-Barr virus
• B. Cytomegalovirus
• C. Varicella-zoster virus
• D. Human papillomavirus

Answer: (A)

Infectious mononucleosis is most classically caused by Epstein-Barr virus, a herpesvirus that predominantly infects B cells. This infection produces the familiar pattern of fever, sore throat with pharyngitis, swollen cervical lymph nodes, and marked fatigue, often with hepatosplenomegaly. It’s transmitted mainly through saliva, which is why it’s often called the kissing disease. EBV is the best answer because it is the virus most strongly linked to the classic mono presentation, driving the characteristic lymphocytosis with atypical lymphocytes. Cytomegalovirus can cause a mono-like illness, but it’s not the typical etiologic agent for mono. Varicella-zoster virus causes chickenpox and shingles, and human papillomavirus causes warts and certain cancers. Diagnosis is supported by heterophile antibody testing or EBV-specific serology, and management is mainly supportive, with caution to avoid strenuous activity if the spleen is enlarged due to risk of rupture.