An 8 year old boy presented with fever and bilateral cervical lymphadenopathy with prior history of sore throat. There was no hepatomegaly. The peripheral blood smear shows > 20% lympho-plasmacytoid cells. The most likely diagnosis is:

Most infections in children are asymptomatic. In symptomatic cases, there is fever, malaise, sore-throat and loss of appetite to begin with. There may be ulceration in oral cavity with enanthem at junction of hard palate and soft palate. Spleen is enlarged in more than half of the patients. Periorbital edema is repoed in 33% of cases. Ref: Kliegman, Behrman, Jenson, Stanton, (2007), Chapter 251, "Epstein Barr Virus", In the book, "Nelson's Textbook of Pediatrics", Volume 1, 18th Edition, New Delhi, Pages 1372-1376