A 14-year-old girl complains of a maculopapular rash along her body, a fever of 38.5°C, and a sore throat. Objectively, she has enlarged cervical and submandibular lymph nodes and hyperemic oropharyngeal mucosa, her tongue and tonsils are coated with white plaque. Palpation revealed hepato and splenomegaly. What is the most likely diagnosis in this case?