A 17-year-old patient complains of headache, sore throat, and fever. According to the patient's medical history, the onset of the disease was 2 days ago. Objectively, the patient's condition is severe, body temperature 38°C. The oropharyngeal mucosa is moderately hyperemic and edematous. Filmy deposits that are difficult to are observed on the tonsils, palate, and uvula. Palpation detects enlarged submandibular lymph nodes and edematous subcutaneous tissue on the neck. What is the most likely diagnosis in this case?