A 16-year-old teenager complains about halitosis, general weakness, body temperature rise up to 37,6°C. These symptoms turned up 2 days ago, the boy has a history of recent angina. Objectively: oral cavity hygiene is unsatisfactory, teeth are covered with soft white deposit. Gums are hyperaemic, gingival papillae are covered with greyish coating. What is the most likely diagnosis?