A child presents with fever, irritability, and painful vesicular lesions involving the gingiva and oral mucosa that rupture and form ulcers. Which of the following is the most likely diagnosis?

Primary herpetic gingivostomatitis, caused by Herpes Simplex Virus type 1 (HSV-1), is the most common viral infection of the oral mucosa in children. It presents acutely with fever, malaise, irritability, cervical lymphadenopathy, and painful vesicles that rapidly rupture to form multiple ulcers on the gingiva, tongue, lips, and oral mucosa. The gingiva appears bright red and inflamed. Vitamin C deficiency (scurvy) causes swollen, bleeding gingiva but without vesicles. Sarcoidosis and drug-induced gingival hyperplasia cause gingival enlargement without vesicular lesions or fever.