23. The correct answer is E. The question stem describes the typical presentation of measles (rubeola), which is caused by a Morbillivirus, an RNA virus belonging to the Paramyxovirus family. Koplik spots, which are pathognomonic for measles, are small, bluish-white spots on the buccal mucosa in the early stages of the disease. These lesions appear just before the onset of the characteristic rash (which can also involve the extremities) and fade as the rash develops.
Leukoplakia is a premalignant condition characterized by adherent whitish patches on the gingiva (choice A) and other sites in the oral cavity.
Cold sores of the lips (choice B) are due to infection with Herpes viruses.
Candida infection (thrush) produces curdy white material loosely attached to an erythematous base (choice C).
Aphthous ulcers are large shallow ulcers of the oral mucosa (choice D), commonly known as canker sores.