Most primary infections asymptomatic; typical presentation: 9–12-month-old child with abrupt onset of high fever (40°C), lasting for 3 days with nonspecific complaints; febrile seizures may occur; rapid defervescence of fever occurring with onset of pink morbilliform exanthem composed of either discrete, small, pale pink papules or a blanchable exanthem, lasting 2 days; enanthem (Nagayama's spots) with erythematous papules on the mucosa of the soft palate and base of the uvula