Five children in Mrs. Thompson's third grade class develop a disease which begins as a bright red rash on the face, turns violet after a few days, then disappears; then, a maculopapular rash appears on the trunk, buttocks, and extremities. It soon fades from the trunk but persists on the thighs and forearms. Two children have also had a slight fever and a sore throat, but none were terribly sick. The genetic material of the most likely causative infectious agent is