A 7-year-old girl with sickle cell anemia was brought to her physician by her parents who reported that she seemed to be extremely fatigued and pale-looking. They stated that several of her classmates had recently had rashes and bright red cheeks. On examination, the doctor did not see a rash, but observed that her conjunctiva, gums, and nail beds were pale and that she had tachycardia. A CBC revealed that her hemoglobin level had fallen by 2 g/dL from her last result 3 months ago; her reticulocyte count was 0.05%. From which of the following is this child suffering?