This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hemoglobinopathies: Sickle cell anemia, Subject name: Pathology
A 24-year-old woman with sickle cell disease is seen in the emergency room for an acute upper respiratory tract infection. Laboratory findings reveal severe, normocytic anemia. The patient develops a rapid drop in the hemoglobin level. However, the reticulocyte count is very low (<0.1%). This finding most likely reflects which of the following conditions? 
Select and explain. 
A. Bone marrow failure due to repeated infarction, B. Expected result for the patient's underlying anemia, C. Parvovirus B19 infection, D. Retroperitoneal hemorrhage
C: Parvovirus B19 infection
Answer: C: Parvovirus B19 infection 
Explanation: Aplastic crisis in sickle cell disease arises from the infection of red cell progenitors by parvovirus B19, which causes a transient cessation of erythropoiesis and a sudden worsening of the anemia. It is triggered by infection of erythroblasts in bone marrow with parvovirus B19.