Parvo infects RBC precursors in the marrow which can cause aplastic crisis in sickle cell patients.
Healthy people who get sick with parvovirus may have a subclinical illness with athralgias as the only symptom. But sickle cell patients and patients with decreases hematopoiesis will develop[ bone marrow failure because the virus affect the hematopoietic stem cells leading to aplastic crises and inability for the bone marrow to adequately compensate hence the low reticulocyte count.
parvovirus causes..slapped cheeks in kids
hydrops fetalis in fetus, aplastic crises in sickle cell and arthralgias in other patients.