This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Which of the following viruses most commonly causes aplastic crises in patients with sickle cell anemia? 
Select and explain. 
A. BK virus, B. Human herpesvirus 8, C. Human papillomavirus 18, D. Parvovirus B19
D: Parvovirus B19
Answer: D: Parvovirus B19 
Explanation: Sickle cell patients are vulnerable to a variety of potentially life-threatening clinical crises. Impoant causes of aplastic crises (also called hematologic crises), in which the marrow fails to produce adequate numbers of erythrocytes, include parvovirus B19 infection and folate deficiency. For your personal information, although the question is usually asked about sickle cell anemia, these two inciting agents can also induce exacerbation of anemia in individuals with thalassemia and a variety of other hereditary red cell disorders. Simple transfusions can be used to treat aplastic crises. BK virus causes renal disease in immunocompromised hosts. Human herpes virus 8 has been implicated in Kaposi sarcoma. Human papilloma virus 18 is an impoant cause of cervical dysplasia and cancer. Ref: Ray C.G., Ryan K.J. (2010). Chapter 10. Mumps Virus, Measles, Rubella, and Other Childhood Exanthems. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.