A 14-year-old girl comes to the emergency department due to rapidly progressive exertional dyspnea and generalized weakness, which were preceded by a mild febrile illness several days ago. She has a history of sickle cell disease and takes a daily folic acid supplement. Her temperature is 37.2 C (99.1 F), blood pressure is 115/70 mm Hg, and pulse is 112/min and regular. On examination, the patient has conjunctival pallor but no icterus. A cardiac flow murmur is present. The abdomen is soft and nontender with no organomegaly. Laboratory studies show a hematocrit of 16% with reticulocyte count of 0.1% (normal range, 0.5%-1.5%). Leukocyte and platelet counts are normal. Which of the following best describes the virus most likely responsible for this patient's current condition?

Question

A 14-year-old girl comes to the emergency department due to rapidly progressive exertional dyspnea and generalized weakness, which were preceded by a mild febrile illness several days ago.  She has a history of sickle cell disease and takes a daily folic acid supplement.  Her temperature is 37.2 C (99.1 F), blood pressure is 115/70 mm Hg, and pulse is 112/min and regular.  On examination, the patient has conjunctival pallor but no icterus.  A cardiac flow murmur is present.  The abdomen is soft and nontender with no organomegaly.  Laboratory studies show a hematocrit of 16% with reticulocyte count of 0.1% (normal range, 0.5%-1.5%).  Leukocyte and platelet counts are normal.  Which of the following best describes the virus most likely responsible for this patient's current condition?

Quizplus · Accepted Answer

This patient has developed severe anemia (eg, pallor, low hematocrit, flow murmur) following a minor febrile illness. If her bone marrow were able to respond appropriately to the degree of anemia, the reticulocyte count would be elevated (normal reticulocyte count is 0.5%-1.5% of red cells). Instead, the patient's reticulocyte count is markedly reduced. This scenario describes an aplastic crisis, which in sickle cell patients is usually due to parvovirus B19 infection of erythroid precursor cells in the bone marrow. Parvovirus is a nonenveloped single-stranded DNA virus. Destruction of the erythroid precursor cells by this virus diminishes the number of reticulocytes available to replace the deformed and/or removed erythrocytes. (Choices A, C, and E) Epstein-Barr virus (enveloped double-stranded DNA virus), hepatitis C virus (enveloped single-stranded positive-sense RNA virus), and hepatitis E virus (nonenveloped single-stranded positive-sense RNA virus) can cause hematopoietic depression and some measure of aplastic anemia (a cause of pancytopenia that should not be confused with aplastic crisis, which is limited to affecting erythrocytes). Anemia with normal leukocyte and platelet counts is more likely to occur with parvovirus B19 due to the virus's predilection for infecting proerythroblasts. (Choice B) Important enveloped negative-sense RNA viruses include orthomyxoviruses (eg, influenza), paramyxoviruses (eg, measles and mumps), and rhabdoviruses (eg, rabies). However, these viruses are not known to infect erythroid progenitor cells in sufficient numbers to significantly impact erythropoiesis. (Choice D) Nonenveloped double-stranded DNA viruses include adenoviruses, papillomaviruses, and polyomaviruses, which are not commonly known to cause hematopoietic depression or aplastic crisis. Educational objective: In patients with sickle cell anemia and other chronic hemolytic disorders, the most common viral cause of an aplastic crisis is infection of erythroid progenitor cells with parvovirus B19, a nonenveloped single-stranded DNA virus.

A 14-Year-Old Girl Comes to the Emergency Department Due to Rapidly