Parvovirus Infected Erythroblasts – A Lesson in Metamorphosis!

Parvovirus B19 is a single-stranded DNA virus which selectively replicates in erythroid precursors in the bone marrow causing transient suppression of erythropoiesis in immunocompromised patients. These patients usually present with acute onset anemia with reticulocytopenia (pure red cell aplasia) but rarely may have bi or pancytopenia.[1] We encountered an interesting bone marrow aspirate smears in a 40-year-old female, who was a known case of systemic lupus erythematosus (SLE) for the past 10 years on follow-up. She had undergone renal transplant about 8 months back and was on tablet tacrolimus (1.5 mg once a day) as immunosuppression she presented to our outpatient department with complaints of fatigue and weakness for past 2 weeks. Blood investigations showed Hb of 4.2 g/dL, total leukocyte count – 5.2 × 103/μL, and platelet count of 110 × 103/μL with reticulocyte count of 0.25%. She underwent red cell transfusion twice in these 2 weeks in view of severe symptomatic anemia. Bone marrow examination showed marked paucity of erythroid elements (6% of all nucleated cells) along with the presence of characteristic giant proerythroblasts (GPE) with inclusions pathognomonic of parvovirus B19 infection. The bone marrow findings were especially interesting as they showed all 3 stages of the infected GPE in a single slide [Figure 1a]. The early GPE were large proerythroblasts with round nuclei with size around 45 μm, fine uncondensed and compact chromatin with basophilic tinge. Intranuclear inclusions were not readily apparent in these. Some basophilic GPE showed an indistinct and irregular purple staining area in the nucleus which was suggestive of evolving inclusions [Figure 1b]. These GPEs were historically referred to as “Lantern cells” due to their resemblance to Chinese lanterns.[2] The intermediate GPE showed a spectrum of morphologic appearances consisting of variable loss of cytoplasmic basophilia concomitant with an apparent increase in the amount of cytoplasm and nuclear volume [Figure 1c]. The late GPE showed a partial extrusion of the nucleus at one pole or complete bare nuclei similar in size to the nuclei of late GPE with visible inclusions. However, they had no discernible cytoplasm [Figure 1d]. The complete metamorphosis of infected erythroblasts was visible in marrow smears to understand the morphological evolution of infected erythroids. The patient’s parvovirus B19 immunoglobulin M (IgM) antibody was positive by enzyme immunoassay. Quantitative polymerase chain reaction detected a very high number of parvovirus DNA copies (86,000 per μL). She was treated as pure red cell aplasia secondary to parvovirus infection and started on intravenous immunoglobulin. The patient recovered the acute episode shortly thereafter. Her complete count showed recovery of hemoglobin to 10.5 g/dL without any transfusion within 4 weeks of treatment.Figure 1: Leishman–Giemsa (×100) stained smears from bone marrow showing marked paucity of erythroid elements with the presence of characteristic giant proerythroblasts as highlighted by black arrows (GPE) (a, LG stained oil immersion). Early GPE, intermediate GPE, and late GPE are seen in Figure b-d, respectively (LG stained, oil immersion), thereby showing complete cycle of morphological changes in an infected erythroblastsFinancial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.