Definitive classification of these agents awaits their biochemical characterization. Multiplication B19 virus replicates in the nucleus of infected cells. B19 DNA synthesis is assumed to be similar to that of other autonomous parvoviruses and involves the formation of double-stranded replicative intermediates. Progeny DNA is formed by strand displacement and depends on some function found only in the late S phase of the cell cycle. Single positive and negative strands are packaged separately within newly synthesized capsids.
Nonstructural proteins cause lysis of the cell, with release of progeny virus.
It is not known whether the virus has a site of replication in the respiratory tract. The erythrocyte P antigen is the cell receptor for B19 virus. This antigen is found on cells of the erythrocyte lineage, vascular endothelium and fetal myocytes. The virus replicates in erythroid precursor cells, causing lysis of these susceptible cells and transient loss of all erythrocyte precursors from the bone marrow. In hematologically normal hosts this leads to a transient reticulocytopenia without a significant fall in the number of circulating erythrocytes.