B19 parvovirus is the only member of the Parvoviridae family known to cause diseases in humans. Parvoviruses are small viruses with unenveloped icosahedral capsids that contain a single-stranded DNA genome. These physical properties contribute to viral resistance to heat, solvents, and extreme chemical conditions. Because of their limited genome, parvoviral propagation depends on infection of mitotically active cells. In the taxonomy of the parvovirus family, B19 and closely related simian parvoviruses constitute the Erythrovirus genus, separated from autonomous animal parvoviruses, dependoviruses (which require coinfection with a second virus for efficient propagation in cell culture), and insect parvoviruses called densoviruses.

B19 parvovirus has extreme tropism for human erythroid progenitor cells, which are responsible for the generation of circulating erythrocytes. In tissue culture, B19 has been propagated only in bone marrow, fetal liver, peripheral blood, and rather inefficiently in a few leukemic cell lines. B19 replication in patients has been detected in blood and marrow. Specificity for erythroid cells follows from the cellular receptor for the virus, globoside or P antigen, a tetrohexoseceramide present on erythroid cells, megakaryocytes, endothelial cells, and some placental cell types, as well as fetal liver and heart. Parvovirus infection is terminated by host production of neutralizing antibodies. Failure to produce neutralizing antibodies can result in persistent infection. Recently, cellular immune responses to parvoviruses have been measured and some CD4 and CD8 T-cell epitopes defined.