Parvovirus B19, or B19 virus, is the causative agent of erythema infectiosum (“fifth disease”-it was fifth of the six classified exanthematous diseases of childhood), a mild viral illness of children, and polyarthralgia–arthritis syndrome in immuno-competent adults.
B19 viruses show the following properties:
· B19 viruses are extremely small viruses, measuring 18–26 nm in diameter.
· They possess a nonenveloped, icosahedral capsid.
· The viral genome contains a single-stranded DNA measur-ing 4000–6000 bases in length.
· The genome is negative-strand DNA, but there is no virion.
· The genome encodes for many proteins, which include three structural, one major nonstructural, and several smaller proteins.
B19 virus shows tropism for (a) bone marrow cells, (b) erythroid cells from fetal liver, and (c) erythroid leukemia cells. Replication of virus occurs in the nucleus. The single-stranded DNA genome has hairpin loops at both of its ends, which facil-itate double-stranded areas for the cellular DNA polymerase to start synthesis of the progeny genomes. The cellular RNA polymerase synthesizes viral mRNA from the double-stranded DNA intermediate. This is followed by assembly of virions in the nucleus. Viral replication results in cell death.
Only one serotype of B19 virus is known to occur.
B19 virus is highly resistant to inactivation but can be inacti-vated by formalin, beta propiolactone, and oxidizing agents. The viruses withstand heating at 56°C for 30 minutes and are stable between pH 3 and 9.