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Chapter 30 : Parvoviruses
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This chapter focuses on the two known human parvoviruses: B19 and human bocavirus (HBoV). While most autonomous parvoviruses possess unique sequences at either terminus, B19 differs in that its termini are inverted terminal repeats. B19 replication follows a modified rolling hairpin model of replication characteristic of the autonomous parvoviruses. The viral nonstructural protein NS1 serves as the “nickase,” which reduces the replicative forms to progeny virus. Nickase reduction results in two distinct configurations of the distal 375-nucleotide palindromes, which are inverted complements of each other. Parvovirus B19, like other parvoviruses, replicates and assembles in the cell nucleus. Upon histological analysis, a parvovirus infection may be suspected on the basis of intranuclear inclusions characterized by a peripheral nuclear presence. The polymerase chain reaction (PCR) offers exquisite sensitivity and the ability to detect B19 DNA in an array of clinical specimens.
Ouchterlony gel diffusion assay showing newly discovered B19 antigen (Δ) nonidentity with HB antigen sub-types ad and ay, using anti-B19 antibody positive antiserum P (reprinted from Cossart et al., 1975, with permission from Elsevier).
(A) Fetal ascites from a hydropic fetus showing viral particles without label, prepared by a pseudoreplica technique, and negatively stained by uranyl acetate. Original magnification, ×100,000; image magnification, ×280,000; bar, 50 nm. (B) The fetal ascites prepared by pseudoreplica technique and identified as B19 by indirect labeling with colloidal gold (arrow) before negative staining with uranyl acetate. Original magnification, ×50,000; image magnification, ×140,000; bar, 100 nm. (Reprinted with permission from Naides and Weiner, 1989.)