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Chapter 2 : Human Bocavirus: a Newly Discovered Human Parvovirus
Category: Clinical Microbiology
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Respiratory tract infections are a leading cause of morbidity and mortality worldwide. New respiratory viruses include human metapneumovirus, the coronaviruses severe acute respiratory syndrome-associated coronavirus, NL63, and HKU1, at least one new human rhinovirus, two novel human polyomaviruses, the "giant" mimivirus, and the human bocavirus (HBoV), the subject of this chapter. Characteristics of the viral life cycle inevitably dictate the types of disease parvoviruses are able to induce. In most studies, HBoV is detected in a small («8%) though significant percentage of respiratory specimens. The initial identification of HBoV in respiratory secretions encouraged many investigators to screen for the virus in individuals with respiratory tract disease. In a population-based surveillance study of pneumonia in Thailand, 4.5% of 1,168 individuals with pneumonia tested positive for HBoV. Respiratory specimens in this study were screened for a variety of viral pathogens, in addition to HBoV, and of those in which HBoV was detected, a copathogen was frequently present. HBoV is frequently detected with other respiratory viral pathogens. Detection of HBoV DNA in serum is also a provocative finding. HBoV was detected in serum of children with wheezing. Two closely related genotypes of HBoV were identified in the initial description of HBoV, differing at 26 of the 5,217 base positions in the single-stranded DNA genome. The seroepidemiology of HBoV has been explored using recombinant proteins. Well-designed studies and the development of techniques to propagate and to detect HBoV virions will allow steps forward in investigating the biology of the new parvovirus.
Phylogeny of the subfamily Parvovirinae, as currently approved by the International Committee on Taxonomy of Viruses, shown as an unrooted tree redrawn from that originally constructed by Z. Zadori and P. Tijssen and presented in reference 61 .
Overview of genetic strategies for the five genera belonging to the Parvovirinae, showing predicted structures for their terminal hairpins magnified approximately ×20 compared to the intervening coding sequences. Viral promoters are depicted by solid arrows and polyadenylation sites by AAAAA. Viral genes are represented by arrowed boxes; light grey is for nonstuctural genes, dark grey is for capsid genes, and the unfilled arrows are for ancillary protein genes. Square brackets denote the P19 promoter and central polyadenylation site present in some, but not all, dependoviruses.
Genomic organization of the HBoV genome and identification of the VP2 gene. The open reading frame map (for all three reading frames) for the predicted sense strand of the HBoV ST2 genome (GenBank accession number DQ000496) is displayed at the top of the figure. The alignments of the amino acid sequences of the VP1 gene of MVM (GenBank accession number J02275), HBoV, and BPV1 (GenBank accession number DQ335247) are shown at the bottom of the figure. Shaded amino acid residues are conserved among the three parvoviruses. The phospholipase A2 (PLA2) domain is indicated. The putative start of the VP2 gene is shown. Reprinted from the Journal of Infectious Diseases ( 25 ). © 2008 by the Infectious Diseases Society of America.
(A) Supernatants of recombinant baculovirus-expressing HBoV VP2-infected cells were centrifuged in an iodixanol gradient. Aliquots of each fraction were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Bovine serum albumin (BSA; 10 μg) was used as a concentration standard. (B) Electron micrograph of HBoV VLPs negatively stained with uranyl acetate. Bar, 100 nm. Reprinted from the Journal of Infectious Diseases ( 25 ). © 2008 by the Infectious Diseases Society of America.
Age distribution of HBoV- and B19-seropositive individuals based on the two VLP ELISAs. (A) Sera from 270 individuals were screened for HBoV-specific antibodies. The number of sera screened and the percentage of seropositive individuals for each age group are shown. The bars indicate the standard errors. (B) Sera from 208 individuals were screened for both HBoV- and B19-specific antibodies. The number of sera screened and the percentage of seropositive individuals for each age group are shown. The bars indicate the standard errors. Shaded bars, HBoV; white bars, B19. Reprinted from the Journal of Infectious Diseases ( 25 ). © 2008 by the Infectious Diseases Society of America.