Abstract
Human bocaviruses (HBoV) are highly prevalent human infections whose pathogenic potential remains unknown. Recent identification of the first non-human primate bocavirus [1] in captive gorillas raised the possibility of the persistent nature of bocavirus infection. To characterize bocavirus infection in humans, we tested intestinal biopsies from 22 children with gastrointestinal disease for the presence of HBoV DNA. Four HBoV-positive tissue samples were analyzed to determine whether viral DNA was present in the linear genomic, the episomal closed circular or the host genome-integrated form. Whereas one tissue sample positive for HBoV3 contained the episomal form (HBoV3-E1), none had the genome-integrated form. The complete genome sequence of HBoV3-E1 contains 5319 nucleotides of which 513 represent the non-coding terminal sequence. The secondary structure of HBoV3-E1 termini suggests several conserved and variable features among human and animal bocaviruses. Our observation that HBoV genome exists as head-to-tail monomer in infected tissue either reflects the likely evolution of alternative replication mechanism in primate bocaviruses or a mechanism of viral persistence in their host. Moreover, we identified the HBoV genomic terminal sequences that will be helpful in developing reverse genetic systems for these widely prevalent parvoviruses.SignificanceHBoV have been found in healthy human controls as well as individuals with respiratory or gastrointestinal disease. Our findings suggest that HBoV DNA can exist as episomes in infected human tissues and therefore can likely establish persistent infection in the host. Previous efforts to grow HBoV in cell culture and to develop reverse genetic systems have been unsuccessful. Complete genomic sequence of the HBoV3 episome and its genomic termini will improve our understanding of HBoV replication mechanism and its pathogenesis.
Highlights
Parvoviruses are small, non-enveloped icosahedral viruses with single-stranded linear DNA genomes that frequently infect animals through the fecal-oral route [2]
Presence of Human bocaviruses (HBoV) DNA in human tissue samples We examined the presence of HBoV DNA in intestinal biopsy samples using a sensitive nested PCR assay (1–10 copies) that targets conserved sequences in HBoV capsid genes and can amplify all known primate bocavirus species [1]
The HBoV3 found in these tissues showed,1–2% nucleotide divergence from published HBoV3 genomes found in Australia, Figure 1
Summary
Parvoviruses are small, non-enveloped icosahedral viruses with single-stranded linear DNA genomes that frequently infect animals through the fecal-oral route [2]. They are members of the Parvoviridae family, which comprises two sub-families, Densovirinae and Parvovirinae that infect non-vertebrate and vertebrate hosts, respectively [2,3]. The non-coding or non-translated regions on the genomic termini contain palindromic sequences, commonly known as inverted terminal repeats (ITR), that play a vital role in viral replication [12] Since their discovery using nucleic acid amplification-based techniques [4,8,9,11], the terminal regions of all primate bocavirus species remain unsequenced, limiting the scope of studies on viral replication and the development of reverse genetic systems. We report the complete genome of the HBoV episome found in infected human intestinal tissue and the secondary structure of its termini
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