29 Parvovirus

Abstract

The Parvoviridae (parvus from Latin, meaning small) are the only known virus family with linear single-stranded DNA genomes. Their chromosomes range from 4 to 6 kb in length and consist of a relatively long (<5.8 kb) single-stranded coding region, bracketed by short imperfect terminal palindromes that fold back on themselves to form duplex hairpin telomeres. Together with a few adjacent nucleotides, these hairpin termini provide all of the cis-acting information required for both viral DNA replication and progeny genome encapsidation, serving both as origins of replication and as critical hinges that allow quasi-circular amplification of the linear chromosome through a series of duplex intermediates. Parvoviruses infect a broad range of invertebrate and vertebrate hosts, from arthropods to man, and although some, such as feline panleukopenia virus (FPV), can be lethal, many others are conspicuously apathogenic. They have rugged T = 1 icosahedral protein capsids, 18–26 nm in diameter, capable of shielding the genome during its sometimes extended extracellular existence, and ultimately transporting it directly into the host cell nucleus. Here we focus on viruses that infect mammals, from the subfamily Parvovirinae, which comprises five genera, of which at least two, the Dependoviruses and the Erythroviruses, contain important members that infect human hosts (Tattersall et al. 2005). These illustrate two very different lifestyles adopted by members of the Parvoviridae, for whereas the human Dependoviruses, generally referred to as the adeno-associated viruses (AAVs), only replicate productively in cells coinfected with a helper virus, most commonly an adenovirus or herpesvirus, but potentially...