Parvoviridae, a diverse family of small single-stranded DNA viruses was established in 1975. It was divided into two subfamilies, Parvovirinae and Densovirinae, in 1993 to accommodate parvoviruses that infect vertebrate and invertebrate animals, respectively. This relatively straightforward segregation, using host association as the prime criterion for subfamily-level classification, has recently been challenged by the discovery of divergent, vertebrate-infecting parvoviruses, dubbed “chapparvoviruses”, which have proven to be more closely related to viruses in certain Densovirinae genera than to members of the Parvovirinae. Viruses belonging to these genera, namely Brevi-, Hepan- and Penstyldensovirus, are responsible for the unmatched heterogeneity of the subfamily Densovirinae when compared to the Parvovirinae in matters of genome organization, protein sequence homology, and phylogeny. Another genus of Densovirinae, Ambidensovirus, has challenged traditional parvovirus classification, as it includes all newly discovered densoviruses with an ambisense genome organization, which introduces genus-level paraphyly. Lastly, current taxon definition and virus inclusion criteria have significantly limited the classification of certain long-discovered parvoviruses and impedes the classification of some potential family members discovered using high-throughput sequencing methods. Here, we present a new and updated system for parvovirus classification, which includes the introduction of a third subfamily, Hamaparvovirinae, resolves the paraphyly within genus Ambidensovirus, and introduces new genera and species into the subfamily Parvovirinae. These proposals were accepted by the ICTV in 2020 March.

Parvoviruses, infecting vertebrates and invertebrates, are a family of single-stranded DNA viruses with small, non-enveloped capsids with T = 1 icosahedral symmetry. A quarter of a century after the first parvovirus capsid structure was published, approximately 100 additional structures have been analyzed. This first structure was that of Canine Parvovirus, and it initiated the practice of structure-to-function correlation for the family. Despite high diversity in the capsid viral protein (VP) sequence, the structural topologies of all parvoviral capsids are conserved. However, surface loops inserted between the core secondary structure elements vary in conformation that enables the assembly of unique capsid surface morphologies within individual genera. These variations enable each virus to establish host niches by allowing host receptor attachment, specific tissue tropism, and antigenic diversity. This review focuses on the diversity among the parvoviruses with respect to the transcriptional strategy of the encoded VPs, the advances in capsid structure-function annotation, and therapeutic developments facilitated by the available structures.

This article reports changes to virus taxonomy and taxon nomenclature that were approved and ratified by the International Committee on Taxonomy of Viruses (ICTV) in April 2024. The entire ICTV membership was invited to vote on 203 taxonomic proposals that had been approved by the ICTV Executive Committee (EC) in July 2023 at the 55th EC meeting in Jena, Germany, or in the second EC vote in November 2023. All proposals were ratified by online vote. Taxonomic additions include one new phylum (Ambiviricota), one new class, nine new orders, three new suborders, 51 new families, 18 new subfamilies, 820 new genera, and 3547 new species (excluding taxa that have been abolished). Proposals to complete the process of species name replacement to the binomial (genus + species epithet) format were ratified. Currently, a total of 14,690 virus species have been established.

Chapparvoviruses (ChPVs) comprise a divergent, recently identified group of parvoviruses (family Parvoviridae), associated with nephropathy in immunocompromised laboratory mice and with prevalence in deep sequencing results of livestock showing diarrhea. Here, we investigate the biological and evolutionary characteristics of ChPVs via comparative in silico analyses, incorporating sequences derived from endogenous parvoviral elements (EPVs) as well as exogenous parvoviruses. We show that ChPVs are an ancient lineage within the Parvoviridae, clustering separately from members of both currently established subfamilies. Consistent with this, they exhibit a number of characteristic features, including several putative auxiliary protein-encoding genes, and capsid proteins with no sequence-level homology to those of other parvoviruses. Homology modeling indicates the absence of a β-A strand, normally part of the luminal side of the parvoviral capsid protein core. Our findings demonstrate that the ChPV lineage infects an exceptionally broad range of host species, including both vertebrates and invertebrates. Furthermore, we observe that ChPVs found in fish are more closely related to those from invertebrates than they are to those of amniote vertebrates. This suggests that transmission between distantly related host species may have occurred in the past and that the Parvoviridae family can no longer be divided based on host affiliation.

There are 13 distinct Adeno-associated virus (AAV) serotypes that are structurally homologous and whose capsid proteins (VP1 to −3) are similar in amino acid sequence. However, AAV9 is one of the most commonly studied and is used as a gene therapy vector.

Chapparvoviruses are a highly divergent group of parvoviruses (family Parvoviridae ) first identified in 2013. Interest in these poorly characterized viruses has been raised by recent studies indicating that they are the cause of chronic kidney disease that arises spontaneously in laboratory mice. In this study, we investigate the biological and evolutionary characteristics of chapparvoviruses via comparative analysis of genome sequence data. Our analysis, which incorporates sequences derived from endogenous viral elements (EVEs) as well as exogenous viruses, reveals that chapparvoviruses are an ancient lineage within the family Parvoviridae , clustering separately from members of both currently established parvoviral subfamilies. Consistent with this, they exhibit a number of characteristic genomic and structural features, i.e. a large number of putative auxiliary protein-encoding genes, capsid protein genes non-homologous to any hitherto parvoviral cap , as well as a putative capsid structure lacking the canonical fifth strand of the ABIDG sheet comprising the luminal side of the jelly roll. Our findings demonstrate that the chapparvovirus lineage infects an exceptionally broad range of host species, including both vertebrates and invertebrates. Furthermore, we observe that chapparvoviruses found in fish are more closely related to those from invertebrates than they are to those that infect amniote vertebrates. This suggests that transmission between distantly related host species may have occurred in the past. Our study provides the first integrated overview of the chapparvovirus group, and revises current views of parvovirus evolution AUTHOR SUMMARY: Chapparvoviruses are a recently identified group of viruses about which relatively little is known. However, recent studies have shown that these viruses cause disease in laboratory mice and are prevalent in the fecal virome of pigs and poultry, raising interest in their potential impact as pathogens, and utility as experimental tools. We examined the genomes of chapparvoviruses and endogenous viral elements (‘fossilized’ virus sequences derived from ancestral viruses) using a variety of bioinformatics-based approaches. We show that the chapparvoviruses have an ancient origin and are evolutionarily distinct from all other related viruses. Accordingly, their genomes and virions exhibit a range of distinct characteristic features. We examine the distribution of these features in the light of chapparvovirus evolutionary history (which we can also infer from genomic data), revealing new insights into chapparvovirus biology.