The family Circoviridae contains viruses with covalently closed, circular, single-stranded DNA (ssDNA) genomes, including the smallest known autonomously replicating, capsid-encoding animal pathogens.

Full-length and partial genome sequences of four members of the genus Aquareovirus, family Reoviridae (Golden shiner reovirus, Grass carp reovirus, Striped bass reovirus and golden ide reovirus) were characterized. Based on sequence comparison, the unclassified Grass carp reovirus was shown to be a member of the species Aquareovirus C. The status of golden ide reovirus, another unclassified aquareovirus, was also examined. Sequence analysis showed that it did not belong to the species Aquareovirus A or C, but assessment of its relationship to the species Aquareovirus B, D, E and F was hampered by the absence of genetic data from these species. In agreement with previous reports of ultrastructural resemblance between aquareoviruses and orthoreoviruses, genetic analysis revealed homology in the genes of the two groups. This homology concerned eight of the 11 segments of the aquareovirus genome (amino acid identity 17-42 %), and similar genetic organization was observed in two other segments. The conserved terminal sequences in the genomes of members of the two groups were also similar. These data are undoubtedly an indication of the common evolutionary origin of these viruses. This clear genetic relatedness between members of distinct genera is unique within the family Reoviridae. Such a genetic relationship is usually observed between members of a single genus. However, the current taxonomic classification of aquareoviruses and orthoreoviruses in two different genera is supported by a number of characteristics, including their distinct GMC contents, unequal numbers of genome segments, absence of an antigenic relationship, different cytopathic effects and specific econiches.

Although single stranded (ss) DNA viruses that infect humans and their domesticated animals do not generally cause major diseases, the arthropod borne ssDNA viruses of plants do, and as a result seriously constrain food production in most temperate regions of the world. Besides the well known plant and animal-infecting ssDNA viruses, it has recently become apparent through metagenomic surveys of ssDNA molecules that there also exist large numbers of other diverse ssDNA viruses within almost all terrestrial and aquatic environments. The host ranges of these viruses probably span the tree of life and they are likely to be important components of global ecosystems. Various lines of evidence suggest that a pivotal evolutionary process during the generation of this global ssDNA virus diversity has probably been genetic recombination. High rates of homologous recombination, non-homologous recombination and genome component reassortment are known to occur within and between various different ssDNA virus species and we look here at the various roles that these different types of recombination may play, both in the day-to-day biology, and in the longer term evolution, of these viruses. We specifically focus on the ecological, biochemical and selective factors underlying patterns of genetic exchange detectable amongst the ssDNA viruses and discuss how these should all be considered when assessing the adaptive value of recombination during ssDNA virus evolution.

No abstract

No abstract

No abstract

No abstract

BackgroundPCV2 has emerged as one of the most devastating viral infections of swine farming, causing a relevant economic impact due to direct losses and control strategies expenses. Epidemiological and experimental studies have evidenced that genetic diversity is potentially affecting the virulence of PVC2. The growing number of PCV2 complete genomes and partial sequences available at GenBank questioned the accepted PCV2 classification.MethodsNine hundred seventy five PCV2 complete genomes and 1,270 ORF2 sequences available from GenBank were subjected to recombination, PASC and phylogenetic analyses and results were used for comparison with previous classification scheme.ResultsThe outcome of these analyses favors the recognition of four genotypes on the basis of ORF2 sequences, namely PCV2a, PCV2b, PCV2c and PCV2d-mPCV2b. To deal with the difficulty of founding an unambiguous classification and accounting the impossibility to define a p-distance cut-off, a set of reference sequences that could be used in further phylogenetic studies for PCV2 genotyping was established. Being aware that extensive phylogenetic analyses are time-consuming and often impracticable during routine diagnostic activity, ORF2 nucleotide positions adequately conserved in the reference sequences were identified and reported to allow a quick genotype differentiation.ConclusionsGlobally, the present work provides an updated scenario of PCV2 genotypes distribution and, based on the limits of the previous classification criteria, proposes new rapid and effective schemes for differentiating the four defined PCV2 genotypes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-015-0361-x) contains supplementary material, which is available to authorized users.