ICTV Virus Taxonomy Profile: Circoviridae.

The family Circoviridae comprises viruses with small, circular, single-stranded DNA (ssDNA) genomes, including the smallest known animal viruses. Members of this family are classified into two genera, Circovirus and Cyclovirus, which are distinguished by the position of the origin of replication relative to the coding regions and the length of the intergenic regions. Within each genus, the species demarcation threshold is 80 % genome-wide nucleotide sequence identity. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Circoviridae, which is available at www.ictv.global/report/circoviridae.

Endogenous hepadnaviruses, bornaviruses and circoviruses in snakes.

We report the discovery of endogenous viral elements (EVEs) from Hepadnaviridae, Bornaviridae and Circoviridae in the speckled rattlesnake, Crotalus mitchellii, the first viperid snake for which a draft whole genome sequence assembly is available. Analysis of the draft assembly reveals genome fragments from the three virus families were inserted into the genome of this snake over the past 50 Myr. Cross-species PCR screening of orthologous loci and computational scanning of the python and king cobra genomes reveals that circoviruses integrated most recently (within the last approx. 10 Myr), whereas bornaviruses and hepadnaviruses integrated at least approximately 13 and approximately 50 Ma, respectively. This is, to our knowledge, the first report of circo-, borna- and hepadnaviruses in snakes and the first characterization of non-retroviral EVEs in non-avian reptiles. Our study provides a window into the historical dynamics of viruses in these host lineages and shows that their evolution involved multiple host-switches between mammals and reptiles.

SEN virus infection.

The SEN virus (SEN-V) belongs to a recently discovered group of DNA viruses whose members (SEN-V-D and SEN-V-H) are associated with post-transfusion hepatitis. It is a single-stranded circular, non-enveloped DNA virus of approximately 3600 to approximately 3800 nucleotides with at least three open reading frames (ORFs). Eight different strains of SEN-V have been identified and provisionally classified as members of the Circoviridae family, a group of small, single-stranded, non-enveloped circular DNA viruses that includes the TT virus (TTV), TUS01, SANBAN, PMV and YONBAN. Prevalences in different populations show great variability with marked differences between different countries and groups. Although parenteral transmission is very likely, other routes of transmission cannot be excluded. Mother to infant transmission has been demonstrated. The effect of SEN-V on chronic liver diseases has been studied. The influence of SEN-V on the response to HCV therapy was investigated in three studies, with contradictory results. Data for other acute and chronic liver diseases are sparse. Further studies are needed to define the pathogenesis and clinical importance of SEN-V infection.

Higher prevalence and viral load of TT virus in saliva than in the corresponding serum: another possible transmission route and replication site of TT virus.

Although TT virus (TTV) is transmissible by blood or blood products, many patients with no history of transfusion of blood and blood products have been shown to be infected, suggesting other possible routes of transmission. To investigate the transmission routes and replication sites of TTV, 85 paired saliva and serum samples were studied by semi-nested polymerase chain reaction. The prevalence of TTV DNA was 38% (32/85 samples) and 21% (18/85) in saliva and serum, respectively. Fifteen patients had TTV DNA both in saliva and serum. Six out of fifteen patients had significantly higher viral titers in saliva than in serum, but none had higher titer in serum than in saliva. When the 222 base-pair nucleotide sequences of PCR products amplified from the samples were analyzed, 12 patients had the same genotype/subtype in saliva and serum and exhibited high homology (96-100%). The other 3 had different genotypes/subtypes in saliva and serum, and the homology was 61.9-87.2%. Mixed infection was observed both in saliva and serum. Further studies are required to determine if a subgroup of TTV has tropism to saliva. The high prevalence and viral load of TTV in saliva suggest that salivary fluid may be a possible route of transmission of TTV and that TTV might replicate not only in liver tissue but also in other tissues such as oropharyngeal tissues and/or salivary glands.