Family: Adenoviridae

Genus: Testadenovirus

Distinguishing features

A lineage of testudinoid (turtle, tortoise and slider) adenoviruses has been documented that is phylogenetically very distinct from all other adenoviruses (Farkas and Gál 2009, Doszpoly et al., 2013, Harrach et al., 2019, Franzen-Klein et al., 2020, Salzmann et al., 2021). These viruses were detected and partially sequenced using PCR but have not yet been isolated. Their hosts (Testudines) are very divergent from those of other adenoviruses. The rare cases when tortoise adenoviruses turned out to belong to other genera are presumed to be the consequence of host switching, examples being the siadenovirus Sulawesi tortoise adenovirus 1 (Rivera et al., 2009, Schumacher et al., 2012) or the atadenovirus found in spur-thighed (Greek) tortoise (Garcia-Morante et al., 2016) and some further tortoise species (Salzmann et al., 2021). Testadenoviruses seem to have balanced G+C content (suggesting constant coevolution with their present hosts the testudines) (Harrach et al., 2019). 

Virion

Morphology

Not known. 

Physicochemical and physical properties

Not known. 

Nucleic acid

The nucleotide composition of the partially sequenced genome (14,776 bp) of red-eared slider adenovirus 1 (RSAdV-1) is 55.18% G+C. The inverted terminal repeats (ITRs) have not been characterised. 

Proteins

The partial RSAdV-1 genome sequence contains orthologues of 10 of the 16 family-common genes, and thus these proteins are presumed to have roles similar to those in other adenoviruses. There is no gene encoding an equivalent of the mastadenovirus protein V. 

Lipids

None reported. 

Carbohydrates

See discussion under family properties. 

Genome organization and replication

The partial RSAdV-1 genome sequence covers part of the conserved adenovirus gene region encompassing 10 of the 16 family-common genes and in the same gene order, but lacks the gene for protein V. In this sequence, only the pTP gene is predicted to be spliced. This gene is also spliced in all other adenoviruses. 

Biology

Testadenoviruses seem to be non-pathogenic for turtles, tortoises and sliders. 

Species demarcation criteria

There is only a single species in the genus: Pond slider testadenovirus A. At least two of the following demarcation criteria could be used to delineate further species:

• Phylogenetic distance (>10–15%, based on distance matrix analysis of the DNA polymerase amino acid sequence)
• Host range
• Nucleotide composition

Related, unclassified viruses

Virus names and virus abbreviations are not official ICTV designations.