Partial characterization of a new adenovirus lineage discovered in testudinoid turtles

- Novel adenoviruses (with balanced G + C) were detected in different turtles.
- These viruses form a lineage different from every earlier adenovirus genus.
- The novel virus lineage is hypothesized to have coevolved with testudinoid turtles.
- Establishment of a new genus (with a putative name Testadenovirus) is proposed.

In the USA and in Hungary, almost simultaneously, adenoviruses of a putative novel lineage were detected by PCR and sequencing in turtles belonging to four different species (including two subspecies) of the superfamily Testudinoidea. In the USA, partial sequence of the adenoviral DNA-dependent DNA polymerase was obtained from samples of a captive pancake tortoise (Malacochersus tornieri), four eastern box turtles (Terrapene carolina carolina) and two red-eared sliders (Trachemys scripta elegans). In Hungary, several individuals of the latter subspecies as well as some yellow-bellied sliders (T. scripta scripta) were found to harbor identical, or closely related, putative new adenoviruses. From numerous attempts to amplify any other genomic fragment by PCR, only a nested method was successful, in which a 476-bp fragment of the hexon gene could be obtained from several samples. In phylogeny reconstructions, based on either DNA polymerase or hexon partial sequences, the putative new adenoviruses formed a clade distinct from the five accepted genera of the family Adenoviridae. Three viral sub-clades corresponding to the three host genera (Malacochersus, Terrapene, Trachemys) were observed. Attempts to isolate the new adenoviruses on turtle heart (TH-1) cells were unsuccessful. Targeted PCR screening of live and dead specimens revealed a prevalence of approximately 25% in small shelter colonies of red-eared and yellow-bellied sliders in Hungary. The potential pathology of these viruses needs further investigation; clinically healthy sliders were found to shed the viral DNA in detectable amounts. Based on the phylogenetic distance, the new adenovirus lineage seems to merit the rank of a novel genus.