Veterinary session

Adenoviruses (Adenoviridae) are non-enveloped, icosahedral, medium-sized viruses, with linear, double-stranded DNA genome. AdVs have been derived from members of all major vertebrate classes, however, the different AdV types possess quite narrow host spectra, that are each animal species may have its own adenovirus. Therefore they are perfectly suitable for investigating co-evolution. According to the previous results, Atadenovirus is supposed to be the genus co-evolved with Squamata out of the five presently approved genera of Adenoviridae, though first members were found in ruminants, birds, and marsupials. Only later, following the widespread usage of molecular methods in virology, a Squamata-origin of the genus was presumed as a result of the revelations of novel reptilian adenoviruses and the first full genome analysis of snake adenovirus 1. Foregoing studies demonstrated an approximate adenovirus prevalence of 10% via screening samples of reptilians kept in captivity or their carcasses, as well as the verification of the Squamata-origin of atadenoviruses. Adenoviruses, however, of distinct chelonian species, as a single cluster of the phylogenetic tree, failed to be submitted to any of the recently existing genera.

The primary objective of this work was to examine further samples of reptilians for adenovirus-infection besides providing new-coming evidences to verify the scaled reptilian origin of atadenoviruses as well as revealing new data on adenoviral evolution in chelonians. As no foregoing studies, concerning the infection rate in healthy animals from a natural habitat, had been performed, this was a principal aim of this work as well.

Cloacae swabs had been previously collected from apparently healthy, wild animals living on a fish farm in the United States, in order to perform their PCR-screening with a consensus nested PCR system. Swabs were preserved in ethanol. Phylogenetic analysis of the acquired PCR fragments was performed.

As a result, 73 samples were screened in total, 52 from chelonids, and 21 from scaled reptilians. No presence of adenovirus infection was detected in chelonians. Nevertheless, we found two positive swabs among scaled reptiles, equaling a prevalence of 9.5%. One of them was the re-detection of snake adenovirus 1 from a corn snake (Pantherophis guttatus) while a yet undescribed, novel snake adenovirus was derived from a southern water snake (Nerodia fasciata).

Based on our data collected by sequencing the 300 bp-long DNA-polymerase gene fragment, both viruses can be submitted to genus Atadenovirus. Our newly-derived prevalence data prove that adenoviruses infect reptiles as secondary pathogens in straight contrast to non-reptilian atadenoviruses that actually cause serious diseases. Considering this and the results of the phylogenetic reconstruction, the Squamata-origin of atadenoviruses has been verified.