Characterisation of the Equine adenovirus 2 genome

•Phylogenetic analysis confirms EAdV-2 falls within the Mastadenovirus genus.•EAdV-2 and EAdV-1 have evolved from separate lineages within the Mastadenoviruses.•The EAdV-2 genome encodes two E1b_55K homologues from different adenovirus lineages.

Equine adenovirus 2 (EAdV-2) is one of two serotypes of adenoviruses known to infect equines. Initial studies did not associate EAdV-2 infections with any specific clinical syndromes, although more recent evidence suggests that EAdV-2 may be associated with clinical and subclinical gastrointestinal infections of foals and adults respectively. In contrast, Equine adenovirus 1 is well recognised as a pathogen associated with upper respiratory tract infections of horses. In this study the complete genome sequence of EAdV-2 is reported. As expected, genes common to the adenoviruses were identified. Phylogenetic reconstructions using selected EAdV-2 genes confirmed the classification of this virus within the Mastadenovirus genus, and supported the hypothesis that EAdV-2 and EAdV-1 have evolved from separate lineages within the adenoviruses. One spliced open reading frame was identified that encoded for a polypeptide with high similarity to the pIX and E1b_55K adenovirus homologues and was designated pIX_E1b_55K. In addition to this fused version of E1b_55K, a separate E1b_55K encoding gene was also identified. These polypeptides do not appear to have evolved from a gene duplication event as the fused and unfused E1b_55K were most similar to E1b_55K homologues from the Atadenovirus and Mastadenovirus genera respectively. The results of this study suggest that EAdV-2 has an unusual evolutionary history that warrants further investigation.