A novel hepadnavirus in domestic dogs

Abstract

Hepadnaviruses have been identified in several animal species. The hepadnavirus prototype, human hepatitis B virus (HBV), is a major public health problem associated with chronic liver diseases and hepatocellular carcinoma. Recently, a novel hepadnavirus, similar to HBV, was identified in domestic cats. Since several pathogens can be shared between cats and dogs, we hypothesized that dogs could also harbor hepadnaviruses and we tested a collection of canine sera with multiple molecular strategies. Overall, hepadnavirus DNA was identified in 6.3% (40/635) of canine serum samples, although the viral load in positive sera was low (geometric mean of 2.70 × 10² genome copies per mL, range min 1.36 × 10²-max 4.03 × 10⁴ genome copies per mL). On genome sequencing, the canine hepadnaviruses revealed high nucleotide identity (about 98%) and similar organization to the domestic cat hepadnavirus. Altered hepatic markers were found in hepadnavirus-positive dogs, although the role of hepadnavirus in canine health remains to be elucidated.

Figure 1

Genome organization of the DDH. The complete genome consists of 3184 bp. The proteins encoded by the polymerase (P), surface (S), core (C) and X ORFs are labelled in grey shades. The predicted Pre-S1/L (large), Pre-S2/M (middle) and Surface/S forms of the S protein are indicated. Also, the Pre-core (PC) region is shown. The length of each protein is indicated in amino acids (aa). The arrows indicate the position of the initiator codons and the ORF direction.

Figure 2

Phylogenetic trees based on three different gene targets, (a) core (partial-length), (b) polymerase (partial-length) and (c) surface (full-length), of hepadnaviruses retrieved from the GenBank database. GenBank accession numbers are provided for reference strains. The trees were generated using the maximum likelihood method, Hasegawa-Kishino-Yano model with a gamma distribution and invariant sites, and bootstrapping up to 1000 replicates. Bootstrap values > 70% are shown. Italian DDH strains 43/ITA and 570/ITA (GenBank accession no. MZ201309) are indicated by black bullets. White Sucker hepadnavirus (NC_027922) was used as outgroup. Scale bar indicates nt substitutions per site.