Evidence of a Possible Viral Host Switch Event in an Avipoxvirus Isolated from an Endangered Northern Royal Albatross (Diomedea sanfordi)

Abstract

Avipoxviruses have been characterized from many avian species. Two recent studies have reported avipoxvirus-like viruses with varying pathogenicity in reptiles. Avipoxviruses are considered to be restricted to avian hosts. However, reports of avipoxvirus-like viruses from reptiles such as the green sea turtle (Chelonia mydas) and crocodile tegu (Crocodilurus amazonicus) suggest that cross-species transmission, within avian species and beyond, may be possible. Here we report evidence for a possible host switching event with a fowlpox-like virus recovered from an endangered northern royal albatross (Diomodea sanfordi)-a species of Procellariiformes, unrelated to Galliformes, not previously known to have been infected with fowlpox-like viruses. Complete genome sequencing of this virus, tentatively designated albatrosspox virus 2 (ALPV2), contained many fowlpox virus-like genes, but also 63 unique genes that are not reported in any other poxvirus. The ALPV2 genome contained 296 predicted genes homologous to different avipoxviruses, 260 of which were homologous to an American strain of fowlpox virus (FWPV). Subsequent phylogenetic analyses indicate that ALPV2 likely originated from a fowlpox virus-like progenitor. These findings highlight the importance of host-switching events where viruses cross species barriers with the risk of disease in close and distantly related host populations.

Keywords: avipoxvirus; evolution; host-switch; northern royal albatross.

Figure 1

Genomic illustration of ALPV2. The arrows depict the direction of transcription of genes and open reading frames (ORFs). Each gene or ORF is color coded, as indicated by the key in the legend.

Figure 2

Dot plots of the ALPV2 genome (x-axis) versus other poxvirus genomes (y-axis). (A) ALPV2 vs. FWPV; (B) ALPV2 vs. PEPV; (C) ALPV2 vs. FGPV; (D) ALPV2 vs. FeP2; (E) ALPV2 vs. ALPV; (F) ALPV2 vs. SWPV1; (G) ALPV2 vs. CNPV; and (H) ALPV2 vs. TKPV (refer to Table 1 for virus details and GenBank accession numbers). The Classic color scheme was chosen in Geneious (version 10.2.2) for the dot plot lines according to the length of the match, from blue for short matches to red for matches over 100 bp long. Window size = 12.

Figure 3

Phylogenetic relationships between ALPV2 and other chordopoxviruses. A maximum likelihood (ML) tree was constructed from multiple alignments of the concatenated amino acid sequences of the selected nine poxvirus core proteins using CLC Genomics Workbench (version 9.5.4). The numbers on the left show bootstrap values as percentages. The labels at branch tips refer to virus species, followed by GenBank accession numbers and abbreviated species names in parentheses. The position of ALPV2 is highlighted using pink text. Details of the poxviruses used in the phylogenetic tree are in Table 1. Saltwater crocodile poxvirus 1 (SwCRV1; MG450915) [53] was used as an outgroup. Major clades and sub-clades are designated according to Gyuranecz et al. (2013) [59].

Figure 4

Maximum likelihood (ML) phylogenetic tree from partial nucleotide sequences of the DNA polymerase gene (a) and P4b gene (b) of selected avipoxviruses. Labels at branch tips refer to GenBank accession number/species/country of origin. The numbers on the left show bootstrap values as percentages. The relevant sub-clade A1 is highlighted using blue shading, whilst the position of ALPV2 is highlighted using pink text. The ML tree is displayed as a phylogram. The bootstrap value assigned to a node in the output tree is the percentage (0–100) of the bootstrap resamples which resulted in a tree containing the same subtree as that rooted at the node. Major clades and sub-clades are designated according to Gyuranecz et al. (2013) [59]. Major clades B and C in both the trees (a) and (b) are collapsed. For the complete ML phylograms, please see Supplementary Figures S1 and S2.