Abstract

Double-stranded DNA viruses are important pathogens of homeothermic and poikilothermic vertebrates. However, only alloherpesviruses and iridoviruses are well studied among poikilothermic vertebrates (e.g., fish, amphibians, and reptiles). In 2002, moribund specimens of endangered Cape seahorse (Hippocampus capensis) from a managed population experiencing elevated mortality were submitted for histopathological examination. Histopathological examination revealed a cutaneous hyperplastic vacuolar dermatopathy. Ultrastructural examination revealed large and complex virions with spherical to reniform profiles (399x168 nm) within the cytoplasm of affected epidermal cells consistent with a poxvirus. The virions displayed a single lateral body as reported previously for poxviruses detected in koi (Cyprinus carpio), Ayu (Plecoglossus altivelis), and Atlantic salmon (Salmo salar). An Illumina Nextera XT DNA library kit was used to construct a DNA library from formalin-fixed, paraffin-embedded (FFPE) tissue DNA. The DNA library was sequenced using a v3 chemistry 600-cycle kit on an Illumina MiSeq sequencer. Assembly of the resulting reads followed by BLASTx analyses resulted in a number of contigs with significant homology to the salmon gill poxvirus. Phylogenomic analyses based on core poxvirus genes revealed the seahorse poxvirus (SHPV) grouped as the sister species to the salmon gill poxvirus within the fish poxvirus clade. The histological and ultrastructural pathology and phylogenetic analyses support SHPV as a novel poxvirus within the recently proposed genus of poxviruses from fish (i.e., Piscipoxvirus). This study confirms the utility of Next Generation Sequencing (NGS) technologies in obtaining phylogenetically useful viral genomic sequences from archived FFPE tissues.

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