Poxviruses (family Poxviridae) are large, double-stranded DNA viruses that replicate in the cytoplasm of the host cells. The subfamily Chordopoxvirinae infects a wide range of vertebrates including marine mammals within the families Balaenidae, Delphinidae, Mustelidae, Otariidae, Phocidae, and Phocoenidae.1-3 Recently, a novel poxvirus was discovered in two orphaned sea otter pups that developed small, superficial ulcerated skin lesions during captive care in 2009 and 2011.3 The pups were from two different Pacific Ocean populations: the northern (Enhydra lutris kenyoni) population in Alaska and the southern (Enhydra lutris neiris) population in California. Histopathologic examination of the skin lesions in both pups revealed epithelial hyperplasia with affected cells displaying intracytoplasmic eosinophilic inclusions, which were consistent with poxvirus infection. Additionally, the epithelial cells in both pups showed different degrees of ballooning degeneration and necrosis. In the northern sea otter, transmission electron microscopy revealed epithelial intracytoplasmic virions. The virions were brick shaped and had dumbbell electron-dense cores, which were also consistent with poxviruses. Despite being known for more than a decade, the phylogenetic relationships of marine mammal poxviruses are not well established because of the lack of complete genome sequences. Therefore, the purpose of the current study was to sequence the entire sea otter poxvirus (SOPV) genome using an Illumina MiSeq Next Generation Sequencer. The approximately 130,000-bp genome is 31.3% G+C, encodes 114 proteins, and has 2,613-bp inverted terminal repeats. Phylogenetic analysis based on 14 core poxvirus genes showed that SOPV is divergent from other known poxviruses and forms a distinct branch between parapoxviruses and orthopoxviruses, which are able to cause zoonotic diseases. The SOPV genome is the first marine mammal poxvirus to be fully sequenced and is the smallest poxvirus genome known. Sequencing of the SOPV genome is the first step in unraveling the position of a marine mammal poxvirus within the larger Poxviridae tree and provides the necessary sequence to develop future molecular tools for diagnostics and epidemiological studies.
The authors wish to thank Dr. Mike Murray and the Monterey Bay Aquarium for providing samples from the southern sea otter pup. We would also like to thank the Alaska SeaLife Center Stranding Program and the US Fish and Wildlife for financial support. The northern sea otter pup in this report was collected under US Fish and Wildlife Letter of Authorization LOA837414, and the southern sea otter pup was collected under Federal Fish and Wildlife Permit MA032027-1 and Letter of Authorization LOA032027-1.
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+ Student presenter
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