Abstract
Herpesviruses are an ancient and successful viral lineage infecting a range of invertebrates and vertebrates including mollusks, fish, amphibians, reptiles, birds, and mammals.1 The herpesvirus virion includes an outer envelope that surrounds the proteinaceous tegument layer which in turn surrounds an icosahedral nucleocapsid that contains the electron dense dsDNA core. The order Herpesvirales is divided into 3 families: Herpesviridae containing mammalian, avian, and reptilian viruses, Alloherpesviridae containing fish and amphibian viruses, and Malacoherpesviridae containing mollusk viruses. The family Herpesviridae is further divided into the subfamilies Alpha-, Beta-, and Gammaherpesvirinae. Alpha- and/or gammaherpesviruses have been detected in the following marine mammal families: Balaenopteridae, Delphinidae, Kogiidae, Monodontidae, Mustelidae, Odobenidae, Otariidae, Phocidae, Phocoenidae, Physeteridae, Trichechidae, Ursidae, and Ziphiidae.2,3,4,5,6,7 Previously, two cases of herpesviruses in beluga whales (Delphinapterus leucas) have been reported.8,9 The first case involved an adult female beluga whale which was captured at Churchill River in Manitoba, Canada, and taken to the Mystic Marinelife Aquarium in Connecticut, USA. It developed a chronic dermatitis determined to be caused by a herpesvirus based on microscopic and ultrastructural examination of the lesions.8 A second case involved the molecular characterization of a herpesvirus in the carcass of a beluga whale that stranded in the St. Lawrence Estuary, Quebec, Canada.9 DNA from a papilloma-like penile lesion tested positive using a PCR targeting the herpesviral DNA dependent DNA polymerase gene. Sanger sequencing revealed the virus was a novel alphaherpesvirus named the beluga whale herpesvirus (BWHV).
In this investigation, we report the phylogenomic characterization of an alphaherpesvirus from a blowhole swab obtained from an overtly healthy adult beluga whale sampled in 2008 as a part of a health assessment project in Bristol Bay, Alaska. Cytopathic effect (e.g., cytomegaly and syncytia) was observed within 1 month following the inoculation of beluga whale kidney (BWK) primary cells. Transmission electron microscopy revealed naked icosahedral nucleocapsids in various states of morphogenesis within the nucleus consistent with a herpesvirus. Following viral enrichment steps, a DNA library was generated using an Illumina Nextera Kit and sequenced on an Illumina MiSeq Next Generation Sequencer. De novo assembly in SPAdes recovered the full genome (144,144 bp; 73.4% G+C) and encodes 86 putative genes. The genomic organization was found to be consistent with alphaherpesviruses within the genus Varicellovirus (e.g., Varicella zoster virus that causes chicken pox and shingles in humans). Phylogenetic analyses based on herpesvirus core genes confirmed the BWHV is a novel alphaherpesvirus clustering with other cetacean alphaherpesviruses. The BWHV is the first marine mammal herpesvirus to be fully sequenced and we propose the name Monodontid alphaherpesvirus 1 (MoHV1) for consideration by the International Committee on the Taxonomy of Herpesviruses. Future research directions include using the genomic sequence to develop molecular diagnostic tools to better understand the pathology (e.g., in situ hybridization) and prevalence (e.g., quantitative PCR and Enzyme Linked Immunosorbent Assay) of MoHV1 within managed and free-ranging beluga whale populations.
Acknowledgements
The authors wish to thank the Department of Fisheries and Oceans Canada for funding the virus isolation work and the University of Florida Graduate Student Fellowship.
* Presenting author
+ Student presenter
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