title: Salmon Gill Poxvirus, the Deepest Representative of the Chordopoxvirinae.
abstract: Poxviruses are large DNA viruses of vertebrates and insects causing disease in many animal species, including reptiles, birds, and mammals. Although poxvirus-like particles were detected in diseased farmed koi carp, ayu, and Atlantic salmon, their genetic relationships to poxviruses were not established. Here, we provide the first genome sequence of a fish poxvirus, which was isolated from farmed Atlantic salmon. In the present study, we used quantitative PCR and immunohistochemistry to determine aspects of salmon gill poxvirus disease, which are described here. The gill was the main target organ where immature and mature poxvirus particles were detected. The particles were detected in detaching, apoptotic respiratory epithelial cells preceding clinical disease in the form of lethargy, respiratory distress, and mortality. In moribund salmon, blocking of gas exchange would likely be caused by the adherence of respiratory lamellae and epithelial proliferation obstructing respiratory surfaces. The virus was not found in healthy salmon or in control fish with gill disease without apoptotic cells, although transmission remains to be demonstrated. PCR of archival tissue confirmed virus infection in 14 cases with gill apoptosis in Norway starting from 1995. Phylogenomic analyses showed that the fish poxvirus is the deepest available branch of chordopoxviruses. The virus genome encompasses most key chordopoxvirus genes that are required for genome replication and expression, although the gene order is substantially different from that in other chordopoxviruses. Nevertheless, many highly conserved chordopoxvirus genes involved in viral membrane biogenesis or virus-host interactions are missing. Instead, the salmon poxvirus carries numerous genes encoding unknown proteins, many of which have low sequence complexity and contain simple repeats suggestive of intrinsic disorder or distinct protein structures.
  
  
  OBJECTIVE
  Aquaculture is an increasingly important global source of high-quality food. To sustain the growth in aquaculture, disease control in fish farming is essential. Moreover, the spread of disease from farmed fish to wildlife is a concern. Serious poxviral diseases are emerging in aquaculture, but very little is known about the viruses and the diseases that they cause. There is a possibility that viruses with enhanced virulence may spread to new species, as has occurred with the myxoma poxvirus in rabbits. Provision of the first fish poxvirus genome sequence and specific diagnostics for the salmon gill poxvirus in Atlantic salmon may help curb this disease and provide comparative knowledge. Furthermore, because salmon gill poxvirus represents the deepest branch of chordopoxvirus so far discovered, the genome analysis provided substantial insight into the evolution of different functional modules in this important group of viruses.
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway mona.gjessing@vetinst.no bmoss@nih.gov.
authors.forename: Mona C
authors.initials: MC
authors.lastname: Gjessing
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Natalya
authors.initials: N
authors.lastname: Yutin
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: Torstein
authors.initials: T
authors.lastname: Tengs
authors.affiliation: Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Tania
authors.initials: T
authors.lastname: Senkevich
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Eugene
authors.initials: E
authors.lastname: Koonin
authors.affiliation: Sisomar AS, Trollbukta, Straumen, Norway.
authors.forename: Hans Petter
authors.initials: HP
authors.lastname: Rønning
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: Marta
authors.initials: M
authors.lastname: Alarcon
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: Sonja
authors.initials: S
authors.lastname: Ylving
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: Kai-Inge
authors.initials: KI
authors.lastname: Lie
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: Britt
authors.initials: B
authors.lastname: Saure
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: Linh
authors.initials: L
authors.lastname: Tran
authors.affiliation: Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA mona.gjessing@vetinst.no bmoss@nih.gov.
authors.forename: Bernard
authors.initials: B
authors.lastname: Moss
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: Ole Bendik
authors.initials: OB
authors.lastname: Dale
mesh_terms: D000818:Animals; D002347:Carps / Q000821:virology*; D018147:Chordopoxvirinae / Q000235:genetics* / Q000378:metabolism; D005393:Fish Diseases / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D005880:Gills / Q000378:metabolism / Q000821:virology*; D010802:Phylogeny; D011213:Poxviridae Infections / Q000235:genetics* / Q000378:metabolism; D011817:Rabbits; D020317:Salmo salar / Q000821:virology*