title: Ca. Branchiomonas cysticola, Ca. Piscichlamydia salmonis and Salmon Gill Pox Virus transmit horizontally in Atlantic salmon held in fresh water.
abstract: Elucidation of the role of infectious agents putatively involved in gill disease is commonly hampered by the lack of culture systems for these organisms. In this study, a farmed population of Atlantic salmon pre-smolts, displaying proliferative gill disease with associated Candidatus Branchiomonas cysticola, Ca. Piscichlamydia salmonis and Atlantic salmon gill pox virus (SGPV) infections, was identified. A subpopulation of the diseased fish was used as a source of waterborne infection towards a population of naïve Atlantic salmon pre-smolts. Ca. B. cysticola infection became established in exposed naïve fish at high prevalence within the first month of exposure and the bacterial load increased over the study period. Ca. P. salmonis and SGPV infections were identified only at low prevalence in exposed fish during the trial. Although clinically healthy, at termination of the trial the exposed, naïve fish displayed histologically visible pathological changes typified by epithelial hyperplasia and subepithelial inflammation with associated bacterial inclusions, confirmed by fluorescent in situ hybridization to contain Ca. B. cysticola. The results strongly suggest that Ca. B. cysticola infections transmit directly from fish to fish and that the bacterium is directly associated with the pathological changes observed in the exposed, previously naïve fish.
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: J
authors.identifier: http://orcid.org/0000-0002-3450-2303
authors.initials: J
authors.lastname: Wiik-Nielsen
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: M
authors.identifier: http://orcid.org/0000-0001-5098-7905
authors.initials: M
authors.lastname: Gjessing
authors.affiliation: Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: H T
authors.initials: HT
authors.lastname: Solheim
authors.affiliation: Aqua Pharma AS, Lillehammer, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Litlabø
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: A-G
authors.initials: AG
authors.lastname: Gjevre
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.
authors.forename: A B
authors.initials: AB
authors.lastname: Kristoffersen
authors.affiliation: Norwegian Institute for Water Research, Bergen, Norway.|University of Bergen, Bergen, Norway.
authors.forename: M D
authors.initials: MD
authors.lastname: Powell
authors.affiliation: Norwegian Veterinary Institute, Oslo, Norway.|University of Bergen, Bergen, Norway.
authors.forename: D J
authors.initials: DJ
authors.lastname: Colquhoun
mesh_terms: D000818:Animals; D000073556:Burkholderiales / Q000502:physiology; D002695:Chlamydiales / Q000502:physiology; D005393:Fish Diseases / Q000382:microbiology / Q000635:transmission* / Q000821:virology; D005618:Fresh Water; D016905:Gram-Negative Bacterial Infections / Q000635:transmission / Q000662:veterinary* / Q000821:virology; D009664:Norway; D011212:Poxviridae / Q000502:physiology; D011213:Poxviridae Infections / Q000635:transmission / Q000662:veterinary* / Q000821:virology; D020317:Salmo salar
keywords: 
  Branchiomonas cysticola
  ; Epitheliocystis; gill disease; recirculation aquaculture systems; water born infection