title: Puffy Skin Disease Is an Emerging Transmissible Condition in Rainbow Trout Oncorhynchus mykiss Walbaum.
abstract: The transmission of puffy skin disease (PSD) to rainbow trout Oncorhynchus mykiss Walbaum was tested in the laboratory by conducting co-habitation challenges with puffy skin (PS)-affected fish (Trojans) collected from the field. Two separate challenges were conducted using Trojans sourced from two different sites and diploid (first trial) or triploid (second trial) naïve fish. PSD-specific clinical signs were observed in both groups of naïve fish, with 66% of the fish sampled during the challenges showing signs of varying severity. The first clinical features of PSD were presented as white oval skin patches on one or both flanks 15-21 days post-challenge (dpc). The extent of the lesions ranged from 10 to 90% of the body surface, depending on the severity of the lesion. Both the severity and number of affected fish increased during the challenge. Macroscopically, oedema of the skin and multifocal petechial haemorrhaging were observed towards the end of the trials. Abnormal fish behaviour consisting of "flashing" and excessive mucous production was noted from 15 dpc onwards. Fish with severe PSD lesions also displayed inappetence and associated emaciation. Rodlet cells were observed in 41% of the fresh skin scrapes analysed from the second trial. Histologically epidermal oedema was observed in 31% of the naive fish showing gross pathology, with additional 12% displaying epidermal hyperplasia, mostly observed at the end of the challenge. Other concomitant features of the PSD lesions in challenged fish were epithelial erosion and sloughing, and occasionally mild or focal inflammation. No consistent pathology of internal organs was observed. The parasites Ichthyophthirius multifiliis and Ichthyobodo necator were observed in skin samples of a proportion of naïve challenged fish and in Trojans but not in control fish. The presence of these and other known fish pathogens in the skin of PSD-fish was confirmed by high-throughput sequencing analysis. In summary, we have demonstrated that PSD is a transmissible condition. However, even though a number of known fish pathogens were identified in the skin tissues of PSD-fish, the actual causative infectious agent(s) remain(s) unknown.
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Irene
authors.initials: I
authors.lastname: Cano
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: David W
authors.initials: DW
authors.lastname: Verner-Jeffreys
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Ronny
authors.initials: R
authors.lastname: van Aerle
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Richard K
authors.initials: RK
authors.lastname: Paley
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Edmund J
authors.initials: EJ
authors.lastname: Peeler
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Matthew
authors.initials: M
authors.lastname: Green
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Georgina S E
authors.initials: GS
authors.lastname: Rimmer
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Savage
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Claire L
authors.initials: CL
authors.lastname: Joiner
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Amanda E
authors.initials: AE
authors.lastname: Bayley
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Jason
authors.initials: J
authors.lastname: Mewett
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Hulland
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Feist
mesh_terms: D000818:Animals; D005260:Female; D005393:Fish Diseases / Q000382:microbiology / Q000469:parasitology* / Q000821:virology; D006470:Hemorrhage / Q000503:physiopathology; D016803:Hymenostomatida; D009093:Mucus; D017686:Oncorhynchus mykiss / Q000382:microbiology / Q000469:parasitology* / Q000821:virology; D012867:Skin / Q000503:physiopathology; D012871:Skin Diseases / Q000382:microbiology / Q000469:parasitology / Q000662:veterinary* / Q000821:virology; D014018:Tissue Distribution