title: An experimental means of transmitting pancreas disease in Atlantic salmon Salmo salar L. fry in freshwater.
abstract: A challenge model for pancreas disease in Atlantic salmon, Salmo salar L. fry, was developed comparing two salmonid alphavirus (SAV) subtypes: SAV1 and SAV5. Viral doses of 3 × 10(5) TCID50  mL(-1) for SAV1 and 3 × 10(4) for SAV5 were tested in triplicate tanks, each containing 450 salmon fry. Cumulative mortalities of 1.2% were recorded. Titres of virus recovered from the mortalities ranged from 10(2) to 10(7) TCID50  mL(-1) . Fry were sampled at 3, 5 and 7.5 weeks post-challenge. Sampling after 3 weeks revealed a high prevalence of infection in the absence of clinical signs, and infectious virus was recovered from 80% and 43% of sampled fry infected with SAV1 and SAV5, respectively. After 5 weeks pancreas, heart and red skeletal muscle lesions were generally observed, whilst degeneration in white skeletal muscle was observed only in fish infected with SAV1. In situ hybridisation confirmed the presence of viral genome in infected pancreas, heart and muscle. After 7.5 weeks, infectious virus (both isolates) was recovered from 13.3% of the fish sampled, with a viral titre of 10(2) TCID50  mL(-1) . Clearly, salmon fry are susceptible to SAV infection and pancreas disease.
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, The Nothe Weymouth, Dorset, UK.
authors.forename: I
authors.initials: I
authors.lastname: Cano
authors.forename: C
authors.initials: C
authors.lastname: Joiner
authors.forename: A
authors.initials: A
authors.lastname: Bayley
authors.forename: G
authors.initials: G
authors.lastname: Rimmer
authors.forename: K
authors.initials: K
authors.lastname: Bateman
authors.forename: S W
authors.initials: SW
authors.lastname: Feist
authors.forename: D
authors.initials: D
authors.lastname: Stone
authors.forename: R
authors.initials: R
authors.lastname: Paley
mesh_terms: D000524:Alphavirus / Q000302:isolation & purification / Q000502:physiology; D018354:Alphavirus Infections / Q000401:mortality / Q000473:pathology / Q000635:transmission / Q000662:veterinary* / Q000821:virology; D000818:Animals; D005393:Fish Diseases / Q000401:mortality / Q000473:pathology / Q000635:transmission* / Q000821:virology*; D005618:Fresh Water; D016679:Genome, Viral / Q000235:genetics; D010182:Pancreatic Diseases / Q000401:mortality / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D020317:Salmo salar; D019562:Viral Load
keywords: RT-PCR; bath infection; histology; in situ hybridisation; salmon pancreas disease; salmonid alphavirus