title: Spatial and non-spatial risk factors associated with cage-level distribution of infectious salmon anaemia at three Atlantic salmon, Salmo salar L., farms in Maine, USA.
abstract: The distribution of infectious salmon anaemia (ISA) was examined among 80 cages from three Atlantic salmon grow-out farms in Maine, USA that were stocked with smolts from a single hatchery. Cage-level disease was broadly defined as one or more moribund fish testing positive for infectious salmon anaemia virus (ISAV) by RT-PCR and a second confirmatory test (IFAT, culture or genotype sequence). Spatio-temporal and cage-level risks were explored using logistic regression and survival analysis. Non-spatial risk factors associated with ISA, or shortened survival time to disease, included increased predation, trucking company choice for smolt transfers, a finely-sedimented benthic substrate, and smaller average size of smolts at stocking. Univariable analysis identified the time-dependent spatial factor 'adjacency to newly infected cages' to be predictive of new infection in neighbouring cages 11-12 weeks later. However, none of the spatial factors, or their lags retained relevance in multiple-variable models. The results suggest a diffuse distribution of virus exposure throughout infected sites, with host-susceptibility factors probably influencing disease manifestation in individual cages. The narrow focus of the current study may limit application of the findings to other sites and year-classes. However, these data support the relevance of husbandry efforts to optimize fish health in regions affected by ISAV.
authors.affiliation: USDA APHIS VS, ISA Program, Eastport, ME, USA. lori.l.gustafson@aphis.usda.gov
authors.forename: L
authors.initials: L
authors.lastname: Gustafson
authors.forename: S
authors.initials: S
authors.lastname: Ellis
authors.forename: T
authors.initials: T
authors.lastname: Robinson
authors.forename: F
authors.initials: F
authors.lastname: Marenghi
authors.forename: P
authors.initials: P
authors.lastname: Merrill
authors.forename: L
authors.initials: L
authors.lastname: Hawkins
authors.forename: C
authors.initials: C
authors.lastname: Giray
authors.forename: B
authors.initials: B
authors.lastname: Wagner
mesh_terms: D000818:Animals; D005393:Fish Diseases / Q000453:epidemiology* / Q000821:virology; D005398:Fisheries; D005455:Fluorescent Antibody Technique; D046829:Isavirus / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D016015:Logistic Models; D008281:Maine / Q000453:epidemiology; D009976:Orthomyxoviridae Infections / Q000453:epidemiology / Q000662:veterinary*; D012189:Retrospective Studies; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D012307:Risk Factors; D020317:Salmo salar / Q000821:virology*; D016019:Survival Analysis