title: Longitudinal serological surveys of Atlantic salmon, Salmo salar L., using a rapid immunoperoxidase-based neutralization assay for salmonid alphavirus.
abstract: Longitudinal serological surveys for salmon pancreas disease virus (SPDV), the causal agent of pancreas disease (PD), were conducted on multiple caged populations of Atlantic salmon, Salmo salar L., on two farms over a 77-week period (farm 1, freshwater and marine stages) and a 36-week period (farm 2, marine stage only), using a microtitre-based virus neutralization (VN) assay. Collected sera were also screened for viraemia with SPDV, and pancreas, heart and muscle tissues were examined for lesions consistent with PD. Outbreaks of PD occurred during the marine phase on both farms, as demonstrated by seroconversion, the isolation of virus and progressive histopathological changes consistent with a PD outbreak. All populations monitored showed a progressive increase in seroprevalence of 90-100%, typically accompanied by rises in geometric mean antibody titres. With the exception of one caged population, which showed a marked biphasic seroprevalence pattern, the seroprevalence figures in the remaining four monitored populations remained high (> or =70%) until the end of the study period. Peak VN titres of > or =1/1280 were detected on both farms. The results provide essential baseline information for the interpretation of SPDV VN serology results, and indicate that this methodology is suited to both the diagnosis and seroepidemiology of SPDV infections.
authors.affiliation: Veterinary Sciences Division, Stormont, Belfast, UK. david.graham@dardni.gov.uk
authors.forename: D A
authors.initials: DA
authors.lastname: Graham
authors.forename: V A
authors.initials: VA
authors.lastname: Jewhurst
authors.forename: H M
authors.initials: HM
authors.lastname: Rowley
authors.forename: M F
authors.initials: MF
authors.lastname: McLoughlin
authors.forename: H
authors.initials: H
authors.lastname: Rodger
authors.forename: D
authors.initials: D
authors.lastname: Todd
mesh_terms: D000524:Alphavirus / Q000302:isolation & purification*; D000818:Animals; D017756:Aquaculture; D003625:Data Collection; D007124:Immunoenzyme Techniques / Q000379:methods*; D008137:Longitudinal Studies; D009500:Neutralization Tests / Q000379:methods*; D020317:Salmo salar / Q000821:virology*; D016036:Seroepidemiologic Studies