A systematic surveillance programme for infectious salmon anaemia virus supports its absence in the Pacific Northwest of the United States.

In response to reported findings of infectious salmon anaemia virus (ISAV) in British Columbia (BC), Canada, in 2011, U.S. national, state and tribal fisheries managers and fish health specialists developed and implemented a collaborative ISAV surveillance plan for the Pacific Northwest region of the United States. Accordingly, over a 3-1/2-year period, 4,962 salmonids were sampled and successfully tested by real-time reverse-transcription PCR. The sample set included multiple tissues from free-ranging Pacific salmonids from coastal regions of Alaska and Washington and farmed Atlantic salmon (Salmo salar L.) from Washington, all representing fish exposed to marine environments. The survey design targeted physiologically compromised or moribund animals more vulnerable to infection as well as species considered susceptible to ISAV. Samples were handled with a documented chain of custody and testing protocols, and criteria for interpretation of test results were defined in advance. All 4,962 completed tests were negative for ISAV RNA. Results of this surveillance effort provide sound evidence to support the absence of ISAV in represented populations of free-ranging and marine-farmed salmonids on the northwest coast of the United States.

Viral hemorrhagic septicemia IVb status in the United States: inferences from surveillance activities and regional context.

The United States (U.S.) response to viral hemorrhagic septicemia virus (VHSV) IVb emergence in the Laurentian Great Lakes (GL) included risk-based surveillance for cost-effective decision support regarding the health of fish populations in open systems. All U.S. VHSV IVb isolations to date derive from free-ranging fish from GL States. Most originate in the region designated by US Geological Survey hydrologic unit code (HUC) 04, with the exception of two detections in neighboring Upper Mississippi (HUC 05) and Ohio (HUC 07) regions. For States outside the GL system, disease probability was assessed using multiple evidence sources. None substantiated VHSV IVb absence using surveillance alone, in part due to the limited temporal relevance of data in open systems. However, Bayesian odds risk-based analysis of surveillance and population context, coupled with exclusions where water temperatures likely preclude viral replication, achieved VHSV IVb freedom assurance for 14 non-GL States by the end of 2012, with partial evidence obtained for another 17 States. The non-GL region (defined as the aggregate of 4-digit HUCs located outside of GL States) met disease freedom targets for 2012 and is projected to maintain this status through 2016 without additional active surveillance. Projections hinge on continued basic biosecurity conditions such as movement restrictions and passive surveillance. Areas with navigable waterway connections to VHSV IVb-affected HUCs (and conducive water temperatures) should receive priority for resources in future surveillance or capacity building efforts. However, 6 years of absence of detections in non-GL States suggests that existing controls limit pathogen spread, and that even spread via natural pathways (e.g., water movement or migratory fish) appears contained to the Great Lakes system. This report exemplifies the cost-effective use of risk-based surveillance in decision support to assess and manage aquatic animal population health in open systems.

Estimating diagnostic test accuracy for infectious salmon anaemia virus in Maine, USA.

Infectious salmon anaemia virus (ISAV) is a pathogen of consequence to farmed Atlantic salmon, Salmo salar L. ISA control centres on active surveillance for early detection by reverse transcription polymerase chain reaction (RT-PCR), indirect fluorescent antibody assay (IFAT) and virus isolation. Because diagnostic test performance varies among populations and laboratories, the Office International des Epizooties (OIE) recommends an evaluation of test accuracy in each region of use. This is complicated in Maine, USA by the co-existence of ISAV genotypes homologous to North American (NA) and European (EU) isolates. While NA ISAV genotypes isolated in Maine are characterized by high morbidity and mortality, the single EU genotype in Maine has not yet been linked to disease or isolated by cell culture. Consequently, distinguishing among genotypes is critical to infection response. Accuracy in NA genotype detection was estimated from ISA surveillance data using latent class models. Results suggested that RT-PCR is an excellent screening test for NA ISAV genotypes in Maine, although probably with reduced specificity in the presence of EU genotypes. IFAT, in contrast, was a poor screening test for detection of ISAV in Maine, although it may be useful in confirmation of NA genotypes during disease outbreaks.

Characterization of a novel pestivirus originating from a pronghorn antelope.

A unique pestivirus, isolated from a pronghorn antelope (Antilocopra americana), was characterized. Serum neutralization studies suggested that this virus was antigenically related to pestiviruses. Genomic characteristics, unique to pestiviruses, indicated that this virus belongs to the Pestivirus genus. These characteristics included the organization of the 5' untranslated region (5'-UTR), the presence and length of a viral Npro coding region, conservation of cysteine residues in Npro, conservation of predicted amino acid sequences flanking the cleavage sites between viral polypeptides Npro and C and between C and Erns and conservation of predicted hydrophobicity plots of Npro protein. While this data indicated the virus belongs to the Pestivirus genus, phylogenetic analysis in 5'-UTR, Npro and E2 regions suggested that it is the most divergent of the pestiviruses identified to date. This conclusion was also supported by the amino acid identity in coding regions. The corresponding values were much lower for the comparison of pronghorn pestivirus to other pestivirus genotypes than only between previous recognized genotypes. These results suggest the virus isolated from pronghorn antelope represents a new pestivirus genotype. It also represents the only pestivirus genotype first isolated from New World wildlife.

Comparative sequence analysis of the 5' noncoding region of classical swine fever virus strains from Europe, Asia, and America.

Polymerase chain reaction was utilized to determine the sequence of a 280 base pair fragment from cDNAs of the 5' noncoding region of 29 isolates of classical swine fever virus. Phylogenetic analysis of the sequences revealed low level genomic variation that correlated with the geographic origins of the isolates.