Comparison of Two Aquatic Alphaviruses, Salmon Pancreas Disease Virus and Sleeping Disease Virus, by Using Genome Sequence Analysis, Monoclonal Reactivity, and Cross-Infection

Abstract

Cell culture isolates of salmon pancreas disease virus (SPDV) of farmed Atlantic salmon and sleeping disease virus (SDV) of rainbow trout were compared. Excluding the poly(A) tracts, the genomic nucleotide sequences of SPDV and SDV RNAs include 11,919 and 11,900 nucleotides, respectively. Phylogenetic analysis places SPDV and SDV between the New World viruses of Venezuelan equine encephalitis virus and Eastern equine encephalitis virus and the Old World viruses of Aura virus and Sindbis virus. When compared to each other, SPDV and SDV show 91.1% nucleotide sequence identity over their complete genomes, with 95 and 93.6% amino acid identities over their nonstructural and structural proteins, respectively. Notable differences between the two viruses include a 24-nucleotide insertion in the C terminus of nsP3 protein of SPDV and amino acid sequence variation at the C termini of the capsid and E1 proteins. Experimental infections of Atlantic salmon and rainbow trout with SPDV and SDV confirmed that the disease lesions induced by SPDV and SDV were similar in nature. Although infections with SPDV and SDV produced similar levels of histopathology in rainbow trout, SDV induced significantly less severe lesions in salmon than did SPDV. Virus neutralization tests performed with sera from experimentally infected salmon indicated that SPDV and SDV belonged to the same serotype; however, antigenic variation was detected among SDV and geographically different SPDV isolates by using monoclonal antibodies. Although SPDV and SDV exhibit minor biological differences, we conclude on the basis of the close genetic similarity that SPDV and SDV are closely related isolates of the same virus species for which the name Salmonid alphavirus is proposed.

Regulation of the Sequential Processing of Semliki Forest Virus Replicase Polyprotein

“…To change the site between nsP1 and nsP2 from HAGA2GVVE to HAEA2GVVE, the site between nsP2 and nsP3 from TAGS2APSY to TAES2APSY, and the site between nsP3 and nsP4 from RAGA2YIFS to RAEV2YIFS, specific primers containing the desired mutations were used (bolded residues highlight the mutations made at the cleavage site). 2 The templates were clones P1234, P123, P23, and P12. All mutations were verified by sequencing, and the mutated clones were designated as P1 ∧ 234, P12 ∧ 34, P123 ∧ 4, P1 ∧ 23, P12 ∧ 3, P1 ∧ 2, and P2 ∧ 3 ( ∧ indicates the mutated site).…”

“…Some alphaviruses are capable of causing encephalitis in humans or domestic animals, whereas others may cause fever and arthritis (1). Recently, alphaviruses pathogenic for fish have been discovered (2), indicating that the biological diversity and significance of alphaviruses is greater than previously anticipated. The alphaviruses best studied at the molecular level are Semliki Forest virus (SFV) 1 and Sindbis virus.…”

Eilat virus, a unique alphavirus with host range restricted to insects by RNA replication

“…Last, the aquatic alphaviruses comprise two groups, Southern elephant seal virus and salmon pancreas disease virus (SPDV) (6,7). SPDV and its subtype sleeping disease virus are distantly related to all other alphaviruses (7).…”

First Laboratory Confirmation of Salmonid Alphavirus Type 2 (SAV2) Infection in Poland

“…This was later supported by the isolation of the virus from cases of pancreas disease that affected salmon in Norway (4) and Scotland (13). SPDV and sleeping disease virus (SDV) are closely related isolates of the same virus species, and the name salmonid alphavirus was proposed (15). Genetic analysis of the salmonid alphavirus from Norway revealed that it formed a distinct subtype, separate from both previously reported subtypes, and was named Norwegian salmonid alphavirus (8).…”

“…Therefore, the virus was classified in 2008 into six subtypes; SPDV or subtype 1 (SAV1) had been isolated from Atlantic salmon in Ireland and the UK whilst SDV or subtype 2 (SAV2) had been isolated from freshwater rainbow trout in the UK, France, and Germany (2). Previous reports, subsequently showed that Norwegian strains belonged to a distinct subtype now referred to as NSAV or SAV3 (8,15), and a more extensive study identified three further subtypes: SAV4, SAV5, and SAV6 (5).…”