Spring viremia of carp (SVC) AHNE, W; BJORKLUND, H. V; ESSBAUER, S ...
Diseases of aquatic organisms,
12/2002, Volume:
52, Issue:
3
Journal Article
Peer reviewed
Open access
Spring viremia of carp (SVC) is an important disease affecting cyprinids, mainly common carp Cyprinus carpio. The disease is widespread in European carp culture, where it causes significant morbidity ...and mortality. Designated a notifiable disease by the Office International des Epizooties, SVC is caused by a rhabdovirus, spring viremia of carp virus (SVCV). Affected fish show destruction of tissues in the kidney, spleen and liver, leading to hemorrhage, loss of water-salt balance and impairment of immune response. High mortality occurs at water temperatures of 10 to 17 degrees C, typically in spring. At higher temperatures, infected carp develop humoral antibodies that can neutralize the spread of virus and such carp are protected against re-infection by solid immunity. The virus is shed mostly with the feces and urine of clinically infected fish and by carriers. Waterborne transmission is believed to be the primary route of infection, but bloodsucking parasites like leeches and the carp louse may serve as mechanical vectors of SVCV. The genome of SVCV is composed of a single molecule of linear, negative-sense, single-stranded RNA containing 5 genes in the order 3'-NPMGL-5' coding for the viral nucleoprotein, phosphoprotein, matrix protein, glycoprotein, and polymerase, respectively. Polyacrylamide gel electrophoresis of the viral proteins, and sequence homologies between the genes and gene junctions of SVCV and vesicular stomatitis viruses, have led to the placement of the virus as a tentative member of the genus Vesiculovirus in the family Rhabdoviridae. These methods also revealed that SVCV is not related to fish rhabdoviruses of the genus Novirhabdovirus. In vitro replication of SVCV takes place in the cytoplasm of cultured cells of fish, bird and mammalian origin at temperatures of 4 to 31 degrees C, with an optimum of about 20 degrees C. Spring viremia of carp can be diagnosed by clinical signs, isolation of virus in cell culture and molecular methods. Antibodies directed against SVCV react with the homologous virus in serum neutralization, immunofluorescence, immunoperoxidase, or enzyme-linked immunosorbent assays, but they cross-react to various degrees with the pike fry rhabdovirus (PFR), suggesting the 2 viruses are closely related. However, SVCV and PFR can be distinguished by certain serological tests and molecular methods such as the ribonuclease protection assay.
RT-PCR methods have been applied to the detection and sequencing of the glycoprotein gene of putative spring viraemia of carp viruses (SVCV) and pike fry rhabdoviruses (PFRV), including isolates from ...tench, grass carp, roach, bream and false harlequin, sheatfish and orfe. Phylogenetic analysis of a 550 nucleotide (nt) region of the glycoprotein gene identified 4 groups, I to IV. Significantly, the majority of viruses previously identified as PFRV formed a distinct cluster (Genogroup IV) which shared <80% nucleotide identity with the PFRV reference strain (Genogroup III). The similarity between another PFRV-like virus isolated from grass carp and representatives of Genogroups III and IV was also <80%, indicating that this virus belonged to a third group (Genogroup II). All of the putative SVC viruses were assigned to a 4th group (Genogroup I), sharing <61% nucleotide identity with viruses in Genogroups II to IV.
Viral agents from 18 different snake species (families
Colubridae,
Viperidae, and
Crotalidae) showing respiratory symptoms and neuronal disease were identified as paramyxoviruses by typical ...cytopathogenic effect (CPE), electron microscopy, and hemagglutination inhibition. Detailed molecular characterization of the viruses was performed by partial
l- and
f-gene-specific reverse transcription polymerase chain reaction (RT-PCR) and sequencing, nucleotide and amino acid sequence alignment, and phylogenetic analysis (PHYLIP). RT-PCR of the partial
l-gene (566 nt) was successful for all 18 viruses; amplicons of the partial F-gene (918 nt) could be obtained in 16 cases.
f- and
l-sequence alignment revealed similarities to Fer de Lance virus (FDLV) ranging from 79 to 88% on a nucleotide basis, and 94 to 99% on an amino acid basis. Phylogenetic analysis of the ophidian paramyxoviruses resulted in three clusters for the
l-gene sequence and corresponding clusters for the
f-gene sequence, indicating no species specificity. We analyzed the
f-protein of the snake paramyxoviruses, which proved to have an identical conserved motif of
heptad repeat A and predicted a furin cleavage site. This uniformity distinguishes the snake virus group from the other type species of the subfamily
Paramyxovirinae. For further classification, we aligned the sequences of the ophidian paramyxoviruses and members of the
Paramyxoviridae, such as Sendai virus (genus Respirovirus), mumps virus (genus Rubulavirus), measles virus (genus Morbillivirus), human respiratory syncytial virus (genus Pneumovirus) (
Van Regenmortel and 10 co-authors, 2000) and Hendra virus, which have recently been suggested as type species of the genus Henipavirus (
Wang et al., 2000). Maximum sequence similarity was found to the partial
l-gene of Sendai virus, with 56% nucleotide and 61% amino acid identity. The FDLV and Sendai virus cluster in the phylogenetic analysis of
l- and
f-protein regarding the
Paramyxovirus type species and Hendra virus and show the closest relationship. Regarding the biological properties, the antigenic distance, and particularly the low homology of available sequences, we propose a new genus for the reptilian paramyxoviruses within the
Paramyxoviridae.
Viral genomic RNA of Fer-de-Lance virus (FDLV), a paramyxovirus highly pathogenic for reptiles, was reverse transcribed and cloned. Plasmids with significant sequence similarities to the ...hemagglutinin–neuraminidase (HN) and polymerase (L) genes of mammalian paramyxoviruses were identified by BLAST search. Partial sequences of the FDLV genes were used to design primers for amplification by nested polymerase chain reaction (PCR) and sequencing of 518-bp L gene and 352-bp HN gene fragments from a collection of 15 previously uncharacterized reptilian paramyxoviruses. Phylogenetic analyses of the partial L and HN sequences produced similar trees in which there were two distinct subgroups of isolates that were supported with maximum bootstrap values, and several intermediate isolates. Within each subgroup the nucleotide divergence values were less than 2.5%, while the divergence between the two subgroups was 20–22%. This indicated that the two subgroups represent distinct virus species containing multiple virus strains. The five intermediate isolates had nucleotide divergence values of 11–20% and may represent additional distinct species. In addition to establishing diversity among reptilian paramyxoviruses, the phylogenetic groupings showed some correlation with geographic location, and clearly demonstrated a low level of host species-specificity within these viruses.
The α-subunit of the eukaryotic initiation factor 2 (eIF-2α) is a key component of the translation machinery of the cell. In response to cellular stress such as viral infections, eIF-2α is ...phosphorylated by double-stranded RNA-dependent protein kinase (PKR) leading to the inhibition of cellular protein synthesis. The importance of eIF-2α as a regulatory mechanism for protein synthesis is illustrated by the wide variety of strategies employed by viruses to down-regulate PKR. Thus, Vaccinia virus encodes K3L protein, which resembles eIF-2α and acts as a pseudo-substrate inhibitor of PKR. Nucleotide sequencing of the genome of epizootic haematopoietic necrosis virus (EHNV), a member of the genus ranavirus of Iridoviridae, has revealed an eIF-2α equivalent gene. We have cloned and sequenced eIF-2α genes of several iridoviruses of fishes and frogs. The eIF-2α open reading frames and deduced proteins of the iridoviruses investigated exhibit a high degree of homology of both nucleotide and amino acid sequences. At the N-terminus, the iridoviral eIF-2α shows significant homology to the N-termini of cellular initiation factor 2-α of various species, to full-length poxviral eIF-2α proteins, and to the S1 domain of ribosomal proteins. Comparison of amino acid sequences of corresponding iridoviral proteins with eIF-2α homologous proteins of poxviruses and eukaryotes has revealed a high conservation of motifs. A phylogenetic analysis of eukaryotic eIF-2α and poxvirus and iridovirus eIF-2α sequences has demonstrated the relationship of these iridoviruses. In order to investigate the role of the eIF-2α equivalent, respective genes have been expressed in prokaryotic and eukaryotic (insect, fish and chicken cell) systems. The iridoviral eIF-2α protein has a molecular weight of 31 kDa and is cytoplasmic. The cellular and viral protein synthesis of iridoviruses is probably regulated by a mechanism similar to that of Vaccinia virus. Frog-virus 3, the type species of the genus ranavirus of Iridoviridae, has a unique translational efficiency and, moreover, down-regulates the cellular protein synthesis of infected cells.
Fourteen reptilian paramyxovirus isolates were chosen to represent the known extent of genetic diversity among this novel group of viruses. Selected regions of the fusion (F) gene were sequenced, ...analyzed and compared. The F gene of all isolates contained conserved motifs homologous to those described for other members of the family Paramyxoviridae including: signal peptide, transmembrane domain, furin cleavage site, fusion peptide, N-linked glycosylation sites, and two heptad repeats, the second of which (HRB-LZ) had the characteristics of a leucine zipper. Selected regions of the fusion gene of isolate Gono-GER85 were inserted into a prokaryotic expression system to generate three recombinant protein fragments of various sizes. The longest recombinant protein was cleaved by furin into two fragments of predicted length. Western blot analysis with virus-neutralizing rabbit-antiserum against this isolate demonstrated that only the longest construct reacted with the antiserum. This construct was unique in containing 30 additional C-terminal amino acids that included most of the HRB-LZ. These results indicate that the F genes of reptilian paramyxoviruses contain highly conserved motifs typical of other members of the family and suggest that the HRB-LZ domain of the reptilian paramyxovirus F protein contains a linear antigenic epitope.
Viruses were isolated in cell culture from tissue homogenates of flounder Pseudopleuronectes americanus and mummichog Fundulus heteroclitus in the Chesapeake Bay, Virginia, USA. Neutralization and ...immunofluorescence tests with aquabirnavirus (West Buxton strain)-specific polyclonal antisera indicated that both viruses were aquabirnaviruses belonging to Serogroup A, the most common aquabirnavirus serogroup in the United States. This was confirmed by RT-PCR, with primers targeting the VP3 and VP2 gene of aquabirnaviruses. The VP2-specific RT-PCR cDNA amplification product was sequenced and deduced amino-acid sequences were compared with known sequences of the type strains of the 9 serotypes of aquabirnavirus Serogroup A. This demonstrated that the viruses from both flounder and mummichog belong to aquabirnavirus Genogroup 1. The flounder isolate exhibited deduced amino acid sequence similarities of 98.1% with the Jasper strain of serotype A9, and 97.7% with the West Buxton strain of serotype A1. The isolate from mummichog exhibited deduced amino acid sequence similarities of 99.1% with the West Buxton strain of Serotype A1 and 94.8% with the Jasper isolate of Serotype A9. Similarities of deduced amino acid sequences ranged from 79.9 to 86.9%, with representatives of the other 7 serotypes. This is the first report of an aquabirnavirus from mummichog F. heteroclitus and only the fifth report of an aquabirnavirus from a flounder species.
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