Characterization of nodavirus and viral encephalopathy and retinopathy in farmed turbot, Scophthalmus maximus (L.).
An outbreak of nodavirus infection in turbot larvae is described with respect to histopathology, immunohistochemistry, cell culture cultivation, RT-PCR amplification and sequence analysis of the capsid protein gene RNA2. Affected turbot developed classical signs of viral encephalopathy and retinopathy (VER) with abnormal swimming behaviour and high mortality levels. In the acute stage of infection, light microscopy revealed vacuolation of the central nervous system (CNS), with positive immunohistochemical staining for nodavirus. Later in the infection, CNS lesions appeared more chronic and contained clusters of cells immunopositive for nodavirus. Bacterial overgrowth in the intestines of the fish may have provoked or influenced the course of the nodavirus infection. We were unable to propagate the virus in cell culture. While RT-PCR using primers designed to detect Atlantic halibut nodavirus gave negative results, further testing with primers complementary to a more conserved region of RNA2 resulted in amplification of a product of the expected size. The entire RNA2 segment was cloned and sequenced. Sequence alignment showed that the turbot nodavirus (TNV) was different from previously described fish nodaviruses. In addition, phylogenetic analysis based on an 823 nt region of the sequence indicated that TNV clustered outside the four established fish nodavirus genotypes, suggesting a fifth genotype within the betanodaviruses.
National Veterinary Institute, Oslo, Norway. renate.johansen@vetinst.no
R
R
Johansen
I
I
Sommerset
B
B
Tørud
K
K
Korsnes
M J
MJ
Hjortaas
F
F
Nilsen
A H
AH
Nerland
B H
BH
Dannevig
D000595:Amino Acid Sequence; D000818:Animals; D017756:Aquaculture; D001483:Base Sequence; D036022:Capsid Proteins / Q000235:genetics; D002490:Central Nervous System / Q000821:virology; D017931:DNA Primers; D004196:Disease Outbreaks / Q000662:veterinary*; D018792:Encephalitis, Viral / Q000453:epidemiology / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D005393:Fish Diseases / Q000453:epidemiology / Q000473:pathology* / Q000821:virology*; D005412:Flatfishes; D006652:Histological Techniques / Q000662:veterinary; D007150:Immunohistochemistry / Q000662:veterinary; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D030381:Nodaviridae; D009664:Norway / Q000453:epidemiology; D010802:Phylogeny; D012327:RNA Virus Infections / Q000453:epidemiology / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D012164:Retinal Diseases / Q000453:epidemiology / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D016415:Sequence Alignment / Q000662:veterinary; D017422:Sequence Analysis, DNA / Q000662:veterinary
D036022:Capsid Proteins; D017931:DNA Primers