title: Evidence for and characterization of nervous necrosis virus infection in Pacific cod (Gadus macrocephalus).
abstract: A mortality rate higher than 90% was observed in a larva-rearing facility for Pacific cod, Gadus macrocephalus, in China. Larvae showing clinical signs of infection were collected. Initial suspicion of nervous necrosis virus (NNV) infection was confirmed by sequencing, absolute quantification real-time PCR (A-qPCR), and electron microscopy. The nucleotide sequence of RNA2 was 1,375 bases long (GenBank no. KM576685), coding for a single ORF corresponding to the capsid protein from residues 21 to 1034. Phylogenetic analysis of the capsid protein sequence showed that PCNNV belongs to the barfin flounder NNV (BFNVV) genotype. An amino acid sequence alignment revealed 39 differences between the cold- and warm-resistant viral groups, suggesting that PCNNV evolved under temperature selection. The 3-D structure of the predicted capsid protein was modeled to identify potential epitopes, and the gene was expressed in Escherichia coli, yielding a protein with a molecular mass of 55 kDa. During PCNNV outbreaks, the viral copy number was found to reach 10(7) per ng of total RNA, which could be considered the lethal copy number of NNV in cod. The gonads, eggs, fertilized eggs and asymptomatic cod fry were all positive for PCNNV, indicating viral vertical transmission as the main source of the viral load. The amount of virus in the apparent healthy fry or survivors seemed to decrease gradually with development. These results might lead to efficient diagnostic methods to help farmers select NNV-free broodfish for cod breeding.
authors.affiliation: Key Laboratory of Mariculture and Stock Enhancement in North China's Sea, Ministry of Agriculture, Dalian Ocean University, Dalian, 116023, People's Republic of China, maomingguang@gmail.com.
authors.forename: Ming-Guang
authors.initials: MG
authors.lastname: Mao
authors.forename: Shi-Hui
authors.initials: SH
authors.lastname: Wen
authors.forename: Alex
authors.initials: A
authors.lastname: Perálvarez-Marín
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Jie-Lan
authors.initials: JL
authors.lastname: Jiang
authors.forename: Zhi-Qiang
authors.initials: ZQ
authors.lastname: Jiang
authors.forename: Xing
authors.initials: X
authors.lastname: Li
authors.forename: Hang
authors.initials: H
authors.lastname: Sun
authors.forename: Hui-Qian
authors.initials: HQ
authors.lastname: Lü
mesh_terms: D000825:Animal Structures / Q000821:virology; D000818:Animals; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics; D002681:China; D016000:Cluster Analysis; D004926:Escherichia coli / Q000235:genetics; D005393:Fish Diseases / Q000821:virology*; D048388:Gadiformes / Q000821:virology*; D015870:Gene Expression; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D030381:Nodaviridae / Q000235:genetics / Q000302:isolation & purification* / Q000648:ultrastructure; D016366:Open Reading Frames; D010802:Phylogeny; D011487:Protein Conformation; D012327:RNA Virus Infections / Q000662:veterinary* / Q000821:virology; D060888:Real-Time Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D019562:Viral Load
chemical_list: D036022:Capsid Proteins