| Oyster herpes virus(OSHV-1)is a double-stranded DNA virus belonging to the family Malacoherpesviridae and Ostreavirus of molluscs.It is widely prevalent in the world and has always been one of the main infectious pathogens that restricting the healthy development of shellfish farming in China.In recent years,Oyster Herpes Virus has been frequently outbreak,which results in shellfish growth hindrance and high mortality,and has caused huge economic losses to shellfish breeding industry in China.At present,the common detection method of Oyster Herpes virus is to design primers for PCR amplification,but in recent years,the emergence of different mutants,the previous detection methods have some limitations.This experiment compares the sequences of different variants of NCBI,selects the conservative region of C region,and established nested PCR detection method.Seven viral DNA with different concentration gradients decreasing ten times in turn were set up to detect their sensitivity.This method has higher sensitivity and better specificity than ordinary PCR.The main breeding economic shellfish(Scapharca,Burnt-end Ark,scallop,oyster,Short Necked Clam,Common orient clam,Mytilidae etc.)and wild economic shellfish(Neverita didyma,The corners of clam,Razor clam,etc..)cultured in the seven various coastal areas of Shandong Province.The epidemiology of Oyster Herpesvirus type I outbreak in the main economic shellfish of Shandong Province from 2017 to 2018 was summarized based on the results and established an early warning mechanism for OsHV-1.A total of 340 samples were collected in different regions of Shandong Province in2017,of which 39 positive samples,with a total positive detection rate of 11.5%.The positive detection was regional,and the detection rate was the highest in Dongying area,with a detection rate of 33.3%.Among the different species,the positive detection rate of The corners of clam was the highest,about 44%.503 samples were collected in different areas along the coast of Shandong Province in 2018,of which 79 were positive,the positive total detection rate was 15.7%,Qingdao had the highest positive detection rate,reaching 68%.Ten different species were tested.The results showed that the positive detection rate of Neverita didyma was the highest(40%),conch was 33.3%,Scapharca was 26.3%,Short Necked Clam was 23%,scallop was 11%,Mytilidae was 6.7%.The corners of clam was 6.3%,oyster was5%.And no positive samples were found in the Speckle clam and razor clam.Oyster herpes virus not only infects bivalve molluscs,but also has great infectivity to some gastropod shellfish,and the host range is enlarged.The water quality is tested by pH,ammonia nitrogen and nitrite,and the environment of aquaculture water is basically normal.Through animal infection tests,the clinical symptoms were as follows: weakness of the closing muscles,slow action,slow response to external stimuli,and food intake.The diseased material collected from the YangKou was sequenced and analyzed in the C region of the variant region(ORF4/5).The NCBI database was compared with different mutant strains,and the phylogenetic tree was drawn.It was concluded that the YangKou dead Scapharca sinensis isolates had the closest relationship with theBurnt-end Ark strain found in China.Recently,through animal infection experiments,the clinical symptoms are as follows,weakness of the closing muscles,slow action,slow response to external stimuli,and food intake.and the oyster herpes virus is confirmed by PCR detection and sequencing.It was confirmed that the Scapharca sinensis is a new host.It was proved by cohabitation experiment that the isolate was horizontally transmitted,and on the 6th day of the cohabitation experiment,the larvae of the Scapharca began to die,and on the 12 th day,all the larvae of the Scapharca died.Virus isolated from YangKou is not only infectious to Scapharca,but also to Short Necked Clam and scallops,which proves the pathogenicity of different species of the virus. |
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