Infectious Hypodermal And Hematopoietic Necrosis Virus And Its Pathogenicity Analysis Effect Of Growth Of Litopenaeus Vannamei

First found in 1981 in the United States in the Hawaiian area fine Litopenaeus stylirostris infectious hypodermal and haematopoietic necrosis virus is one of the global aquaculture shrimp diseases in the main pathogenic, IHHNV infection of wild and farmed shrimp also all over the world, the world organization for animal health will be included IHHNV for crustaceans, one of the most important diseases, The virus was classified into the subfamily Densoirinae, genus Brevidensovirus, as Penaeus stylirostris densovirus(Pst DNV).Its host spread all over the world containing wild and farmed penaeid shrimp.For Litopenaeus stylirostris,the mortality is up to 90%.And furthermore, this virus also causes chronic infections called runt deformity syndrome(RDS) in P. monodon, Litopenaeus vannamei and Marsupenaeus japonicas,affecting the growth of penaeid shrimp.The infected shrimp can infect others or descendantthrough horizontal or vertical way. IHHNV is the smallest penaeid shrimp virus with 20 to 22 nm sizes and non-enveloped icosahedral virions and possesses approximately 4.0 kb of linear ss DNA.The genome contains partially overlapping open reading frames(ORFs),encoding non-structural protein1,non-structural 2and capsid protein,respectively.Genebank has included differentgeographical origins,including AF218266,AY362548,AF273215,EF633688,AY355306,AY355307,Y355308,AY362547 and so on.At present, our country is still not mature enough for the research of IHHNV, the related report about IHHNV research is less, start late. And abroad started earlier, the relative improvement of research. Especially for the current stage of IHHNV in shrimp culture model of domestic epidemic situation and the degree of harm only in virus carrying rate, but not for IHHNV infectivity and pathogenicity of the lack of relevant data, then there is no viral load level and the correlation analysis of data. This study is through the artificially infected Litopenaeus vannamei postlarvae and natural state infection of Litopenaeus vannamei in two kinds of infection, pathogenicity analysis; by the ordinary PCR and real-time fluorescence quantitative PCR of Litopenaeus vannamei detection. Analysis the virus copy number analysis of viral load related to body length. So as to understand the prevalence of IHHNV infection in china. This work mainly focuses on: 1. Artificial infection of shrimp Litopenaeus vannamei IHHNVIHHNV can infect a variety of shrimp, the shrimp harm is most obvious, there is no better method of prevention and treatment. The virus can make Litopenaeus vannamei postlarvae slow growth, leading to the growth of output specifications uneven, serious decline, serious losses. This paper simulates the plant breeding breeding patterns of artificially infected Litopenaeus vannamei postlarvae, then the infection type of IHHNV in shrimp disease material gradient dilution, by way of feeding on the healthy postlarvae were artificially infected. Observe and record the shrimp death and changes of body length. The results showed that of Litopenaeus vannamei postlarvae IHHNV infection rate is very high. In artificial infection after 24 days began to appear obvious death, the mortality rate is maintained at 20.28%-44.25%. After 40 days mortality in stable state, and between different pathogens without significant difference; between 16-44 days after artificial infection in the Litopenaeus vannamei postlarvae long cut 0.74-0.80 cm. Provide macro reference for the study of IHHNV pathogenicity.2. Real time PCR detection of infected shrimp Litopenaeus vannameiReal time PCR method has become more and more widely used in the detection of shrimp virus because of its high sensitivity, good accuracy and convenience. The detection of infected Litopenaeus vannamei postlarvae, primers according to the OIE recommended probe, system, procedure etc.Artificial infection during 12 days, Litopenaeus vannamei postlarvae in copies of the virus in the upward trend, after virus attack two days between the groups IHHNV in copy number at around 103, when to 12 days IHHNV concentrations highest copy number reached the maximum 7.91 x 104 copies/μg DNA. 12d-14 d copy start counting down. After 14 d groups of IHHNV copy remained stable. 3. IHHNV and EHP mixed infection of Litopenaeus vannamei PCR detectionInfectious hypodermal and hematopoietic necrosis virus(IHHNV) is one of the pathogens causing the significant diseases of crustaceans listed by the OIE(Office international despizooties) Manual of Diagnostic Tests for Aquatic Animals. Infection with IHHNV does not produce any pathognomonic gross clinical signs, although runt-deformity syndrome(RDS) has been noted in infected juvenile L. vannamei and Penaeus monodon. Enterocytozoonhepatopenaei(EHP) was first found and isolated in Thailand in 2009, which caused slow growth of Penaeus monodon. IHHNV and EHP were found in the samples of L. vannamei postlarvae which collected from hatchery farm in Tianjin and Hebei province in 2013. The diseases shrimp showed some clinical signs with high mortality, slow growth and difference of individual growth rate. A total of 108 cultivated were collected from the rearing ponds, and the IHHNV and EHP individual detection were conducted on these samples using the real-time PCR technique. In total, 108 out of 108(100%) L. vannamei postlarvae samples exhibited IHHNV positive and 53 out of 108(49.1%) L. vannamei postlarvae samples exhibited EHP positive. Positive samples contained approximately 103~107 copies /(μg tissue DNA) of IHHNV and big size of individual shrimp carried high number of virus copies. Positive samples contained approximately 103~105 copies /(μg tissue DNA) of EHP and focused on small size of individual shrimp. The analysis showed that the IHHNV loads positive correlation with the shrimp growth rate. IHHNV loads above 8.51×104copies/μg DNA represents a high risk level. EHP loads negative correlation with the shrimp growth rate. EHP loads above 2.19×104copies/μg DNA represents a high risk level. Our study showed that the diseased L. vannamei postlarvae samples occurred in the hatchery farm of Tianjin and Hebai province infected with shrimp pathogens of IHHNV and EHP. Data Provides scientific basis on the effects of pathogens infection on the growth of cultured penaeid shrimp.