Hematodinium perezi naturally infects Asian brush-clawed crab (Hemigrapsus takanoi).

The parasitic dinoflagellates of the genus Hematodinium have been considered one of the most important emerging pathogens for a broad range of marine crustaceans around the world. In China, frequent outbreaks of Hematodinium infections have caused serious economic losses for local farmers since 2004. Wild crabs were recently indicated to play a vital role in the transmission and spreading of the Hematodinium disease in polyculture pond systems. Based on PCR amplification and histopathological examination, we demonstrated that H. perezi can naturally infect a wild crab species, Hemigrapsus takanoi, which were collected from the waterways located on the coast of Rizhao or Weifang, Shandong Peninsula, China. According to the sequence similarity analysis and phylogenetic analysis, the Hematodinium isolates were identified as H. perezi and belonged to genotype II. The prevalence of H. perezi ranged from 3.3% to 5.7% in H. takanoi originating from Rizhao (n = 165 wild crabs) and from 0.9% to 20.0% in that originating from Weifang (n = 1386 wild crabs), respectively. To our knowledge, H. takanoi is, for the first time, reported as a new host for Hematodinium. Given the wide distribution of H. takanoi on the coasts along the Shandong Peninsula and the relative high prevalence of infection we monitored in our study, we speculate that H. takanoi contributes to the introducing and spreading parasitic Hematodinium between ponds via waterways in a poly-culturing system. Findings in this study broaden the host range of this parasite and expand the scope of our surveillance for Hematodinium disease in China.

Characterization of a novel shrimp pathogen, Vibrio brasiliensis, isolated from Pacific white shrimp, Penaeus vannamei.

A novel pathogenic strain Vibrio 20190611023 was isolated from the hepatopancreas of moribund cultured Penaeus vannamei suffering from black gill disease. This strain was identified as V. brasiliensis based on the phylogenetic analyses of 16S rDNA gene and five other housekeeping genes (i.e., gapA, ftsZ, mreB, topA and gyrB). Some biochemical features of this strain were determined with an API 20NE system, and its haemolytic activity was determined using a sheep blood agar plate. The pathogenicity of this isolate 20190611023 was confirmed by the experimental challenge tests and histopathological examinations. P. vannamei were challenged via reverse gavage with different doses of bacterial suspensions. The calculated median lethal dose (LD50 ) was (3.16 ± 1.78) × 105  CFU/g (body weight). Moreover, antibiotic susceptibility tests were performed, the results of which showed that the strain 20190611023 was sensitive to chloramphenicol, compound sulphamethoxazole, ciprofloxacin, doxycycline and oxacillin, but resistant to erythromycin, kanamycin, gentamicin, cefoperazone, ceftriaxone, cefamezin and piperacillin. To our knowledge, this is the first report for demonstrating V. brasiliensis as a shrimp pathogen, which expands the host range of V. brasiliensis infection. The present study highlights that more attention should be paid to this novel pathogen in intensive shrimp aquaculture.

Development of a cost-efficient micro-detection slide system for the detection of multiple shrimp pathogens.

In view of the current demand for rapid detection and identification of pathogens, point-of-care testing (POCT) with fast portability, low consumption, and increased sensitivity and specificity has become more and more popular. The emerging nucleic acid isothermal amplification technology (NAIAT) has shown potential advantages in the development of rapid microbial detection. In this study, a micro-detection slide system was developed based on the NAIAT of various nucleic acids of shrimp pathogens. The system included a micro-detection slide with 48 identical detecting cells precoated with all detection reagents, except the sample template. The process of producing the micro-detection slides mainly combined super-hydrophobic/super-oleophobic and super-hydrophilic materials to obtain separated spaces for detection, and aerosol pollution was eliminated in the form of water-in-oil. The micro-detection slide system was capable of simultaneously detecting 4 groups of samples and 8 important shrimp pathogens and is a relatively low-cost, portable, and high-throughput nucleic acid (RNA and DNA) detection technology. The establishment of this technology will provide key technical support for the construction of biosecurity systems for healthy shrimp culture.

A novel research on isolation and characterization of Photobacterium damselae subsp. damselae from Pacific white shrimp, Penaeus vannamei, displaying black gill disease cultured in China.

In June 2019, massive mortalities of cultured Penaeus vannamei occurred in a local farm in Hainan Province, China. The diseased shrimp displayed evident black gills. Three bacterial strains 20190611001, 20190611007 and 20190611022 were isolated from hepatopancreas and gills of the diseased shrimp and identified as Photobacterium damselae subsp. damselae based on the sequence analysis of 16S rRNA and toxR genes. These three isolates showed haemolytic activities. Of them, strain 20190611022 isolated from hepatopancreas was selected and processed for pathogenic analysis. The calculated median lethal dose (LD50 ) was 9.75 ± 4.29 × 105 CFU/g (body weight) by challenging P. vannameivia reverse gavage. The diseased shrimp displayed enlarged hepatopancreatic tubules and sloughing of epithelial cells in tubular lumens. The strain 20190611022 was also characterized by the testing of API 20NE systems and antibiotic susceptibility. The results of disc diffusion test showed that strain 20190611022 was sensitive to chloramphenicol, compound sulfamethoxazole, cefoperazone, ceftriaxone, ceftazidime and cefuroxime. To our knowledge, this is the first report of isolation and characterization of Photobacterium damselae subsp. damselae from natural diseased P. vannamei. Our findings can serve as a basis for further studies of its pathogenicity and provide technological support for disease controlling in shrimp aquaculture.

Delivery of plasmid DNA to shrimp hemocytes by Infectious hypodermal and hematopoietic necrosis virus (IHHNV) nanoparticles expressed from a baculovirus insect cell system.

Virus-like particles (VLPs) are potential containers for delivery of therapeutic agents at the nanoscale. In this study, the capsid protein of Infectious hypodermal and hematopoietic necrosis virus (IHHNV) was expressed in a baculovirus insect cell system. The 37-kDa recombinant protein containing the hexahistidine residues (His Tag) at N-terminal was purified using immobilized metal affinity chromatography (IMAC) and assembled into VLPs with a diameter of 23 ±â€¯3 nm analyzed by transmission electron microscopy. We also verified that disassembly/reassembly of IHHNV-VLPs was controlled in the presence and absence of DTT. The efficiency of IHHNV-VLPs to encapsulate plasmid DNA was about 48.2%, and the VLPs encapsulating the pcDNA3.1(+)-EGFP plasmid DNA could recognize the primary shrimp hemocytes and deliver the loaded plasmid into cells by detection of expressed enhanced green fluorescent protein (EGFP). These results implied that the IHHNV-VLPs might be a good candidate for packaging and delivery of expressible plasmid DNA, and may produce an antiviral product in shrimp cells for gene therapy.

Complete genome sequence of shrimp hemocyte iridescent virus (SHIV) isolated from white leg shrimp, Litopenaeus vannamei.

Infection with shrimp hemocyte iridescent virus (SHIV), a new virus of the family Iridoviridae isolated in China, results in a high mortality rate in white leg shrimp (Litopenaeus vannamei). The complete genome sequence of SHIV was determined and analyzed in this study. The genomic DNA was 165,809 bp long with 34.6% G+C content and 170 open reading frames (ORFs). Dotplot analysis showed that the longest repetitive region was 320 bp in length, including 11 repetitions of an 18-bp sequence and 3.1 repetitions of a 39-bp sequence. Two phylogenetic trees were constructed based on 27 or 16 concatenated sequences of proteins encoded by genes that are conserved between SHIV homologous and other iridescent viruses. The results of this study, suggest that SHIV should be considered a member of the proposed new genus "Xiairidovirus".

Detection and quantification of shrimp hemocyte iridescent virus by TaqMan probe based real-time PCR.

Shrimp hemocyte iridescent virus (SHIV) is a recently reported shrimp virus, which threats the cultured white-leg shrimp Litopenaeus vannamei and can cause huge economic loss in shrimp farming industry in China. A quantitative real time polymerase chain reactio (qPCR) assay was developed using a TaqMan probe to detect and quantify SHIV. A pair of qPCR primers, which amplify a 188 bp DNA fragment, and a TaqMan probe were selected from ATPase gene (ORF114R) of the SHIV genome. The primers and TaqMan probe used in this assay were shown to be specific for SHIV and did not react with White spot syndrome virus (WSSV), Infectious hypodermal and hematopoietic necrosis virus (IHHNV), Hepatopancreatic parvovirus (HPV), Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (VPAHPND), and Enterocytozoon hepatopenaei (EHP), or healthy shrimp DNA. The detection limit of the qPCR method was as low as 4 copies per reaction. The diagnostic sensitivity and the diagnostic specificity of the qPCR compared with nested PCR were 95.3% and 99.2%, respectively. The resulting standard curves showed high correlation coefficient values (R2 = 0.998) in the range of 4 × 109 to 4 × 100 DNA copies/reaction. Test of farm samples showed that SHIV was detected in L. vannamei, Fenneropenaeus chinensis and Macrobrachium rosenbergii contained SHIV ranged from 1.21E+02 to 7.95E+07 copies (µg DNA)-1. Quantitative detection of different tissues in artificial infected shrimp showed that haemolymph contained the highest SHIV load and muscle contained lowest SHIV load.

Quantitative detection method of Enterocytozoon hepatopenaei using TaqMan probe real-time PCR.

A TaqMan probe and a pair of specific primers were selected from the small subunit ribosomal DNA (SSU rDNA) sequence of Enterocytozoon hepatopenaei (EHP); this real-time PCR assay was developed and optimized. It showed a good linearity in detecting standards of EHP SSU rDNA fragments from 4 × 102 to 4 × 108 copies/reaction using the established method. The detection limit of the qPCR method was as low as 4 × 101 copies per reaction, which was higher than the conventional PCR and SYBR Green I-based EHP qPCR reported. Using the qPCR assay, EHP was detected in four batches of slow-growing Penaeus vannamei specimens collected from Tianjin and Zhejiang Province in China was detected using qPCR. The results showed that all the hepatopancreas from the slow-growing P. vannamei specimens were detected as EHP-positive. EHP copies of hepatopancreas in some batches had a negative correlation with the body mass index (BMI) of shrimps; however, not all batches of specimens had this negative correlation between EHP copies of hepatopancreas and BMI. This qPCR technique is sensitive, specific and easy to perform (96 tests in <3 h), which provides technical support for the detection and prevention of EHP.

Complete genome sequence of an isolate of a novel genotype of yellow head virus from Fenneropenaeus chinensis indigenous in China.

Genotype 8 of yellow head virus (YHV-8) was identified recently, but the complete genome sequence of this new genotype has not been reported. In this study, the complete genome of YHV-8 isolate 20120706 collected from Hebei Province of China in 2012 was sequenced. It was found to be 26,769 nucleotides (nt) in length, including a 20,060-nt open reading frame 1 (ORF1), a 435-nt ORF2, and a 4971-nt ORF3. Isolate 20120706 shared 79.7-83.9% nucleotide sequence identity with all seven of the complete genome sequences of YHV that have been reported so far. The topology of a phylogenetic tree constructed based on the ORF1b region clearly showed that strain 20120706, together with five other YHV-8 strains isolated in China, represents a new genotype of YHV. This is the first report of the complete genome sequence of a YHV-8 isolate, and the 20120706 isolate will be useful for further analysis of the epidemiology and evolution of YHV-8.

Reverse transcription loop-mediated isothermal amplification for rapid and quantitative assay of covert mortality nodavirus in shrimp.

A disease known as covert mortality disease has become an increasing problem in the shrimp farming industry in recent years in China and several countries of Southeast Asia, leading to serious losses in production. Litopenaeus vannamei (also known as Pacific white shrimp) is affected by this disease that leads to a range of clinical symptoms including hepatopancreas atrophy and necrosis, soft shell, slow growth, and abdominal muscle whitening and necrosis in the acute stage of disease. A new nodavirus, termed covert mortality nodavirus (CMNV), has been shown to be the etiological agent. In this study, we report a sensitive and specific real-time reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for the rapid and quantitative detection of CMNV. The optimal conditions for this newly developed RT-LAMP reaction were found to be 6mM MgCl2 and 1.6mM dNTPs, an incubation temperature of 65°C and a reaction time of 50min. The analytical sensitivity of the RT-LAMP assay was estimated to be 6.3pg total RNA of CMNV-infected shrimp and 27 copies of the target plasmid. The diagnostic sensitivity and specificity of the newly developed assay versus the standard nested reverse transcription PCR (RT-PCR) assay was 96.4% and 94.4%, respectively. The reaction products were detected by visual inspection after staining with an in-tube DNA fluorescent dye, a measure taken to eliminate the risk of contamination. The quantitative RT-LAMP assay for CMNV showed high correlation coefficient (r2=0.9953) when the initial templates were above 1000 copies, however the correlation coefficient decreased when the initial templates were lower than 1000 copies. Test of viral load in shrimp indicated that the viral loads varied from 1.5×102 to 6.7×106 copies per mg of cephalothorax tissue. Thus, the CMNV RT-LAMP assay is a sensitive and specific new tool for the field detection and quantification of CMNV in the diagnosis and surveillance of covert mortality disease.

Chemoselective Hydroheteroarylation of Alkenes via Photoredox-Neutral Proton- and BF3-Mediated Electron Transfer.

Herein, we have developed a complementary entry to enable hydroheteroarylation of alkenes involving basically photoredox dearomatizative heterocyclic carbon radical formation through acid-coupled electron transfer followed by Giese addition. While protonic solvent and thiophenol additive enabled two molecular hydroheteroarylations of alkenes, the nonproton environment with BF3 altered the chemoselectivity over cascade hydroheteroarylation of alkenes by radical addition of heteroaromatics with two molecular alkenes. This chemoselectivity can be mechanistically attributed to the dynamically favored hydrogen atom transfer via the cyclic transition state.

Radical-mediated photoredox hydroarylation with thiosulfonate.

Herein, we report a novel visible light-induced photocatalytic system that enables intramolecular hydroarylation of unactivated alkenes. Thiosulfonate compounds were found to be the key radical precursor that mediates the Minisci-type intramolecular cyclization reaction. Under the optimal reaction conditions, a wide range of pyridyquinazolinone and pyrroloquinazolinone products were obtained in moderate to good yields.

Macrophthalmus (Macrophthalmus) abbreviatus Manning & Holthuis, 1981, a new natural host for Hematodinium perezi infection.

Recent reports have shown that wild crabs may be important hosts involved in the transmission and spread of the parasitic Hematodinium in cultured marine crustaceans. Therefore, monitoring the prevalence of Hematodinium infections in wild crabs is necessary to develop effective strategies for the prevention and control of Hematodinium disease. Here we report a wild crab species, Macrophthalmus (Macrophthalmus) abbreviatus Manning & Holthuis, 1981, as a new natural host for Hematodinium sp. infection. It is one of the common wild crab species dwelling in the ponds or waterways connected to the polyculture ponds located on the coast of Rizhao or Weifang, Shandong Peninsula, China. According to the results of PCR detection and phylogenetic analysis targeting the internal transcribed spacer 1 (ITS 1) region, these Hematodinium sp. isolates were identified as H. perezi and fell into the genotype II category within H. perezi. A high monthly prevalence of H. perezi infection was observed during the 2021-2022 field survey, ranging from 33.3% to 90.6% in M. abbreviatus originating from Weifang (n=304 wild crabs) and from 53.6% to 92.9% in those from Rizhao (n=42 wild crabs). Artificial inoculation infection experiments demonstrated that M. abbreviatus could be infected by H. perezi, and massive Hematodinium cells and typical histopathological changes were observed in the hepatopancreas and gill tissues of the infected crabs. To our knowledge, this is the first report of M. abbreviatus as a new natural host for H. perezi infection. Results in the present study extend the known host spectrum for this emerging parasite pathogen, and also provide valuable information for epidemic surveillance of the Hematodinium disease as well.

Spotlight on a novel bactericidal mechanism and a novel SXT/R391-like integrative and conjugative element, carrying multiple antibiotic resistance genes, in Pseudoalteromonas flavipulchra strain CDM8.

Many Pseudoalteromonas strains can produce bioactive compounds with antimicrobial activities. This study focused on a probiotic candidate P.flavipulchra CDM8 to reveal its novel antibacterial mechanism and risks for antibiotic resistance dissemination. Strain CDM8 could form floating biofilm, displayed strikingly broad antibacterial activities against multiple Vibrio and Bacillus species, and decreased the competitor's concentration in their co-cultures in the microtiter plate tests. It could also form vesicle/pilus-like structures on the outer surface, which were indicated to participate in the bactericidal activity and represent a novel antibacterial mechanism of CDM8, according to the scanning electron microscopic observation. However, CDM8 displayed multi-antibiotic resistance, conferred by the multidrug resistance regions in hotspot 4 and variable region III of a novel SXT/R391-like integrative and conjugative element (ICEPflCDM8). Summing up, our results provided a better understanding of the bactericidal mechanism of P. flavipulchra and highlighted the role of SXT/R391-like ICEs in conferring multidrug resistance phenotype of probiotic P. flavipulchra candidates.

Genetic characterization of E2 gene of classical swine fever virus by restriction fragment length polymorphism and phylogenetic analysis.

An RT-nested PCR (RT-nPCR)-based restriction fragment length polymorphism (RFLP) analyses of the E2 gene were developed for genetic subtyping and differentiation of vaccinated and infected classical swine fever virus (CSFV) strains. RT-nPCR identified 96 CSFV-positive samples from 321 clinical specimens from southeastern China during 2003-2008. The PCR products of positive samples were further differentiated using MspI digestion, 23 were identified as the C-strain, 62 as field strains, and 11 as mixture of the vaccine strain and field ones. RFLP with BglI, DdeI, DraI, and PstI were then used for subtyping of the field CSFV isolates. Thirty-eight field isolates phylogenetically classified as subgroup 2.1 based on E2 were divided into 11 subtypes by this RFLP scheme. Both RFLP profiling and sequence-based phylogenetic analysis revealed genetic diversity of CSFV in the field. Three novel substitutions at amino acid positions 17, 93, and 286 were identified in the predominant subtype VI strains isolated in 2008 as compared to other strains including historical subtype VI strains. These results suggest that CSFV in China experienced gradual variations and evolutionary accumulation progress. Thus, the RFLP methods targeting on the CSFV E2 gene are suitable for epidemiological survey in endemic area where the C-strain is applied for vaccination. Combination of the RFLP schemes with sequence-based phylogenetic analysis could provide more detailed information on transmission of CSFV in the region or even its evolution.

Determination of the Infectious Agent of Translucent Post-Larva Disease (TPD) in Penaeus vannamei.

A new emerging disease called "translucent post-larvae disease" (TPD) or "glass post-larvae disease" (GPD) of Penaeus vannamei, characterized by pale or colorless hepatopancreas and digestive tract, has become an urgent threat to the shrimp farming industry. Following this clue that treatment of an antibacterial agent could alleviate the disease, systematic investigation of the potential infectious agent of TPD was conducted using bacterial identification and artificial challenge tests to fulfill Koch's postulates. A dominant bacterial isolate, Vp-JS20200428004-2, from the moribund individuals was isolated and identified as Vibrio parahaemolyticus based on multi-locus sequence analysis. However, Vp-JS20200428004-2 differed from the V. parahaemolyticus that caused typical acute hepatopancreatic necrosis disease. Immersion challenge tests revealed that Vp-JS20200428004-2 could cause 100% mortality within 40 h at a dose of 1.83 × 106 CFU/mL, and experimental infected shrimp showed similar clinical signs of TPD. The Vp-JS20200428004-2 could be re-isolated and identified from the experimental infected individuals. Moreover, histopathological analysis of diseased samples indicated that Vp-JS20200428004-2 caused severe necrosis and sloughing of epithelial cells of the hepatopancreas and midgut in shrimp individuals both naturally and experimentally infected. Our present results indicated that Vp-JS20200428004-2 is a highly virulent infectious agent associated with the TPD and deserves further attention.

Development and validation of a TaqMan RT-qPCR for the detection of convert mortality nodavirus (CMNV).

Covert mortality nodavirus (CMNV), an emerging RNA virus, is the pathogen of viral covert mortality disease (VCMD), which has emerged as a cause of serious losses in shrimp aquaculture in China. To improve VCMD diagnosis, a one-step, real-time TaqMan probe-based reverse transcription quantitative PCR (RT-qPCR) was developed in this study. The TaqMan RT-qPCR was optimized firstly, whereby the best results were obtained with 0.2 µM of each primer, 0.2 µM probe, and 0.5 µL Enzyme Mix II. The optimal reaction program was determined as 15 min at 51ºC for reverse transcription and 5 min at 95 ºC, followed by 40 cycles of denaturation at 94 ºC for 10 s, and annealing and extension at 52.7 ºC for 30 s. The optimized assay detected as little as 9.6 pg total RNA from CMNV-infected shrimp and 5.7 copies of the target plasmid. The RT-qPCR assay for CMNV with a high correlation coefficient (r2 = 0.996) was developed basing on the standard curve generated by plotting the threshold cycle values (y) against the common logarithmic copies (log10nc as x; nc is copy number) of pMD20-CMNV. The diagnostic sensitivity and specificity of this assay versus the previously reported RT-qPCR was 96.2% and 98.0%, respectively. This method is highly specific to CMNV, as it showed no cross-reactivity with other common shrimp viruses. It is anticipated that the newly developed and optimized RT-qPCR assay will be instrumental for the rapid diagnosis and quantitation of CMNV.

Prevalence and distribution of covert mortality nodavirus (CMNV) in cultured crustacean.

An emerging covert mortality nodavirus (CMNV) was proved to be the infectious agent of shrimp viral covert mortality disease (VCMD). Prevalence and distribution of CMNV were investigated by using the methods of reverse transcription loop-mediated isothermal amplification (RT-LAMP), nested reverse transcription PCR, gene sequencing, histopathology, in situ RNA hybridization (ISH) and transmission electron microscope (TEM) in this study. RT-LAMP results showed that CMNV positive samples appeared in the cultured crustaceans including Litopenaeus vannamei, Fenneropenaeus chinensis, Marsupenaeus japonicus, Penaeus monodon, and Macrobrachium rosenbergii, and mostly distributed the coastal provinces in China. The prevalence rates of CMNV among the collected samples in 2013, 2014 and 2015 were 45.93% (130/283), 27.91% (84/301) and 20.85% (54/259), respectively. CMNV infection in M. japonicas and P. monodon was verified by ISH. The presence of CMNV particles were confirmed by TEM analysis in the CMNV positive samples diagnosed by RT-LAMP. The high prevalence and wide epidemic distribution of CMNV in this investigation revealed that it was necessary to pay close attention to the high risk of CMNV transmission in farmed crustaceans.

pirABvp -Bearing Vibrio parahaemolyticus and Vibrio campbellii Pathogens Isolated from the Same AHPND-Affected Pond Possess Highly Similar Pathogenic Plasmids.

Acute hepatopancreatic necrosis disease (AHPND) is a severe shrimp disease originally shown to be caused by virulent strains of Vibrio parahaemolyticus (VPAHPND). Rare cases of AHPND caused by Vibrio species other than V. parahaemolyticus were reported. We compared an AHPND-causing V. campbellii (VCAHPND) and a VPAHPND isolate from the same AHPND-affected pond. Both strains are positive for the virulence genes pirABvp . Immersion challenge test with Litopenaeus vannamei indicated the two strains possessed similar pathogenicity. Complete genome comparison showed that the pirABvp -bearing plasmids in the two strains were highly homologous, and they both shared high homologies with plasmid pVA1, the reported pirABvp -bearing plasmid. Conjugation and DNA-uptake genes were found on the pVA1-type plasmids and the host chromosomes, respectively, which may facilitate the dissemination of pirABvp . Novel variations likely driven by ISVal1 in the genetic contexts of the pirABvp genes were found in the two strains. Moreover, the VCAHPND isolate additionally contains multiple antibiotic resistance genes, which may bring difficulties to control its future outbreak. The dissemination of the pirABvp in non-parahaemolyticus Vibrio also rises the concern of missing detection in industrial settings since the isolation method currently used mainly targeting V. parahaemolyticus. This study provides timely information for better understanding of the causes of AHPND and molecular epidemiology of pirABvp and also appeals for precautions to encounter the dissemination of the hazardous genes.

Characterization of a new member of Iridoviridae, Shrimp hemocyte iridescent virus (SHIV), found in white leg shrimp (Litopenaeus vannamei).

A newly discovered iridescent virus that causes severe disease and high mortality in farmed Litopenaeus vannamei in Zhejiang, China, has been verified and temporarily specified as shrimp hemocyte iridescent virus (SHIV). Histopathological examination revealed basophilic inclusions and pyknosis in hematopoietic tissue and hemocytes in gills, hepatopancreas, periopods and muscle. Using viral metagenomics sequencing, we obtained partial sequences annotated as potential iridoviridae. Phylogenetic analyses using amino acid sequences of major capsid protein (MCP) and ATPase revealed that it is a new iridescent virus but does not belong to the five known genera of Iridoviridae. Transmission electron microscopy showed that the virus exhibited a typical icosahedral structure with a mean diameter of 158.6 ± 12.5 nm (n = 30)(v-v) and 143.6 ± 10.8 nm (n = 30)(f-f), and an 85.8 ± 6.0 nm (n = 30) nucleoid. Challenge tests of L. vannamei via intermuscular injection, per os and reverse gavage all exhibited 100% cumulative mortality rates. The in situ hybridization showed that hemopoietic tissue, gills, and hepatopancreatic sinus were the positively reacting tissues. Additionally, a specific nested PCR assay was developed. PCR results revealed that L. vannamei, Fenneropenaeus chinensis, and Macrobrachium rosenbergii were SHIV-positive, indicating a new threat existing in the shrimp farming industry in China.