Propagation of IHHNV (Infectious hypodermal and haematopoietic necrosis virus)/PstDVI and MBV (Monodon baculovirus)/PmNV in shrimp primary haemocyte culture.

In vitro propagation of shrimp viruses IHHNV (Infectious hematopoietic hypodermal necrosis virus)/PstDV1 and MBV (Monodon baculovirus)/PmNV in the primary haemocyte culture was successfully be accomplished in the present study. The haemocytes were maintained in double-strength L15 medium with growth supplements and antibiotics. Cytopathic changes observed in the cells were detachment, slendering of cells, vacuolation, and rounding of the cells. Replication of viruses in the culture was confirmed through the expression of DNA polymerase, polyhedrin and lef 4 of MBV and capsid gene of IHHNV. Ultrathin sections of haemocytes observed through electron microscopy revealed scattered chromatin, virogenic stroma and presence of viruses and occlusion bodies (MBV). The study revealed that primary haemocyte culture could be used as a platform for the propagation of a variety of shrimp viruses.

Comparison of Polymerase Chain Reaction (PCR) assay performance in detecting Decapod penstylhamaparvovirus 1 in penaeid shrimp.

Decapod Penstylhamaparvovirus 1, commonly known as infectious hypodermal and hematopoietic necrosis virus (IHHNV), remains an economically important viral pathogen for penaeid shrimp aquaculture due to its effects on growth performance. The World Organization for Animal Health (WOAH, Paris, France) recommended methods for the detection of IHHNV include both conventional and real-time PCR. However, published reports and anecdotal evidence suggest the occurrence of non-specific amplifications when testing for IHHNV using the WOAH protocols. Studies were designed to develop a sensitive, robust TaqMan PCR method for detection of IHHNV in the three commercially important penaeid shrimp: Penaeus vannamei, P. monodon and P. stylirostris. We compared the performance of the WOAH-recommended real-time PCR method to several published as well as in-house designed primer/probe sets spanning the entire genome of IHHNV. Our results show that (1) more than one primer/ probe set is needed when testing for the infectious form of IHHNV in all three species of shrimp and (2) primer pairs qIH-Fw/qIH-Rv and 3144F/ 3232R have diagnostic characteristics that would enable IHHNV detection in all three shrimp species. These findings are valuable for a large-scale screening of shrimp using a TaqMan real-time PCR assay.

Development of a real-time enzymatic recombinase amplification assay for rapid detection of infectious hypodermal and hematopoietic necrosis virus (IHHNV) in shrimp Penaeus vannamei.

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is classified as a reportable crustacean disease by the World Organisation for Animal Health (WOAH), which causes poor growth in Penaeus vannamei. According to genome sequence alignment analysis, enzymatic recombinase amplification (ERA) primers and probe were designed based on the ORF1 region of IHHNV, and a real-time ERA assay for IHHNV detection (IHHNV-ERA) was established. The experimental results show that IHHNV-F2/IHHNV-R2 and IHHNV-Probe can effectively amplify the target gene, and the sensitivity is 1.4 × 101 copies/µL within 14.97 ± 0.19 min, while the qPCR using primers 309F/309R could reach the detection limit of 1.4 × 101 copies/µL within 21.76 ± 0.63 min, and the sensitivity results of one-step PCR could be as low as 1.4 copies/µL with expense of time and false positives. The IHHNV-ERA system can effectively amplify the target gene at 42 ℃ within 20 min, and has no cross-reaction with white spot syndrome virus (WSSV), Ecytonucleospora hepatopenaei (EHP), Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (VpAHPND), and healthy shrimp genomic DNA. Test results of practical samples showed that the detection rate of IHHNV-ERA (18/20) was better than the industrial standard qPCR assay (17/20). Compared with the existing technology, the useful results of this detection assay are: (1) get rid of the dependence on the thermal cycle instrument in the PCR process; (2) the experimental procedure is simple, time-consuming and fast; (3) the detection sensitivity is high. This study provides an ERA based detection assay for IHHNV, which can be used not only for the rapid detection of IHHNV infection, but also for the field screening of pathogens. This assay can also be applied to clinical inspection, customs detection, enterprise quality inspection and other fields, and has obvious practical application value.

Development of a duplex PCR for the simultaneous detection of EHP and IHHNV and analysis of the correlation between these two pathogens.

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is one of the linearly single-stranded DNA viruses. Ecytonucleospora hepatopenaei (EHP) is an intracellular parasitic microsporidian. IHHNV and EHP are pathogens that have been widely prevalent in shrimp farming. Both of them are associated with growth retardation of the penaeid shrimp, which causes serious economic losses to shrimp farming. Shrimp can be co-infected with IHHNV and EHP. In this study, a rapid duplex polymerase chain reaction (PCR) was developed and optimized for the simultaneous detection of EHP and IHHNV. The detection limit of the duplex PCR could reach 1.5 × 102 copies for EHP and IHHNV. A total of 578 Litopenaeus vannamei samples were detected by the established duplex PCR detection method. The results suggested that 398 samples were infected with EHP, 362 samples were infected with IHHNV, and 265 samples were co-infected with EHP and IHHNV. The case-control analysis of the detected shrimp samples showed a certain synergistic effect between EHP and IHHNV.

In vitro propagation of infectious hypodermal hematopoietic necrosis virus (Penaeus stylirostris penstyldensovirus) in PmLyO-Sf9 cells.

Infectious hypodermal hematopoietic necrosis virus (IHHNV/PstDVI) was isolated and propagated in the hybrid shrimp-insect cell line PmLyO-Sf9. A few hours after inoculation with an infected tissue extract or virus suspension, cytopathic changes could be observed in the cell line, including clustering, enlargement, syncytium formation, granulation, vacuole formation, tapering, irregularities in the plasma membrane with extended tails, detachment, cell death, and accumulation of cellular debris. Expression of viral genes, the presence of virions, and cytological changes observed using transmission electron microscopy suggested replication of the virus in these cells. The virus was purified by ultracentrifugation, negatively stained, and examined using an electron microscope, and the purified virus was found to be infectious both in vitro and in vivo. This development opens avenues for the study of the basic molecular mechanism of IHHNV infection, pathogenesis, and replication, which is much needed for developing an antiviral strategy in aquaculture.

Study of infectious hypodermal and hematopoietic necrosis virus (IHHNV) infection in different organs of Penaeus vannamei.

Infectious hypodermal and haematopoietic necrosis virus (IHHNV) is a major viral pathogen in cultured shrimp. It is generally believed that the target organs of IHHNV in shrimp include tissues of ectodermal and mesodermal origin, but do not normally include organ systems of endodermal origin, such as hepatopancreas. In this study, the feeding challenge of IHHNV in different organs (pleopods, muscles, gills, and hepatopancreas) of Penaeus vannamei was studied. The PCR results showed that hepatopancreas of P. vannamei had the strongest IHHNV positivity (100% positive, 19.4 copies/mg) in the feeding challenge experiment. Gills and pleopods had similar infectivity to IHHNV (86.7% positive, 10.6 and 10.5 copies/mg). Among the four organs tested in this study, the IHHNV positivity of muscles was the weakest (33.3% positive, 4.7 copies/mg). The IHHNV infection to hepatopancreas of P. vannamei was also histological confirmed. Our current data indicated that the shrimp tissues derived from the endoderm such as hepatopancreas could also be infected by IHHNV.

Simultaneous Production of a Virus-Like Particle Linked to dsRNA to Enhance dsRNA Delivery for Yellow Head Virus Inhibition.

A co-expressed Penaeus stylirostris densovirus (PstDNV) capsid and dsRNA specific to the yellow head virus (YHV) protease (CoEx cpPstDNV/dspro) has been shown to suppress YHV replication in the Pacific white-legged shrimp (Litopenaeus vannamei). However, maintaining two plasmids in a single bacterial cell is not desirable; therefore, a single plasmid harboring both the PstDNV capsid and the dsRNA-YHV-pro gene was constructed under the regulation of a single T7 promoter, designated pET28a-Linked cpPstDNV-dspro. Following induction, this novel construct expressed an approximately 37-kDa recombinant protein associated with a roughly 400-bp dsRNA (Linked cpPstDNV-dspro). Under a transmission electron microscope, the virus-like particles (VLP; Linked PstDNV VLPs-dspro) obtained were seen to be monodispersed, similar to the native PstDNV virion. A nuclease digestion assay indicated dsRNA molecules were both encapsulated and present outside the Linked PstDNV VLPs-dspro. In addition, the amount of dsRNA produced from this strategy was higher than that obtained with a co-expression strategy. In a YHV infection challenge, the Linked PstDNV VLPs-dspro was more effective in delaying and reducing mortality than other constructs tested. Lastly, the linked construct provides protection for the dsRNA cargo from nucleolytic enzymes present in the shrimp hemolymph. This is the first report of a VLP carrying virus-inhibiting dsRNA that could be produced without disassembly and reassembly to control virus infection in shrimp.

Shrimp genome sequence contains independent clusters of ancient and current Endogenous Viral Elements (EVE) of the parvovirus IHHNV.

BACKGROUND: Shrimp have the ability to accommodate viruses in long term, persistent infections without signs of disease. Endogenous viral elements (EVE) play a role in this process probably via production of negative-sense Piwi-interacting RNA (piRNA)-like fragments. These bind with Piwi proteins to dampen viral replication via the RNA interference (RNAi) pathway. We searched a genome sequence (GenBank record JABERT000000000) of the giant tiger shrimp (Penaeus monodon for the presence of EVE related to a shrimp parvovirus originally named infectious hypodermal and hematopoietic necrosis virus (IHHNV). RESULTS: The shrimp genome sequence contained three piRNA-like gene clusters containing scrambled IHHNV EVE. Two clusters were located distant from one another in pseudochromosome 35 (PC35). Both PC35 clusters contained multiple sequences with high homology (99%) to GenBank records DQ228358 and EU675312 that were both called "non-infectious IHHNV Type A" (IHHNV-A) when originally discovered. However, our results and those from a recent Australian P. monodon genome assembly indicate that the relevant GenBank records for IHHNV-A are sequence-assembly artifacts derived from scrambled and fragmental IHHNV-EVE. Although the EVE in the two PC35 clusters showed high homology only to IHHNV-A, the clusters were separate and distinct with respect to the arrangement (i.e., order and reading direction) and proportional content of the IHHNV-A GenBank records. We conjecture that these 2 clusters may constitute independent allele-like clusters on a pair of homologous chromosomes. The third EVE cluster was found in pseudochromosome 7 (PC7). It contained EVE with high homology (99%) only to GenBank record AF218266 with the potential to protect shrimp against current types of infectious IHHNV. One disadvantage was that some EVE in PC7 can give false positive PCR test results for infectious IHHNV. CONCLUSIONS: Our results suggested the possibility of viral-type specificity in EVE clusters. Specificity is important because whole EVE clusters for one viral type would be transmitted to offspring as collective hereditary units. This would be advantageous if one or more of the EVE within the cluster were protective against the disease caused by the cognate virus. It would also facilitate gene editing for removal of non-protective EVE clusters or for transfer of protective EVE clusters to genetically improve existing shrimp breeding stocks that might lack them.

Current status of infection with infectious hypodermal and hematopoietic necrosis virus (IHHNV) in the Peruvian and Ecuadorian shrimp industry.

Infection with infectious hypodermal and hematopoietic necrosis virus (IHHNV) is a crustacean disease that caused large-scale mortality in Penaeus stylirostris, deformity and growth retardation in Penaeus vannamei and Penaeus monodon. We surveyed the presence of IHHNV in three major shrimp-producing regions in Ecuador, namely Guayas, El Oro, and Esmeralda. The data show that IHHNV is endemic (3.3-100% prevalence) to shrimp farms in these regions. The whole genome sequences of representative circulating IHHNV genotypes in Ecuador and Peru showed that these genotypes formed a separate cluster within the Type II genotypes and were divergent from other geographical isolates of IHHNV originating in Asia, Africa, Australia, and Brazil. In experimental bioassays using specific pathogen-free (SPF) P. vannamei, P. monodon, and P. stylirostris and representative IHHNV isolates from Ecuador and Peru, the virus did not cause any mortality or induce clinical signs in any of the three penaeid species. Although IHHNV-specific Cowdry type A inclusion bodies were histologically detected in experimentally challenged P. vannamei and P. monodon and confirmed by in situ hybridization, no such inclusions were observed in P. stylirostris. Moreover, P. vannamei had the highest viral load, followed by P. monodon and P. stylirostris. Based on IHHNV surveillance data, we conclude that the currently farmed P. vannamei lines in Ecuador are tolerant to circulating IHHNV genotypes. The genome sequence and experimental bioassay data showed that, although the currently circulating genotypes are infectious, they do not induce clinical lesions in the three commercially important penaeid species. These findings suggest a potentially evolving virus-host relationship where circulating genotypes of IHHNV co-exist in equilibrium with P. vannamei raised in Peru and Ecuador.

Prevalence and phylogenetics of infectious hypodermal and hematopoietic necrosis virus (IHHNV) in market-sold Litopenaeus vannamei in Luzon, Philippines.

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is a World Organization for Animal Health (OIE)-classified notifiable crustacean disease. There is limited information on the current status of IHHNV in the Philippines. Thus, this research focuses on collecting samples from various municipality markets of known shrimp producers in Central Luzon to provide an update on the status of IHHNV. These samples were subjected to IHHNV detection using PCR. Results showed that 56 out of the 276 (~20%) samples were positive for IHHNV. This indicates that IHHNV persists in Philippine shrimps despite preventive measures such as testing of broodstock. Furthermore, the sequences of the isolates acquired from different municipalities reveal a high degree of similarity, suggesting transboundary movement of the infection. Our findings also support research that demonstrated a strong link between IHHNV strains in the western hemisphere and those in the Philippines. Our data suggest that farm-monitoring processes must be tightened and strictly implemented to prevent the spread of IHHNV.

Genome assembly of the Australian black tiger shrimp (Penaeus monodon) reveals a novel fragmented IHHNV EVE sequence.

Shrimp are a valuable aquaculture species globally; however, disease remains a major hindrance to shrimp aquaculture sustainability and growth. Mechanisms mediated by endogenous viral elements have been proposed as a means by which shrimp that encounter a new virus start to accommodate rather than succumb to infection over time. However, evidence on the nature of such endogenous viral elements and how they mediate viral accommodation is limited. More extensive genomic data on Penaeid shrimp from different geographical locations should assist in exposing the diversity of endogenous viral elements. In this context, reported here is a PacBio Sequel-based draft genome assembly of an Australian black tiger shrimp (Penaeus monodon) inbred for 1 generation. The 1.89 Gbp draft genome is comprised of 31,922 scaffolds (N50: 496,398 bp) covering 85.9% of the projected genome size. The genome repeat content (61.8% with 30% representing simple sequence repeats) is almost the highest identified for any species. The functional annotation identified 35,517 gene models, of which 25,809 were protein-coding and 17,158 were annotated using interproscan. Scaffold scanning for specific endogenous viral elements identified an element comprised of a 9,045-bp stretch of repeated, inverted, and jumbled genome fragments of infectious hypodermal and hematopoietic necrosis virus bounded by a repeated 591/590 bp host sequence. As only near complete linear ∼4 kb infectious hypodermal and hematopoietic necrosis virus genomes have been found integrated in the genome of P. monodon previously, its discovery has implications regarding the validity of PCR tests designed to specifically detect such linear endogenous viral element types. The existence of joined inverted infectious hypodermal and hematopoietic necrosis virus genome fragments also provides a means by which hairpin double-stranded RNA could be expressed and processed by the shrimp RNA interference machinery.

Genetic Relatedness of Infectious Hypodermal and Hematopoietic Necrosis Virus Isolates, United States, 2019.

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is a nonenveloped, linear, single-stranded DNA virus belonging to the family Parvoviridae and is a World Organisation for Animal Health (OIE)-notifiable crustacean pathogen. During screening of Penaeus vannamei shrimp from 3 commercial shrimp facilities in the United States for a panel of OIE-listed (n = 7) and nonlisted (n = 2) crustacean diseases, shrimp from these facilities tested positive for IHHNV. Nucleotide sequences of PCR amplicons showed 99%-100% similarity to IHHNV isolates from Latin America and Asia. The whole genome of the isolates also showed high similarity to type 2 infectious forms of IHHNV. Phylogenetic analysis using capsid gene and whole-genome sequences demonstrated that the isolates clustered with an IHHNV isolate from Ecuador. The detection of an OIE-listed crustacean pathogen in the United States highlights the need for biosecurity protocols in hatcheries and grow-out ponds to mitigate losses.

Viral Capsid Change upon Encapsulation of Double-Stranded DNA into an Infectious Hypodermal and Hematopoietic Necrosis Virus-like Particle.

In this study, we aimed to encapsulate the sizable double-stranded DNA (dsDNA, 3.9 kbp) into a small-sized infectious hypodermal and hematopoietic necrosis virus-like particle (IHHNV-VLP; T = 1) and compared the changes in capsid structure between dsDNA-filled VLP and empty VLP. Based on our encapsulation protocol, IHHNV-VLP was able to load dsDNA at an efficiency of 30-40% (w/w) into its cavity. Structural analysis revealed two subclasses of IHHNV-VLP, so-called empty and dsDNA-filled VLPs. The three-dimensional (3D) structure of the empty VLP produced in E. coli was similar to that of the empty IHHNV-VLP produced in Sf9 insect cells. The size of the dsDNA-filled VLP was slightly bigger (50 Å) than its empty VLP counterpart; however, the capsid structure was drastically altered. The capsid was about 1.5-fold thicker due to the thickening of the capsid interior, presumably from DNA-capsid interaction evident from capsid protrusions or nodules on the interior surface. In addition, the morphological changes of the capsid exterior were particularly observed in the vicinity of the five-fold axes, where the counter-clockwise twisting of the "tripod" structure at the vertex of the five-fold channel was evident, resulting in a widening of the channel's opening. Whether these capsid changes are similar to virion capsid maturation in the host cells remains to be investigated. Nevertheless, the ability of IHHNV-VLP to encapsulate the sizable dsDNA has opened up the opportunity to package a dsDNA vector that can insert exogenous genes and target susceptible shrimp cells in order to halt viral infection.

Shrimp Parvovirus Circular DNA Fragments Arise From Both Endogenous Viral Elements and the Infecting Virus.

Some insects use endogenous reverse transcriptase (RT) to make variable viral copy DNA (vcDNA) fragments from viral RNA in linear (lvcDNA) and circular (cvcDNA) forms. The latter form is easy to extract selectively. The vcDNA produces small interfering RNA (siRNA) variants that inhibit viral replication via the RNA interference (RNAi) pathway. The vcDNA is also autonomously inserted into the host genome as endogenous viral elements (EVE) that can also result in RNAi. We hypothesized that similar mechanisms occurred in shrimp. We used the insect methods to extract circular viral copy DNA (cvcDNA) from the giant tiger shrimp (Penaeus monodon) infected with a virus originally named infectious hypodermal and hematopoietic necrosis virus (IHHNV). Simultaneous injection of the extracted cvcDNA plus IHHNV into whiteleg shrimp (Penaeus vannamei) resulted in a significant reduction in IHHNV replication when compared to shrimp injected with IHHNV only. Next generation sequencing (NGS) revealed that the extract contained a mixture of two general IHHNV-cvcDNA types. One showed 98 to 99% sequence identity to GenBank record AF218266 from an extant type of infectious IHHNV. The other type showed 98% sequence identity to GenBank record DQ228358, an EVE formerly called non-infectious IHHNV. The startling discovery that EVE could also give rise to cvcDNA revealed that cvcDNA provided an easy means to identify and characterize EVE in shrimp and perhaps other organisms. These studies open the way for identification, characterization and use of protective cvcDNA as a potential shrimp vaccine and as a tool to identify, characterize and select naturally protective EVE to improve shrimp tolerance to homologous viruses in breeding programs.

Co-Infection of Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) and White Spot Syndrome Virus (WSSV) in the Wild Crustaceans of Andaman and Nicobar Archipelago, India.

The present study was intended to screen the wild crustaceans for co-infection with Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) and White Spot Syndrome Virus (WSSV) in Andaman and Nicobar Archipelago, India. We screened a total of 607 shrimp and 110 crab samples using a specific polymerase chain reaction, and out of them, 82 shrimps (13.5%) and 5 (4.5%) crabs were found positive for co-infection of IHHNV and WSSV. A higher rate of co-infection was observed in Penaeus monodon and Scylla serrata than other shrimp and crab species. The nucleotide sequences of IHHNV and WSSV obtained from crab in this present study exhibited very high sequence identity with their counterparts retrieved from various countries. Histopathological analysis of the infected shrimp gill sections further confirmed the eosinophilic intra-nuclear cowdry type A inclusion bodies and basophilic intra-nuclear inclusion bodies characteristics of IHHNV and WSSV infections, respectively. The present study serves as the first report on co-infection of WSSV and IHHNV in Andaman and Nicobar Archipelago, India and accentuates the critical need for continuous monitoring of wild crustaceans and appropriate biosecurity measures for brackishwater aquaculture.

Endogenous piRNA-guided slicing triggers responder and trailer piRNA production from viral RNA in Aedes aegypti mosquitoes.

In the germline of animals, PIWI interacting (pi)RNAs protect the genome against the detrimental effects of transposon mobilization. In Drosophila, piRNA-mediated cleavage of transposon RNA triggers the production of responder piRNAs via ping-pong amplification. Responder piRNA 3' end formation by the nuclease Zucchini is coupled to the production of downstream trailer piRNAs, expanding the repertoire of transposon piRNA sequences. In Aedes aegypti mosquitoes, piRNAs are generated from viral RNA, yet, it is unknown how viral piRNA 3' ends are formed and whether viral RNA cleavage gives rise to trailer piRNA production. Here we report that in Ae. aegypti, virus- and transposon-derived piRNAs have sharp 3' ends, and are biased for downstream uridine residues, features reminiscent of Zucchini cleavage of precursor piRNAs in Drosophila. We designed a reporter system to study viral piRNA 3' end formation and found that targeting viral RNA by abundant endogenous piRNAs triggers the production of responder and trailer piRNAs. Using this reporter, we identified the Ae. aegypti orthologs of Zucchini and Nibbler, two nucleases involved in piRNA 3' end formation. Our results furthermore suggest that autonomous piRNA production from viral RNA can be triggered and expanded by an initial cleavage event guided by genome-encoded piRNAs.

Research progress on hosts and carriers, prevalence, virulence of infectious hypodermal and hematopoietic necrosis virus (IHHNV).

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is one of the major viral pathogens of penaeid shrimp and it has spread worldwide. IHHNV causes substantial economic loss to the shrimp farming industry and has been listed as a notifiable crustacean disease pathogen by the World Organization for Animal Health (OIE). In this paper, we reviewed studies on the hosts and carriers, prevalence, genotypes and virulence of IHHNV. The pathogenesis mechanisms of IHHNV and the viral interference between IHHNV and white spot syndrome virus (WSSV) were also discussed. The mechanism of IHHNV infection and its virulence difference in different hosts and different developmental stages have not been fully studied yet. The mechanisms underlying viral interference between IHHNV and WSSV are not yet fully understood. Further studies are needed to elucidate the precise molecular mechanisms underlying IHHNV infection and to apply the insights gained from such studies for the effective control and prevention of IHHNV disease.

A fast and visual method for duplex shrimp pathogens detection with high specificity using rapid PCR and molecular beacon.

Molecular diagnosis of genome is one of the major methods for pathogens detection. The commonly used PCR method can realize an exponential amplification of the target gene but is time-consuming. In this work, we proposed a duplex and visual method using rapid PCR combined with molecular beacons to specifically detect two kinds of shrimp pathogens in one reaction tube. We only need to observe the fluorescence change of the reaction tube with naked eye to determine the result. A home-made automatic transfer equipment allows reaction tubes shuttling quickly between two water baths to achieve rapid PCR amplification. A simple device was also designed to present the detection results easily determined with naked eye. This duplex and visual detection method is fast, low-cost and of high specificity. From DNA extraction to results judgment, only 15 min was enough. Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) and Vibrio parahaemolyticus (VP) are two common shrimp pathogens which were chosen as our detection objects. This method may give a possibility to conduct end-point visual duplex detection, which may make a positive influence on the pathogen prevention.

Real-time PCR tests to specifically detect IHHNV lineages and an IHHNV EVE integrated in the genome of Penaeus monodon.

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) can cause mass mortalities in western blue shrimp Penaeus stylirostris, runt deformity syndrome in Pacific white shrimp P. vannamei and scalloped abdominal shell deformities in black tiger shrimp P. monodon. In P. monodon, however, PCR-based diagnosis of IHHNV can be complicated by the presence of a chromosome-integrated, non-replicating endogenous viral element (EVE). To facilitate high-throughput screening of P. monodon for IHHNV infection and/or EVE sequences, here we report real-time PCR tests designed to specifically detect IHHNV Lineage I, II and III but not EVE Type A sequences and vice versa. Using 108 dsDNA copies of plasmid (p)DNA controls containing either IHHNV or EVE-Type A sequences, both tests displayed absolute specificity. The IHHNV-q309 PCR reliably detected down to ≤10 copies of pDNA, at which levels a 309F/R PCR amplicon was just detectable, and the presence of an IHHNV-EVE sequence did not significantly impact its sensitivity. The IHHNV-qEVE PCR was similarly sensitive. Testing of batches of P. monodon clinical samples from Vietnam/Malaysia and Australia identified good diagnostic concordance between the IHHNV-q309 and 309F/R PCR tests. As expected for a sequence integrated into host chromosomal DNA, IHHNV-qEVE PCR Ct values were highly uniform among samples from shrimp in which an EVE was present. The highly specific and sensitive IHHNV-q309 and IHHNV-qEVE real-time PCR tests described here should prove useful for selecting broodstock free of IHHNV infection and in maintaining breeding populations of P. monodon specific pathogen free for IHHNV, and if desired, also free of IHHNV-EVE sequences.

Moderate heritability of hepatopancreatic parvovirus titre suggests a new option for selection against viral diseases in banana shrimp (Fenneropenaeus merguiensis) and other aquaculture species.

BACKGROUND: In shrimp farming, major production losses are caused by viruses. Hepatopancreatic parvovirus (HPV) is one of the viral pathogens that infect banana shrimp (Fenneropenaeus merguiensis). HPV is thought to slow down growth and cause mortality in the juvenile stages of banana shrimp. Genetic improvement through selection of shrimp resistant to viral diseases is one approach to address this issue. This is the first detailed report on an aquaculture species that investigates whether viral titre varies among families and is heritable, and thus whether viral titre per se is a possible candidate trait for selection to produce resistant stock. RESULTS: HPV titre was measured by quantitative polymerase chain reaction of DNA extracted from 1137 offspring (from 48 full-sib families). Estimated heritability of HPV titre, based on the linear animal mixed model, was moderate (h(2) = 0.41). Genetic correlations of HPV with body traits (weight, length and width of body, head and tail) ranged from -0.13 to -0.38. HPV titre was negatively correlated with raw and cooked body colour (-0.33 and -0.43, respectively). CONCLUSIONS: This is the first study based on a large dataset that provides evidence that viral titre may have a genetic component in penaeid shrimp or even in any aquaculture species. The moderate heritability estimated for this trait suggests that resistance to HPV may be achieved by selecting for low HPV titre. With moderate and negative correlations, selection for resistance to HPV should gradually improve body traits and colour of banana shrimp.