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Peter J. Walker - One of the best experts on this subject based on the ideXlab platform.

  • RNA-Binding Domain in the Nucleocapsid Protein of Gill-Associated NidoVirus of Penaeid Shrimp
    2016
    Co-Authors: Chumporn Soowannayan, Jeff A. Cowley, Wojtek P. Michalski, Peter J. Walker
    Abstract:

    Gill-Associated Virus (GAV) infects Penaeus monodon shrimp and is the type species okaVirus in the Roniviridae, the only invertebrate nidoViruses known currently. Electrophoretic mobility shift assays (EMSAs) using His6-tagged full-length and truncated proteins were employed to examine the nucleic acid binding properties of the GAV nucleocapsid (N) protein in vitro. The EMSAs showed full-length N protein to bind to all synthetic single-stranded (ss)RNAs tested independent of their sequence. The ssRNAs included (+) and (2) sense regions of the GAV genome as well as a (+) sense region of the M RNA segment of Mourilyan Virus, a crustacean bunya-like Virus. GAV N protein also bound to double-stranded (ds)RNAs prepared to GAV ORF1b gene regions and to bacteriophage M13 genomic ssDNA. EMSAs using the five N protein constructs with variable-length N-terminal and/or C-terminal truncations localized the RNA binding domain to a 50 amino acid (aa) N-terminal sequence spanning Met11 to Arg60. Similarly to other RNA binding proteins, the first 16 aa portion of this sequence was proline/arginine rich. To examine this domain in more detail, the 18 aa peptide (M11PVRRPLPPQPPRNARLI29) encompassing this sequence was synthesized and found to bind nucleic acids similarly to the full-length N protein in EMSAs. The data indicate a fundamental role for the GAV N protein proline/arginine-rich domain in nucleating genomic ssRNA to form nucleocapsids. Moreover, as the synthetic peptide formed higher-order complexes in the presence of RNA, the domai

  • possess 5H-leader sequences
    2015
    Co-Authors: Jeff A. Cowley, Christine M Dimmock, Peter J. Walker
    Abstract:

    Sequence analysis of the C20 kb 5«-terminal portion of the ssRNA genome of Gill-Associated Virus (GAV) of Penaeus monodon prawns has previously established that it contains an ORF1a–1b replicase gene equivalent to those of the coronaVirus and arteriVirus members of the order Nidovirales. Sequence analysis of the remaining C6–2 kb of the GAV genome downstream of ORF1a–1b to a 3«-poly(A) tail has identified two highly conserved intergenic sequences in which 29/32 nucleotides are conserved. Northern hybridization using probes to the four putative GAV ORFs and either total or poly(A)-selected RNA identified two 3«-coterminal subgenomic (sg) mRNAs of C6 kb and C5–5 kb. Primer extension and 5«-RACE analyses showed that the sgmRNAs initiate at the same 5«-AC positions in the central region of the two conserved intergenic sequences. Neither method provided any evidence that the GAV sgmRNAs are fused to genomic 5«-leader RNA sequences as is the case with vertebrate coronaViruses and arteriViruses. Intracellular double-stranded (ds)RNAs equivalent in size to the 26–2 kb genomic RNA and two sgRNAs were also identified by RNase/DNase digestion of total RNA from GAV-infected prawn tissue. The identification of only two sgmRNAs that initiate at the same position in conserved intergenic sequences and the absence of 5«-genomic leader sequences fused to these sgmRNAs confirms tha

  • a key gene of the rna interference pathway in the black tiger shrimp penaeus monodon identification and functional characterisation of dicer 1
    Fish & Shellfish Immunology, 2008
    Co-Authors: Dang Thi Hoang Oanh, Peter J. Walker, Russell E Lyons, Lisa Leeton, Marielle C W Van Hulten, S H Tan, Linsheng Song, K V Rajendran
    Abstract:

    RNA interference (RNAi) is an evolutionarily conserved mechanism by which double-stranded RNA (dsRNA) initiates post-transcriptional silencing of homologous genes. Here we report the amplification and characterisation of a full length cDNA from black tiger shrimp (Penaeus monodon) that encodes the bidentate RNAase III Dicer, a key component of the RNAi pathway. The full length of the shrimp Dicer (Pm Dcr1) cDNA is 7629 bp in length, including a 51 untranslated region (UTR) of 130 bp, a 3' UTR of 77 bp, and an open reading frame of 7422 bp encoding a polypeptide of 2473 amino acids with an estimated molecular mass of 277.895 kDa and a predicted isoelectric point of 4.86. Analysis of the deduced amino acid sequence indicated that the mature peptide contains all the seven recognised functional domains and is most similar to the mosquito (Aedes aegypti) Dicer-1 sequence with a similarity of 34.6%. Quantitative RT-PCR analysis showed that Pm Dcr1 mRNA is most highly expressed in haemolymph and lymphoid organ tissues (P 0.05). However, there was no correlation between Pm Dcr1 mRNA levels in lymphoid organ and the viral genetic loads in shrimp naturally infected with Gill-Associated Virus (GAV) and Mourilyan Virus (P > 0.05). Treatment with synthetic dsRNA corresponding to Pm Dcr1 sequence resulted in knock-down of Pm Dcr1 mRNA expression in both uninfected shrimp and shrimp infected experimentally with GAV. Knock-down of Pm Dcr1 expression resulted in more rapid mortalities and higher viral loads. These data demonstrated that Dicer is involved in antiviral defence in shrimp. (c) 2007 Elsevier Ltd. All rights reserved.

  • identification and analysis of gp116 and gp64 structural glycoproteins of yellow head nidoVirus of penaeus monodon shrimp
    Journal of General Virology, 2003
    Co-Authors: Sarawut Jitrapakdee, Peter J. Walker, Jeff A. Cowley, Sasimanas Unajak, Nusra Sittidilokratna, Richard A J Hodgson, Sakol Panyim, Vichai Boonsaeng
    Abstract:

    Yellow head Virus (YHV) is a major agent of disease in farmed penaeid shrimp. YHV virions purified from infected shrimp contain three major structural proteins of molecular mass 116 kDa (gp116), 64 kDa (gp64) and 20 kDa (p20). Two different staining methods indicated that the gp116 and gp64 proteins are glycosylated. Here we report the complete nucleotide sequence of ORF3, which encodes a polypeptide of 1666 amino acids with a calculated molecular mass of 185 713 Da (pI=6·68). Hydropathy analysis of the deduced ORF3 protein sequence identified six potential transmembrane helices and three ectodomains containing multiple sites for potential N-linked and O-linked glycosylation. N-terminal sequence analysis of mature gp116 and gp64 proteins indicated that each was derived from ORF3 by proteolytic cleavage of the polyprotein between residues Ala228 and Thr229, and Ala1127 and Leu1128, located at the C-terminal side of transmembrane helices 3 and 5, respectively. Comparison with the deduced ORF3 protein sequence of Australian Gill-Associated Virus (GAV) indicated 83 % amino acid identity in gp64 and 71 % identity in gp116, which featured two significant sequence deletions near the N terminus. Database searches revealed no significant homology with other proteins. Recombinant gp64 expressed in E. coli with and without the C-terminal transmembrane region was shown to react with antibody raised against native gp64 purified from virions.

  • gill associated Virus of penaeus monodon prawns an invertebrate Virus with orf1a and orf1b genes related to arteri and coronaViruses
    Journal of General Virology, 2000
    Co-Authors: Jeff A. Cowley, Christine M Dimmock, Kirsten Spann, Peter J. Walker
    Abstract:

    A 20089 nucleotide (nt) sequence was determined for the 5′ end of the (+)-ssRNA genome of Gill-Associated Virus (GAV), a yellow head-like Virus infecting Penaeus monodon prawns. Clones were generated from a ∼22 kb dsRNA purified from lymphoid organ total RNA of GAV-infected prawns. The region contains a single gene comprising two long overlapping open reading frames, ORF1a and ORF1b, of 4060 and 2646 amino acids, respectively. The ORFs are structurally related to the ORF1a and ORF1ab polyproteins of coronaViruses and arteriViruses. The 99 nt overlap between ORF1a and ORF1b contains a putative AAAUUUU ‘slippery’ sequence associated with −1 ribosomal frameshifting. A 131 nt stem–loop with the potential to form a complex pseudoknot resides 3 nt downstream of this sequence. Although different to the G/UUUAAAC frameshift sites and ‘H-type’ pseudoknots of nidoViruses, in vitro transcription/translation analysis demonstrated that the GAV element also facilitates read-through of the ORF1a/1b junction. As in coronaViruses, GAV ORF1a encodes a 3C-like cysteine protease domain located between two hydrophobic regions. However, its sequence suggests some structural relationship to the chymotrypsin-like serine proteases of arteriViruses. ORF1b encodes homologues of the ‘SDD’ polymerase, which among (+)-RNA Viruses is unique to nidoViruses, as well as metal-ion-binding and helicase domains. The presence of a dsRNA replicative intermediate and ORF1a and ORF1ab polyproteins translated by a −1 frameshift suggests that GAV represents the first invertebrate member of the Order Nidovirales.

Jeff A. Cowley - One of the best experts on this subject based on the ideXlab platform.

  • TaqMan real-time and conventional nested PCR tests specific to yellow head Virus genotype 7 (YHV7) identified in giant tiger shrimp in Australia.
    Journal of virological methods, 2019
    Co-Authors: Jeff A. Cowley, Peter G. Mohr, Nicholas J. G. Moody, Min Rao, Melony J. Sellars, Mark St. J. Crane
    Abstract:

    In 2013, a unique seventh yellow head Virus genotype (YHV7) was detected in Black Tiger shrimp (Penaeus monodon) broodstock that suffered high mortality following their capture from Joseph Bonaparte Gulf (JBG) in northern Australia. To assist with its diagnosis and assessment of its distribution, prevalence and pathogenicity, YHV7-specific TaqMan real-time qPCR and conventional nested PCR primer sets were designed to ORF1b gene sequences divergent from the other YHV genotypes. Using high (≥108) copies of plasmid (p)DNA controls containing ORF1b gene inserts of representative strains of YHV genotypes 1-7, both PCR tests displayed specificity for YHV7. Amplifications of serial 10-fold dilutions of quantified YHV7 pDNA and synthetic ssRNA showed that both tests could reliably detect 10 genome copies. Pleopods/gills from wild P. monodon sourced from locations in geographically disparate regions across northern Australia as well as 96 juveniles (48 either appearing normal or displaying signs of morbidity) from a commercial pond experiencing mortalities were screened to partially validate the diagnostic capacity of the qPCR test. Based on these data and PCR primer/probe sequence mismatches with other newly identified YHV genotypes, both YHV7-specific PCR tests should prove useful in the sensitive detection and discrimination of this genotype from YHV 2 (Gill-Associated Virus) and YHV6 that can occur in Australian P. monodon, as well as from YHV genotypes currently listed as exotic to Australia.

  • RNA-Binding Domain in the Nucleocapsid Protein of Gill-Associated NidoVirus of Penaeid Shrimp
    2016
    Co-Authors: Chumporn Soowannayan, Jeff A. Cowley, Wojtek P. Michalski, Peter J. Walker
    Abstract:

    Gill-Associated Virus (GAV) infects Penaeus monodon shrimp and is the type species okaVirus in the Roniviridae, the only invertebrate nidoViruses known currently. Electrophoretic mobility shift assays (EMSAs) using His6-tagged full-length and truncated proteins were employed to examine the nucleic acid binding properties of the GAV nucleocapsid (N) protein in vitro. The EMSAs showed full-length N protein to bind to all synthetic single-stranded (ss)RNAs tested independent of their sequence. The ssRNAs included (+) and (2) sense regions of the GAV genome as well as a (+) sense region of the M RNA segment of Mourilyan Virus, a crustacean bunya-like Virus. GAV N protein also bound to double-stranded (ds)RNAs prepared to GAV ORF1b gene regions and to bacteriophage M13 genomic ssDNA. EMSAs using the five N protein constructs with variable-length N-terminal and/or C-terminal truncations localized the RNA binding domain to a 50 amino acid (aa) N-terminal sequence spanning Met11 to Arg60. Similarly to other RNA binding proteins, the first 16 aa portion of this sequence was proline/arginine rich. To examine this domain in more detail, the 18 aa peptide (M11PVRRPLPPQPPRNARLI29) encompassing this sequence was synthesized and found to bind nucleic acids similarly to the full-length N protein in EMSAs. The data indicate a fundamental role for the GAV N protein proline/arginine-rich domain in nucleating genomic ssRNA to form nucleocapsids. Moreover, as the synthetic peptide formed higher-order complexes in the presence of RNA, the domai

  • New yellow head Virus genotype (YHV7) in giant tiger shrimp Penaeus monodon indigenous to northern Australia
    Diseases of aquatic organisms, 2015
    Co-Authors: Peter G. Mohr, Jeff A. Cowley, Nicholas J. G. Moody, John Hoad, Lynette M. Williams, Rachel O. Bowater, David M. Cummins, Mark St. J. Crane
    Abstract:

    In 2012, giant tiger shrimp Penaeus monodon originally sourced from Joseph Bonaparte Gulf in northern Australia were examined in an attempt to identify the cause of elevated mortalities among broodstock at a Queensland hatchery. Nucleic acid extracted from ethanol-fixed gills of 3 individual shrimp tested positive using the OIE YHV Protocol 2 RT-PCR designed to differentiate yellow head Virus (YHV1) from Gill-Associated Virus (GAV, synonymous with YHV2) and the OIE YHV Protocol 3 RT-nested PCR designed for consensus detection of YHV genotypes. Sequence analysis of the 794 bp (Protocol 2) and 359 bp (Protocol 3) amplicons from 2 distinct regions of ORF1b showed that the yellow-head-complex Virus detected was novel when compared with Genotypes 1 to 6. Nucleotide identity on the Protocol 2 and Protocol 3 ORF1b sequences was highest with the highly pathogenic YHV1 genotype (81 and 87%, respectively) that emerged in P. monodon in Thailand and lower with GAV (78 and 82%, respectively) that is enzootic to P. monodon inhabiting eastern Australia. Comparison of a longer (725 bp) ORF1b sequence, spanning the Protocol 3 region and amplified using a modified YH30/31 RT-nPCR, provided further phylogenetic evidence for the Virus being distinct from the 6 described YHV genotypes. The Virus represents a unique seventh YHV genotype (YHV7). Despite the mortalities observed, the role of YHV7 remains unknown.

  • possess 5H-leader sequences
    2015
    Co-Authors: Jeff A. Cowley, Christine M Dimmock, Peter J. Walker
    Abstract:

    Sequence analysis of the C20 kb 5«-terminal portion of the ssRNA genome of Gill-Associated Virus (GAV) of Penaeus monodon prawns has previously established that it contains an ORF1a–1b replicase gene equivalent to those of the coronaVirus and arteriVirus members of the order Nidovirales. Sequence analysis of the remaining C6–2 kb of the GAV genome downstream of ORF1a–1b to a 3«-poly(A) tail has identified two highly conserved intergenic sequences in which 29/32 nucleotides are conserved. Northern hybridization using probes to the four putative GAV ORFs and either total or poly(A)-selected RNA identified two 3«-coterminal subgenomic (sg) mRNAs of C6 kb and C5–5 kb. Primer extension and 5«-RACE analyses showed that the sgmRNAs initiate at the same 5«-AC positions in the central region of the two conserved intergenic sequences. Neither method provided any evidence that the GAV sgmRNAs are fused to genomic 5«-leader RNA sequences as is the case with vertebrate coronaViruses and arteriViruses. Intracellular double-stranded (ds)RNAs equivalent in size to the 26–2 kb genomic RNA and two sgRNAs were also identified by RNase/DNase digestion of total RNA from GAV-infected prawn tissue. The identification of only two sgmRNAs that initiate at the same position in conserved intergenic sequences and the absence of 5«-genomic leader sequences fused to these sgmRNAs confirms tha

  • identification and analysis of gp116 and gp64 structural glycoproteins of yellow head nidoVirus of penaeus monodon shrimp
    Journal of General Virology, 2003
    Co-Authors: Sarawut Jitrapakdee, Peter J. Walker, Jeff A. Cowley, Sasimanas Unajak, Nusra Sittidilokratna, Richard A J Hodgson, Sakol Panyim, Vichai Boonsaeng
    Abstract:

    Yellow head Virus (YHV) is a major agent of disease in farmed penaeid shrimp. YHV virions purified from infected shrimp contain three major structural proteins of molecular mass 116 kDa (gp116), 64 kDa (gp64) and 20 kDa (p20). Two different staining methods indicated that the gp116 and gp64 proteins are glycosylated. Here we report the complete nucleotide sequence of ORF3, which encodes a polypeptide of 1666 amino acids with a calculated molecular mass of 185 713 Da (pI=6·68). Hydropathy analysis of the deduced ORF3 protein sequence identified six potential transmembrane helices and three ectodomains containing multiple sites for potential N-linked and O-linked glycosylation. N-terminal sequence analysis of mature gp116 and gp64 proteins indicated that each was derived from ORF3 by proteolytic cleavage of the polyprotein between residues Ala228 and Thr229, and Ala1127 and Leu1128, located at the C-terminal side of transmembrane helices 3 and 5, respectively. Comparison with the deduced ORF3 protein sequence of Australian Gill-Associated Virus (GAV) indicated 83 % amino acid identity in gp64 and 71 % identity in gp116, which featured two significant sequence deletions near the N terminus. Database searches revealed no significant homology with other proteins. Recombinant gp64 expressed in E. coli with and without the C-terminal transmembrane region was shown to react with antibody raised against native gp64 purified from virions.

Mark St. J. Crane - One of the best experts on this subject based on the ideXlab platform.

  • TaqMan real-time and conventional nested PCR tests specific to yellow head Virus genotype 7 (YHV7) identified in giant tiger shrimp in Australia.
    Journal of virological methods, 2019
    Co-Authors: Jeff A. Cowley, Peter G. Mohr, Nicholas J. G. Moody, Min Rao, Melony J. Sellars, Mark St. J. Crane
    Abstract:

    In 2013, a unique seventh yellow head Virus genotype (YHV7) was detected in Black Tiger shrimp (Penaeus monodon) broodstock that suffered high mortality following their capture from Joseph Bonaparte Gulf (JBG) in northern Australia. To assist with its diagnosis and assessment of its distribution, prevalence and pathogenicity, YHV7-specific TaqMan real-time qPCR and conventional nested PCR primer sets were designed to ORF1b gene sequences divergent from the other YHV genotypes. Using high (≥108) copies of plasmid (p)DNA controls containing ORF1b gene inserts of representative strains of YHV genotypes 1-7, both PCR tests displayed specificity for YHV7. Amplifications of serial 10-fold dilutions of quantified YHV7 pDNA and synthetic ssRNA showed that both tests could reliably detect 10 genome copies. Pleopods/gills from wild P. monodon sourced from locations in geographically disparate regions across northern Australia as well as 96 juveniles (48 either appearing normal or displaying signs of morbidity) from a commercial pond experiencing mortalities were screened to partially validate the diagnostic capacity of the qPCR test. Based on these data and PCR primer/probe sequence mismatches with other newly identified YHV genotypes, both YHV7-specific PCR tests should prove useful in the sensitive detection and discrimination of this genotype from YHV 2 (Gill-Associated Virus) and YHV6 that can occur in Australian P. monodon, as well as from YHV genotypes currently listed as exotic to Australia.

  • New yellow head Virus genotype (YHV7) in giant tiger shrimp Penaeus monodon indigenous to northern Australia
    Diseases of aquatic organisms, 2015
    Co-Authors: Peter G. Mohr, Jeff A. Cowley, Nicholas J. G. Moody, John Hoad, Lynette M. Williams, Rachel O. Bowater, David M. Cummins, Mark St. J. Crane
    Abstract:

    In 2012, giant tiger shrimp Penaeus monodon originally sourced from Joseph Bonaparte Gulf in northern Australia were examined in an attempt to identify the cause of elevated mortalities among broodstock at a Queensland hatchery. Nucleic acid extracted from ethanol-fixed gills of 3 individual shrimp tested positive using the OIE YHV Protocol 2 RT-PCR designed to differentiate yellow head Virus (YHV1) from Gill-Associated Virus (GAV, synonymous with YHV2) and the OIE YHV Protocol 3 RT-nested PCR designed for consensus detection of YHV genotypes. Sequence analysis of the 794 bp (Protocol 2) and 359 bp (Protocol 3) amplicons from 2 distinct regions of ORF1b showed that the yellow-head-complex Virus detected was novel when compared with Genotypes 1 to 6. Nucleotide identity on the Protocol 2 and Protocol 3 ORF1b sequences was highest with the highly pathogenic YHV1 genotype (81 and 87%, respectively) that emerged in P. monodon in Thailand and lower with GAV (78 and 82%, respectively) that is enzootic to P. monodon inhabiting eastern Australia. Comparison of a longer (725 bp) ORF1b sequence, spanning the Protocol 3 region and amplified using a modified YH30/31 RT-nPCR, provided further phylogenetic evidence for the Virus being distinct from the 6 described YHV genotypes. The Virus represents a unique seventh YHV genotype (YHV7). Despite the mortalities observed, the role of YHV7 remains unknown.

Walker, Peter J. - One of the best experts on this subject based on the ideXlab platform.

  • Homologous genetic recombination in the yellow head complex of nidoViruses infecting Penaeus monodon shrimp
    Published by Elsevier Inc., 2009
    Co-Authors: Wijegoonawardane, Priyanjalie K.m., Sittidilokratna Nusra, Petchampai Natthida, Cowley, Jeff A., Gudkovs Nicholas, Walker, Peter J.
    Abstract:

    AbstractYellow head Virus (YHV) is a highly virulent pathogen of Penaeus monodon shrimp. It is one of six known genotypes in the yellow head complex of nidoViruses which also includes mildly pathogenic Gill-Associated Virus (GAV, genotype 2) and four other genotypes (genotypes 3–6) that have been detected only in healthy shrimp. In this study, comparative phylogenetic analyses conducted on replicase- (ORF1b) and glycoprotein- (ORF3) gene amplicons identified 10 putative natural recombinants amongst 28 Viruses representing all six genotypes from across the Indo-Pacific region. The ∼4.6 kb genomic region spanning the two amplicons was sequenced for three putative recombinant Viruses from Vietnam (genotype 3/5), the Philippines (genotype 5/2) and Indonesia (genotype 3/2). SimPlot analysis using these and representative parental Virus sequences confirmed that each was a recombinant genotype and identified a recombination hotspot in a region just upstream of the ORF1b C-terminus. Maximum-likelihood breakpoint analysis predicted identical crossover positions in the Vietnamese and Indonesian recombinants, and a crossover position 12 nt upstream in the Philippine recombinant. Homologous genetic recombination in the same genome region was also demonstrated in recombinants generated experimentally in shrimp co-infected with YHV and GAV. The high frequency with which natural recombinants were identified indicates that genetic exchange amongst genotypes is occurring commonly in Asia and playing a significant role in expanding the genetic diversity in the yellow head complex. This is the first evidence of genetic recombination in Viruses infecting crustaceans and has significant implications for the pathogenesis of infection and diagnosis of these newly emerging invertebrate pathogens

  • Consensus RT-nested PCR detection of yellow head complex genotypes in penaeid shrimp
    'Elsevier BV', 2008
    Co-Authors: Wijegoonawardane, Priyanjalie K.m., Cowley, Jeff A., Walker, Peter J.
    Abstract:

    A consensus RT-nested (n)PCR is described that detects the six distinct genotypic variants in the yellow head Virus (YHV) complex. The PCR primers targeted ORF1b gene regions more highly conserved amongst the reference strains of YHV (genotype 1) and Gill-Associated Virus (GAV, genotype 2) and a set of 57 field isolates containing multiple representatives of each genotype. The test employed short PCR (359 bp) and nPCR (147 bp) amplicons to minimise the effects of RNA degradation. To ensure ≤8-primer degeneracy, two primers were designed to each site, one accommodating sequence variations amongst genotype 1 isolates and the other variations amongst isolates of the other genotypes. The analytical sensitivity limits of the PCR and nPCR were estimated to be ∼1250 and ∼1.25 RNA copies, respectively. The superior group-specificity of the consensus RT-nPCR compared to other OIE-recommended PCR tests for YHV/GAV was demonstrated using RNA from 17 Penaeus monodon shrimp infected with representatives of each of the six genotypes. Phylogenetic analysis using the 94 nt ORF1b gene sequence spanned by the nPCR primers generated genotype assignments that were consistent with those obtained using the extended 671 nt sequence used for the initial identification of genotypes

Jerry, Dean R. - One of the best experts on this subject based on the ideXlab platform.

  • Genetic parameters for tolerance to Gill-Associated Virus under challenge-test conditions in the black tiger shrimp (Penaeus monodon)
    'Elsevier BV', 2020
    Co-Authors: Noble, Tansyn H., Coman G. J., Wade, Nicholas M., Thomson, Peter C., Raadsma, Herman W., Khatkar, Mehar S., Guppy, Jarrod L., Jerry, Dean R.
    Abstract:

    Diseases in shrimp aquaculture cause significant economic losses, particularly those caused by Viruses. Genetic improvement of disease tolerance through selective breeding can be an important tool for managing the risk of disease in shrimp farming as long as the trait has a genetic basis (i.e. heritable) and is able to be accurately and reliably measured. This study presents the first estimates of genetic variation associated with tolerance to Gill-Associated Virus (GAV) in Penaeus monodon using a unique controlled challenge test design. Shrimp families (n = 72) were communally spawned and reared prior to replicated communal challenge testing when they reached an average size of ~8 g. Pedigree determination was carried out using genotyping and shrimp were challenged by intramuscular injection with a weight standardised dose of GAV. Daily mortality data were collected over 15 days from 1717 individuals and GAV infection load was measured on the challenge test survivors (n = 963). Overall mortality after 15 days was 35.5% and ranged from 0 to 71% among families. Heritability estimates for mortality were 0.11 ± 0.03 using a binomial model and 0.14 (standard error not estimated) using Cox's proportional hazards model. The estimated heritability for GAV infection load was 0.21 ± 0.07. The genetic correlation between mortality and GAV infection load was not significantly different from zero, r = 0.30 ± 0.23, suggesting that the two traits may be genetically independent, at least in the way they were measured in this study. Results from this study suggest a low but significant genetic basis for GAV tolerance in P. monodon and that selection may be a viable option to manage GAV-related disease. The study also demonstrated, for the first time in shrimp, communal-based spawning and rearing can be used for large-scale genetic analysis of disease tolerance, eliminating the need for single family rearing tanks and associated confounding environmental effects

  • Genetic parameters of Gill-Associated Virus infection and body weight under commercial conditions in black tiger shrimp, Penaeus monodon
    'Elsevier BV', 2020
    Co-Authors: Noble, Tansyn H., Coman G. J., Wade, Nicholas M., Raadsma, Herman W., Khatkar, Mehar S., Guppy, Jarrod L., Thomson Peter, Jerry, Dean R.
    Abstract:

    Selective breeding to improve performance of growth and increase disease resistance is becoming commonplace within shrimp aquaculture. Whilst estimated breeding values (EBV) for growth can be evaluated easily in on-farm trials, EBVs for disease resistance are usually obtained from controlled laboratory challenges and may not be indicative of natural infection and resistance in a commercial setting. If they are not the same trait, this will result in a low genetic correlation between the traits and application of EBVs derived from the laboratory challenge will lead to overall slow genetic progress for improved disease resistance in on-farm conditions. There is a need for alternative measures of predicting disease resistance based on performance in farm environments. Two such estimates may be viral infection status (presence/absence) and load of farm reared shrimp. This study presents genetic parameter estimates of Gill-Associated Virus (GAV) infection (viral infection presence and viral loading) and body weight traits from Penaeus monodon reared under commercial farm conditions. Body weight and GAV infection traits were assessed by sampling similar to 2000 shrimp from 80 full-sib families from two replicate commercial ponds. In addition, the Pearson correlation of EBVs of pond-reared shrimp with those of siblings derived from communal laboratory GAV challenge tests (intramuscular injection of standard doses of Virus) were calculated to establish if prediction of genetic merit in controlled trials would be similar to disease resistance seen on-farm. Heritability under commercial farm conditions for GAV infection status was 0.06 +/- 0.03 (percent GAV positive 45.5%) and infection load 0.21 +/- 0.10 (mean GAV infection load 3.11 +/- 1.14 log(10) GAV copies mu g(-1) TNA) and for body weight h(2) = 0.38 +/- 0.07. A high genetic correlation was observed among the two on-farm GAV infection traits (r(g) = 0.90 +/- 0.24), whereas the genetic correlation between the two GAV infection traits and body weight on-farm were positive although weak (r(g) = 0.26 +/- 0.25; 0.36 +/- 0.26). No significant correlation was found for EBVs of GAV infection (infection status and load) on-farm and GAV-induced mortality or viral load under laboratory challenge testing (R-EBV ranged from -0.06 +/- 0.14 to -0.27 +/- 0.15). Additionally, there was no correlation of EBVs between body weight of shrimp on-farm and GAV-induced disease under controlled challenge. In conclusion, measures of GAV infection from shrimp on-farm and GAV induced mortality measured under controlled challenge conditions may represent different genetic traits, at least when mortality is measured using an 'unnatural' challenge method and when no apparent disease outbreak occurs on farm