Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
  • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
  • C12Q1/70—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving virus or bacteriophage
  • C12Q1/701—Specific hybridization probes

Definitions

• the invention relates to the field of diagnostic testing. More specifically, new primers have been developed for use in detection of the Infectious Hypodermal and Hematopoietic Necrosis Virus pathogen of shrimp.
• IHHNV Infectious Hypodermal and Hematopoietic Necrosis Virus
• IHHNV Infectious Hypodermal and Hematopoietic Necrosis Virus
• IHHNV causes mass mortality among the Western blue shrimp (Penaeus styHrostris) and severe deformation in the Pacific white shrimp (Penaeus vannamei).
• IHHNV is a small, single stranded DNA-contai ⁇ ing parvovirus, the complete genome of which has been sequenced (Bonami et al., J. Gen. Virology 71 (Pt 11):657-2664 (1990); GenBank AF218266).
• IHHNV is extremely detrimental to the shrimp farming industry, being responsible for catastrophic epidemics worldwide. Detection of IHHNV in hatchery broodstock and in post-larvae allows infected shrimp to be eliminated before entry into a commercial production system. Consequently, a variety of methods have been developed for the detection of IHHNV in shrimp, including nucleic acid-based methods and immunological methods (Lightner et al., Aquaculture 164(1):201-220 (1998)). Nucleic acid amplification methods such as polymerase chain reaction (PCR) and isothermal amplification are of particular interest because they are simple, rapid, and sensitive.
• PCR polymerase chain reaction
• PCR methods for the detection of IHHNV which are based on amplifying different diagnostic regions of the genome, have been described (see for example Nunan et al., Mar. Biotechnol. 2(4):319-328 (2000); Yue et al., J. AOAC International 89(1):240-244 (2006); Tang et al. Dis. Aquat. Org. 44(2):79- 85 (2001); Hu et al., CN 1410549; and Dhar et al. J. Clin. Microbiol. 39(8):2835-2845 (2001)). Additionally, a loop mediated isothermal method for the detection of IHHNV is described by Sun et al. (J. Virol. Methods 131(1):41-46 (2006)).
• the present invention provides an isolated IHHNV diagnostic primer sequence as set forth in any one of SEQ ID NOs: 1-8 or an isolated nucleic acid molecule that is completely complementary to SEQ ID NOs:1-8.
• the invention provides a pair of two different IHHNV diagnostic primer sequences as disclosed herein, wherein the pair is capable of priming a nucleic acid amplification reaction that amplifies a region of nucleic acid within the IHHNV genome.
• the invention provides a kit for the detection of IHHNV comprising at least one pair of IHHNV diagnostic primer sequences disclosed herein. In another embodiment, the invention provides a method for detecting the presence of IHHNV in a sample comprising:
• the detection methods identify DNA samples that are not infected with IHHNV.
• the invention provides a method for detecting the presence of IHHNV in a sample comprising: (i) providing DNA from a sample suspected of containing
• IHHNV IHHNV
• IHHNV diagnostic primer sequences disclosed herein amplifying the DNA with at least one pair of IHHNV diagnostic primer sequences disclosed herein such that amplification products are generated; wherein the presence of amplification products confirms the presence of IHHNV.
• the invention provides a method for quantifying the amount of IHHNV in a sample comprising:
• FIG. 1A shows the melting curve for the IHHNV4 product and the actin internal sample control product formed by simultaneous PCR amplification of the IHHNV virus DNA and actin DNA, as described in Example 10.
• the melting temperature (Tm) values of the IHHNV and actin products are indicated on their corresponding melting curves.
• Figure 1 B shows the results of the agarose gel electrophoresis separation of samples containing the IHH NV4 product and the actin internal sample control product formed by simultaneous PCR amplification of the IHHNV virus DNA and actin DNA 1 as described in Example 10.
• the quantity of IHHNV and shrimp DNA is shown above each lane; "M” is a 100-bp DNA ladder.
• the following sequences conform with 37 CF. R. 1.821-1.825
• SEQ ID NOs: 1-8 are the nucleotide sequences of IHHNV diagnostic primers useful for detection of IHHNV.
• SEQ ID NOs:9-12 are the nucleotide sequences of synthetic IHHNV templates described in the General Methods Section of the Examples. These sequences are also the nucleotide sequences of amplification products obtained using pairs of IHHNV diagnostic primers disclosed herein.
• SEQ ID Nos:13-16 are the nucleotide sequences of internal sample control primers described in Example 10.
• SEQ ID Nos: 17 and 18 are the nucleotide sequences of fluorescently labeled probes.
• primers useful in assays for the detection of infectious hypodermal and hematopoietic necorsis virus IHHNV.
• the primers may be used in nucleic acid amplification methods as well as in hybridization assays for the efficient detection and quantification of virulent infectious hypodermal and hematopoietic necorsis virus.
• PCR Polymerase chain reaction
• IHHNV Infectious Hypodermal and Hematopoietic Necorsis Virus
• isolated IHHNV diagnostic primer sequence refers to a sequence corresponding to a portion of the IHHNV genome being diagnostic for the presence of IHHNV.
• an "isolated nucleic acid fragment” is a polymer of RNA or DNA that is single- or double-stranded, optionally containing synthetic, non-natural or altered nucleotide bases.
• An isolated nucleic acid fragment in the form of a polymer of DNA may be comprised of one or more segments of cDNA, genomic DNA or synthetic DNA.
• amplification product refers to the nucleic acid fragment that is produced during a primer directed amplification reaction.
• Typical methods of primer directed amplification include polymerase chain reaction (PCR) 1 ligase chain reaction (LCR), strand displacement amplification (SDA) 1 or other isothermal amplification processes.
• PCR methodology is selected, the replication composition would typically include, for example: deoxy nucleotide triphosphates, two primers with appropriate sequences, a thermostable DNA polymerase and proteins.
• the nucleic acid replication compositions would comprise, for example: a thermostable ligase (e.g., T. aq ⁇ aticus ligase), two sets of adjacent oligonucleotides (wherein one member of each set is complementary to each of the target strands), Tris- HCI buffer, KCI, EDTA, NAD 1 dithiothreitol and salmon sperm DNA (see for example, Tabor et al., Proc. Natl. Acad. ScL U.S.A., 82:1074-1078 (1985)).
• a thermostable ligase e.g., T. aq ⁇ aticus ligase
• two sets of adjacent oligonucleotides wherein one member of each set is complementary to each of the target strands
• Tris- HCI buffer KCI
• KCI KCI
• EDTA NAD 1 dithiothreitol
• salmon sperm DNA see for example, Tabor e
• primer refers to an oligonucleotide (synthetic or occurring naturally), which is capable of acting as a point of initiation of nucleic acid synthesis or replication along a complementary strand when placed under conditions in which synthesis of a complementary stand is catalyzed by a polymerase.
• thermal cycling refers to the entire pattern of changing temperature used during certain nucleic acid amplification methods, such as PCR and LCR. This process is common and well known in the art. See, for example, Sambrook, J., Fritsch, E. F. and Maniatis, T., Molecular Cloning: A Laboratory Manual, 2 nd ed., Cold Spring Harbor Laboratory Press: Cold Spring Harbor, NY (1989); and U.S. Patent No. 4,683,202 to Mullis et al. and U.S. Patent No. 4,683,195 to Mullis et al.
• PCR thermal cycling includes an initial denaturing step at high temperature, followed by a repetitive series of temperature cycles designed to allow template denaturation, primer annealing, and extension of the annealed primers by the polymerase.
• cycle threshold number also referred to herein as “CT” refers to the cycle number during thermal cycling at which the amount of fluorescence due to product formation reaches a fixed threshold value above a baseline value.
• probe refers to an oligonucleotide (synthetic or occurring naturally) that is significantly complementary to a target sequence, also referred to herein as a "fragment", (i.e., the sequence to be detected or a portion of the sequence to be detected) and forms a duplexed structure by hybridization with at least one strand of the target sequence.
• the probe can be labeled to facilitate detection, for example, using a fluorescent label or a ligand label.
• replication inhibitor moiety refers to any atom, molecule or chemical group that is attached to the 3' terminal hydroxyl group of an oligonucleotide that will block the initiation of chain extension for replication of a nucleic acid strand.
• examples include, but are not limited to, 3' deoxynucleotides (e.g., cordycepin), dideoxynucleotides, phosphate, ligands (e.g., biotin and dinitrophenol), reporter molecules (e.g., fluorescein and rhodamine), carbon chains (e.g., propanol), a mismatched nucleotide or polynucleotide, or peptide nucleic acid units.
• 3' deoxynucleotides e.g., cordycepin
• dideoxynucleotides phosphate
• ligands e.g., biotin and dinitrophenol
• reporter molecules e.g., fluorescein and
• non-participatory refers to the lack of participation of a probe or primer in a reaction for the amplification of a nucleic acid molecule.
• a non-participatory probe or primer is one that will not serve as a substrate for, or be extended by, a DNA polymerase.
• a "non-participatory probe” is inherently incapable of being chain extended by a polymerase. It may or may not have a replication inhibitor moiety.
• a nucleic acid molecule is "hybridizable" to another nucleic acid molecule, such as a cDNA, genomic DNA, or RNA, when a single stranded form of the nucleic acid molecule can anneal to the other nucleic acid molecule under suitable conditions of temperature and solution ionic strength.
• Hybridization and washing conditions are well known and exemplified in Sambrook, J., Fritsch, E. F. and Maniatis, T. Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press: Cold Spring Harbor, NY (1989), particularly Chapter 11 and Table 11.1 therein (entirely incorporated herein by reference).
• the conditions of temperature and ionic strength determine the "stringency" of the hybridization.
• low stringency hybridization conditions corresponding to a melting temperature (Tm) of 55 0 C
• Tm melting temperature
• Moderate stringency hybridization conditions correspond to a higher Tm, e.g., 40% formamide, with 5X or 6X SSC.
• Hybridization requires that the two nucleic acids contain complementary sequences, although depending on the stringency of the hybridization, mismatches between bases are possible.
• the appropriate stringency for hybridizing nucleic acids depends on the length of the nucleic acids and the degree of complementation, variables well known in the art.
• equations for calculating Tm have been derived (see Sarribrook et al., supra, 9.50-9.51).
• the length for a hybridizable nucleic acid is at least about 10 nucleotides.
• a minimum length for a hybridizable nucleic acid is at least about
• the temperature and wash solution salt concentration may be adjusted as necessary according to factors such as length of the probe.
• Gene refers to a nucleic acid fragment that expresses a specific protein, including regulatory sequences preceding (5 1 non-coding sequences) and following (3' non-coding sequences) the coding sequence.
• Native gene refers to a gene as found in nature with its own regulatory sequences.
• Chimeric gene refers to any gene that is not a native gene, comprising regulatory and coding sequences that are not found together in nature. Accordingly, a chimeric gene may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source, but arranged in a manner different than that found in nature.
• Endogenous gene refers to a native gene in its natural location in the genome of an organism.
• a “foreign” gene refers to a gene not normally found in the host organism, but that is introduced into the host organism by gene transfer. Foreign genes can comprise native genes inserted into a non-native organism, or chimeric genes.
• a “transgene” is a gene that has been introduced into the genome by a transformation procedure.
• the term “operably linked” refers to the association of nucleic acid sequences on a single nucleic acid fragment so that the function of one is affected by the other.
• a promoter is operably linked with a coding sequence when it is capable of effecting the expression of that coding sequence (i.e., that the coding sequence is under the transcriptional control of the promoter). Coding sequences can be operably linked to regulatory sequences in sense or antisense orientation.
• expression refers to the transcription and stable accumulation of sense (mRNA) or antisense RNA derived from the nucleic acid fragment of the invention. Expression may also refer to translation of mRNA into a polypeptide.
• Plasmid refers to an extra chromosomal element often carrying genes which are not part of the central metabolism of the cell, and usually in the form of circular double- stranded DNA molecules.
• Such elements may be autonomously replicating sequences, genome integrating sequences, phage or nucleotide sequences, linear or circular, of a single- or double-stranded DNA or RNA, derived from any source, in which a number of nucleotide sequences have been joined or recombined into a unique construction which is capable of introducing a promoter fragment and DNA sequence for a selected gene product along with appropriate 3' untranslated sequence into a cell.
• Transformation cassette refers to a specific vector containing a foreign gene and having elements in addition to the foreign gene that facilitate transformation of a particular host cell.
• Expression cassette refers to a specific vector containing a foreign gene and having elements in addition to the foreign gene that allow for enhanced expression of that gene in a foreign host.
• sequence analysis software refers to any computer algorithm or software program that is useful for the analysis of nucleotide or amino acid sequences.
• Sequence analysis software may be commercially available or independently developed. Typical sequence analysis software will include, but is not limited to, the GCG suite of programs (Wisconsin Package Version 9.0, Genetics Computer Group (GCG) 1 Madison, Wl) 1 BLASTP 1 BLASTN, BLASTX (Altschul et al., J. MoI.
• IHHNV is a major shrimp pathogen with a high mortality rate and a broad host range.
• the complete genome of IHHNV has been sequenced (Bonami et al., J. Gen. Virology 71 (Pt 11):657-2664 (1990); GenBank AF218266).
• the genome consists of single stranded DNA containing 4,075 bases and 3 open reading frames (ORFs).
• diagnostic primer sequences useful in a variety of assay formats for high sensitive detection of IHHNV. These primers are directed to regions of the IHHNV genome not previously used for IHHNV detection. Primer sequences were empirically identified using a series of "in silica” (i.e., computer-based) sequence analysis tools. In this process, a database was assembled containing all known IHHNV sequences. These sequences were first aligned and then analyzed for primer sites using
• Vector NTI software (InforMax Inc., Bethesda, MD) based on homology with other IHHNV sequences, a specified amplico ⁇ length, salt concentration, Tm (melting temperature), C+G content and freedom from hairpin and secondary structure parameters.
• Prospective primers were then screened against GenBank sequences. Those primers established to contain less than 5 bases of homology with other non-target gene sequences were selected for experimental investigation of PCR amplification efficiency and minimal primer-dimer formation. Primers showing both high amplification efficiency and minimal primer-dimer formation were selected for testing with a panel of DNA isolated from shrimp infected with various shrimp pathogens and DNA from shrimp certified to be disease-free. Those primers amplifying all IHHNV strains and showing no response to both DNA from shrimp infected with non- IHHNV pathogens and to DNA isolated from different species of certified disease free shrimp were selected as useful primers.
• primer sequences found to be useful in the detection of IHHNV and their location in the IHHNV genome are given in Table 1. These primers may be synthesized using standard phosphoramidite chemistry or may be purchased from companies such as Sigma Genosys (The Woodlands, TX).
• the primer sequences disclosed herein may be used in a variety of assay formats for the detection and quantification of IHHNV.
• the two most convenient formats rely on methods of nucleic acid hybridization or primer directed amplification methods such as PCR.
• Primer Directed Amplification Assay Methods In one embodiment, the present IHHNV diagnostic primer sequences may be used in primer directed nucleic acid amplification for the detection of the presence of IHHNV.
• a variety of primer directed nucleic acid amplification methods are well known in the art and are suitable for use with the primers disclosed herein.
• LCR nucleic acid replication compositions comprise, for example: a thermostable ligase (e.g., T.
• aquaticus ligase two sets of adjacent oligonucleotide primers (wherein one member of each set is complementary to each of the target strands), Tris-HCI buffer, KCI, EDTA, NAD 1 dithiothreitol and salmon sperm DNA.
• SDA methods are also well known in the art. An in depth discussion of SDA methodology is given by Walker et al. (Proc. Natl. Acad. ScL U.S.A., 89:392 (1992)).
• two oligonucleotide primers are used, each having regions complementary to only one of the stands in the target. After heat denaturation, the single-stranded target fragments bind to the respective primers which are present in excess. Both primers contain asymmetric restriction enzyme recognition sequences located 5' to the target binding sequences.
• Each primer-target complex cycles through nicking and polymerization/displacement steps in the presence of a restriction enzyme, a DNA polymerase and three deoxynucleotide triphosphates (dNTPs) and one deoxynucleotide ⁇ -thio triphosphate (dNTP[aS]).
• dNTPs deoxynucleotide triphosphates
• dNTP[aS] deoxynucleotide ⁇ -thio triphosphate
• the IHHNV diagnostic primer sequences disclosed herein and their complete complimentary sequences are used in pairs which are capable of priming a nucleic acid amplification reaction that amplifies a region within the IHHNV genome.
• Suitable primer pairs include, but are not limited to, SEQ ID NOs:1 and 2, SEQ ID NOs:3 and 4, SEQ ID NOs:5 and 6, SEQ ID NOs:7 and 8, and SEQ ID NOs:1 and 4.
• the two primers are mixed with the sample DNA, a mixture of four deoxynucleotide triphosphates (i.e., dATP, dCTP, dTTP, and dGTP), a thermostable DNA polymerase, such as Taq DNA polymerase, in a buffer solution.
• a thermostable DNA polymerase such as Taq DNA polymerase
• This mixture is then thermal cylcled using a thermal cycler instrument to amplify the desired target region.
• Thermal cyclers are commercially available from many sources (e.g., Applied Biosystems (Foster City, CA); Brinkmann (Westbury, NY); MJ Research (Waltham, MA); and Stratagene (La JoIIa, CA)).
• PCR thermal cycling includes an initial denaturing step at high temperature, followed by a repetitive series of temperature cycles designed to allow template de ⁇ aturation, primer annealing, and extension of the annealed primers by the polymerase.
• the samples are heated initially for about 2 to 10 minutes at a temperature of about 95 0 C to denature the double stranded DNA sample.
• the samples are denatured for about 10 to 60 seconds, depending on the samples and the type of instrument used.
• the primers are allowed to anneal to the target DNA at a lower temperature, from about 40 0 C to about 60 0 C for about 20 to 60 seconds.
• Extension of the primers by the polymerase is often carried out at a temperature ranging from about 60 0 C to about 72 0 C.
• the amount of time used for extension will depend on the size of the amplicon and the type of enzymes used for amplification and is readily determined by routine experimentation.
• the annealing step can be combined with the extension step, resulting in a two step cycling.
• Thermal cycling may also include additional temperature shifts in PCR assays.
• the number of cycles used in the assay depends on many factors, including the primers used, the amount of sample DNA present, and the thermal cycling conditions. The number of cycles to be used in any assay may be readily determined by one skilled in the art using routine experimentation.
• a final extension step may be added after the completion of thermal cycling to ensure synthesis of all amplification products.
• the amplified nucleotide sequence may be ligated to a suitable vector followed by transformation of a suitable host organism with said vector. One thereby ensures a more readily available supply of the amplified sequence.
• the amplified sequence or a portion thereof may be chemically synthesized for use as a nucleotide probe for use in a hybridization assay, as described below. In either situation the DNA sequence of the variable region may be established using methods such as the dideoxy method (Sanger, F. et al. Proc. Natl. Acad. Sci. 74:5463-5467 (1977)). The sequence obtained is used to guide the choice of the probe for the organism and the most appropriate sequence(s) is/are selected.
• DNA from the sample must be provided in a form that is capable of being amplified.
• the DNA must be free from the cell and sample materials and may be treated to eliminate proteins and other cell components.
• the DNA may be obtained from any suitable tissue, fluid or sample material including, but not limited to, shrimp tissue (e.g., gills, pleopods, hemolymph, muscle, tail, eyestalk, stomach, leg, and connective tissue), wash fluids, and pond water samples.
• the samples may be suspected of containing IHHNV for any number of reasons, including proximity to a known contaminant or otherwise, or may only be suspected of contamination by virtue of IHHNVs common presence in the commercial shrimp industry.
• a sample suspected of containing IHHNV can be any DNA sample described above.
• DNA may be extracted from a sample by homogenizing the sample material or tissue in Tris-HCI buffer containing NaCI, centrifuging to remove solid debris, and using the resulting supernatant fluid in the PCR reaction, as described by Nunan et al. (Mar. Biotechnol. 2(4):319-328 (2000)).
• the methods for isolating white spot syndrome viral DNA from various tissues described by Yoganandhan et al. (Aquaculture Research 34(12): 1093-1097 (2003)) and Kou et al. (U.S. Patent No. 6,190,862) may be used.
• the DNA may also be provided in a form which is suitable for amplification using a commercially available DNA isolation kit, such as the QIAamp DNA Mini Kit (Qiagen, Valencia CA) 1 or DNAzol Genomic DNA Isolation Reagent (Molecular Research Center, Inc., Cincinnati, OH).
• a commercially available DNA isolation kit such as the QIAamp DNA Mini Kit (Qiagen, Valencia CA) 1 or DNAzol Genomic DNA Isolation Reagent (Molecular Research Center, Inc., Cincinnati, OH).
• the DNA is then amplified with at least one pair of diagnostic primer sequences disclosed herein using a nucleic acid amplification method, as described above. A combination of different pairs of diagnostic primer sequences may also be used.
• PCR is used to amplify the DNA.
• test results can be misinterpreted due to reagent failure, procedural errors, and instrument malfunction. Additionally, problems arise due to the presence of inhibitory substances in the sample materials or degradation of the sample DNA or RNA during sample processing and nucleic acid recovery. To overcome these problems, internal control tests can be performed in combination with the IHHNV assay to alert users to these types of errors and to aid in quantification of test results.
• ITC internal template control
• ISC internal sample control
• the internal sample control can be a DNA or RNA gene sequence conserved or consistently present in sample materials (e.g. shrimp tissue and hemolymph).
• the primers used to amplify the ISC target DNA or RNA are chosen so that they do not amplify IHHNV DNA and the IHHNV test primers are chosen so that they do not amplify the internal sample control DNA or RNA targets. In this way, the ISC and IHHNV targets amplify independently.
• both the ISC and the IHHNV targets are processed using the same reagents and conditions.
• both target templates are amplified using the same reagents and reaction conditions. Because the ISC template and primers are present in the test samples, ISC product should be produced during amplification.
• the ISC product is not formed, it is an indication that the test chemistry did not function correctly and the IHHNV test results are incorrect and should not be relied on. If the correct ISC product formation occurs, it indicates that the test chemistry worked correctly, and the IHHNV sample processing and test reactions are assumed to have functioned correctly so that the IHHNV test can be more accurately interpreted.
• ISC primers can be selected from gene sequences of genes coding for structural proteins, metabolic enzymes or ribosomal products of the pathogen host species which are subject to IHHNV infections.
• the ISC primers can be gene sequences derived from the shrimp actin gene, or 18S, 23S or 5S ribosomal genes of shrimp, or other constitutive genes.
• Suitable examples of ISC primer pairs include, but are not limited to, SEQ ID NOs: 13, 14, and SEQ ID NOs: 15, 16, derived from the Penaeus monodon actin 1 gene (GenBank AF100986), as shown in Table 2.
• At least one pair of ISC primers is included in the nucleic acid amplification reagent mixture in order to produce an internal sample control product in the amplification reaction.
• the at least one pair of ISC primers is selected from the group consisting of SEQ ID NOs:13,14, and SEQ ID NOs:15,16.
• an internal template control ITC
• Primer requirements for the ITC are similar to those of the ISC primers with the exception that both the ITC template and primers are added to the amplification reagent mixture.
• the ITC primers are chosen so that they do not amplify genomic DNA or RNA from the test species, such as shrimp, which are subject to IHHNV.
• the ITC template is added at a known concentration so that the copy number per reaction is known. Because the ITC template is included in the amplification reagent mixture, the ITC product is produced during amplification. The amount of ITC product will vary from reaction to reaction depending on the amplification efficiency of the reaction and other variables. Since these same variables also affect the IHHNV DNA amplification, the amount of IHHNV product produced will be proportionately related to the amount of the ITC product produced in the reaction.
• the copy number of the IHHNV template in the assay can be inferred from the proportionality between the ITC originally added, the ITC product formed, and the IHHNV product produced.
• Relative product formation can be determined in CT units when labeled internal probes are used or by the derivative of the melting curves at the products' respective melting temperature.
• the ITC primer sequences can be rationally designed or derived from gene sequences from non-test species such as other viruses or genes from plants and animals which are not present in the test samples. In this way, sample materials do not contain other DNA or RNA which could be amplified by the ITC primers.
• At least one internal template control and at least one pair of ITC primers are included in the nucleic acid amplification reagent mixture in order to produce at least one ITC product in the amplification reaction.
• detection methods include, but are not limited to, standard non-denaturing gel electrophoresis (e.g., acrylamide or agarose), denaturing gradient gel electrophoresis, temperature gradient gel electrophoresis, capillary electrophoresis, and fluorescence detection.
• Fluorescence detection methods provide rapid and sensitive detection of amplification products. Fluorescence detection also provides the capability of real-time detection, wherein the formation of amplification products is monitored during the thermal cycling process. Additionally, the amount of the initial target may be quantified using fluorescence detection. Fluorescence detection may be done by adding a nucleic acid- binding fluorescent agent to the reaction mixture either before or after the thermal cycling process.
• the nucleic acid-binding fluorescent agent is an intercalating dye that is capable of non-covalent insertion between stacked base pairs in the nucleic acid double helix.
• non-intercalating nucleic acid-binding fluorescent agents are also suitable.
• Non-limiting examples of nucleic acid-binding fluorescent agents useful in the present disclosure include:
• nucleic acid-binding fluorescent agent available from Molecular Probes; Eugene, OR.
• Addition of the nucleic acid-binding fluorescent agent to the reaction mixture prior to thermal cycling permits monitoring of the formation of amplification products in real-time, as described by Higuchi (U.S. Patent No. 5,994,056).
• Thermal cyclers capable of real-time fluorescence measurements are commercially available from companies such as Applied Biosystems (Foster City, CA), MJ Research (Waltham, MA) 1 and Stratagene (La JoIIa, CA).
• confirmation of the amplification product can be assessed by determining the melting temperature of the product using methods know in the art, for example, by generating a melting curve using fluorescence measurement.
• Fluorescence detection of amplification products may also be accomplished using other methods known in the art, such as the use of a fluorescently labeled probe.
• the probe comprises a complimentary sequence to at least a portion of the amplification product.
• probes examples include TaqMan probes (Applied Biosystems) and Molecular Beacons (Goel et al., J. Appl. Microbiol. 99(3):435-442 (2005)).
• gene sequences for the construction of fluorescently labeled probes for use with the IHHNV primers disclosed herein can be selected by analysis of the IHHNV genes and test amplic ⁇ ns using commercially available analysis software such as Primer Express® v2.0 (Applied BioSystems Inc., Foster City California), as described in detail in Example 11 below. Probe sequences are selected to fall within the proximal ends of the specific IHHNV test amplicons. Suitable probe sequences include, but are not limited, to the sequences set forth in SEQ ID NOs: 17 and 18.
• the probes may be fluorescently labeled using methods known in the art, such as those described below for labeling hybridization probes.
• probes can be dual labeled.
• the 5' end of the probe can be labeled with a fluorophore, such as 6FAM TM (Applied BioSystems)
• the 3' end can be labeled with a quencher dye, such as 6- carboxytetramethylrhodamine (TAMRA).
• TAMRA 6- carboxytetramethylrhodamine
• the 3'end can be labeled with a quencher dye and a minor groove binder complex.
• Fluorescently labeled probes may be obtained from commercial sources such as Applied BioSystems.
• the invention provides a method for quantifying the amount of IHHNV in a sample.
• DNA is provided from a sample suspected of containing IHHNV 1 as described above.
• the DNA is amplified with at least one pair of the oligonucleotide primers disclosed herein by thermal cycling between at least a denaturing temperature and an extension temperature in the presence of a nucleic acid-binding fluorescent agent or a fluorescently labeled probe.
• the amount of fluorescence generated by the nucleic acid-binding fluorescent agent or the fluorescently labeled probe is measured during thermal cycling.
• a cycle threshold number is determined at which the amount of fluorescence generated by the nucleic acid-binding fluorescent agent or the fluorescently labeled probe reaches a fixed threshold value above a baseline value.
• the cycle threshold number is referred to herein as the CT number or value.
• the CT number can be determined manually or determined automatically by the instrument.
• the baseline fluorescence is determined for each sample during the initial amplification cycles.
• a mathematical algorithm is then employed to establish what a statistically significant change in fluorescence would need to be for the fluorescence signal to be above the background.
• the cycle number at which the florescence exceeds this threshold is referred to as the CT number.
• the CT number is inversely related to the initial amount of IHHNV in the sample.
• the amount of IHHNV originally present in the sample can be calculated by comparing the cycle threshold number determined for the IHHNV in the sample with a standard curve of the cycle threshold number versus the logarithm of template concentration determined using standard solutions of known concentration, as is well known in the art.
• the basic components of a nucleic acid hybridization test for IHHNV include a DNA probe, a sample suspected of containing IHHNV, and a specific hybridization method.
• Probes of the present invention are single stranded nucleic acid sequences which are complementary to the nucleic acid sequences to be detected and are "hybridizable" thereto.
• the probe length can vary from as few as 5 bases to several kilobases and will depend upon the specific test to be done. Only part of the probe molecule need be complementary to the nucleic acid sequence to be detected. In addition, the complementarity between the probe and the target sequence need not be perfect.
• the DNA probes disclosed herein are derived from the IHHNV diagnostic primer sequences described above.
• the phrase "derived from the IHHNV diagnostic primer sequences” means that the DNA probes can be the IHHNV diagnostic primer sequences, the amplification product sequences obtained therefrom using a nucleic acid amplification method, portions of the IHHNV diagnostic primer sequences or the amplification product sequences, or the complete complementary sequences of any of the aforementioned sequences.
• portion refers to any part of the IHHNV diagnostic primer sequences or the amplification products obtained therefrom that is less than the complete sequence.
• the length of the portion for use as a probe is at least about 15 bases, more preferably, at least about 20 bases.
• DNA probes derived from the IHHNV diagnostic primer sequences include the IHHNV diagnostic primer sequences given as SEQ ID NOs: 1-8, the amplification product sequences given as SEQ ID NOs:9, 10, 11 , and 12, and the complete complimentary sequences of SEQ ID NOs: 1-12.
• the probe may be labeled to facilitate detection.
• Methods of attaching labels to nucleic acid probes are well known in the art.
• the probe can be labeled during synthesis by incorporation of labeled nucleotides.
• probe labeling can be done by nick translation or end-labeling.
• the label may comprise a fluorophore for fluorescence detection, or a ligand, such as biotin, which is detected using an enzyme-labeled binding molecule that binds to the ligand (e.g., enzyme-labeled streptavidin) subsequent to hybridization.
• DNA is provided from the sample, as described above.
• the sample DNA is made available to contact the probe before any hybridization of probe and target molecule can occur.
• the DNA must be free from the cell and placed under the proper conditions before hybridization can occur.
• a variety of methods of nucleic acid purification, such as phenol-chloroform extraction, are known to those skilled in the art (Maniatis, supra). Additionally, kits are available from
• DNA extraction and purification e.g., IsoQuick Nucleic Acid Extraction Kit (MicroProbe Corp., Bothell, WA); and QIAamp DNA Mini Kit (Qiagen, Valencia CA)).
• Pre-hybridization purification is particularly useful for standard filter hybridization assays.
• hybridization assays may be conducted directly on cell lysates, without the need to extract the nucleic acids. This eliminates several steps from the sample-handling process and speeds up the assay.
• a chaotropic agent is typically added to the cell lysates prepared as described above. The chaotropic agent stabilizes nucleic acids by inhibiting nuclease activity. Furthermore, the chaotropic agent allows sensitive and stringent hybridization of short oligonucleotide probes to DNA at room temperature (Van Ness and Chen, Nucl. Acids Res. 19:5143-5151 (1991)).
• Suitable chaotropic agents include guanidinium chloride, guanidinium thiocyanate, sodium thiocyanate, lithium tetrachloroacetate, sodium perchlorate, rubidium tetrachloroacetate, potassium iodide, and cesium trifluoroacetate, among others.
• the chaotropic agent is present at a final concentration of about 3 M. If desired, one can add formamide to the hybridization mixture, typically 30 to 50% by volume.
• Hybridization methods are well defined and include solution (i.e., homogeneous) and solid phase (i.e., heterogeneous) hybridization methods.
• the sample DNA is probed (i.e. contacted under conditions which will permit nucleic acid hybridization) with a probe derived from the IHHNV diagnostic primer sequences disclosed herein.
• the probe and sample nucleic acids must be in contact for a long enough time such that any possible hybridization between the probe and sample nucleic acid may occur.
• the concentration of probe or target in the mixture will determine the time necessary for hybridization to occur. The higher the probe or target concentration, the shorter the hybridization incubation time needed.
• hybridization solutions can be employed. Typically, these may comprise from about 20 to 60% by volume, preferably 30%, of a polar organic solvent.
• a common hybridization solution employs about 30 to 50% by volume formamide, about 0.15 to 1 M sodium chloride, about 0.05 to 0.1 M buffers, such as sodium citrate, Tris-HCI, PIPES or HEPES (pH range about 6-9), about 0.05 to 0.2% detergent, such as sodium dodecylsulfate (SDS), between 0.5 to 20 mM EDTA, FICOLL (Amersham Bioscience Inc., Piscataway, NJ) (molecular weight of about 300-500 kilodaltons), polyvinylpyrrolidone (molecular weight of about 250-500 kilodaltons), and serum albumin.
• SDS sodium dodecylsulfate
• unlabeled carrier nucleic acids from about 0.1 to 5 mg/mL, fragmented nucleic DNA (e.g., calf thymus or salmon sperm DNA, or yeast RNA), and optionally from about 0.5 to 2% weight per volume glycine.
• Other additives may also be included, such as volume exclusion agents which include a variety of polar water-soluble or swellable agents (e.g., polyethylene glycol), anionic polymers (e.g., polyacrylate or poly methylacry late), and anionic saccharidic polymers (e.g., dextran sulfate).
• Nucleic acid hybridization is adaptable to a variety of assay formats. One of the most suitable is the sandwich assay format.
• the sandwich assay is particularly adaptable to hybridization under non- denaturing conditions.
• a primary component of a sandwich-type assay is a solid support.
• the solid support has adsorbed to it or covalently coupled to it, an immobilized nucleic acid capture probe that is unlabeled and is complementary to one portion of the sample DNA sequence.
• Probes particularly useful in the present invention are those derived from the present IHHNV diagnostic sequences, as described above.
• the captured DNA is detected using a second probe that is labeled, as described above, and is complimentary to a different portion of the sample DNA sequence.
• the label may be detected using methods known in the art (e.g., fluorescence, chemiluminescence, binding pair enzyme assay and the like).
• Hybridization methods may also be used in combination with nucleic acid amplification methods, such as PCR.
• the instant IHHNV diagnostic sequences may be used as 3 1 blocked detection probes in either a homogeneous or heterogeneous assay format.
• a probe generated from the instant sequences may be 3' blocked or non-participatory and will not be extended by, or participate in, a nucleic acid amplification reaction.
• the probe incorporates a label that can serve as a reactive ligand that acts as a point of attachment for the immobilization of the probe/analyte hybrid or as a reporter to produce detectable signal.
• genomic DNA isolated from a sample suspected of harboring the IHHNV is amplified by standard primer-directed amplification protocols in the presence of an excess of the 3' blocked detection probe to produce amplification products. Because the probe is 3 1 blocked, it does not participate or interfere with the amplification of the target. After the final amplification cycle, the detection probe anneals to the relevant portion of the amplified DNA and the annealed complex is then captured on a support through the reactive ligand.
• the instant probe is versatile and may be designed in several alternate forms.
• the 3 1 end of the probe may be blocked from participating in a primer extension reaction by the attachment of a replication inhibiting moiety.
• Typical replication inhibitor moieties include, but are not limited to, dideoxynuleotides, 3 1 deoxynucleotides, a sequence of mismatched nucleosides or nucleotides, 3 1 phosphate groups and chemical agents, such as biotin, dinitrophenol, fluorescein, rhodamine, and carbon chains.
• the replication inhibitor is covalently attached to the 3' hydroxy group of the 3 1 terminal nucleotide of the non-participatory probe during chemical synthesis, using standard cyanoethyl phosphoramidite chemistry.
• This process uses solid phase synthesis chemistry in which the 3 1 end is covalently attached to an insoluble support (controlled pore glass, or "CPG") while the newly synthesized chain grows on the 5' terminus.
• CPG controlled pore glass
• 3-deoxyribonucleotides are the preferred replication inhibitors.
• Cordycepin (3-deoxyadenosine) is most preferred. Since the cordycepin will be attached to the 3' terminal end of the probe, the synthesis is initiated from a cordycepin covalently attached to CPG, 5-dimethoxytrityl- N-benzoyl-3-deoxyadenosine (cordycepin), 2-succinoyl-long chain alkylamino-CPG (Glen Research, Sterling, VA).
• the dimethoxytrityl group is removed and the initiation of the chain synthesis starts at the deprotected 5 1 hydroxyl group of the solid phase cordycepin.
• the oligonucleotide probe is cleaved off the solid support leaving a free 2 1 hydroxyl group on the 3-terminally attached cordycepin.
• Other reagents can also be attached to the 3' terminus during the synthesis of the non-participatory probe to serve as replication inhibitors. These include, but are not limited to, other 3-deoxyribonucleotides, biotin, dinitrophenol, fluorescein, and digoxigenin. CPG supports, derivatized with each of these reagents, are available from commercial sources (e.g., Glen Research, Sterling, VA; and CLONTECH Laboratories, Palo Alto, CA).
• asymmetric amplification may be used to generate a strand complementary to the detection probe.
• Asymmetric PCR conditions for producing single-stranded DNA are similar to the conditions described above for PCR; however, the primer concentrations are adjusted so that one primer is in excess and the other primer is limiting. It is contemplated that this procedure would increase the sensitivity of the method. This improvement in sensitivity would occur by increasing the number of available single strands for binding with the detection probe. Assessment of Infection Risk and DNA Damage or IHHNV Inactivation
• the methods for detecting the presence of and quantifying the amount of IHHNV in a sample disclosed herein may be used to assess the extent of DNA damage or IHHNV inactivation.
• the methods disclosed herein may be used in combination with a chemical treatment to improve the health and grow out of shrimp. Specifically, during production and grow-out, the shrimp, samples taken from the production facilities, or samples taken from the shrimp's environment may be sampled and tested for the presence of IHHNV using the methods disclosed herein. If IHHNV is found, the facilities and/or the shrimp can be treated to kill or control the virus. Because of the high sensitivity of the test, IHHNV can be detected early, before devastation and loss of the crop. Thus, use of the methods disclosed herein in combination with chemical intervention can improve production efficiency and yield.
• Examples of chemical treatments include, but are not limited to, oxidative
• ® disinfectants such as Virkon S disinfectant (a registered trademark of E.I. Du Pont de Nemours and Co.), peracetic acids, hydrogen peroxide, permanganate, potassium monopersulfate, hypochlorous acid, hypochlorite, iodine and the like; probiotics, immunostimulants, feed supplements, and recombinant protein/nucleic acids that prevent viral host binding.
• the primers disclosed herein may be used in various combinations to ascertain the integrity and extent of damage to the viral genome resulting from chemical treatment.
• the forward primer of IHHNV1 F (SEQ ID NO:1) and the reverse primer of IHHNV2R (SEQ ID NO:4) may be used in combination to produce an amplification product of 480 bases.
• This longer product can form only if the viral genome remains intact and undamaged. Therefore, by comparing the ratio of the smaller products (SEQ ID NO:9 or SEQ ID NO: 10) to the longer product formed during amplification (or the absence of the longer product), the extent of viral genome damage resulting from chemical treatment or intervention can be assessed. This can aid in establishing the efficacy of chemical treatment or intervention.
• SEQ ID NO:1 or SEQ ID NO:8 may be used in combination with other primers disclosed herein to interrogate the integrity of longer segments of the IHHNV genome. Detection Kits
• the invention provides a kit for the detection of IHHNV based on a nucleic acid amplification method.
• the kit comprises at least one pair of IHHNV diagnostic primer sequences, as described above. Additionally, the kit may further comprise at least one of the following reagents: a thermostable DNA polymerase, a mixture of four different deoxynucleotide triphosphates, a nucleic acid-binding fluorescence agent, at least one pair of internal sample control primers, at least one internal template control and at least one pair of internal template control primers, and a probe comprising a complementary sequence to a portion of at least one region of nucleic acid within the IHHNV genome which is capable of being amplified with the IHHNV diagnostic primer sequences contained in the kit.
• the primers and other reagents of the kit may be in various forms, such as a liquid, dried, or tablet and may be present in any suitable container or multiple containers, such as vials, tubes, and the like.
• the invention provides a kit for the detection of IHHNV based on a sandwich assay hybridization method.
• This kit comprises a first component for the collection of samples from a shrimp or other crustacean suspected of having contracted the IHHNV and buffers for the disbursement and lysis of the sample.
• a second component includes media in either dry or liquid form for the hybridization of target and probe nucleic acids, as well as for the removal of undesirable and non-hybridized forms by washing.
• a third component includes a solid support (e.g., dipstick, bead, and the like) upon which is fixed (or to which is conjugated) unlabeled nucleic acid probe(s) that is (are) derived from the isolated IHHNV diagnostic primer sequences disclosed herein.
• a fourth component contains labeled probe that is complementary to a second and different region of the same DNA strand to which the immobilized, unlabeled nucleic acid probe of the third component is hybridized.
• the labeled probe may also be derived from the isolated IHHNV diagnostic primer sequences disclosed herein.
• kits and reagents were purchased from the following vendors: SYBR ® Green PCR Master Mix (Applied Biosystems, Foster City, CA; Catalog No. 4309155); and QIAamp DNA Mini Kit (Qiagen, Valencia, CA; Catalog No. 51304).
• All shrimp DNA samples were obtained from Donald V. Lightner, Department of Veterinary Science and Microbiology, The University of Arizona, Arlington, AZ 85721, USA. These included DNA samples from certified disease free shrimp (SPF) and infected shrimp containing Penaeus monodon-type baculoviruses (MBV), Taura syndrome virus (TSV), white spot syndrome virus (WSSV), yellow head virus of P. monodon (YHV), Infectious Hypodermal and Hematopoietic Necrosis virus (IHHNV) and Infectious Myonecrosis virus (IMNV).
• SPF certified disease free shrimp
• MMV Penaeus monodon-type baculoviruses
• TSV Taura syndrome virus
• WSSV white spot syndrome virus
• YHV yellow head virus of P. monodon
• IHHNV Infectious Hypodermal and Hematopoietic Necrosis virus
• IMNV Infectious Myonecrosis virus
• IHHNV templates were prepared from the Infectious Hypodermal and Hematopoietic Necrosis Virus (IHNNV) DNA genome (GenBank Accession Number AF218266; Bonami, J. R. et al., J. Gen. Virology 71 (Pt 11):657-2664 (1990)) and were synthesized using standard phosphoramidite chemistry or purchased commercially (Sigma Genosys Company, The Woodlands, TX). The DNA concentration and copy number of the synthetic template targets and samples were measured spectrophotometrically at 260 nm (OD 2 6o)- The templates were diluted to specific copy numbers in purified water and were used as the positive controls and standards for assay quantification. Table 3 displays the genome locations, sequence identification, and lengths of the template targets. The sequences of the primers useful for IHHNV detection are given as SEQ ID NOs:1-8.
• Template standards were prepared by 10 fold serial dilutions of the synthetic IHHNV templates (described above) in DNase free water.
• template concentrations of the standards ranged from 10 7 to 0
• a master mix was prepared by adding 25 ⁇ L of the SYBR
• a template standard was first added to the PCR reaction well and then 45 ⁇ L of the master mix was added.
• the reactions were then thermal cycled for 40 cycles using a temperature program of 95 0 C for 15 sec and 60 0 C for 1 min with an initial denaturing step of 95 0 C for 10 min.
• the amplifications were carried out in a MicroAmp optical 96-well reaction plate using the ABI PRISM 7900 thermal cycler (Applied Biosystems, Foster City, CA). During each cycle,
• PCR product formation was analyzed by agarose gel electrophoresis using 4% agarose Egels (Invitrogen Life Technologies, Carlsbad, CA; Cat No. G6018-02) and the gel manufacture's protocols.
• CT Amplification
• amplicon product formation were, respectively, inversely and directly proportional to the logarithm of the starting template concentration.
• IHHNV was used.
• the total DNA (347 ng/ ⁇ L) was serially diluted in purified water and used to provide a series of samples ranging in DNA concentration from 1 ng/ ⁇ L to 1 fg/ ⁇ L of total DNA.
• Negative controls included a water control containing no template and two DNA shrimp samples (50 ng/rxn) from two strains of non-infected (SPF) shrimp (Litopenaeus vannamei and Penaeus monodon).
• the diluted samples were then amplified using one of the primer pairs (see Table 5) and the same amplification, master mix, thermal cycling conditions and instrument stated in Examples 1-4.
• the CT value for each diluted DNA sample was then assessed from the PCR amplification reactions.
• the copies of viral genome in the samples were then estimated from the CT value and the slope of the standard CT versus log template concentration plot.
• the PCR products were also analyzed by agarose gel electrophoresis, as described in Examples 1-4.
• the results are summarized in Table 5.
• the IHHNV copy number per reaction is given as the mean of three replicates along with the 95% confidence interval. The results indicate that all of the primer sets produced the correct amplicon product size from the infected shrimp DNA and detected IHHNV DNA in the infected shrimp samples.
• the detection limits ranged from about 2 copies/rxn to about 40 copies/rxn of the viral genome, depending on the primer pair used. No amplification products were detected in the water control sample or the two SPF shrimp samples. The results obtained with the negative control samples demonstrate that the assay is non-responsive to non-viral DNA from the two shrimp strains tested.
• the purpose of this Example was to demonstrate that the primers disclosed herein amplify DNA from IHHNV strains from different geographical areas of the World, but do not amplify DNA or RNA of shrimp infected with other shrimp pathogens.
• DNA from shrimp infected with other shrimp pathogens was used. Specifically, DNA samples isolated from shrimp infected with IHHNV strains from different geographical regions (Hawaii, Philippines, Thailand, Panama, Mexico Mozambique and Madagascar) along with non-IHHNV shrimp viruses (MBV, WSSV, YHV and IMNV) were tested using the primers and PCR method described in Examples 5- 8. All IHHNV strains were detected with similar detection limits as the strain described in Examples 5-8. No PCR amplification was observed when testing the non-IHHNV infected shrimp DNA samples.
• IHHNV primers disclosed herein can be used in combination with internal sample control (ISC) primers to produce an ISC product in addition to the IHHNV product.
• ISC primers independently amplify sample DNA and do not interfere with the amplification of IHHNV DNA.
• the presence of the ISC product provides a marker that can be used as an indication that sample DNA of sufficient quantity and quality had been recovered for testing.
• ISC primers were derived from the Penaeus monodon actin 1 gene sequence (GenBank: AF 100986). In order to promote preferential amplification of the IHHNV amplicon, the ISC primers were designed to amplify a DNA fragment that was larger than the target IHHNV amplicons.
• the ISC primer pair sequences are given as SEQ ID NOs: 13, 14, and SEQ ID NOs: 15, 16 (see Table 2).
• Samples containing IHHNV and shrimp acitn DNA were prepared by 10-fold serial dilutions of a genomic DNA preparation from a IHHNV infected shrimp (Penaeus monodon) with DNase free water. The DNA content of the samples ranged from 0.1 ng to 0.1 pg per reaction. Genomic shrimp DNA (10 ng) from a non-infected shrimp was then added to each IHHNV sample and to negative control samples containing no IHHNV DNA.
• a master PCR mix was prepared by combining 15 ⁇ Ureaction of the SYBR ® Green PCR Master Mix (Applied Biosystems, Foster City, CA; Catalog No. 4309155) with a volume of primer stock solutions (20 ⁇ M for each of the IHHNV primers and 10 ⁇ M for each of the actin primers) sufficient to give a final concentration of 125 nM for each of the IHHNV4 forward and reverse primers (SEQ ID N0s:7 and 8, respectively) and 32 nM for each of the actin2 forward and reverse primers (SEQ ID NOs:13 and 14). DNase free water was added to make up a final volume of 25 ⁇ LVreaction. The master mix was maintained on ice until use.
• FIGS 1A and 1 B The results obtained using ISC primers ActinF2 (SEQ ID NO:13) and ActinR2 (SEQ ID NO:14) are shown in Figures 1A and 1 B, which demonstrate the simultaneous amplification of both template targets.
• the specific IHHNV DNA produced a 116 bp product with a melting temperature of 80 0 C.
• the IHHNV product and actin internal control products were detected by both melting curve analysis ( Figure 1A) and gel electrophoresis (Figure 1 B) based on these size and melting temperature differences.
• EXAMPLE 11 Real Time Detection of IHHNV DNA using a Fluorescently Labeled Probe This Example demonstrates that the IHHNV primers disclosed herein can be used in combination with a fluorescently labeled probe for real time detection and quantification of IHHNV.
• probe sequences were chosen to fall within the proximal ends of the specific IHHNV test amplicons and were 50 to 110 bases in length, depending on the size and sequence of the amplicon. Preference for the probe sequences was given to regions with G/C content of 30 to 80% and with higher C than G content, and with no 5' G. Generally, probe sequences were selected having a Tm of 8 to 10 0 C above the respective Tm of the test primers. Probes sequences which cross-hybridized to other species were not selected for use. The probe sequences selected to meet these criteria are listed in Table 6.
• the probe sequences were dual labeled. Two different labeling approaches were employed. The 5 1 end of the probes were labeled with a fluorophore (6FAMTM, Applied Biosystems). The 3' end was labeled either with a quencher dye or in the case of minor grove binding (MGB) probe, the 3' end was labeled with a quencher dye and a minor grove binder complex.
• the labeled probes were prepared and purchased commercially from Applied BioSystems. The data presented below was obtained using the IHHNV4PT probe (SEQ ID NO:18). It is anticipated that the IHHNV4PM probe (SEQ ID NO:17) may be used in a similar manner.
• FAM 6FAM TM reagent
• Applied Biosystems 2MGB is MGB TM
• 3TAMRA is 6-carboxytetramethylrhodamine
• Template standards were prepared by 10-fold serial dilutions of the synthetic IHHNV templates (described above) in DNase free water. Generally, template concentrations of the standards ranged from 10 7 to 0 copies/ ⁇ L.
• a master mix was prepared by combining 25 ⁇ L/reaction of the TaqMan® Universal Master Mix (Applied Biosystems, Foster City, CA; Catalog No. 4326708) with a volume of primer stock solutions (20 ⁇ M for each of the IHHNV primers) sufficient to give a final concentration of 125 nM for each of the IHHNV forward and reverse primers, as shown in Table 7, a volume of the probe stock solution to give a final concentration of 50 nM and enough DNase free water to make up a final volume of 45 ⁇ L/reaction.
• the master mix was maintained on ice until use.
• PCR reaction well For each reaction, 5 ⁇ L of template standard and then 45 ⁇ L of the master mix were added to each PCR reaction well. The reactions were then thermal cycled for 40 cycles using a temperature program of 95 0 C for 15 sec and 60 0 C for 1 min with an initial denaturing step of 95 0 C for 10 min. The amplifications were carried out in a MicroAmp optical 96-well reaction plate using the ABI PRISM 7900 thermal cycler (Applied Biosystems, Foster City, CA). During each cycle, PCR product formation was detected by monitoring the increase in fluorescence arising from the fluorescently labeled probe.
• CT Amplification
• amplicon product formation were, respectively, inversely and directly proportional to the logarithm of the starting template concentration.

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