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Li Y, Xu L, Jiao D, Zheng Z, Chen Z, Jing Y, Li Z, Ma Z, Feng Y, Guo X, Wang Y, He Y, Zheng H, Xiao S. Genomic similarity and antibody-dependent enhancement of immune serum potentially affect the protective efficacy of commercial MLV vaccines against NADC30-like PRRSV. Virol Sin 2023; 38:813-826. [PMID: 37660949 PMCID: PMC10590703 DOI: 10.1016/j.virs.2023.08.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Accepted: 08/28/2023] [Indexed: 09/05/2023] Open
Abstract
Porcine reproductive and respiratory syndrome (PRRS) is one of the most significant diseases affecting the pig industry worldwide. The PRRSV mutation rate is the highest among the RNA viruses. To date, NADC30-like PRRSV and highly pathogenic PRRSV (HP-PRRSV) are the dominant epidemic strains in China; however, commercial vaccines do not always provide sufficient cross-protection, and the reasons for insufficient protection are unclear. This study isolated a wild-type NADC30-like PRRSV, SX-YL1806, from Shaanxi Province. Vaccination challenge experiments in piglets showed that commercial modified live virus (MLV) vaccines provided good protection against HP-PRRSV. However, it could not provide sufficient protection against the novel strain SX-YL1806. To explore the reasons for this phenomenon, we compared the genomic homology between the MLV strain and HP-PRRSV or NADC30-like PRRSV and found that the MLV strain had a lower genome similarity with NADC30-like PRRSV. Serum neutralization assay showed that MLV-immune serum slightly promoted the homologous HP-PRRSV replication and significantly promoted the heterologous NADC30-like PRRSV strain replication in vitro, suggesting that antibody-dependent enhancement (ADE) might also play a role in decreasing MLV protective efficacy. These findings expand our understanding of the potential factors affecting the protective effect of PRRSV MLV vaccines against the NADC30-like strains.
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Affiliation(s)
- Yang Li
- State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730046, China
| | - Lele Xu
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Dian Jiao
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Zifang Zheng
- State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730046, China
| | - Zhihao Chen
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Yang Jing
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Zhiwei Li
- State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730046, China; College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Zhiqian Ma
- State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730046, China
| | - Yingtong Feng
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Xuyang Guo
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Yumiao Wang
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Yuan He
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Haixue Zheng
- State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730046, China
| | - Shuqi Xiao
- State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730046, China.
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Kibenge F, Kibenge M. Orthomyxoviruses of Fish. AQUACULTURE VIROLOGY 2016. [PMCID: PMC7173593 DOI: 10.1016/b978-0-12-801573-5.00019-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
The family Orthomyxoviridae is well known for containing influenza viruses with a segmented RNA genome that is prone to gene reassortment in mixed infections (known as antigenic shift) resulting in new virus subtypes that cause pandemics, and cumulative mutations (known as antigenic drift), resulting in new virus strains that cause epidemics. This family also contains infectious salmon anemia virus (ISAV) and tilapia lake virus (TiLV), which are a unique orthomyxoviruses that infect fish and is unable to replicate above room temperature (24°C). This chapter describes the comparative virology of members in the family Orthomyxoviridae in general, helping to understand the emergent teleost orthomyxoviruses, ISAV and TiLV. The most current information on virus–host interactions of the fish orthomyxoviruses, particularly ISAV, as they relate to variations in virus structure, virulence, persistence, host range and immunological aspects is presented in detail.
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Kavaliauskis A, Arnemo M, Kim SH, Ulanova L, Speth M, Novoa B, Dios S, Evensen Ø, Griffiths GW, Gjøen T. Use of Poly(I:C) Stabilized with Chitosan As a Vaccine-Adjuvant Against Viral Hemorrhagic Septicemia Virus Infection in Zebrafish. Zebrafish 2015; 12:421-31. [PMID: 26509227 DOI: 10.1089/zeb.2015.1126] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
There is an urgent need for more efficient viral vaccines in finfish aquaculture worldwide. Here, we report the use of poly(I:C) stabilized with chitosan as an adjuvant for development of better finfish vaccines. The adjuvant was co-injected with inactivated viral hemorrhagic septicemia virus (VHSV) (CSpIC+iV vaccine) in adult zebrafish and its efficiency in protection against VHSV infection was compared to a live, attenuated VHS virus vaccine (aV). Both free and stabilized poly(I:C) were strong inducers of an antiviral state, measured by transcriptional activation of the genes of viral sensors: toll-like receptors, interferons, and interferon-stimulated genes, such as MXa within 48 h after injection. Both the CSpIC+iV and the aV formulations provided a significant protection against VHSV-induced mortality. However, when plasma from survivors was tested for neutralizing antibodies in an in vitro protection assay, we could not demonstrate any protective effect. On the contrary, plasma from aV vaccinated fish enhanced cytopathic effects, indicating that antibody-dependent entry may play a role in this system. Our results show that poly(I:C) is a promising candidate as an adjuvant for fish vaccination against viral pathogens, and that the zebrafish is a promising model for aquaculture-relevant vaccination studies.
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Affiliation(s)
- Arturas Kavaliauskis
- 1 Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo , Oslo, Norway
| | - Marianne Arnemo
- 1 Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo , Oslo, Norway
| | - Sung-Hyun Kim
- 2 Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences , Oslo, Norway
| | - Lilia Ulanova
- 3 Department of Biosciences, University of Oslo , Oslo, Norway
| | - Martin Speth
- 3 Department of Biosciences, University of Oslo , Oslo, Norway
| | | | - Sonia Dios
- 4 Institute of Marine Research, CSIC , Vigo, Spain
| | - Øystein Evensen
- 2 Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences , Oslo, Norway
| | | | - Tor Gjøen
- 1 Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo , Oslo, Norway
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Lauscher A, Krossøy B, Frost P, Grove S, König M, Bohlin J, Falk K, Austbø L, Rimstad E. Immune responses in Atlantic salmon (Salmo salar) following protective vaccination against infectious salmon anemia (ISA) and subsequent ISA virus infection. Vaccine 2011; 29:6392-401. [PMID: 21554914 DOI: 10.1016/j.vaccine.2011.04.074] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 04/18/2011] [Accepted: 04/19/2011] [Indexed: 01/13/2023]
Abstract
Infectious salmon anemia (ISA) is an orthomyxoviral disease that has had devastating effects on farmed Atlantic salmon. ISA is still a disease resulting in continued loss of revenues and therefore development of effective vaccines is of great importance. Commercial vaccines against ISA are available, but the efficacy is poorly described. There is little information about vaccine-induced immune factors preventing ISA virus (ISAV) infection today. In this study we assessed the protective effects and immunogenicity of vaccines containing three different quantities of the inactivated ISAV antigen. Our findings indicated that immunization induced effective protection in Atlantic salmon with a relative percent survival (RPS) as high as 86. The level of protection was correlated to the amount of ISAV antigen in the vaccine, and fish immunized with high antigen amounts produced detectable ISAV-specific and neutralizing antibodies. While ISAV infection was detectable in non-vaccinated control fish challenged by cohabitation, no infection was detected in fish immunized with high antigen amounts. After challenge, transcriptional analysis of selected immune-related genes demonstrated activation of innate immune responses in ISAV-infected control fish, but not in vaccine protected fish. This study furthers the knowledge about vaccine efficacy and vaccine-induced immunity to ISAV challenge in Atlantic salmon.
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Affiliation(s)
- Astrid Lauscher
- Department of Food Safety and Infection Biology, The Norwegian School of Veterinary Science, P.O. 8146 Dep, N-0033 Oslo, Norway.
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Eaton HE, Penny E, Brunetti CR. Antibody dependent enhancement of frog virus 3 infection. Virol J 2010; 7:41. [PMID: 20167100 PMCID: PMC2830962 DOI: 10.1186/1743-422x-7-41] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2009] [Accepted: 02/18/2010] [Indexed: 12/02/2022] Open
Abstract
Background Viruses included in the family Iridoviridae are large, icosahedral, dsDNA viruses that are subdivided into 5 genera. Frog virus 3 (FV3) is the type species of the genus Ranavirus and the best studied iridovirus at the molecular level. Typically, antibodies directed against a virus act to neutralize the virus and limit infection. Antibody dependent enhancement occurs when viral antibodies enhance infectivity of the virus rather than neutralize it. Results Here we show that anti-FV3 serum present at the time of FV3 infection enhances infectivity of the virus in two non-immune teleost cell lines. We found that antibody dependent enhancement of FV3 was dependent on the Fc portion of anti-FV3 antibodies but not related to complement. Furthermore, the presence of anti-FV3 serum during an FV3 infection in a non-immune mammalian cell line resulted in neutralization of the virus. Our results suggest that a cell surface receptor specific to teleost cell lines is responsible for the enhancement. Conclusions This report represents the first evidence of antibody dependent enhancement in iridoviruses. The data suggests that anti-FV3 serum can either neutralize or enhance viral infection and that enhancement is related to a novel antibody dependent enhancement pathway found in teleosts that is Fc dependent.
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Affiliation(s)
- Heather E Eaton
- Department of Biology, Trent University, Peterborough, ON, Canada
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Pettersen EF, Ingerslev HC, Stavang V, Egenberg M, Wergeland HI. A highly phagocytic cell line TO from Atlantic salmon is CD83 positive and M-CSFR negative, indicating a dendritic-like cell type. FISH & SHELLFISH IMMUNOLOGY 2008; 25:809-19. [PMID: 18817880 DOI: 10.1016/j.fsi.2008.08.014] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Revised: 08/27/2008] [Accepted: 08/27/2008] [Indexed: 05/26/2023]
Abstract
Leucocyte cell lines are valuable tools for immunological studies. In this study the TO cell line, originating from Atlantic salmon head kidney leucocytes, is described with respect to enzyme cytochemistry, functional studies, reactivity with leucocyte specific antibodies and immune gene expression. Pronounced characteristics of the TO cell line are the rapid adherence to the plastic growth surface, high phagocytic capacity and bactericidal functions. No respiratory burst activity, and little or no NO production were detected under the experimental conditions tested, and thus the TO cells appear to have other effective killing mechanisms. The cells are reactive with a leucocyte specific monoclonal antibody (MAb), but does not bind a neutrophil specific MAb or stain for myeloperoxidase. Real-time RT-PCR showed the expression in TO cells of several immune genes, some of which were significantly regulated following LPS stimulation. The expression of CD83 might indicate a dendritic cell (DC) origin of the TO cells, as this marker is considered a hallmark for DC. Expression of TCR-alpha or the macrophage marker M-CSFR was not detected. Based on the present analyses the TO cells display a mixture of known characteristics for macrophages and DCs. At the same time the TO cells lack some central functions of phagocytic/myeloid cells. As the TO cells are developed to a long-term culture one cannot exclude that some functions might have been lost in this process. Nevertheless, the features of the TO cells indicate their potential as a model system for immunological studies of salmon phagocytic cells.
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Affiliation(s)
- Eirin Fausa Pettersen
- Department of Biology, University of Bergen, Bergen High-Technology Center, PO Box 7800, NO-5020 Bergen, Norway.
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Barnes DW, Parton A, Tomana M, Hwang JH, Czechanski A, Fan L, Collodi P. Stem cells from cartilaginous and bony fish. Methods Cell Biol 2008; 86:343-67. [PMID: 18442656 DOI: 10.1016/s0091-679x(08)00016-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- David W Barnes
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, USA
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8
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Munir K. Characterization of Chinook head salmon embryo phenotypes of infectious salmon anemia virus by real-time RT-PCR. J Vet Sci 2006; 7:167-76. [PMID: 16645343 PMCID: PMC3242110 DOI: 10.4142/jvs.2006.7.2.167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
We have previously described the development of a one-tube SYBR Green real-time RT-PCR assay for the detection and quantitation of infectious salmon anemia virus (ISAV) in various biological samples. The twofold aim of the present study was to verify that the optimized SYBR Green real-time RT-PCR conditions could detect ISAV isolates of different geographic origins, and to analyze the growth patterns of the selected ISAV isolates in the Chinook head salmon embryo (CHSE)-214 cells by this assay to better characterize their CHSE-phenotypes. A total of 24 ISAV isolates were used in this study. The results indicated that the SYBR Green real-time RT-PCR could detect ISAV of different geographic origins or laboratory sources. The capacity of ISAV isolates to cause cytopathic effects (CPE) in the CHSE-214 cell line, viral titration of the infected CHSE-cell harvests, and analysis of viral RNA levels in CHSE-214 cells at post-infection day zero, 7 and 14 by SYBR Green real-time RT-PCR confirmed the existence of three CHSE-phenotypes of ISAV: replicating cytopathic, replicating non-cytopathic, and non-replicating non-cytopathic. The identification of these three CHSE-phenotypes of ISAV has important implications from diagnostic and biological points of view.
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Affiliation(s)
- Khalid Munir
- Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI C1A 4P3, Canada.
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Mikalsen AB, Sindre H, Torgersen J, Rimstad E. Protective effects of a DNA vaccine expressing the infectious salmon anemia virus hemagglutinin-esterase in Atlantic salmon. Vaccine 2005; 23:4895-905. [PMID: 16005119 DOI: 10.1016/j.vaccine.2005.05.025] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2005] [Revised: 05/05/2005] [Accepted: 05/24/2005] [Indexed: 11/30/2022]
Abstract
Infectious salmon anemia (ISA) is a disease, caused by an orthomyxovirus, which has considerable economic impact on farming of Atlantic salmon. Here we describe the results of immunization against ISA using plasmids expressing the ISA virus hemagglutinin-esterase (HE). Immunized Atlantic salmon demonstrated moderate protection after challenge with ISA virus, with relative percent survival of 39.5 and 60.5 in two parallel groups. No protection was seen after immunization using a plasmid expressing the ISA virus nucleoprotein. Fish in the HE-immunized group had earlier onset of clearance of the virus than control fish. There was no detectable ISA virus specific humoral response after immunization. After challenge a specific humoral response could be demonstrated in the fish in all groups, but no correlation between this response and protection was found.
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Affiliation(s)
- Aase B Mikalsen
- Department of Food Safety and Infection Biology, The Norwegian School of Veterinary Science, N-0033 Oslo, Norway.
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10
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Mjaaland S, Markussen T, Sindre H, Kjøglum S, Dannevig BH, Larsen S, Grimholt U. Susceptibility and immune responses following experimental infection of MHC compatible Atlantic salmon (Salmo salar L.) with different infectious salmon anaemia virus isolates. Arch Virol 2005; 150:2195-216. [PMID: 16012784 DOI: 10.1007/s00705-005-0588-8] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2005] [Accepted: 05/13/2005] [Indexed: 10/25/2022]
Abstract
Infectious salmon anaemia virus (ISAV) is an aquatic orthomyxovirus causing a multisystemic disease in farmed Atlantic salmon (Salmo salar) where disease development, clinical signs, and histopathology vary to a large extent. Here, an experimental trial was designed to determine the effect of variation in viral genes on virus-host interactions, as measured by disease susceptibility and immune responses. The fish were infected using cohabitant transmission, representing a natural route of infection. Variation caused by host factors was minimized using MHC compatible A. salmon half-siblings as experimental fish. Virus isolates were selected according to HE genotype, as European ISAV isolates can be genotyped according to deletion patterns in their hemagglutinin-esterase (HE) surface glycoprotein, and the course of disease they typically induce, classified as acute versus protracted. The different ISAV isolates induced large variations in death prevalence, ranging from 0-47% in the test-group and 3-75% in the cohabitant fish. The use of MHC compatible experimental fish made it possible to determine the relative contribution of humoral versus cellular response in protection against ISA. Ability to induce a strong proliferative response correlated with survival and virus clearance, while induction of a humoral response was less protective.
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Affiliation(s)
- S Mjaaland
- Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, Oslo, Norway.
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Joseph T, Cepica A, Brown L, Ikede BO, Kibenge FSB. Mechanism of cell death during infectious salmon anemia virus infection is cell type-specific. J Gen Virol 2004; 85:3027-3036. [PMID: 15448366 DOI: 10.1099/vir.0.80091-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Infectious salmon anemia virus (ISAV) is a very important fish virus in the Northern hemisphere and there is continued interest in understanding the mechanisms of its pathogenesis and persistence in fish. In this study, the permissive fish cell lines SHK-1, CHSE-214 and TO were used to determine whether ISAV-induced cytopathic effect (CPE) is due to apoptosis or necrosis. Characteristic apoptotic DNA fragmentation was observed only in ISAV-infected SHK-1 and CHSE-214 cells. Apoptosis in ISAV-infected SHK-1 cells was confirmed by fragment end-labelling assay, suggesting that CPE in these cells is associated with apoptosis. ISAV-infected TO cells did not undergo apoptosis, but showed leakage of high-mobility group 1 (HMGB1) protein from the nucleus, which is characteristic of cells undergoing necrosis; this suggests that CPE in these cells is associated with necrosis. ISAV-infected SHK-1 cells did not show leakage of HMGB1 protein. Infection with two different strains of ISAV showed that induction of apoptosis was correlated with the appearance of CPE in SHK-1 cells. ISAV-induced apoptosis was inhibited by a pan-caspase inhibitor, Z-VAD-fmk, indicating a caspase-activation pathway. The ISAV putative PB2 protein and proteins encoded by RNA segment 7 bound caspase-8 specifically in vitro, suggesting that these viral proteins may have a role in ISAV-induced apoptosis. These findings demonstrate for the first time that the mechanism of cell death during ISAV infection is dependent on the cell type, which may have implications for ISAV pathogenesis and persistence.
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Affiliation(s)
- Tomy Joseph
- Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, Canada C1A 4P3
| | - Arnost Cepica
- Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, Canada C1A 4P3
| | - Laura Brown
- Institute of Marine Biosciences, National Research Council, Halifax, NS, Canada
| | - Basil O Ikede
- Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, Canada C1A 4P3
| | - Frederick S B Kibenge
- Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, Canada C1A 4P3
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Munir K, Kibenge FS. Detection of infectious salmon anaemia virus by real-time RT-PCR. J Virol Methods 2004; 117:37-47. [PMID: 15019258 PMCID: PMC7172414 DOI: 10.1016/j.jviromet.2003.11.020] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2003] [Revised: 11/27/2003] [Accepted: 11/27/2003] [Indexed: 11/23/2022]
Abstract
A one-tube real-time reverse transcription-polymerase chain reaction (RT-PCR) using LightCycler technology and SYBR Green chemistry that quantitatively detects infectious salmon anaemia virus (ISAV) in biological samples is described. The assay utilized primers targeting ISAV RNA segment 8, with ISAV isolate U5575-1 as template. The entire optimized assay, including one cycle of reverse transcription, 50 cycles of complementary DNA amplification, and data acquisition and analysis took only 80min. The melting curve and gel electrophoresis analyses of real-time RT-PCR showed harmony with each other as a virus-specific single melting peak and a product of the expected size of 211 bp were obtained. A regression line between the mean threshold cycle (Ct) values and viral template concentrations over a 1:10(5) dilution range with an r(2) value of 0.962 and a slope of -3.771 indicated that the assay was highly reproducible. This assay was 100 times more sensitive than the conventional one-tube RT-PCR assay when compared on the same sample. Analysis of different tissues from fish that survived an ISAV experimental infection further confirmed that real-time RT-PCR was more sensitive than regular RT-PCR for detection of ISAV nucleic acids. Temporal analysis of ISAV-infected TO cell cultures showed that the amount of the specific viral RNA increased more than 100-fold within 32 h post-inoculation (p.i.) and over 1200-fold by 144 h p.i. The melting curve analysis throughout the duration of the infection sampled had a single melting peak suggesting that the virus population was uniform in the targeted region. Quantitative analysis of CHSE-214 cell cultures infected with different ISAV isolates indicated that ISAV isolates, based on their ability to replicate and cause cytopathic effects in CHSE-214 cells, may be differentiated into three CHSE phenotypes: replicating cytopathic, replicating non-cytopathic, and non-replicating. Thus, the SYBR Green real-time RT-PCR is a sensitive, rapid, and highly reproducible assay that can be used to quantitate ISAV in biological samples.
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