The Experts below are selected from a list of 858 Experts worldwide ranked by ideXlab platform
Nathan M. Beach - One of the best experts on this subject based on the ideXlab platform.
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real time pcr based infectivity assay for the titration of turkey Hemorrhagic Enteritis virus an adenovirus in live vaccines
Journal of Virological Methods, 2017Co-Authors: Nathan M. Beach, Hassan M Mahsoub, Nicholas P Evans, Lijuan Yuan, Kurt L Zimmerman, F W PiersonAbstract:The current in vitro titration method for turkey Hemorrhagic Enteritis virus (THEV) is the end-point dilution assay (EPD) in suspension cell culture (CC). This assay is subjective and results in high variability among vaccine lots. In this study, a new in vitro infectivity method combining a SYBR Green I-based qPCR assay and CC was developed for titration of live Hemorrhagic Enteritis (HE) CC vaccines. The qPCR was used to determine the virus genome copy number (vGCN) of the internalized virus particles following inoculation of susceptible RP19 cells with 1 vaccine label dose. The measured vGCN represents the number of infectious viral particles (IVP) per 1 dose. This method was used to compare 9 vaccine lots from 3 companies in the United States. Significant lot-to-lot variations within the same company and among the various companies were found in genomic and qPCR-based infectious titer per label dose. A positive linear relationship was found between qPCR infectious titer and genomic titer. Further, considerable variations in CCID50 titers were found among tested vaccine lots, indicating the high variability of the current titration methods. The new method provides an alternative to classical titration assays and can help reduce variation among HE vaccine products.
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Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus
Avian Diseases, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F W PiersonAbstract:Abstract The Virginia avirulent strain (VAS) of turkey Hemorrhagic Enteritis virus (THEV), which is commonly used in live vaccines for commercial turkeys, was studied to determine characteristics of infection. It has been observed that turkeys infected with the VAS maintain protective antibody levels in excess of 20 wk postvaccination. It is theorized that this immune response is modulated by either a persistent or latent infection. A series of studies have been undertaken to determine changes in virus location and serology over time. A trial was also conducted to evaluate the effect of corticosteroid administration on viral recrudescence, and an attempt was made to isolate live virus from tissues of birds 10 wk postinfection (pi). Antibody titers were determined by enzyme-linked immunosorbent assay, and PCR was used to detect viral DNA. Histopathology was performed on formalin-fixed paraffinized tissues. Viral DNA was detected in various tissues through 15 wk pi in the presence of high antibody titers. V...
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Comparison of 12 turkey Hemorrhagic Enteritis virus isolates allows prediction of genetic factors affecting virulence
Journal of General Virology, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F. William PiersonAbstract:Turkey Hemorrhagic Enteritis virus (THEV) is a member of the genus Siadenovirus and causes disease in turkey poults characterized by splenomegaly, bloody diarrhoea and death. The mechanism responsible for intestinal lesion formation and mortality is not known, although there is strong evidence that it is immune-mediated. All strains of THEV are serologically indistinguishable, although there are naturally occurring avirulent strains of THEV that replicate efficiently in turkeys without the intestinal haemorrhage or mortality associated with more virulent strains. The purpose of this study was to determine which viral genes are involved in virulence. The full-length genome of an avirulent vaccine strain was sequenced and compared with the genome of a virulent field isolate from Israel that was sequenced in 1998. Comparison of the two 26.3 kb genomes revealed 49 nucleotide differences resulting in 14 putative amino acid changes within viral proteins. Sequencing of the regions surrounding the 14 missense mutations revealed variations in ORF1, E3 and the fiber (fib) knob domain in five additional strains with varying degrees of virulence. Complete sequences of these genes were determined in a total of 11 different strains of THEV. All strains had at least one missense mutation in ORF1, and all but two of the strains had one missense mutation in E3. At least one missense mutation was found in the fiber knob domain in six out of seven virulent strains. Sequence variation of ORF1, E3 and fib in strains of THEV with different phenotypes strongly indicates that these genes are the key factors affecting virulence.
F W Pierson - One of the best experts on this subject based on the ideXlab platform.
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real time pcr based infectivity assay for the titration of turkey Hemorrhagic Enteritis virus an adenovirus in live vaccines
Journal of Virological Methods, 2017Co-Authors: Nathan M. Beach, Hassan M Mahsoub, Nicholas P Evans, Lijuan Yuan, Kurt L Zimmerman, F W PiersonAbstract:The current in vitro titration method for turkey Hemorrhagic Enteritis virus (THEV) is the end-point dilution assay (EPD) in suspension cell culture (CC). This assay is subjective and results in high variability among vaccine lots. In this study, a new in vitro infectivity method combining a SYBR Green I-based qPCR assay and CC was developed for titration of live Hemorrhagic Enteritis (HE) CC vaccines. The qPCR was used to determine the virus genome copy number (vGCN) of the internalized virus particles following inoculation of susceptible RP19 cells with 1 vaccine label dose. The measured vGCN represents the number of infectious viral particles (IVP) per 1 dose. This method was used to compare 9 vaccine lots from 3 companies in the United States. Significant lot-to-lot variations within the same company and among the various companies were found in genomic and qPCR-based infectious titer per label dose. A positive linear relationship was found between qPCR infectious titer and genomic titer. Further, considerable variations in CCID50 titers were found among tested vaccine lots, indicating the high variability of the current titration methods. The new method provides an alternative to classical titration assays and can help reduce variation among HE vaccine products.
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Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus
Avian Diseases, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F W PiersonAbstract:Abstract The Virginia avirulent strain (VAS) of turkey Hemorrhagic Enteritis virus (THEV), which is commonly used in live vaccines for commercial turkeys, was studied to determine characteristics of infection. It has been observed that turkeys infected with the VAS maintain protective antibody levels in excess of 20 wk postvaccination. It is theorized that this immune response is modulated by either a persistent or latent infection. A series of studies have been undertaken to determine changes in virus location and serology over time. A trial was also conducted to evaluate the effect of corticosteroid administration on viral recrudescence, and an attempt was made to isolate live virus from tissues of birds 10 wk postinfection (pi). Antibody titers were determined by enzyme-linked immunosorbent assay, and PCR was used to detect viral DNA. Histopathology was performed on formalin-fixed paraffinized tissues. Viral DNA was detected in various tissues through 15 wk pi in the presence of high antibody titers. V...
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the production of colibacillosis in turkeys following sequential exposure to newcastle disease virus or bordetella avium avirulent Hemorrhagic Enteritis virus and escherichia coli
Avian Diseases, 1996Co-Authors: F W Pierson, C T Larsen, C. H. DomermuthAbstract:SUMMARY. Female large white turkeys were intranasally inoculated with either Newcastle disease virus (ND) or Bordetella avium (BA) at 4 weeks of age. This was followed by oral inoculation with an avirulent (vaccine) strain of Hemorrhagic Enteritis virus (HE) at 5 weeks and intravenous inoculation with Escherichia coli (EC) at 6 weeks. Control birds received ND, BA, or HE followed by EC; EC alone; or nothing at all. Turkeys receiving one agent prior to EC challenge did not experience a significant increase in mortality or pericarditis. Those exposed to ND or BA followed by HE and EC experienced a significant elevation in mortality and pericarditis. A highly significant positive correlation between the number of infectious agents encountered during primary exposure and the incidence of colibacillosis after EC challenge was demonstrated.
Calvert T. Larsen - One of the best experts on this subject based on the ideXlab platform.
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Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus
Avian Diseases, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F W PiersonAbstract:Abstract The Virginia avirulent strain (VAS) of turkey Hemorrhagic Enteritis virus (THEV), which is commonly used in live vaccines for commercial turkeys, was studied to determine characteristics of infection. It has been observed that turkeys infected with the VAS maintain protective antibody levels in excess of 20 wk postvaccination. It is theorized that this immune response is modulated by either a persistent or latent infection. A series of studies have been undertaken to determine changes in virus location and serology over time. A trial was also conducted to evaluate the effect of corticosteroid administration on viral recrudescence, and an attempt was made to isolate live virus from tissues of birds 10 wk postinfection (pi). Antibody titers were determined by enzyme-linked immunosorbent assay, and PCR was used to detect viral DNA. Histopathology was performed on formalin-fixed paraffinized tissues. Viral DNA was detected in various tissues through 15 wk pi in the presence of high antibody titers. V...
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Comparison of 12 turkey Hemorrhagic Enteritis virus isolates allows prediction of genetic factors affecting virulence
Journal of General Virology, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F. William PiersonAbstract:Turkey Hemorrhagic Enteritis virus (THEV) is a member of the genus Siadenovirus and causes disease in turkey poults characterized by splenomegaly, bloody diarrhoea and death. The mechanism responsible for intestinal lesion formation and mortality is not known, although there is strong evidence that it is immune-mediated. All strains of THEV are serologically indistinguishable, although there are naturally occurring avirulent strains of THEV that replicate efficiently in turkeys without the intestinal haemorrhage or mortality associated with more virulent strains. The purpose of this study was to determine which viral genes are involved in virulence. The full-length genome of an avirulent vaccine strain was sequenced and compared with the genome of a virulent field isolate from Israel that was sequenced in 1998. Comparison of the two 26.3 kb genomes revealed 49 nucleotide differences resulting in 14 putative amino acid changes within viral proteins. Sequencing of the regions surrounding the 14 missense mutations revealed variations in ORF1, E3 and the fiber (fib) knob domain in five additional strains with varying degrees of virulence. Complete sequences of these genes were determined in a total of 11 different strains of THEV. All strains had at least one missense mutation in ORF1, and all but two of the strains had one missense mutation in E3. At least one missense mutation was found in the fiber knob domain in six out of seven virulent strains. Sequence variation of ORF1, E3 and fib in strains of THEV with different phenotypes strongly indicates that these genes are the key factors affecting virulence.
Nammalwar Sriranganathan - One of the best experts on this subject based on the ideXlab platform.
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Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus
Avian Diseases, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F W PiersonAbstract:Abstract The Virginia avirulent strain (VAS) of turkey Hemorrhagic Enteritis virus (THEV), which is commonly used in live vaccines for commercial turkeys, was studied to determine characteristics of infection. It has been observed that turkeys infected with the VAS maintain protective antibody levels in excess of 20 wk postvaccination. It is theorized that this immune response is modulated by either a persistent or latent infection. A series of studies have been undertaken to determine changes in virus location and serology over time. A trial was also conducted to evaluate the effect of corticosteroid administration on viral recrudescence, and an attempt was made to isolate live virus from tissues of birds 10 wk postinfection (pi). Antibody titers were determined by enzyme-linked immunosorbent assay, and PCR was used to detect viral DNA. Histopathology was performed on formalin-fixed paraffinized tissues. Viral DNA was detected in various tissues through 15 wk pi in the presence of high antibody titers. V...
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Comparison of 12 turkey Hemorrhagic Enteritis virus isolates allows prediction of genetic factors affecting virulence
Journal of General Virology, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F. William PiersonAbstract:Turkey Hemorrhagic Enteritis virus (THEV) is a member of the genus Siadenovirus and causes disease in turkey poults characterized by splenomegaly, bloody diarrhoea and death. The mechanism responsible for intestinal lesion formation and mortality is not known, although there is strong evidence that it is immune-mediated. All strains of THEV are serologically indistinguishable, although there are naturally occurring avirulent strains of THEV that replicate efficiently in turkeys without the intestinal haemorrhage or mortality associated with more virulent strains. The purpose of this study was to determine which viral genes are involved in virulence. The full-length genome of an avirulent vaccine strain was sequenced and compared with the genome of a virulent field isolate from Israel that was sequenced in 1998. Comparison of the two 26.3 kb genomes revealed 49 nucleotide differences resulting in 14 putative amino acid changes within viral proteins. Sequencing of the regions surrounding the 14 missense mutations revealed variations in ORF1, E3 and the fiber (fib) knob domain in five additional strains with varying degrees of virulence. Complete sequences of these genes were determined in a total of 11 different strains of THEV. All strains had at least one missense mutation in ORF1, and all but two of the strains had one missense mutation in E3. At least one missense mutation was found in the fiber knob domain in six out of seven virulent strains. Sequence variation of ORF1, E3 and fib in strains of THEV with different phenotypes strongly indicates that these genes are the key factors affecting virulence.
Xiang-jin Meng - One of the best experts on this subject based on the ideXlab platform.
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Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus
Avian Diseases, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F W PiersonAbstract:Abstract The Virginia avirulent strain (VAS) of turkey Hemorrhagic Enteritis virus (THEV), which is commonly used in live vaccines for commercial turkeys, was studied to determine characteristics of infection. It has been observed that turkeys infected with the VAS maintain protective antibody levels in excess of 20 wk postvaccination. It is theorized that this immune response is modulated by either a persistent or latent infection. A series of studies have been undertaken to determine changes in virus location and serology over time. A trial was also conducted to evaluate the effect of corticosteroid administration on viral recrudescence, and an attempt was made to isolate live virus from tissues of birds 10 wk postinfection (pi). Antibody titers were determined by enzyme-linked immunosorbent assay, and PCR was used to detect viral DNA. Histopathology was performed on formalin-fixed paraffinized tissues. Viral DNA was detected in various tissues through 15 wk pi in the presence of high antibody titers. V...
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Comparison of 12 turkey Hemorrhagic Enteritis virus isolates allows prediction of genetic factors affecting virulence
Journal of General Virology, 2009Co-Authors: Nathan M. Beach, Robert B. Duncan, Calvert T. Larsen, Xiang-jin Meng, Nammalwar Sriranganathan, F. William PiersonAbstract:Turkey Hemorrhagic Enteritis virus (THEV) is a member of the genus Siadenovirus and causes disease in turkey poults characterized by splenomegaly, bloody diarrhoea and death. The mechanism responsible for intestinal lesion formation and mortality is not known, although there is strong evidence that it is immune-mediated. All strains of THEV are serologically indistinguishable, although there are naturally occurring avirulent strains of THEV that replicate efficiently in turkeys without the intestinal haemorrhage or mortality associated with more virulent strains. The purpose of this study was to determine which viral genes are involved in virulence. The full-length genome of an avirulent vaccine strain was sequenced and compared with the genome of a virulent field isolate from Israel that was sequenced in 1998. Comparison of the two 26.3 kb genomes revealed 49 nucleotide differences resulting in 14 putative amino acid changes within viral proteins. Sequencing of the regions surrounding the 14 missense mutations revealed variations in ORF1, E3 and the fiber (fib) knob domain in five additional strains with varying degrees of virulence. Complete sequences of these genes were determined in a total of 11 different strains of THEV. All strains had at least one missense mutation in ORF1, and all but two of the strains had one missense mutation in E3. At least one missense mutation was found in the fiber knob domain in six out of seven virulent strains. Sequence variation of ORF1, E3 and fib in strains of THEV with different phenotypes strongly indicates that these genes are the key factors affecting virulence.