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To evaluate the effect of the vaccine and differentiate vaccine from virulent MDV, a new quadruplex real-time PCR assay based on TaqMan probes was developed to differentiate and accurately quantify HVT, CVI988 and virulent MDV-1. The results showed that the limit of detection (LOD) of the new assay was 10 copies with correlation coefficients >0.994 of CVI988, HVT and virulent MDV DNA molecules without cross-reactivity with other avian disease viruses. The intra-assay and inter-assay coefficients of variation (CVs) of Ct values for the new assay were less than 3%. Analysis of replication kinetics of CVI988 and virulent MDV of collected feathers between 7 and 60 days post-infection (dpi) showed MD5 had no significant effect on the genomic load of CVI988 ( > 0.05), while vaccination with CVI988 could significantly reduce the viral load of MD5 ( < 0.05). Combined with gene PCR, this method can effectively identify virulent MDV infections in immunized chickens. These results demonstrated that this assay could distinguish between the vaccine and virulent MDV strains and had the advantages of being reliable, sensitive and specific to confirm the immunization status and monitor the circulation of virulent MDV strains.
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http://dx.doi.org/10.3389/fvets.2023.1161441 | DOI Listing |
PLoS Pathog
August 2025
Departments of Biology.
Comparative genomic studies of Marek's disease virus (MDV) have suggested that attenuated and virulent strains share >98% sequence identity. However, these estimates fail to account for variation in regions of the MDV genome harboring tandem repeats. To resolve these loci and enable assessments of intrapopulation diversity, we used a PacBio Sequel II platform to sequence MDV strains CVI988/Rispens (attenuated), HPRS-B14 (virulent), Md5 (very virulent) and 675A (very virulent plus).
View Article and Find Full Text PDFViruses
June 2025
Department of Disease Control, Faculty of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan.
Marek's disease virus (MDV) is the etiological agent of Marek's disease (MD), a lymphoproliferative disorder in chickens. Polymorphisms in the MDV-encoded oncoprotein Meq are shared among field strains and correlate with their virulence. The attenuated vaccine strain CVI988 harbors unique amino acid polymorphisms in Meq, particularly at positions 71, 77, and 326.
View Article and Find Full Text PDFMicrobiol Spectr
August 2025
Department of Disease Control, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
Marek's disease virus (MDV) causes lymphomas (Marek's disease) in chickens. Despite vaccination, MDV field strains exhibit increased virulence, and sporadic outbreaks are still reported. An insertion/deletion in Meq has been identified in several MDV strains, and our previous study using recombinant MDV (rMDV) demonstrated that an insertion in Meq enhanced MDV virulence, whereas a deletion reduced its virulence.
View Article and Find Full Text PDFPoult Sci
July 2025
Department of Veterinary Microbiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand; Center of Excellence for Emerging and Re-emerging Infectious Diseases in Animals (CUEIDAs), Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand; Center of Excelle
Marek's disease (MD) is a highly contagious lymphoproliferative disease of chickens caused by serotype 1 Marek's disease virus (MDV-1). Frequent outbreaks of MD in vaccinated chicken flocks have been reported worldwide, including in Thailand. Recently, we reported the circulation of several genotypes/clusters of MDV-1 with molecular characteristics of highly virulent strains in chicken populations in Thailand.
View Article and Find Full Text PDFPathogens
May 2025
Department of Pathobiology, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802, USA.
The glycoprotein C (gC) of gallid alphaherpesvirus 2-better known as Marek's disease (MD) virus (MDV)-and gallid alphaherpesvirus 3 is required for horizontal transmission in chickens. Since gC is conserved within the subfamily, we hypothesized that gC was also essential for the horizontal transmission of meleagrid alphaherpesvirus 1 (MeAHV1) or turkey herpesvirus (HVT). To test this hypothesis, we generated a fluorescent protein-tagged clone of recombinant (r)HVT (vHVT47G), removed the open reading frame of HVT gC from the genome (vHΔgC), and rescued the deletion by inserting an HA-epitope tagged HVT gC (vHΔgC-R) to test their ability to transmit in chickens and turkeys.
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