Immunization Dose-Dependent In Vivo Replication Kinetics and Protective Efficacy of the Gene-Deleted Marek’s Disease Vaccine SC9-1
- 1Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100089, China
Abstract
In this study, we evaluated the replication kinetics and protective efficacy of the gene-deleted Marek’s disease (MD) vaccine strain SC9-1 in specific-pathogen-free (SPF) chickens immunized with different doses. Chickens were divided into two groups: one group received a high dose (5000 PFU) and the other a low dose (500 PFU) of the vaccine at 1 day of age, with a non-vaccinated group serving as the control. Vaccine viral copy numbers in the spleen and feather tips were detected by quantitative PCR (qPCR) at different days post-vaccination (dpv) (3, 5, 7, 11, and 14 dpv). Meanwhile, a challenge trial was conducted where chickens were challenged with the very virulent Md5 strain (1000 PFU/bird) at 5 dpv and observed until 70 days of age. Results from the vaccination-only experiment revealed that viral replication in the spleen was detectable in 100% of chickens as early as 3 dpv, reaching its peak at 5 dpv, with the high-dose group exhibiting significantly higher viral loads than the low-dose group. In feather tips, replication was detectable in 100% of chickens by 5 dpv and peaked at 7 dpv, but no significant difference was observed between the two dose groups. The unvaccinated control group exhibited 100% mortality with characteristic gross and histopathological lesions of Marek’s disease. In stark contrast, both vaccinated groups (high and low dose) demonstrated 100% survival until the end of the observation period (70 days). No clinical signs or pathological abnormalities were observed in these groups. Furthermore, vaccination with SC9-1 did not adversely impact growth performance and the development of major immune organs, even following subsequent Md5 challenge. The results indicated that a higher initial vaccination dose of the SC9-1 vaccine was associated with elevated peak early in vivo replication level, whereas vaccination dose may not govern viral maturation and shedding levels of SC9-1 in feather-tip tissues. However, peak replication level was not a direct determinant of final protective efficacy. Notably, even the lowest tested dose (500 PFU) afforded full protection against early challenge with a very virulent MDV strain. Collectively, these observations contribute to our understanding of dose-dependent protection induced by gene-deleted MD vaccines and inform rational vaccination strategies.
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BibTeX
@article{ye2026immunization,
title = {{Immunization Dose-Dependent In Vivo Replication Kinetics and Protective Efficacy of the Gene-Deleted Marek’s Disease Vaccine SC9-1}},
author = {Rujun Ye and Ruihan Shi and Haijun Jiang and Chang Liu and Mengzhu Dong and Hairong Tian and Tingwen Zheng and Yu Zhou},
journal = {Viruses},
year = {2026},
month = sep,
doi = {10.3390/v18101052},
url = {https://europepmc.org/article/PMC/PMC13709888},
note = {CC BY},
}
RIS
TY - JOUR
TI - Immunization Dose-Dependent In Vivo Replication Kinetics and Protective Efficacy of the Gene-Deleted Marek’s Disease Vaccine SC9-1
AU - Rujun Ye
AU - Ruihan Shi
AU - Haijun Jiang
AU - Chang Liu
AU - Mengzhu Dong
AU - Hairong Tian
AU - Tingwen Zheng
AU - Yu Zhou
PY - 2026
DA - 2026/09/01
JO - Viruses
DO - 10.3390/v18101052
UR - https://europepmc.org/article/PMC/PMC13709888
AB - In this study, we evaluated the replication kinetics and protective efficacy of the gene-deleted Marek’s disease (MD) vaccine strain SC9-1 in specific-pathogen-free (SPF) chickens immunized with different doses. Chickens were divided into two groups: one group received a high dose (5000 PFU) and the other a low dose (500 PFU) of the vaccine at 1 day of age, with a non-vaccinated group serving as the control. Vaccine viral copy numbers in the spleen and feather tips were detected by quantitative PCR (qPCR) at different days post-vaccination (dpv) (3, 5, 7, 11, and 14 dpv). Meanwhile, a challenge trial was conducted where chickens were challenged with the very virulent Md5 strain (1000 PFU/bird) at 5 dpv and observed until 70 days of age. Results from the vaccination-only experiment revealed that viral replication in the spleen was detectable in 100% of chickens as early as 3 dpv, reaching its peak at 5 dpv, with the high-dose group exhibiting significantly higher viral loads than the low-dose group. In feather tips, replication was detectable in 100% of chickens by 5 dpv and peaked at 7 dpv, but no significant difference was observed between the two dose groups. The unvaccinated control group exhibited 100% mortality with characteristic gross and histopathological lesions of Marek’s disease. In stark contrast, both vaccinated groups (high and low dose) demonstrated 100% survival until the end of the observation period (70 days). No clinical signs or pathological abnormalities were observed in these groups. Furthermore, vaccination with SC9-1 did not adversely impact growth performance and the development of major immune organs, even following subsequent Md5 challenge. The results indicated that a higher initial vaccination dose of the SC9-1 vaccine was associated with elevated peak early in vivo replication level, whereas vaccination dose may not govern viral maturation and shedding levels of SC9-1 in feather-tip tissues. However, peak replication level was not a direct determinant of final protective efficacy. Notably, even the lowest tested dose (500 PFU) afforded full protection against early challenge with a very virulent MDV strain. Collectively, these observations contribute to our understanding of dose-dependent protection induced by gene-deleted MD vaccines and inform rational vaccination strategies.
SN - 1999-4915
ER -