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Title: Evaluation of Factors Affecting Vaccine Efficacy of Recombinant Marek's Disease Virus Lacking the Meq Oncogene in Chickens

Author
item Lee, Lucy
item Zhang, Huanmin
item Heidari, Mohammad
item LUPIANI, BLANCA - Texas A&M University
item REDDY, SANJAY - Texas A&M University

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2010
Publication Date: 6/30/2011
Citation: Lee, L.F., Zhang, H., Heidari, M., Lupiani, B., Reddy, S. 2011. Evaluation of factors affecting vaccine efficacy of recombinant Marek's disease virus lacking the Meq oncogene in chickens. Avian Diseases. 55(2):172-179.

Interpretive Summary: Marek’s disease (MD), a virus-induced cancer-like disease of chickens, is a major disease problem in commercial poultry. The objective of this research was to elucidate factors affecting efficacy of a novel recombinant MD virus vaccine named rMd5delta MEQ. These factors included host genetics, strain or dose of challenge virus, interval between vaccination and vaccine challenge, and maternal antibody status. Our results demonstrated that rMd5deltaMeq vaccine performs well under the most severe challenge virus or dosage up to 100,000 PFU. This vaccine protects 85-100% of chickens from five genetic lines regardless of whether they are susceptible or resistant to MD. This information is of great importance to the poultry industry as vaccine companies seek future vaccine for control of MD.

Technical Abstract: We have previously reported that deletion of Meq gene from oncogenic rMd5 virus rendered it apathogenic for chickens. Here we examined multiple factors affecting Marek’s disease (MD) vaccine efficacy of this non-pathogenic recombinant Meq null rMd5 virus (rMd5deltaMeq). These factors included host genetics (MHC haplotype), strain or dose of challenge virus, vaccine challenge intervals and maternal antibody status of the vaccinated chicks. Studies on host genetic were carried out in five chicken lines of four different MHC B-haplotypes. Results showed that chicken lines tested were highly protected with protection indexes of 100% (B2B15), 94% (B2B2), 87% (B19B19) and 83% (B21B21). At challenge dose above 8,000 PFU differences in protection were observed between the two highly virulent strains examined (648A and 686). Interval between vaccination and challenge indicated the protective efficacy from 0-2 days varied greatly (19-82%) after challenge with vv+ 686, the most virulent virus. Less variation and significant protection began at 3 days post vaccination and reached a maximum at 5 days post vaccination with about 80-100% protection. Our results indicate that taken together these factors are important for vaccine efficacy and need to be considered in comparative evaluation of vaccines.