Submitted to: American Veterinary Medical Association Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 11, 2009
Publication Date: July 11, 2009
Citation: Lee, L.F. 2009. Factors Affecting the Efficacy of Recombinant Marek's Disease Vaccine Protection [abstract]. In: 146th American Veterinary Medical Association Convention Notes, July 11-14, 2009, Seattle, Washington. Paper No. 7652. Technical Abstract: Many factors have the potential to influence the efficacy of Marek's disease (MD) vaccination. Some of these factors include maternal antibody, vaccine dose, age of birds at vaccination or challenge, challenge virus strain and genetic background of chickens. The objective of this study was to evaluate the effect of challenge virus dose and age of chickens at exposure on the efficacy of recombinant vaccine protection. The vaccine used in this study was a gene deletion mutant of rMd5 (rMd5delMeq) and the challenge virus was 686, very virulent and very virulent plus strains of MDV, respectively. In the first experiment, six groups of 17 birds each were vaccinated at day of age with 2000 PFU of rMd5delMeq and challenged on different days ranging from zero to 5 days post vaccination. In the second experiment, six groups of 17 birds each were vaccinated at day of age with rMd5delMeq and challenged with 686MDV, ranging from 500 to 100,000 PFU per group five days later. Data from the first experiment shows a higher protective index at day zero than day 1. A protection index of 100% was obtained only when birds were challenged 5 days after vaccination. The data from the second experiment indicate that the vaccine dose of 2000 PFU could protect 100% of chickens challenged at a dose from 500 to 32,000 PFU/bird. However, at a dose of 100,000 PFU/bird, the protective index was only 85%. These data taken together indicate that dose and time post vaccination play an important role in the efficacy of vaccine protection.