Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/2010
Publication Date: 10/18/2010
Citation: Zhang, H., Chang, S., Dunn, J.R., Heidari, M., Lee, L.F. 2010. Low dose vaccination revealed an interaction between vaccine and chicken line affecting protective efficacy [abstract]. In: 5th International Workshop on the Molecular Pathogenesis of Marek's Disease Virus and 1st Symposium on Avian Herpesviruses, October 17-20, 2010, Athens, Georgia, p. 129. Interpretive Summary:
Technical Abstract: Marek’s disease (MD), caused by a highly oncogenic and contagious cell-associated alpha-herpesvirus, also known as Marek’s disease virus (MDV), remains as a highly potential threat to poultry industry worldwide. This threat has been continuously sustained by persistent viral evolution with increasing virulence and dominant susceptibility to MD in large numbers of commercial flocks of chickens. MD has been controlled by vaccination since the 1970s. Vaccine efficacy depends on multiple factors including host genetic variation, maternal antibody status, virulence of challenge virus, dosage of vaccination, type of vaccine, and vaccine-challenge interval. This study comparatively evaluated the protective efficacy of two commonly used MD vaccines (CVI/988 Rispens and HVT) and a candidate recombinant DNA vaccine (rMd5deltaMeq) at a low dosage. Chickens from two highly inbred lines and a series of 19 recombinant congenic strains were divided into four treatment groups. Three groups were vaccinated with 500 PFU of rMd5deltaMeq, CVI/988 Rispens, or HVT per bird, respectively. The other group was not vaccinated. All chickens of the four groups were challenged with a vv+ strain of MDV at five days of age. The protective indices of the vaccines ranked (from high to low) as rMd5deltaMeq > HVT > CVI/988 Rispens in the inbred line 6, known as relatively resistant to MD, and rMd5deltaMeq > CVI/988 > HVT in the inbred line 7, known as highly susceptible to MD. The change in ranking orders of protective indices for two of the three vaccines between the two chicken lines indicated a vaccine by chicken line interaction affecting the vaccine protective efficacy. The overall protective indices of the vaccines for the 19 recombinant congenic strains ranked as rMd5deltaMeq > HVT > CVI/988 Rispens as expected since each of the recombinant congenic strains on average resembles line 6 by 7/8 of the genome, but line 7, by 1/8. It is noted that the results observed in the line 6 and combined recombinant congenic strains are contrary to results commonly seen in the field, in which CVI/988 Rispens protects much better than HVT as observed in the line 7, when challenged with highly virulent MDV strains. The data suggests that use of chicken line-specific vaccine is of critical importance to maximize protection efficacy.