Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2009
Publication Date: 2/3/2010
Citation: Lee, L.F., Kreager, K.S., Arango, J., Paraguassu, A., Beckman, B., Zhang, H., Fadly, A.M., Lupiani, B., Reddy, S.M. 2010. Comparative Evaluation of Vaccine Efficacy of Recombinant Marek's Disease Virus Vaccine Lacking Meq Oncogene in Commercial Chickens. Vaccine. 28(5):1294-1299. 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 compare the vaccine efficacy between a novel recombinant virus named rMd5delMEQ and the best currently available MD vaccine, CVI988/Rispens vaccine, in commercial chickens. We have previously shown that deletion of a cancer-inducing gene, Meq, in rMd5 virus resulted in a virus that is no longer pathogenic (causing disease) in chickens, and confers 100% protection against a very virulent challenge virus. The protective efficacy was significantly better than the CVI988/Rispens vaccine in laboratory studies. This result led us to collaborate with Hy-Line International, a major breeding company, to carry out three large-scale field trials. All three trials indicate that rMd5delMEQ vaccine is superior to the best source of CVI988/Rispens vaccine. This information is of great importance to the poultry industry as they look for vaccines of the future.
Technical Abstract: Marek's disease virus oncogene meq has been identified as the gene involved in tumorigenesis in chickens. We have recently developed a Meq-null virus, rMd5delMeq, in which the oncogene Meq was deleted. Vaccine efficacy experiments conducted in ADOL 15I5 x 71 chickens vaccinated with rMd5delMeq virus or an ADOL preparation of CVI988/Rispens indicated that rMd5delMeq provided superior protection than CVI988/Rispens when challenged with the very virulent plus MDV 648A strain. In the present study we set to investigate the vaccine efficacy of rMd5delMeq in the field compared to several commercial preparations of CVI988/Rispens. Three large- scale field experiments were conducted in a model developed by Hy-Line International. In addition, comparisons were made with bi-valent HVT + SB-1 vaccine and several commercial HVT vector vaccines individually or in combination with CVI988/Rispens. For all three trials, seeder birds were inoculated with a very virulent plus strain of 686, vv+ MDV. Experimental results conclusively showed that addition of HVT to either of the two commercial CVI988/Rispens preparations tested (A or B) did not enhance protection conferred CVI988/Rispens alone and that rMd5delMeq was a superior vaccine compared to any of the CVI988/Rispens vaccines tested under the conditions of the field trials presented herein.