[Comparison of immunoprotection between vaccination with meq-deleted Marek's disease virus and vaccine strain CVI988/Rispens].

OBJECTIVE:To evaluate and compare the immunoprotection between a meq-deleted Marek's disease virus (MDV) and CVI988/Rispens against MDV very virulent strain GX0101. METHODS:In total 120 one-day-old SPF chickens were divided into 4 groups (30 each) and kept in 5 isolators with positive pressure-filtered air. At 1 day of age, 2000 PFU of SC9-1 was inoculated subcutaneously into each bird in group 1; 2000 PFU of commercial vaccine CVI988/ Rispens was inoculated subcutaneously into each bird in group 2. No viral challenge was made in group 3 and 4 as controls. Five days later chickens in group 1, 2, 3 were challenged intra-abdominally with 2000 PFU of very virulent MDV strain GX0101. During 90 days after challenge, all dead birds were recorded and checked for necropsy. The tumor-suspected tissues were examined by histopathological biopsy. The antibody titers induced by AIV and NDV vaccination and propagation dynamics of MDV GX0101 were detected. At the same time, parallel tests were performed on Hy-Line Brown chickens containing MDV maternal antibody. RESULTS:SC9-1 stain provided 100% protective efficiency against very virulent GX0101 challenge in SPF and Hy-Line Brown chickens. CVI988/Rispens provided 86. 7% protective efficiency against very virulent GX0101 challenge in SPF chickens and 93% in Hy-Line Brown chickens. Challenge with GX0101 caused 53.3% mortality and 16.7% of birds with gross tumors in SPF chickens while there was 36.7% mortality and 16.7% of birds with gross tumors in Hy-Line Brown chickens, and there was no tumor lesion in histopathological biopsy in control group. The results of qPCR demonstrated that the copies of GX0101 viral genomes in SC9-1 vaccinated chickens was lower than CVI988/Rispens vaccinated chickens in lymphocyte and feather follicle DNA. The results of hemagglutination inhibition test demonstrated that antibody titers of AIV and NDV was higher in SC9-1 vaccinated chickens than that in CVI988/Rispens vaccinated chickens. CONCLUSION:SC9-1 stain's immunoprotection against MDV is more effective than CVI988/Rispens strain's both in SPF chickens and commercial Hy-Line Brown chickens containing maternal antibody.