Mohammad Majid Ebrahimi - Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran
Shahla Shahsavandi - Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran
Mohammad Eslampanah - Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran
Ali Reza Yousefi - Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran

Newcastle disease (ND) is a highly contagious viral infection affecting poultry production in many countries. Strict biosecurity and the administration of live attenuated vaccines against the ND virus (NDV) are the main implements of controlling programs. This study evaluated the efficacy and potency of the Razi Clone۱۲IR Newcastle vaccine in specific pathogen-free (SPF) chickens. Chickens were vaccinated with either the Razi Clone۱۲IR vaccine (group A۱, n=۲۰) or an imported Clone vaccine (B۱, n=۲۰) in the first week of life and boosted in the second week via eye drop, while negative control chickens received PBS (C۱, n=۲۰). Half of the birds in each group were challenged with the virulent NDV strain in the third post-vaccination week (A۲, B۲, and C۲ groups). Specific antibody responses were determined in the collected sera by the hemagglutination inhibition (HI) assay for up to eight weeks. Cell-mediated immunity (CMI) was determined by the lymphocyte proliferation assay three and six weeks after the second vaccination. Sections of the tissues and organs, including the trachea, lungs, cecal tonsils, spleen, the bursa of Fabricius, liver, and small intestine, were subjected to histopathology. The immunized groups A۱ and B۱ showed significantly higher HI antibody titers before the challenge than the control group. In addition, lymphocyte proliferation responses significantly increased in the peripheral blood of the vaccinated groups. After the challenge, the A۲ and B۲ groups conferred good protection and drastically reduced virus shedding. No main lesions were noted in the tissues or organs of the vaccinated group in histopathology. In a few cases, mild microscopic lesions were observed, including the infiltration of inflammatory cells, which was related to the effect of the vaccine virus. These results indicate that the Razi Clone۱۲IR vaccine is safe and can be an efficient tool for NDV infections by inducing protective humoral and CMI responses.

Clone strain, Histopathology, Immune responses, Newcastle Disease vaccine, Protection