Development and pilot production of live Newcastle clone vaccine

Newcastle disease (ND) is a highly contagious and widespread disease, which caused by one single serotype of the avian Paramyxovirus serotype 1. ND virus (NDV) strains can be grouped, in order of increasing pathogenicity, into five pathotypes as highly virulent (viscerotropic velogenic and neurotropic velogenic), intermediate (mesogenic), low virulent (lentogenic), and asymptomatic. In ND endemic areas, the live lentogenic vaccines include Hitchner B1 and LaSota have a key role in vaccination programs. To access the effective and potentiate ND vaccine, a homogenous subpopulation from LaSota strain is considered. The purpose of this study was develop a cloned vaccine and evaluate its immune responses in both specific pathogen free (SPF) and commercial chickens. The NDV LaSota strain was cultivated on primary chicken embryofibroblast (CEF) cells and the pathogenicity indices and molecular characterization of several plaques at 3rd passage were analyzed. Based on the obtained results, a clone was candidate for vaccine production. SPF chickens were divided into two treatment groups. Chickens in group A were received the developed vaccine, Clone12IR (Razi Institute), and group B received the imported same vaccine via eye drop method. One group of birds at the same origin and age was kept as non-vaccinated control. Three weeks post-vaccination sera were collected and assayed for antibody levels against NDV by hemagglutination-inhibition (HI). Twenty chickens per groups were challenged by intramuscular with 105 EID50 of a virulent NDV Herts-33 strain at 3 weeks post vaccination. Groups of Ross-308 commercial chickens were tested as the same manner. The NDV strain was cloned after three rounds of plaque purification on CEF cells. The cloned virus exhibited ICPI, IVPI and MDT values of 0.32, 0, and 104 characterizing as lentogenic NDV. Nucleotide sequence of the virus F gene and deduced amino acid were determined. Phylogenic data was revealed that Clone12IR clustered with LaSota and other lentogen ND viruses with 98% identity. The proteolytic cleavage site of the virus is characterized by five basic amino acids at the carboxyl terminus of F2 and a phenylalanine at the amino terminus of F1 (112G-R-Q-G-R*L117) associated with the lentogenic NDV. The immunogenicity of the Clone12IR vaccine was examined in SPF and commercial chickens. The geometric mean HI titers induced in chickens vaccinated with the cloned vaccine were not significantly differ than those induced in chickens vaccinated with the similar ND clone vaccine. Efficacy of the ND vaccine was estimated against the virus challenge. The results indicate that the Razi Clone12IR vaccine could confer a complete protection against NDV.