Adaptation of Newcastle Disease Virus Vaccinal Strain on Chicken Embryo Fibroblast and Vero Cell Lines and Evaluation of the Protective Efficacy of the Vaccine in Chickens

Abstract

Newcastle disease is caused by virulent strains of avian paramyxovirus type 1 (APMV-1) and is one of the most important poultry diseases that influence poultry production in the poultry industry worldwide. The main objective of this study was to compare Chicken Embryo Fibroblast (CEF) and Vero cell lines adapted thermostable ND I-2 vaccine and evaluate the efficacy of the vaccine on experimental chickens in order to control and prevent Newcastle disease. For this purpose, in vitro and in vivo experimental designs were employed to compare the adaptation and titration of NDV in CEF and Vero cell lines. The virus was serially passaged up to passages 8 and 15 in CEF and Vero cell lines, respectively. Besides, the cell culture adapted experimental vaccine immunogenicity, efficacy, and safety were evaluated on eighty 14- day-old, unvaccinated, apparently healthy chickens. Chickens were randomly divided into four experimental groups, each having twenty (20) chickens. The study demonstrated the successful adaptation of the virus on Vero and CEF cell lines, exhibiting typical cytopathic effects. CEF and Vero cell lines infectivity titers rose from 3.9 log10 to 7.7 log10 TCID50/ml and 5.3 log10 to 6.7 log10 TCID50/ml, respectively. The mean antibody titers of experimental group 1, 2, and 3 showed 75.8 ±5.1, 50.0 ±19.5 and 86.5 ±41.2 respectively and the unvaccinated group was 0.8 ±0.4. These results confirmed the entire vaccinated group produces the best immunological response against challenge infection. All treatment and control groups were challenged with a velogenic ND virus with 105 ELD50 per chicken via the nasal route on the 35th day. The current study showed that all of the chickens in the unvaccinated group were dead, whereas the chickens in groups 1 and 3 had induced a protective index of 100% and group 2 had induced a protective index of 95%. Hence, the CEF and Vero cell lines adapted NDI-2 vaccine as well as current ND vaccines produced at National Veterinary Institute induce a protective immune response against the circulating virulent ND virus using vaccination-boost and challenge protocols in experimental Specific Pathogen Free chickens. Finally, this study concluded that CEF and Vero cell lines were the most preferable cell lines for the production of Newcastle thermostable I-2 vaccine.