Dr. Fufa DawoDr./Fufa DawoBogale Gossaye2023-12-122023-12-122021http://etd.aau.edu.et/handle/123456789/778Newcastle disease (ND) is the first most economically important endemic viral disease of chickens that has a potential threat to village chickens and commercial poultry farms in Ethiopia. Reports from NVI Sales and Customer service directorate evidenced that customers are complaining against the effectiveness of lentogenic ND vaccines. Therefore, this study was designed to isolate and molecularly identify Newcastle disease virus and to assess the protective efficacy of ND vaccines against the current circulating viruses. The study was carried out from December 2019 to May 2021 in Ada’a district; Bishoftu town and Dhankaka village. A Cross-sectional study method was used to investigate ND in suspected cases and a total of 52 samples were collected for virus isolation and virus gene detection. ND virus was isolated in specific-pathogen-free (SPF) embryonated chicken eggs and virulence of the isolates were determined in vitro and in vivo. The current findings confirmed the circulation of virulent strains of ND virus in the study areas. The isolates were further identified by molecular assay, targeting the amplification of avian paramyxovirus-1 (APMV-1). Vaccine protection efficiency was evaluated in chickens hatched from SPF eggs. The chickens were selected randomly and assigned to five experimental groups. Experiment groups were vaccinated by the lentogenic vaccines (HB1, Lasota, and I-2) produced in the National Veterinary Institute (NVI) using 106.5Embryo infective dose (EID)50 per chicken at day zero (age of 7 days), and boosted at days 14 and 35. Group 1 was vaccinated by HB1 on day zero, revaccinated using Lasota on day 14 and boosted by Lasota on day 35 (HB1-Lasota-Lasota). Similarly, groups 2 - 4 were vaccinated, and boosted as (HB1-I2-I2), (I2-Lasota-Lasota), and (HB1- I2-Lasota) vaccines, respectively while group 5 were unvaccinated and threated as a control group. On day 49 all treatment groups were challenged by ‘Dhankaka’ ND virus isolate with 106.5ELD50 per chicken through occulo-nasal route. The result indicated that chickens in group 1 were induced a protective index of 94%, chickens in groups 2, 3, and 4 were revealed 100% survival while chickens in the unvaccinated group were all dead. Hence, the current ND vaccines produced at NVI induced an immune response against the circulating virulent ND virus using vaccination-boost-boost and challenge protocol in experimental SPF chickens challenge.enBishoftuChickenDhankakaNewcastle disease virusVaccineThesis