الفهرس 
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Abstract
ABSTRACT
Despite the frequent use of Newcastle Disease Virus (NDV) vaccines in Egypt, NDV still causes outbreaks in the commercial, backyard, and wild poultry. To explore the evolution of the NDV and evaluate the efficacy of the vaccine regimens currently being used in Egypt’s commercial poultry. Spleen, brain, ileocecal tonsil, and tracheal tissue specimens were collected from 23 different vaccinated broiler flocks of four Egyptian governorates (Kafr-Elsheikh, Alexandria, Matrouh, and El-Behera) between 2017 and 2020. For NDV screening, q RT-PCR was conducted using primers specific for the M gene, seventeen samples were positive for the M gene of NDV and six were negative for NDV. Isolation of the virus was carried out for NDV-positive samples in 9-day-old specific-pathogen-free embryonated chicken eggs (SPF-ECE) via the allantoic sac. Five isolates were screened by q RT-PCR for virulent NDV and for other endemic avian respiratory viruses’ avian influenza (AI) and infectious bronchitis viruses (IBV). Five samples were positive for NDV and negative for both AI and IBV. Partial F-gene amplification was conducted for the five isolates, results confirmed that all the five isolates shared the cleavage site motif 112RRQKR ↓F117. Meanwhile, isolated strains are belonging to class II/ genotype VII; sub genotype VII.1.1 formerly classified as VII.b. The study of the host immune response of Newcastle disease virus (NDV) infected chickens and the relation between the innate immune response and the intensity of disease during infection in vivo can explain the pathogenesis of NDV. Sixty specific pathogen free (SPF) chickens were divided into four groups. Three groups were inoculated intra nasally by three different strains of NDV; highly virulent velogenic viscerotropic (VVNDV) (NDV.VII.1.1/Egy-Matr/ELH.5/2018), velogenic neurotropic (VNNDV) (NDV.VII.1.1/Egy-Elbeh/ELH.1/2020) and lentogenic strain (LaSota). The fourth group was used as negative control group. The virus shedding, cytokine measurement, clinical signs, mortality rate, and pathological lesions were compared among these different groups. Our findings revealed that the amount of IFN- α and IFN-γ were increased at 48- and 72-hour post-infection by 2-3 folds in the VVNDV group more than VNNDV group. In addition, the VVNDV group showed higher level of IFN- α and IFN-γ more than LaSota group by 5-6 folds. The course of the disease was severe and rapid 2–4 days in the VVNDV group and much longer 3-6 days in the VNNDV group ending in 100% mortality in both groups but no signs or mortality in the LaSota group. VNNDV group displayed neurological lesions in brain including non-suppurative encephalitis, gliosis, and perivascular cuffing. The three-group infected with velogenic and lentogenic sheded the virus till the 4th day post infection.
Key words: NDV, genotype VII, isolation, phylogenetic analysis, velogenic viscerotropic, velogenic neurotropic, lentogenic, interferon infected.