الفهرس 
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Abstract
Abstract
Newcastle disease virus (NDV) causes huge economic losses in birds all over the world. This study aimed to isolate and genetically characterize NDV circulating among Egyptian chicken flocks and development methods for control of infection. For these purposes, we designed two experiments. In the first experiment aimed to isolate, identify, pathotype, and genetically characterize field isolates of NDV from various governorates in Egypt in 2020 Giza, Gharbya, Qulyubia, Cairo, and Menoufia. After the third passage, 23 of 50 infected samples (46%) showed positive hemagglutination activity in the collected allantoic fluid. The results revealed that all isolates from Menoufia, Cairo, and Giza were velogenic, with a Mean death time (MDT) of 48 hours and an Intracerebral pathogenicity index (ICPI) ranging from 1.55-1.65 Sequencing the 766-bp segment including the 3’ end of the M gene and the 5’ end of the F gene from three different strains indicated that they all possessed the 112RRQKRF117 motif, which is characteristic of virulent strains. The sequenced strains were grouped with class II genotype VIIb and had a high genetic distance to the LaSota reference strain. It is concluded that NDV isolates circulating among chickens are virulent (Genotype VII) and related to outbreaks in poultry farms in Egypt, resulting in significant economic losses. The second experiment in the study was to examine the effect of many immunostimulants on the immunological response of chicks having the ND vaccine. One-day-old Cobb chicks total of 180 were divided into 6 equal groups (A–F), each including 30 chicks. ND vaccine Nobilis® ND Clone 30 vaccine (7th day), Nobilis ND Lasota vaccine (14th day), and Nobilis® Gumboro D78 vaccine (10th day) were administrated to chicken groups C, D, E, and F before they were challenged with (vNDV) genotype VII. However, group A and group B were not vaccinated and represented as non-vaccinated negative control and non-vaccinated positive control, respectively. The tested immune stimulants were administered to groups D, E, and F as follows: N. Sativa in the ration 6%, Curcumin 1% in the ration, and Orego® solution (sol.) 1.25 ml/L in water; at 7 days of age, respectively. GroupsA, B and C, however, did not received any treatment because they were non-vaccinated negative control, non-vaccinated positive control and vaccinated positive control respectively. The velogenic ND (vNDV) genotype VII (Chicken/ Giza/Egypt/2020) (isolated from the field, identified, and sequenced) virus used in the challenge has the accession number (OM243951). Groups, B, C, D, E, and F, and vNDV (106 EID50/ 0.1ml/bird) were administered intra-nasally (IN) at 21th old day. For a serological analysis, serum samples from all groups were taken on the first day of life, the pre-challenge day (20 days old), and the 3rd, 5th, and 7th post-challenge days. The results showed that on the zero-day, the average maternal-derived antibodies titers in all groups were between log2 7.9 and log2 7.2), but on the pre-challenged day, they decreased log2 2.8 and log22.5 in groups A and B, respectively. Groups C, D, E, and F had MDAs titers of log2 3, log2 5.6, log2 6.1, and log2 6.6, respectively. The birds in the curcumin and orego treated groups were protected from the vNDV challenge’s neurological symptoms, and no mortality rate was observed. However, the mortality rates in groups B, C, and D were 43.3%, 13.3%, and 10%, respectively. The orego treated group showed the highest ND-HI antibodies titers based on the serological response, followed by the curcumin treated group, and finally, N. Sativa treated group. Histopathological examination of tissues from the caecal tonsils, proventriculus, and spleen showed a significant improvement in the group F and D (orego, N. Sativa) treatment groups as compared to the curcumin group. The groups given curcumin and orego may offer better protection by decreasing viral shedding than N. sativa treated group. Quantitative real-time PCR (qRT-PCR) was used to investigate the effects of the treatments on cell-mediated immunity of chicken after NDV vaccination. IFN mRNA expression was higher in group F than in group E and lowest in group D. Orego solution treated chickens showed greater reductions in viral shedding and enhanced immune responses