الفهرس 
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Abstract
Newcastle disease virus (NDV) is a highly contagious virus belongs to Paramyxoviridae family, which infects a wide range of avian species including chickens and ducks. The disease can be fatal for many types of them. It was believed that ducks and geese act as natural reservoirs for NDV because of their natural resistance. However, recently, many NDV isolates were pathogenic for ducks. NDV remains a constant threat to the poultry industry causing serious economic losses despite of intensive vaccination schedules. Clinical signs produced by the ND virus are influenced by numerous factors, including the species infected, the age, and the production status or health of the host and routes of inoculation, as well as the level of immunity to the virus which may be passively derived from maternal antibodies or actively induced by vaccination.
Therefore, our study aimed to investigate the pathogenicity of a new isolated virulent field NDV strain of genotype VII through different routes of inoculation including intra-ocular, choanal slit, intranasal, mixed oculo-nasal routes in white Ross male broiler chicks. Pathogenesis and a detailed time dependent comparative clinico-pathological picture (at 2, 5, and 10-days post inoculation) were examined in different tested groups of chicken. Also comparing the NDV pathogenicity between different breeds (white Ross male broiler chicks and Mallard ducks) by inoculation via intranasal route was performed. The pathogenicity was investigated on the basis of clinical, histological observations and immunohistochemistry findings of virus antigen through studying the sequential pathological lesions on 2nd, 5th and 10th dpi. A new isolated field NDV strain published in GenBank under the accession number (MT887290) was used to induce the infection. In the present study, the infected groups either of chicken or ducks were challenged with 0.1 ml of 106 (EID50) of the isolated viral suspension.
The infected chicken inoculated by different routes showed greenish soft diarrhea which was clearly seen in choanal slit-inoculated group. Nervous and respiratory signs were more pronounced in intraocular, intranasal, and mixed intranasal and intra-ocular-inoculated groups with the highest mortality in intranasal-inoculated group. The highest respiratory manifestations were exhibited in intranasal, oculo-nasal, and choanal slit-inoculated groups while the intranasal inoculated group showed the weakest nervous lesions. Histopathology and immunohistochemistry for NDV nucleoprotein displayed widespread systemic distribution and pantropism. High intensity of viral nucleoprotein’s immunolabelling was detected in nasal and mixed intranasal and intra-ocular-inoculated birds. In addition, the onset of clinical signs, distribution, and severity of the observed lesions as well as viral antigen detection by immunohistochemistry were remarkably different between different inoculation routes.
Moreover, in white Ross commercial broiler chicken and Mallard ducks the clinical lesions and mortalities were evident mostly in chicken rather than in ducks. Respiratory, digestive and nervous signs were clearly manifested in chicken. Ducks showed low level of mortalities and the nervous signs were the most obvious symptoms. Microscopic findings of chicken showed severe pancreatitis, pneumonia, enteritis as well as pericarditis and brain malacia. Similar findings were noticed in ducks but with lower degree of severity. Brain lesions in ducks were in the form of encephalitis and perivascular reaction mostly within the cerebellar tissue. Immunohistochemistry reaction against NDV antigen showed marked immunostaining within epithelial cells, purkinje cells and inflammatory cells mostly the macrophages. The immunohistochemistry reaction was correlated with the pathological findings in both species.