الفهرس 
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Abstract
Poultry industry in Egypt is still threatened by Newcastle disease even with the intensive vaccination programs. Vaccinated and unvaccinated poultry flocks suffered from Newcastle disease virus (NDV) genotype VII outbreaks in the last few years. The efficacy of vaccination with LaSota, Avinew and inactivated Newcastle disease vaccines against challenge with NDV genotype VII was investigated. Two hundred and forty chicks were randomly divided to six groups 40 chicks per each. group A non-vaccinated non challenged, group B non-vaccinated challenged, group C vaccinated with LaSota vaccine and challenged, group D vaccinated with Avinew vaccine and challenged, group E vaccinated with LaSota and inactivated vaccines and challenged and group F vaccinated with Avinew and inactivated Newcastle disease vaccines and challenged. The vaccination was done at 10th day of age and the challenge was performed at 25th day of age by intranasal inoculation 0.1 ml containing 106 EID50 of NDV genotype VII. Three chicks were scarified from each group at 2, 5, 10 and 15 days post vaccination and at 2, 5 and 10 days post challenge. Samples from nasal chonchea, larynx, trachea, lungs, kidneys, heart, brain, Harderian gland, spleen, thymus, bursa of Fabrious, cecal tonsils, gizzard, proventriculus, liver, pancreas, small and large intestine were collected for histopathology, immunohistochemistry (IHC) and qRT-PCR. All vaccination programs could protect chickens from mortalities but not prevent the clinical signs and histopathological lesions. Grossly, congested tracheal mucosa, hemorrhages in proventricular glands, cecal tonsils and large intestine, mottled spleen, congested atrophied thymus and bursa of Fabrious were recorded. Microscopically there was significant decreasing in severity of histopathological lesions and viral expression scores by IHC in vaccinated groups compared with challenged not vaccinated group. Newcastle disease virus loading by qRT-PCR was lower in vaccinated groups compared with the challenged not vaccinated group. showing decreasing Simultaneous administration of live and inactivated vaccines did not prevent NDV shedding and replications in different tissues compared with vaccination with live vaccines only.