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Abstract
In the present study, chemical attenuation was carried out for local NDV genotype vIId designated as NDV-F278-RLQP-CH-EG circulating in Egypt. The virus was propagated in 9-11 day SPF eggs via allantoic cavity and was serially passaged for 35 passages. Then, nitrous acid was used for attenuation and the treated virus was inoculated into SPF eggs. After incubation at 26{u00B0}C for 4-6 days, the harvested allantoic fluid revealed negative hemagglutination even after five passages of such harvest. Assaying of the allantoic fluid harvested from fifth passage of treated virus by real time RT-PCR revealed positive result indicating that nitrous acid affects the HA property of the virus. Inoculation of treated virus in SPF chickens, mortalities developed along ten days observation period and HA property of the virus was recovered again following isolation in SPF eggs indicating failure of attenuation. Therefore, second cycle of treatment using saponin was applied on the propagated virus after 35 passages. Saponin was used to treat virus at different times 10,20,30,45 and 60 minutes then, inoculated into SPF eggs and incubated at 37{u00B0}C for 3-5 days. The harvested allantoic fluid revealed positive hemagglutination. When treated virus incubated with saponin for 30 to 60 minutes inoculated in SPF chickens no clinical signs or mortalities were appeared. Challenge trial of different chicken groups with the virulent NDV genotype vIId designated as NDV-B7-RLQP-CH-EG-12 revealed 100%, 90% and 90% protection at times 30, 45 and 60 minutes respectively; indicating that the reaction of virus with saponin for 30 minutes was the best time to be used in vaccine preparation.