الفهرس 
Title : Investigation of mutations in prevalent NDV genotype VIId in Egypt
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Abstract
The outbreaks caused by Newcastle disease (ND) continues to spread in Egypt in poultry flocks resulting in high mortalities and serious economic losses. In this study, 450 samples were collected from different chicken farms showing clinical signs from many Egyptian governorates between 2015 and 2018. Out of the 450 samples, 95 (95/450; 21%) were positive for velogenic NDV based on specific real-time RT-PCR. 13 selected samples were subjected to virus isolation and tested for the haemagglutination activity by HI.These samples were subjected to conventional RT-PCR using primers amplify the fusion (F) gene for genetic analysis based on sequencing and phylogeny. Results of the sequencing analysis indicated the belonging of the samples to genotype VII due to the presence of the characteristic amino acid sequences of the F0 protein pro-teolytic cleavage site motifs (112RRQKRF1117). This means the continuous circulation and presence of this genotype in Egypt. Moreover, Phylogeny analyses revealed that the detected NDVs are clustering within velogenic subgenotype VIId with close relationship to previously isolated Egyptian NDVs. For more confirmation, the pathogenicity of the seven selected isolates were evaluated by inoculation of five 10-day old SPF ECE with fresh infective diluted (1/10) allantoic fluid and incubated at 37{u00B0}C. The incubated eggs were examined twice daily to record deaths for determination of the Mean death time (MDT). The results ranged from 54-60 hours which confirms that the isolates are velogenic. In addition to the MDT, Intravenous pathogenicity index (IVPI) was done, 5 6-week-old chickens were inoculated intravenously with the allantoic fluids and observed for 10 days, the chickens was observed every 24. IVPI for samples VRL1, VRL2, VRL3, VRL4, VRL5, VRL6 and VRL8 were 2.26, 1.4, 1.15, 1.94, 1.32, 1.98 and 1.84 respectively. Also, symptoms caused by the NDVs in inoculated Chickens were very characteristic to velogenic pathotypes