Insights Into Isolation and Molecular Identification of Newcastle Disease Virus Circulating in Chicken Flocks in Egypt from 2023 To 2024

Newcastle disease (ND) outbreaks associated with significant economic losses in chicken populations, continued in Egypt despite the introduction of comprehensive immunization programs. Enhancing ND control methods requires knowledge of the genetic mapping of Newcastle disease virus (NDV) strains isolated from chicken populations immunized against ND. Thus, this study aimed to molecular detection of the circulated NDV in Egypt. As a result, during 2023–2024, outbreaks in broilers that had received the NDV vaccine under various regimes in seven Egyptian governorates including Beni Suef, Fayoum, Dakahlia, Giza, Sharqia, Menoufia, and Qalubia were investigated led to the emergence of 19 NDV strains. The investigated broiler chickens had mortality rates varied from 8% to 20% at the age of 25-40 days. Collected samples were subjected to extraction of nucleic acid (RNA), quantitative reverse transcriptase-PCR (qRT-PCR), isolation of viruses as well as phylogenetic inquiry and the entire sequencing of fusion (F) genes. Results of qRT-PCR displayed that all 19 samples positive for velogenic NDV (vNDV) with cycle threshold between 15 and 33, none of the farms investigated showed avian influenza virus infection utilizing primer probe set for matrix gene. The analysis of the entirely coding (F) gene executing phylogeny for three isolates that were sequenced and then submitted in the GenBank with accession numbers PV334946, PV334947 and PV334948 for the isolates vNDV_02_VSVRI_2023, vNDV_06_VSVRI_2023 vNDV_19_VSVRI_2023, respectively. Being evolutionary dissimilar from vaccine viruses especially Clone 30 and LaSota (genotype II), which have been routinely used to protect chicken farms, these isolates grouped into VII.1.1 sub-genotype. Three strains of the current investigation had the vNDV hallmark of cleavage site motif 112 RRQKRF117. Numerous domains of the F gene were thoroughly examined, and the results showed that most of the gene's domains were conserved in genotype VII 1.1. Continuous monitoring of the circulating virulent NDV is recommended beside evaluation of vaccine and the vaccination programs.