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Simple Summary: Infectious bursal disease virus (IBDV) is a potent immunosuppressive, persistent pathogen that can thrive in a range of environmental conditions and withstand even potent disinfectants. The common circulating pathotypes of IBDV in Egypt are classical virulent, attenuated, very virulent IBDV, and novel variant (nVarIBDV). The current study describes the incidence of nVarIBDV in 18 Egyptian chicken flocks although they were vaccinated against IBD. Partial sequence analysis of viral protein 2 (VP2) in two obtained isolates identified them as nVarIBDV (genotype A2d) exhibiting 100% identity to SD-2020 and 99.5–98.1% similarity to ZD-2018-1, QZ, GX and SG19 strains. Similarity to USA variant strains was 95.5–92.6%. Moreover, the similarities in the aa of the VP2 hypervariable region of both isolates to vaccine strains were 86–90.4%. Histopathological examination of both the bursa of Fabricius and spleen collected from diseased chickens in flock no. 18 revealed severe atrophy. In conclusion, this study identified the nVarIBDV genotype which is identical to the nVarIBDV circulating in China. Further studies are required to investigate the epidemiological situation of this novel genotype across the country, and to assess various vaccine protections against nVarIBDV. Additionally, it is crucial to incorporate nVarIBDV into the inactivated vaccines administered to breeder chickens prior to egg production to ensure complete protective and specific maternal immunity in their offspring during their first three weeks of life. After an extended period of detecting classical virulent, attenuated, and very virulent IBDV, a novel variant (nVarIBDV) was confirmed in Egypt in this study in 18, IBD vaccinated, chicken flocks aged 19–49 days. Partial sequence of viral protein 2 (VP2) [219 aa, 147–366, resembling 657 bp] of two obtained isolates (nos. 3 and 4) revealed nVarIBDV (genotype A2d) and OR682618 and OR682619 GenBank accession numbers were obtained. Phylogenetic analysis revealed that both nVarIBDV isolates were closely related to nVarIBDV strains (A2d) circulating in China, exhibiting 100% identity to SD-2020 and 99.5–98.1% similarity to ZD-2018-1, QZ, GX and SG19 strains, respectively. Similarity to USA variant strains, belonging to genotypes A2b (9109), A2c (GLS) and A2a (variant E), respectively, was 95.5–92.6%. Also, the VP2 hypervariable region in those two, A2d, isolates revealed greater similarities to Faragher 52/70 (Vaxxitek®) at 90.4% and to an Indian strain (Ventri-Plus®) and V217 (Xtreme®) at 89.7% and 86–88.9% in other vaccines. Histopathological examination of both the bursa of Fabricius and spleen collected from diseased chickens in flock no. 18 revealed severe atrophy. In conclusion, further studies are required to investigate the epidemiological situation of this novel genotype across the country, and to assess various vaccine protections against nVarIBDV. Additionally, vaccination of breeders with inactivated IBD vaccines including this nVarIBDV is essential to obtain specific maternal antibodies in their broilers. [ABSTRACT FROM AUTHOR]

Simple Summary: Newcastle disease is an acute fatal disease of poultry. All broiler chickens and 8/15 pigeons were killed when infected intramuscularly (IM), while 7/10 chickens and only 1/15 pigeons were killed when infected intranasally (IN) with the virus in an experimental setting. Chickens in contact with infected pigeons developed severe respiratory, digestive and nervous signs. The mortality rates in chickens in contact with IM and IN infected pigeons were 2/5 and 3/5, respectively. Chickens in contact with IM infected pigeons had higher viral shedding titres than those in contact with IN infected pigeons. Free-range pigeons are considered an efficient carrier and transmitter of NDV-VIId to commercial broiler chickens raised in open houses. Newcastle disease is an acute fatal disease of poultry. The aim of this study was to determine the dynamics of the transmission of avian avulavirus (velogenic viscerotropic Newcastle disease-genotype VIId) from either intramuscularly (IM)- or intranasally (IN) infected 8-week-old Egyptian Baladi pigeons in contact with commercial Arbor Acres broiler chickens (4 weeks of age). The mortality of IM infected chickens and pigeons was 10/10 for chickens and 8/15 for pigeons, while the mortality of IN infected chickens and pigeons was 7/10 for chickens and only 1/15 for pigeons. The concentration of viral shedding in the oropharynx was higher than that in the cloaca for both IN and IM infected pigeons. Pigeons infected IN continued shedding the virus from the oropharynx from the 4th day post-infection (dpi) up to the 16th dpi, while IM infected pigeons stopped oropharyngeal shedding at the 11th dpi. Chickens in contact with infected pigeons developed severe respiratory, digestive and nervous signs. The mortality rates in chickens in contact with IM and IN infected pigeons were 2/5 and 3/5, respectively. Chickens in contact with IM infected pigeons showed higher viral shedding titres in both the oropharynx and cloaca than chickens in contact with pigeons infected IN. In conclusion, free-range pigeons are considered an efficient carrier and transmitter of NDV-VIId compared to commercial broiler chickens raised in open houses. [ABSTRACT FROM AUTHOR]