Molecular detection and genetic analysis of a virulent NDV strain causing high mortality in vaccinated broilers in Al-Najaf province, Iraq

Abstract

Newcastle Disease (ND) outbreaks were investigated in vaccinated broiler flocks in Al-Najaf, Iraq, with mortality rates of 81-85%. Despite vaccination with Clone 30, LaSota, and inactivated ND and H9 vaccines, affected birds showed respiratory, digestive, and neurological signs, accompanied by characteristic lesions. ELISA revealed high antibody titers, PCR confirmed systemic infection, and sequencing of the fusion gene identified two virulent isolates (Hayder 1 and Hayder 2). These results confirm vaccine failure and highlight the importance of molecular surveillance and genotype-matched vaccines to improve ND control in Iraq.