Evolution and control of Avian Orthoavulavirus 1 in endemic regions: challenges of vaccine failure and inadequate immunisation

SUMMARYNewcastle disease (ND), caused by virulent strains of Avian Orthoavulavirus 1 (AOAV-1), poses a major threat to global poultry production, particularly in endemic regions of Asia, Latin America, and Africa. Despite the widespread availability and use of ND vaccines, persistent outbreaks raise concerns regarding vaccine efficacy and the implementation of control measures. This review emphasises the molecular epidemiology of AOAV-1 and the impact of genetic variability on vaccine performance. Effective ND control requires stringent biosecurity to prevent exposure of poultry to virulent AOAV-1 strains, alongside proper administration of efficacious vaccines. Since the 1950s, live attenuated and inactivated vaccines have been extensively used, with recent adoption of antigenically matched vaccines in some countries and ongoing experimental advances in vaccine development. However, suboptimal vaccination practices remain a primary cause of disease outbreaks and mortality. Additionally, maternally derived antibodies at hatch may neutralise vaccines, further reducing their effectiveness. This article comprehensively explores the evolution, classification, and genetic diversity of AOAV-1, its host range and global distribution, and critically evaluates current vaccination strategies in endemic settings.