History of Newcastle disease.: 1.: Molecular epidemiology and evolution of Newcastle disease virus

An overview is presented on the epidemiology of Newcastle disease (ND) and its virus (NDV) in the last century. Based on its global distribution, ND is considered as an emerging infection (Figure 1, Table), therefore the authors focus on the evolutionary processes. Phylogenetic analysis revealed the presence of hierarchically distinct delineations (early and late lineages, genotypes and subtypes). These were characterised not only by spatial distribution suitable for the study of epidemiological relationships, but by temporal and host associations apposite to the exploration of evolutionary relationships (Figure 2). It was clarified that global epizootic periods of ND were characterised by the simultaneous occurrence of aetiologically distinct genotypes rather than influenza-like pandemics. it was shown that early genotypes (II-IV.) prevalent before the 1960s were replaced by recent genetic groups (V-VIII.) following the introduction of vaccination. This was evolutionary replacement rather than random epidemiological alterations in the distribution of NDV strains. In the background, emergence of viruses with the ability to break through immunity could be ascertained. Incidences and the significance of interspecies transmission and avirulent -> virulent transition of NDV are also discussed.