APMVs are frequently isolated from a wide variety of avian species and are grouped into nine serotypes based on antigenic analysis [33] , with a likely tenth serotype recently described in penguins [34] that was not evaluated in the present study. APMV-1 (NDV) is the most extensively characterized member of the APMV serotypes. APMV-2 to -9 have been isolated from both wild and domestic birds, but their disease potential in wild or domestic birds was largely unknown. APMV-1 also has been shown to infect a number of non-avian species [35] and presently is being evaluated as a potential human vaccine vector for human pathogens [36] . There is a possibility that APMV-2 to -9 could also be used as human vaccine vectors for human pathogens, providing multiple vectors with minimal cross-restriction from vector-specific immunity. Our previous studies demonstrated that APMV-2 to -9 can replicate in mammalian hosts, specifically in the hamster and mouse models [29, 30] . However, their replication and pathogenicity in avian host has not been comprehensively Chicks were inoculated with each virus by the intracerebral route, and brain tissue was harvested for immunohistopathology on 3 dpi. The tissues were fixed in phosphate-buffered formalin, and sections were prepared and stained using an antibody against the respective N protein (stained red). doi:10.1371/journal.pone.0034927.g005 evaluated and compared. Therefore, in this study, we evaluated in vitro and in vivo replication and pathogenicity of APMVs in chickens and their in vivo replication and pathogenicity in ducks and characterized differences in their tropisms, including neurotropism in chickens.