NDV, a single-stranded, non-segmented, negative-sense RNA virus of the genus Avulavirus, family Paramyxoviridae, infects a wide range of domestic and wild bird species worldwide, and causes a significant economic burden to the poultry industry [1] . The first outbreaks of NDV were reported during the mid 1920s in Java, Indonesia and Newcastle-upon-Tyne, England [2] , and within a few years were occurring throughout the world [3] . The name ND is reserved exclusively for the disease that results from infection with strains of aPMV-1 that are pathogenic for domestic chickens [4] . aPMV-1 has been grouped by virulence phenotype, with lentogenic, mesogenic, and velogenic strains representing increasing levels of virulence, ranging from subclinical infections with moderate respiratory involvement to extensive hemorrhagic lesions and neurological signs [5] . Inactivated vaccines were first made commercially available to the poultry industry in 1946, but because they provided incomplete protection against ND [6] , they were replaced with live lentogenic NDV vaccines. Although these vaccines reduce disease, they do not always prevent infection and birds can shed both vaccine and challenge strains of the virus [7, 8, 9] .